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MDADM(8)                             System Manager's Manual                             MDADM(8)

NAME
       mdadm - manage MD devices aka Linux Software RAID

SYNOPSIS
       mdadm [mode] <raiddevice> [options] <component-devices>

DESCRIPTION
       RAID devices are virtual devices created from two or more real block devices.  This allows
       multiple devices (typically disk drives or partitions thereof) to be combined into a  sin-
       gle device to hold (for example) a single filesystem.  Some RAID levels include redundancy
       and so can survive some degree of device failure.

       Linux Software RAID devices are implemented  through  the  md  (Multiple  Devices)  device
       driver.

       Currently,  Linux  supports LINEAR md devices, RAID0 (striping), RAID1 (mirroring), RAID4,
       RAID5, RAID6, RAID10, MULTIPATH, FAULTY, and CONTAINER.

       MULTIPATH is not a Software RAID mechanism, but does involve multiple devices: each device
       is a path to one common physical storage device.  New installations should not use md/mul-
       tipath as it is not well supported and has no ongoing development.  Use the Device  Mapper
       based multipath-tools instead.

       FAULTY is also not true RAID, and it only involves one device.  It provides a layer over a
       true device that can be used to inject faults.

       CONTAINER is different again.  A CONTAINER is a collection of devices that are managed  as
       a  set.   This  is  similar to the set of devices connected to a hardware RAID controller.
       The set of devices may contain a number of different RAID arrays each utilising  some  (or
       all) of the blocks from a number of the devices in the set.  For example, two devices in a
       5-device set might form a RAID1 using the whole devices.  The remaining three might have a
       RAID5 over the first half of each device, and a RAID0 over the second half.

       With  a  CONTAINER,  there  is one set of metadata that describes all of the arrays in the
       container.  So when mdadm creates a CONTAINER device, the device just represents the meta-
       data.  Other normal arrays (RAID1 etc) can be created inside the container.

MODES
       mdadm has several major modes of operation:

       Assemble
              Assemble the components of a previously created array into an active array.  Compo-
              nents can be explicitly given or can be searched for.  mdadm checks that the compo-
              nents do form a bona fide array, and can, on request, fiddle superblock information
              so as to assemble a faulty array.

       Build  Build an array that doesn't have  per-device  metadata  (superblocks).   For  these
              sorts of arrays, mdadm cannot differentiate between initial creation and subsequent
              assembly of an array.  It also cannot perform any checks  that  appropriate  compo-
              nents have been requested.  Because of this, the Build mode should only be used to-
              gether with a complete understanding of what you are doing.

       Create Create a new array with per-device metadata (superblocks).  Appropriate metadata is
              written  to  each device, and then the array comprising those devices is activated.
              A 'resync' process is started to make sure that the array is consistent (e.g.  both
              sides of a mirror contain the same data) but the content of the device is left oth-
              erwise untouched.  The array can be used as soon as it has been created.  There  is
              no need to wait for the initial resync to finish.

       Follow or Monitor
              Monitor one or more md devices and act on any state changes.  This is only meaning-
              ful for RAID1, 4, 5, 6, 10 or multipath arrays,  as  only  these  have  interesting
              state.   RAID0  or  Linear never have missing, spare, or failed drives, so there is
              nothing to monitor.

       Grow   Grow (or shrink) an array, or otherwise reshape it in  some  way.   Currently  sup-
              ported  growth  options including changing the active size of component devices and
              changing the number of active devices in Linear and RAID levels 0/1/4/5/6, changing
              the  RAID  level  between  0, 1, 5, and 6, and between 0 and 10, changing the chunk
              size and layout for RAID 0,4,5,6,10 as well as adding or  removing  a  write-intent
              bitmap and changing the array's consistency policy.

       Incremental Assembly
              Add  a  single device to an appropriate array.  If the addition of the device makes
              the array runnable, the array will be started.  This provides a  convenient  inter-
              face  to  a hot-plug system.  As each device is detected, mdadm has a chance to in-
              clude it in some array as appropriate.  Optionally, when the --fail flag is  passed
              in we will remove the device from any active array instead of adding it.

              If  a  CONTAINER  is passed to mdadm in this mode, then any arrays within that con-
              tainer will be assembled and started.

       Manage This is for doing things to specific components of an  array  such  as  adding  new
              spares and removing faulty devices.

       Misc   This is an 'everything else' mode that supports operations on active arrays, opera-
              tions on component devices such as erasing old superblocks, and information gather-
              ing operations.

       Auto-detect
              This  mode  does  not act on a specific device or array, but rather it requests the
              Linux Kernel to activate any auto-detected arrays.

OPTIONS
Options for selecting a mode are:
       -A, --assemble
              Assemble a pre-existing array.

       -B, --build
              Build a legacy array without superblocks.

       -C, --create
              Create a new array.

       -F, --follow, --monitor
              Select Monitor mode.

       -G, --grow
              Change the size or shape of an active array.

       -I, --incremental
              Add/remove a single device to/from an appropriate array, and possibly start the ar-
              ray.

       --auto-detect
              Request  that the kernel starts any auto-detected arrays.  This can only work if md
              is compiled into the kernel -- not if it is a module.  Arrays can be  auto-detected
              by the kernel if all the components are in primary MS-DOS partitions with partition
              type FD, and all use v0.90 metadata.  In-kernel autodetect is not  recommended  for
              new  installations.   Using  mdadm  to detect and assemble arrays -- possibly in an
              initrd -- is substantially more flexible and should be preferred.

       If a device is given before any options, or if the first option is one of --add, --re-add,
       --add-spare,  --fail,  --remove,  or --replace, then the MANAGE mode is assumed.  Anything
       other than these will cause the Misc mode to be assumed.

Options that are not mode-specific are:
       -h, --help
              Display general help message or, after one of the above  options,  a  mode-specific
              help message.

       --help-options
              Display  more  detailed  help about command line parsing and some commonly used op-
              tions.

       -V, --version
              Print version information for mdadm.

       -v, --verbose
              Be more verbose about what is happening.  This can be used twice to  be  extra-ver-
              bose.   The  extra  verbosity  currently only affects --detail --scan and --examine
              --scan.

       -q, --quiet
              Avoid printing purely informative messages.  With this, mdadm will be silent unless
              there is something really important to report.

       -f, --force
              Be  more  forceful  about  certain operations.  See the various modes for the exact
              meaning of this option in different contexts.

       -c, --config=
              Specify the config file or directory.  Default is to use /etc/mdadm/mdadm.conf  and
              /etc/mdadm/mdadm.conf.d,   or   if  those  are  missing  then  /etc/mdadm.conf  and
              /etc/mdadm.conf.d.  If the config file given is partitions  then  nothing  will  be
              read, but mdadm will act as though the config file contained exactly
                  DEVICE partitions containers
              and  will read /proc/partitions to find a list of devices to scan, and /proc/mdstat
              to find a list of containers to examine.  If the word none is given for the  config
              file, then mdadm will act as though the config file were empty.

              If  the  name  given  is of a directory, then mdadm will collect all the files con-
              tained in the directory with a name ending  in  .conf,  sort  them  lexically,  and
              process all of those files as config files.

       -s, --scan
              Scan  config file or /proc/mdstat for missing information.  In general, this option
              gives mdadm permission to get any missing information (like component devices,  ar-
              ray  devices,  array identities, and alert destination) from the configuration file
              (see previous option); one exception is MISC mode when using --detail or --stop, in
              which case --scan says to get a list of array devices from /proc/mdstat.

       -e, --metadata=
              Declare the style of RAID metadata (superblock) to be used.  The default is 1.2 for
              --create, and to guess for other operations.  The default can be overridden by set-
              ting the metadata value for the CREATE keyword in mdadm.conf.

              Options are:

              0, 0.90
                     Use  the  original  0.90 format superblock.  This format limits arrays to 28
                     component devices and limits component devices of levels 1 and greater to  2
                     terabytes.   It is also possible for there to be confusion about whether the
                     superblock applies to a whole device or just the  last  partition,  if  that
                     partition starts on a 64K boundary.

              1, 1.0, 1.1, 1.2 default
                     Use  the  new version-1 format superblock.  This has fewer restrictions.  It
                     can easily be moved between hosts with different endian-ness, and a recovery
                     operation  can  be  checkpointed  and restarted.  The different sub-versions
                     store the superblock at different locations on the device, either at the end
                     (for  1.0),  at  the start (for 1.1) or 4K from the start (for 1.2).  "1" is
                     equivalent to "1.2" (the  commonly  preferred  1.x  format).   "default"  is
                     equivalent to "1.2".

              ddf    Use  the  "Industry Standard" DDF (Disk Data Format) format defined by SNIA.
                     When creating a DDF array a CONTAINER will be created, and normal arrays can
                     be created in that container.

              imsm   Use  the  Intel(R)  Matrix  Storage Manager metadata format.  This creates a
                     CONTAINER which is managed in a similar manner to DDF, and is  supported  by
                     an option-rom on some platforms:

                     https://www.intel.com/content/www/us/en/support/products/122484/memory-and-
                     storage/ssd-software/intel-virtual-raid-on-cpu-intel-vroc.html

       --homehost=
              This will override any HOMEHOST setting in the config file and provides  the  iden-
              tity of the host which should be considered the home for any arrays.

              When  creating  an  array, the homehost will be recorded in the metadata.  For ver-
              sion-1 superblocks, it will be prefixed to the array name.   For  version-0.90  su-
              perblocks,  part  of the SHA1 hash of the hostname will be stored in the later half
              of the UUID.

              When reporting information about an array, any array which is tagged for the  given
              homehost will be reported as such.

              When using Auto-Assemble, only arrays tagged for the given homehost will be allowed
              to use 'local' names (i.e. not ending in '_' followed by a digit string).  See  be-
              low under Auto Assembly.

              The  special  name  "any"  can be used as a wild card.  If an array is created with
              --homehost=any then the name "any" will be stored in the array and it can be assem-
              bled  in the same way on any host.  If an array is assembled with this option, then
              the homehost recorded on the array will be ignored.

       --prefer=
              When mdadm needs to print the name for a device it normally finds the name in  /dev
              which  refers  to  the device and is shortest.  When a path component is given with
              --prefer mdadm will prefer a longer name if it contains that component.  For  exam-
              ple --prefer=by-uuid will prefer a name in a subdirectory of /dev called by-uuid.

              This functionality is currently only provided by --detail and --monitor.

       --home-cluster=
              specifies  the  cluster name for the md device. The md device can be assembled only
              on the cluster which matches the name specified. If this option  is  not  provided,
              mdadm tries to detect the cluster name automatically.

For create, build, or grow:
       -n, --raid-devices=
              Specify  the number of active devices in the array.  This, plus the number of spare
              devices (see below) must equal the number of component-devices (including "missing"
              devices) that are listed on the command line for --create.  Setting a value of 1 is
              probably a mistake and so requires that --force be specified first.  A value  of  1
              will  then  be allowed for linear, multipath, RAID0 and RAID1.  It is never allowed
              for RAID4, RAID5 or RAID6.
              This number can only be changed using --grow for RAID1, RAID4, RAID5 and RAID6  ar-
              rays, and only on kernels which provide the necessary support.

       -x, --spare-devices=
              Specify  the number of spare (eXtra) devices in the initial array.  Spares can also
              be added and removed later.  The number of component devices listed on the  command
              line must equal the number of RAID devices plus the number of spare devices.

       -z, --size=
              Amount (in Kilobytes) of space to use from each drive in RAID levels 1/4/5/6.  This
              must be a multiple of the chunk size, and must leave about 128Kb of  space  at  the
              end  of the drive for the RAID superblock. When specified as ,max, (as it often is)
              the smallest drive (or partition) sets the size.  In that case, a warning will fol-
              low if the drives, as a group, have sizes that differ by more than one percent.

              A suffix of 'K', 'M', 'G' or 'T' can be given to indicate Kilobytes, Megabytes, Gi-
              gabytes or Terabytes respectively.

              Sometimes a replacement drive can be a little  smaller  than  the  original  drives
              though  this should be minimised by IDEMA standards.  Such a replacement drive will
              be rejected by md.  To guard against this it can be useful to set the initial  size
              slightly  smaller than the smaller device with the aim that it will still be larger
              than any replacement.

              This value can be set with --grow for RAID level 1/4/5/6 though DDF arrays may  not
              be  able  to  support  this.  If the array was created with a size smaller than the
              currently active drives, the extra space can be accessed using  --grow.   The  size
              can be given as max which means to choose the largest size that fits on all current
              drives.

              Before reducing the size of the array (with --grow --size=) you  should  make  sure
              that  space  isn't needed.  If the device holds a filesystem, you would need to re-
              size the filesystem to use less space.

              After reducing the array size you should check that the data stored in  the  device
              is  still  available.   If  the  device  holds  a filesystem, then an 'fsck' of the
              filesystem is a minimum requirement.  If there are problems the array can  be  made
              bigger again with no loss with another --grow --size= command.

              This value cannot be used when creating a CONTAINER such as with DDF and IMSM meta-
              data, though it perfectly valid when creating an array inside a container.

       -Z, --array-size=
              This is only meaningful with --grow and its effect is not persistent: when the  ar-
              ray is stopped and restarted the default array size will be restored.

              Setting  the  array-size causes the array to appear smaller to programs that access
              the data.  This is particularly needed before reshaping an array so that it will be
              smaller.   As the reshape is not reversible, but setting the size with --array-size
              is, it is required that the array size is reduced as appropriate before the  number
              of devices in the array is reduced.

              Before reducing the size of the array you should make sure that space isn't needed.
              If the device holds a filesystem, you would need to resize the  filesystem  to  use
              less space.

              After  reducing  the array size you should check that the data stored in the device
              is still available.  If the device holds  a  filesystem,  then  an  'fsck'  of  the
              filesystem  is  a minimum requirement.  If there are problems the array can be made
              bigger again with no loss with another --grow --array-size= command.

              A suffix of 'K', 'M', 'G' or 'T' can be given to indicate Kilobytes, Megabytes, Gi-
              gabytes  or  Terabytes  respectively.  A value of max restores the apparent size of
              the array to be whatever the real amount of available space is.

              Clustered arrays do not support this parameter yet.

       -c, --chunk=
              Specify chunk size of kilobytes.  The default when creating an array is 512KB.   To
              ensure compatibility with earlier versions, the default when building an array with
              no persistent metadata is 64KB.  This is only meaningful for RAID0,  RAID4,  RAID5,
              RAID6, and RAID10.

              RAID4,  RAID5, RAID6, and RAID10 require the chunk size to be a power of 2.  In any
              case it must be a multiple of 4KB.

              A suffix of 'K', 'M', 'G' or 'T' can be given to indicate Kilobytes, Megabytes, Gi-
              gabytes or Terabytes respectively.

       --rounding=
              Specify  rounding  factor  for  a Linear array.  The size of each component will be
              rounded down to a multiple of this size.  This is a synonym for --chunk  but  high-
              lights  the different meaning for Linear as compared to other RAID levels.  The de-
              fault is 64K if a kernel earlier than 2.6.16 is in use, and is 0K (i.e.  no  round-
              ing) in later kernels.

       -l, --level=
              Set  RAID  level.   When used with --create, options are: linear, raid0, 0, stripe,
              raid1, 1, mirror, raid4, 4, raid5, 5, raid6, 6, raid10, 10, multipath, mp,  faulty,
              container.  Obviously some of these are synonymous.

              When a CONTAINER metadata type is requested, only the container level is permitted,
              and it does not need to be explicitly given.

              When used with --build, only linear, stripe, raid0, 0, raid1,  multipath,  mp,  and
              faulty are valid.

              Can  be used with --grow to change the RAID level in some cases.  See LEVEL CHANGES
              below.

       -p, --layout=
              This option configures the fine details of data layout for RAID5, RAID6, and RAID10
              arrays, and controls the failure modes for faulty.  It can also be used for working
              around a kernel bug with RAID0, but generally doesn't need to be used explicitly.

              The layout of the RAID5 parity block can be one of left-asymmetric, left-symmetric,
              right-asymmetric, right-symmetric, la, ra, ls, rs.  The default is left-symmetric.

              It  is  also  possible  to  cause RAID5 to use a RAID4-like layout by choosing par-
              ity-first, or parity-last.

              Finally   for   RAID5   there   are   DDF-compatible   layouts,   ddf-zero-restart,
              ddf-N-restart, and ddf-N-continue.

              These  same  layouts  are  available for RAID6.  There are also 4 layouts that will
              provide an intermediate stage for converting between RAID5 and RAID6.   These  pro-
              vide a layout which is identical to the corresponding RAID5 layout on the first N-1
              devices, and has the 'Q' syndrome (the second 'parity' block used by RAID6) on  the
              last device.  These layouts are: left-symmetric-6, right-symmetric-6, left-asymmet-
              ric-6, right-asymmetric-6, and parity-first-6.

              When setting the failure mode for level faulty, the options  are:  write-transient,
              wt,  read-transient,  rt,  write-persistent,  wp,  read-persistent,  rp, write-all,
              read-fixable, rf, clear, flush, none.

              Each failure mode can be followed by a number, which is used as  a  period  between
              fault generation.  Without a number, the fault is generated once on the first rele-
              vant request.  With a number, the fault will be generated after that many requests,
              and will continue to be generated every time the period elapses.

              Multiple  failure modes can be current simultaneously by using the --grow option to
              set subsequent failure modes.

              "clear" or "none" will remove any pending or periodic failure  modes,  and  "flush"
              will clear any persistent faults.

              The  layout  options for RAID10 are one of 'n', 'o' or 'f' followed by a small num-
              ber.  The default is 'n2'.  The supported options are:

              'n' signals 'near' copies.  Multiple copies of one data block are at  similar  off-
              sets in different devices.

              'o'  signals  'offset'  copies.   Rather  than the chunks being duplicated within a
              stripe, whole stripes are duplicated but are rotated by  one  device  so  duplicate
              blocks are on different devices.  Thus subsequent copies of a block are in the next
              drive, and are one chunk further down.

              'f' signals 'far' copies (multiple copies have very different offsets).  See  md(4)
              for more detail about 'near', 'offset', and 'far'.

              The  number  is the number of copies of each datablock.  2 is normal, 3 can be use-
              ful.  This number can be at most equal to the number of devices in the  array.   It
              does not need to divide evenly into that number (e.g. it is perfectly legal to have
              an 'n2' layout for an array with an odd number of devices).

              A bug introduced in Linux 3.14 means that RAID0 arrays with  devices  of  differing
              sizes started using a different layout.  This could lead to data corruption.  Since
              Linux 5.4 (and various stable releases that received backports),  the  kernel  will
              not  accept  such  an  array  unless  a layout is explicitly set.  It can be set to
              'original' or 'alternate'.  When creating a new array, mdadm will select 'original'
              by  default,  so the layout does not normally need to be set.  An array created for
              either 'original' or 'alternate' will not be recognized by  an  (unpatched)  kernel
              prior  to 5.4.  To create a RAID0 array with devices of differing sizes that can be
              used on an older kernel, you can set the layout  to  'dangerous'.   This  will  use
              whichever  layout  the running kernel supports, so the data on the array may become
              corrupt when changing kernel from pre-3.14 to a later kernel.

              When an array is converted between RAID5 and RAID6 an intermediate RAID6 layout  is
              used in which the second parity block (Q) is always on the last device.  To convert
              a RAID5 to RAID6 and leave it in this new layout (which does not require  re-strip-
              ing) use --layout=preserve.  This will try to avoid any restriping.

              The  converse  of this is --layout=normalise which will change a non-standard RAID6
              layout into a more standard arrangement.

       --parity=
              same as --layout (thus explaining the p of -p).

       -b, --bitmap=
              Specify a file to store a write-intent bitmap in.  The file should not exist unless
              --force is also given.  The same file should be provided when assembling the array.
              If the word internal is given, then the bitmap is stored with the metadata  on  the
              array,  and so is replicated on all devices.  If the word none is given with --grow
              mode, then any bitmap that is present is removed. If the word clustered  is  given,
              the  array  is  created for a clustered environment. One bitmap is created for each
              node as defined by the --nodes parameter and are stored internally.

              To help catch typing errors, the filename must contain at least one slash ('/')  if
              it is a real file (not 'internal' or 'none').

              Note:  external  bitmaps  are  only known to work on ext2 and ext3.  Storing bitmap
              files on other filesystems may result in serious problems.

              When creating an array on devices which are 100G  or  larger,  mdadm  automatically
              adds  an  internal bitmap as it will usually be beneficial.  This can be suppressed
              with --bitmap=none or by selecting a different consistency  policy  with  --consis-
              tency-policy.

       --bitmap-chunk=
              Set  the  chunksize  of the bitmap.  Each bit corresponds to that many Kilobytes of
              storage.  When using a file based bitmap, the default is to use the  smallest  size
              that  is  at-least 4 and requires no more than 2^21 chunks.  When using an internal
              bitmap, the chunksize defaults to 64Meg, or larger if necessary to fit  the  bitmap
              into the available space.

              A suffix of 'K', 'M', 'G' or 'T' can be given to indicate Kilobytes, Megabytes, Gi-
              gabytes or Terabytes respectively.

       -W, --write-mostly
              subsequent devices listed in a --build, --create, or --add command will be  flagged
              as  'write-mostly'.   This  is  valid for RAID1 only and means that the 'md' driver
              will avoid reading from these devices if at all possible.  This can  be  useful  if
              mirroring over a slow link.

       --write-behind=
              Specify that write-behind mode should be enabled (valid for RAID1 only).  If an ar-
              gument is specified, it will set the maximum number of outstanding writes  allowed.
              The default value is 256.  A write-intent bitmap is required in order to use write-
              behind mode, and write-behind is only attempted on drives marked as write-mostly.

       --failfast
              subsequent devices listed in a --create or --add command will be flagged as  'fail-
              fast'.  This is valid for RAID1 and RAID10 only.  IO requests to these devices will
              be encouraged to fail quickly rather than cause long delays due to error  handling.
              Also no attempt is made to repair a read error on these devices.

              If  an  array becomes degraded so that the 'failfast' device is the only usable de-
              vice, the 'failfast' flag will then be ignored and extended  delays  will  be  pre-
              ferred to complete failure.

              The  'failfast' flag is appropriate for storage arrays which have a low probability
              of true failure, but which may sometimes cause unacceptable delays due to  internal
              maintenance functions.

       --assume-clean
              Tell  mdadm  that the array pre-existed and is known to be clean.  It can be useful
              when trying to recover from a major failure as you can be sure that no data will be
              affected unless you actually write to the array.  It can also be used when creating
              a RAID1 or RAID10 if you want to avoid the initial resync, however this practice --
              while  normally  safe -- is not recommended.  Use this only if you really know what
              you are doing.

              When the devices that will be part of a new array were  filled  with  zeros  before
              creation  the operator knows the array is actually clean. If that is the case, such
              as after running badblocks, this argument can be used to tell mdadm the  facts  the
              operator knows.

              When an array is resized to a larger size with --grow --size= the new space is nor-
              mally resynced in that same way that the whole array is resynced at creation.  From
              Linux  version 3.0, --assume-clean can be used with that command to avoid the auto-
              matic resync.

       --backup-file=
              This is needed when --grow is used to increase the  number  of  raid-devices  in  a
              RAID5  or  RAID6 if there are no spare devices available, or to shrink, change RAID
              level or layout.  See the GROW MODE section below  on  RAID-DEVICES  CHANGES.   The
              file must be stored on a separate device, not on the RAID array being reshaped.

       --data-offset=
              Arrays  with  1.x  metadata can leave a gap between the start of the device and the
              start of array data.  This gap can be used for various metadata.  The start of data
              is known as the data-offset.  Normally an appropriate data offset is computed auto-
              matically.  However it can be useful to set it explicitly such as when  re-creating
              an array which was originally created using a different version of mdadm which com-
              puted a different offset.

              Setting the offset explicitly over-rides the default.  The value given is in  Kilo-
              bytes  unless a suffix of 'K', 'M', 'G' or 'T' is used to explicitly indicate Kilo-
              bytes, Megabytes, Gigabytes or Terabytes respectively.

              Since Linux 3.4, --data-offset can also be used with --grow for  some  RAID  levels
              (initially  on  RAID10).   This allows the data-offset to be changed as part of the
              reshape process.  When the data offset is changed, no backup file  is  required  as
              the difference in offsets is used to provide the same functionality.

              When  the  new  offset is earlier than the old offset, the number of devices in the
              array cannot shrink.  When it is after the old offset, the number of devices in the
              array cannot increase.

              When  creating  an  array, --data-offset can be specified as variable.  In the case
              each member device is expected to have a offset appended to the name, separated  by
              a  colon.   This  makes  it possible to recreate exactly an array which has varying
              data offsets (as can happen when different versions of mdadm are used to  add  dif-
              ferent devices).

       --continue
              This  option  is  complementary  to the --freeze-reshape option for assembly. It is
              needed when --grow operation is interrupted and it is not  restarted  automatically
              due  to --freeze-reshape usage during array assembly.  This option is used together
              with -G , ( --grow ) command and device for a pending reshape to be continued.  All
              parameters  required for reshape continuation will be read from array metadata.  If
              initial --grow command had required --backup-file= option to be  set,  continuation
              option will require to have exactly the same backup file given as well.

              Any other parameter passed together with --continue option will be ignored.

       -N, --name=
              Set  a name for the array.  This is currently only effective when creating an array
              with a version-1 superblock, or an array in a DDF container.  The name is a  simple
              textual  string  that can be used to identify array components when assembling.  If
              name is needed but not specified, it is taken from the basename of the device  that
              is  being  created.  e.g. when creating /dev/md/home the name will default to home.
              (Does not work in Grow mode.)

       -R, --run
              Insist that mdadm run the array, even if some of the components appear to be active
              in  another  array  or filesystem.  Normally mdadm will ask for confirmation before
              including such components in an array.  This option causes that question to be sup-
              pressed.

       -f, --force
              Insist  that mdadm accept the geometry and layout specified without question.  Nor-
              mally mdadm will not allow creation of an array with only one device, and will  try
              to  create  a  RAID5 array with one missing drive (as this makes the initial resync
              work faster).  With --force, mdadm will not try to be so clever.

       -o, --readonly
              Start the array read only rather than read-write as normal.  No writes will be  al-
              lowed  to  the array, and no resync, recovery, or reshape will be started. It works
              with Create, Assemble, Manage and Misc mode.

       -a, --auto{=yes,md,mdp,part,p}{NN}
              Instruct mdadm how to create the device file if needed, possibly allocating an  un-
              used  minor number.  "md" causes a non-partitionable array to be used (though since
              Linux 2.6.28, these array devices are in fact partitionable).  "mdp", "part" or "p"
              causes  a partitionable array (2.6 and later) to be used.  "yes" requires the named
              md device to have a 'standard' format, and the type and minor number will be deter-
              mined  from  this.   With mdadm 3.0, device creation is normally left up to udev so
              this option is unlikely to be needed.  See DEVICE NAMES below.

              The argument can also come immediately after "-a".  e.g. "-ap".

              If --auto is not given on the command line or in the config file, then the  default
              will be --auto=yes.

              If  --scan  is  also given, then any auto= entries in the config file will override
              the --auto instruction given on the command line.

              For partitionable arrays, mdadm will create the device file for the whole array and
              for  the  first 4 partitions.  A different number of partitions can be specified at
              the end of this option (e.g.  --auto=p7).  If the device name ends  with  a  digit,
              the partition names add a 'p', and a number, e.g.  /dev/md/home1p3.  If there is no
              trailing  digit,  then  the  partition  names  just  have  a  number  added,   e.g.
              /dev/md/scratch3.

              If  the md device name is in a 'standard' format as described in DEVICE NAMES, then
              it will be created, if necessary, with the appropriate device number based on  that
              name.  If the device name is not in one of these formats, then a unused device num-
              ber will be allocated.  The device number will be considered unused if there is  no
              active  array  for  that  number, and there is no entry in /dev for that number and
              with a non-standard name.  Names that are not in 'standard' format are only allowed
              in "/dev/md/".

              This is meaningful with --create or --build.

       -a, --add
              This option can be used in Grow mode in two cases.

              If  the  target  array is a Linear array, then --add can be used to add one or more
              devices to the array.  They are simply catenated on to the end of the array.   Once
              added, the devices cannot be removed.

              If  the  --raid-disks  option is being used to increase the number of devices in an
              array, then --add can be used to add some extra devices to be included in  the  ar-
              ray.   In most cases this is not needed as the extra devices can be added as spares
              first, and then the number of raid-disks can be changed.  However for RAID0, it  is
              not possible to add spares.  So to increase the number of devices in a RAID0, it is
              necessary to set the new number of devices, and to add the new devices, in the same
              command.

       --nodes
              Only  works  when  the array is for clustered environment. It specifies the maximum
              number of nodes in the cluster that will use this  device  simultaneously.  If  not
              specified, this defaults to 4.

       --write-journal
              Specify journal device for the RAID-4/5/6 array. The journal device should be a SSD
              with reasonable lifetime.

       --symlinks
              Auto creation of symlinks in /dev to /dev/md, option --symlinks  must  be  'no'  or
              'yes' and work with --create and --build.

       -k, --consistency-policy=
              Specify  how  the array maintains consistency in case of unexpected shutdown.  Only
              relevant for RAID levels with redundancy.  Currently supported options are:

              resync Full resync is performed and all redundancy is regenerated when the array is
                     started after unclean shutdown.

              bitmap Resync  assisted  by  a  write-intent bitmap. Implicitly selected when using
                     --bitmap.

              journal
                     For RAID levels 4/5/6, journal device is used to log transactions and replay
                     after unclean shutdown. Implicitly selected when using --write-journal.

              ppl    For RAID5 only, Partial Parity Log is used to close the write hole and elim-
                     inate resync. PPL is stored in the metadata region of RAID member drives, no
                     additional journal drive is needed.

              Can be used with --grow to change the consistency policy of an active array in some
              cases. See CONSISTENCY POLICY CHANGES below.

For assemble:
       -u, --uuid=
              uuid of array to assemble.  Devices which don't have this uuid are excluded

       -m, --super-minor=
              Minor number of device that array was created for.  Devices which don't  have  this
              minor  number  are  excluded.   If  you  create  an array as /dev/md1, then all su-
              perblocks will contain the minor number 1, even if the array is later assembled  as
              /dev/md2.

              Giving  the  literal word "dev" for --super-minor will cause mdadm to use the minor
              number of the md device that is being assembled.  e.g.  when  assembling  /dev/md0,
              --super-minor=dev will look for super blocks with a minor number of 0.

              --super-minor is only relevant for v0.90 metadata, and should not normally be used.
              Using --uuid is much safer.

       -N, --name=
              Specify the name of the array to assemble.  This must be the name that  was  speci-
              fied  when  creating  the  array.   It must either match the name stored in the su-
              perblock exactly, or it must match with the current homehost prefixed to the  start
              of the given name.

       -f, --force
              Assemble  the array even if the metadata on some devices appears to be out-of-date.
              If mdadm cannot find enough working devices to start the array, but can  find  some
              devices  that  are  recorded  as  having failed, then it will mark those devices as
              working so that the array can be started. This works only for native. For  external
              metadata  it  allows to start dirty degraded RAID 4, 5, 6.  An array which requires
              --force to be started may contain data corruption.  Use it carefully.

       -R, --run
              Attempt to start the array even if fewer drives were given than were  present  last
              time  the  array was active.  Normally if not all the expected drives are found and
              --scan is not used, then the array will be assembled but not started.   With  --run
              an attempt will be made to start it anyway.

       --no-degraded
              This  is  the  reverse of --run in that it inhibits the startup of array unless all
              expected drives are present.  This is only needed with --scan, and can be  used  if
              the physical connections to devices are not as reliable as you would like.

       -a, --auto{=no,yes,md,mdp,part}
              See this option under Create and Build options.

       -b, --bitmap=
              Specify the bitmap file that was given when the array was created.  If an array has
              an internal bitmap, there is no need to specify this when assembling the array.

       --backup-file=
              If --backup-file was used while reshaping an array (e.g. changing number of devices
              or  chunk  size)  and the system crashed during the critical section, then the same
              --backup-file must be presented to --assemble to allow possibly corrupted  data  to
              be restored, and the reshape to be completed.

       --invalid-backup
              If  the  file  needed for the above option is not available for any reason an empty
              file can be given together with this option to indicate that the backup file is in-
              valid.   In  this  case the data that was being rearranged at the time of the crash
              could be irrecoverably lost, but the rest of the array may  still  be  recoverable.
              This  option should only be used as a last resort if there is no way to recover the
              backup file.

       -U, --update=
              Update the superblock on each device while  assembling  the  array.   The  argument
              given  to this flag can be one of sparc2.2, summaries, uuid, name, nodes, homehost,
              home-cluster, resync, byteorder, devicesize, no-bitmap, bbl, no-bbl,  ppl,  no-ppl,
              layout-original, layout-alternate, layout-unspecified, metadata, or super-minor.

              The  sparc2.2  option  will adjust the superblock of an array what was created on a
              Sparc machine running a patched 2.2 Linux kernel.  This kernel got the alignment of
              part of the superblock wrong.  You can use the --examine --sparc2.2 option to mdadm
              to see what effect this would have.

              The super-minor option will update the preferred minor field on each superblock  to
              match the minor number of the array being assembled.  This can be useful if --exam-
              ine reports a different "Preferred Minor" to --detail.  In some cases  this  update
              will  be  performed  automatically  by the kernel driver.  In particular the update
              happens automatically at the first write to an array with redundancy (RAID level  1
              or greater) on a 2.6 (or later) kernel.

              The  uuid  option  will  change the uuid of the array.  If a UUID is given with the
              --uuid option that UUID will be used as a new UUID and will NOT  be  used  to  help
              identify the devices in the array.  If no --uuid is given, a random UUID is chosen.

              The  name  option  will  change  the name of the array as stored in the superblock.
              This is only supported for version-1 superblocks.

              The nodes option will change the nodes of the array as stored  in  the  bitmap  su-
              perblock. This option only works for a clustered environment.

              The  homehost  option  will change the homehost as recorded in the superblock.  For
              version-0 superblocks, this is the same as updating the UUID.   For  version-1  su-
              perblocks, this involves updating the name.

              The  home-cluster option will change the cluster name as recorded in the superblock
              and bitmap. This option only works for clustered environment.

              The resync option will cause the array to be marked dirty meaning that  any  redun-
              dancy  in  the  array  (e.g.  parity for RAID5, copies for RAID1) may be incorrect.
              This will cause the RAID system to perform a "resync" pass to make  sure  that  all
              redundant information is correct.

              The  byteorder  option  allows  arrays  to be moved between machines with different
              byte-order, such as from a big-endian machine like a Sparc or some  MIPS  machines,
              to  a  little-endian  x86_64  machine.  When assembling such an array for the first
              time after a move, giving --update=byteorder will cause mdadm to expect superblocks
              to have their byteorder reversed, and will correct that order before assembling the
              array.  This is only valid with original (Version 0.90) superblocks.

              The summaries option will correct the summaries in the  superblock.   That  is  the
              counts of total, working, active, failed, and spare devices.

              The  devicesize  option  will  rarely be of use.  It applies to version 1.1 and 1.2
              metadata only (where the metadata is at the start of the device) and is only useful
              when  the component device has changed size (typically become larger).  The version
              1 metadata records the amount of the device that can be used to store data, so if a
              device  in  a  version  1.1 or 1.2 array becomes larger, the metadata will still be
              visible, but the extra space will not.  In this case it might be useful to assemble
              the array with --update=devicesize.  This will cause mdadm to determine the maximum
              usable amount of space on each device and update the relevant field  in  the  meta-
              data.

              The  metadata  option  only works on v0.90 metadata arrays and will convert them to
              v1.0 metadata.  The array must not be dirty (i.e. it must not need a sync)  and  it
              must not have a write-intent bitmap.

              The  old  metadata  will  remain on the devices, but will appear older than the new
              metadata and so will usually be ignored. The old metadata (or indeed the new  meta-
              data)  can  be  removed  by giving the appropriate --metadata= option to --zero-su-
              perblock.

              The no-bitmap option can be used when an array has an internal bitmap which is cor-
              rupt  in  some  way so that assembling the array normally fails.  It will cause any
              internal bitmap to be ignored.

              The bbl option will reserve space in each device for a bad block list.   This  will
              be  4K in size and positioned near the end of any free space between the superblock
              and the data.

              The no-bbl option will cause any reservation of space for a bad block  list  to  be
              removed.   If  the bad block list contains entries, this will fail, as removing the
              list could cause data corruption.

              The ppl option will enable PPL for a RAID5 array and reserve space for PPL on  each
              device.  There  must  be  enough  free  space between the data and superblock and a
              write-intent bitmap or journal must not be used.

              The no-ppl option will disable PPL in the superblock.

              The layout-original and layout-alternate options are for RAID0 arrays with non-uni-
              form  devices  size that were in use before Linux 5.4.  If the array was being used
              with Linux 3.13 or earlier, then to assemble the  array  on  a  new  kernel,  --up-
              date=layout-original  must be given.  If the array was created and used with a ker-
              nel from Linux 3.14 to Linux 5.3, then  --update=layout-alternate  must  be  given.
              This  only  needs  to  be given once.  Subsequent assembly of the array will happen
              normally.  For more information, see md(4).

              The layout-unspecified option reverts the effect of layout-orignal or layout-alter-
              nate  and  allows  the array to be again used on a kernel prior to Linux 5.3.  This
              option should be used with great caution.

       --freeze-reshape
              Option is intended to be used in start-up scripts during initrd boot  phase.   When
              array under reshape is assembled during initrd phase, this option stops reshape af-
              ter reshape critical section is being restored. This  happens  before  file  system
              pivot operation and avoids loss of file system context.  Losing file system context
              would cause reshape to be broken.

              Reshape can be continued later using the --continue option for the grow command.

       --symlinks
              See this option under Create and Build options.

For Manage mode:
       -t, --test
              Unless a more serious error occurred, mdadm will exit with a  status  of  2  if  no
              changes  were made to the array and 0 if at least one change was made.  This can be
              useful when an indirect specifier such as missing, detached or faulty  is  used  in
              requesting  an  operation on the array.  --test will report failure if these speci-
              fiers didn't find any match.

       -a, --add
              hot-add listed devices.  If a device appears to have recently been part of the  ar-
              ray  (possibly it failed or was removed) the device is re-added as described in the
              next point.  If that fails or the device was never part of the array, the device is
              added  as  a hot-spare.  If the array is degraded, it will immediately start to re-
              build data onto that spare.

              Note that this and the following options are only meaningful on array  with  redun-
              dancy.  They don't apply to RAID0 or Linear.

       --re-add
              re-add  a device that was previously removed from an array.  If the metadata on the
              device reports that it is a member of the array, and the slot that it used is still
              vacant, then the device will be added back to the array in the same position.  This
              will normally cause the data for that device to be recovered.  However based on the
              event  count on the device, the recovery may only require sections that are flagged
              by a write-intent bitmap to be recovered or may not require any recovery at all.

              When used on an array that has no metadata (i.e. it was built with --build) it will
              be assumed that bitmap-based recovery is enough to make the device fully consistent
              with the array.

              When used with v1.x metadata, --re-add can be accompanied  by  --update=devicesize,
              --update=bbl, or --update=no-bbl.  See the description of these option when used in
              Assemble mode for an explanation of their use.

              If the device name given is missing then mdadm will try to  find  any  device  that
              looks like it should be part of the array but isn't and will try to re-add all such
              devices.

              If the device name given is faulty then mdadm will find all devices  in  the  array
              that  are  marked faulty, remove them and attempt to immediately re-add them.  This
              can be useful if you are certain that the reason for failure has been resolved.

       --add-spare
              Add a device as a spare.  This is similar to --add except that it does not  attempt
              --re-add first.  The device will be added as a spare even if it looks like it could
              be an recent member of the array.

       -r, --remove
              remove listed devices.  They must not be active.  i.e. they  should  be  failed  or
              spare devices.

              As  well  as the name of a device file (e.g.  /dev/sda1) the words failed, detached
              and names like set-A can be given to --remove.  The first causes all failed  device
              to  be  removed.   The second causes any device which is no longer connected to the
              system (i.e an 'open' returns ENXIO) to be removed.  The third will remove a set as
              describe below under --fail.

       -f, --fail
              Mark  listed devices as faulty.  As well as the name of a device file, the word de-
              tached or a set name like set-A can be given.  The former  will  cause  any  device
              that  has been detached from the system to be marked as failed.  It can then be re-
              moved.

              For RAID10 arrays where the number of copies evenly divides the number of  devices,
              the  devices can be conceptually divided into sets where each set contains a single
              complete copy of the data on the array.  Sometimes a RAID10 array will  be  config-
              ured  so that these sets are on separate controllers.  In this case all the devices
              in one set can be failed by giving a name like set-A or set-B to --fail.   The  ap-
              propriate set names are reported by --detail.

       --set-faulty
              same as --fail.

       --replace
              Mark  listed devices as requiring replacement.  As soon as a spare is available, it
              will be rebuilt and will replace the marked device.  This is similar to  marking  a
              device  as faulty, but the device remains in service during the recovery process to
              increase resilience against multiple failures.  When the replacement  process  fin-
              ishes, the replaced device will be marked as faulty.

       --with This  can follow a list of --replace devices.  The devices listed after --with will
              be preferentially used to replace the devices listed after --replace.  These device
              must already be spare devices in the array.

       --write-mostly
              Subsequent  devices  that  are  added or re-added will have the 'write-mostly' flag
              set.  This is only valid for RAID1 and means that the 'md' driver will avoid  read-
              ing from these devices if possible.

       --readwrite
              Subsequent  devices  that  are  added or re-added will have the 'write-mostly' flag
              cleared.

       --cluster-confirm
              Confirm the existence of the device. This is issued in response to an --add request
              by  a  node in a cluster. When a node adds a device it sends a message to all nodes
              in the cluster to look for a device with a UUID. This translates to a udev  notifi-
              cation  with  the UUID of the device to be added and the slot number. The receiving
              node must acknowledge this message  with  --cluster-confirm.  Valid  arguments  are
              <slot>:<devicename>  in  case the device is found or <slot>:missing in case the de-
              vice is not found.

       --add-journal
              Add journal to an existing array, or recreate journal  for  RAID-4/5/6  array  that
              lost  a journal device. To avoid interrupting on-going write opertions, --add-jour-
              nal only works for array in Read-Only state.

       --failfast
              Subsequent devices that are added or re-added will have the  'failfast'  flag  set.
              This  is  only valid for RAID1 and RAID10 and means that the 'md' driver will avoid
              long timeouts on error handling where possible.

       --nofailfast
              Subsequent devices that are re-added will be re-added without the  'failfast'  flag
              set.

       Each of these options requires that the first device listed is the array to be acted upon,
       and the remainder are component devices to be added, removed, marked as faulty, etc.  Sev-
       eral different operations can be specified for different devices, e.g.
            mdadm /dev/md0 --add /dev/sda1 --fail /dev/sdb1 --remove /dev/sdb1
       Each operation applies to all devices listed until the next operation.

       If  an  array  is using a write-intent bitmap, then devices which have been removed can be
       re-added in a way that avoids a full reconstruction but instead just  updates  the  blocks
       that  have changed since the device was removed.  For arrays with persistent metadata (su-
       perblocks) this is done automatically.  For arrays created with --build mdadm needs to  be
       told that this device we removed recently with --re-add.

       Devices can only be removed from an array if they are not in active use, i.e. that must be
       spares or failed devices.  To remove an active device, it must first be marked as faulty.

For Misc mode:
       -Q, --query
              Examine a device to see (1) if it is an md device and (2) if it is a  component  of
              an md array.  Information about what is discovered is presented.

       -D, --detail
              Print details of one or more md devices.

       --detail-platform
              Print  details  of  the platform's RAID capabilities (firmware / hardware topology)
              for a given metadata format. If used without argument, mdadm  will  scan  all  con-
              trollers  looking  for  their  capabilities. Otherwise, mdadm will only look at the
              controller specified by the argument in form of an absolute  filepath  or  a  link,
              e.g.  /sys/devices/pci0000:00/0000:00:1f.2.

       -Y, --export
              When used with --detail, --detail-platform, --examine, or --incremental output will
              be formatted as key=value pairs for easy import into the environment.

              With --incremental The value MD_STARTED indicates  whether  an  array  was  started
              (yes)  or  not,  which  may include a reason (unsafe, nothing, no).  Also the value
              MD_FOREIGN indicates if the array is expected on this host (no),  or  seems  to  be
              from elsewhere (yes).

       -E, --examine
              Print  contents  of  the metadata stored on the named device(s).  Note the contrast
              between --examine and --detail.  --examine applies to devices which are  components
              of an array, while --detail applies to a whole array which is currently active.

       --sparc2.2
              If  an  array  was  created on a SPARC machine with a 2.2 Linux kernel patched with
              RAID support, the superblock will have been created incorrectly, or at least incom-
              patibly  with 2.4 and later kernels.  Using the --sparc2.2 flag with --examine will
              fix the superblock before displaying it.  If this appears to do  the  right  thing,
              then the array can be successfully assembled using --assemble --update=sparc2.2.

       -X, --examine-bitmap
              Report  information about a bitmap file.  The argument is either an external bitmap
              file or an array component in case of an internal bitmap.  Note that  running  this
              on an array device (e.g.  /dev/md0) does not report the bitmap for that array.

       --examine-badblocks
              List  the bad-blocks recorded for the device, if a bad-blocks list has been config-
              ured. Currently only 1.x and IMSM metadata support bad-blocks lists.

       --dump=directory

       --restore=directory
              Save metadata from lists devices, or restore metadata to listed devices.

       -R, --run
              start a partially assembled array.  If --assemble did not find  enough  devices  to
              fully  start  the array, it might leaving it partially assembled.  If you wish, you
              can then use --run to start the array in degraded mode.

       -S, --stop
              deactivate array, releasing all resources.

       -o, --readonly
              mark array as readonly.

       -w, --readwrite
              mark array as readwrite.

       --zero-superblock
              If the device contains a valid md superblock, the block is overwritten with  zeros.
              With  --force  the  block  where  the superblock would be is overwritten even if it
              doesn't appear to be valid.

              Note: Be careful to call --zero-superblock with clustered  raid,  make  sure  array
              isn't used or assembled in other cluster node before execute it.

       --kill-subarray=
              If the device is a container and the argument to --kill-subarray specifies an inac-
              tive subarray in the container, then the subarray is deleted.  Deleting all  subar-
              rays  will  leave  an  'empty-container'  or  spare  superblock on the drives.  See
              --zero-superblock for completely removing a superblock.  Note that some formats de-
              pend  on  the  subarray  index  for generating a UUID, this command will fail if it
              would change the UUID of an active subarray.

       --update-subarray=
              If the device is a container and the argument to --update-subarray specifies a sub-
              array  in  the  container, then attempt to update the given superblock field in the
              subarray. See below in MISC MODE for details.

       -t, --test
              When used with --detail, the exit status of mdadm is set to reflect the  status  of
              the device.  See below in MISC MODE for details.

       -W, --wait
              For  each  md  device  given, wait for any resync, recovery, or reshape activity to
              finish before returning.  mdadm will return with success if it actually waited  for
              every device listed, otherwise it will return failure.

       --wait-clean
              For  each  md  device given, or each device in /proc/mdstat if --scan is given, ar-
              range for the array to be marked clean as soon as possible.  mdadm will return with
              success if the array uses external metadata and we successfully waited.  For native
              arrays this returns immediately as the kernel handles  dirty-clean  transitions  at
              shutdown.  No action is taken if safe-mode handling is disabled.

       --action=
              Set  the  "sync_action" for all md devices given to one of idle, frozen, check, re-
              pair.  Setting to idle will abort any currently running action though some  actions
              will  automatically  restart.   Setting to frozen will abort any current action and
              ensure no other action starts automatically.

              Details of check and repair can be found it md(4) under SCRUBBING AND MISMATCHES.

For Incremental Assembly mode:
       --rebuild-map, -r
              Rebuild the map file (/run/mdadm/map) that mdadm uses to help  track  which  arrays
              are currently being assembled.

       --run, -R
              Run  any  array  assembled  as  soon  as a minimal number of devices are available,
              rather than waiting until all expected devices are present.

       --scan, -s
              Only meaningful with -R this will scan the map file for arrays that are  being  in-
              crementally  assembled  and will try to start any that are not already started.  If
              any such array is listed in mdadm.conf as requiring an external bitmap, that bitmap
              will be attached first.

       --fail, -f
              This  allows the hot-plug system to remove devices that have fully disappeared from
              the kernel.  It will first fail and then remove the device from any  array  it  be-
              longs  to.  The device name given should be a kernel device name such as "sda", not
              a name in /dev.

       --path=
              Only used with --fail.  The 'path' given will be recorded so that if a  new  device
              appears at the same location it can be automatically added to the same array.  This
              allows the failed device to be automatically replaced by a new device without meta-
              data  if it appears at specified path.   This option is normally only set by a udev
              script.

For Monitor mode:
       -m, --mail
              Give a mail address to send alerts to.

       -p, --program, --alert
              Give a program to be run whenever an event is detected.

       -y, --syslog
              Cause all events to be reported through 'syslog'.  The messages  have  facility  of
              'daemon' and varying priorities.

       -d, --delay
              Give  a  delay in seconds.  mdadm polls the md arrays and then waits this many sec-
              onds before polling again.  The default is 60 seconds.  Since 2.6.16, there  is  no
              need  to  reduce  this  as  the  kernel  alerts mdadm immediately when there is any
              change.

       -r, --increment
              Give a percentage increment.  mdadm will generate RebuildNN events with  the  given
              percentage increment.

       -f, --daemonise
              Tell  mdadm  to run as a background daemon if it decides to monitor anything.  This
              causes it to fork and run in the child, and to disconnect from the  terminal.   The
              process  id  of  the  child is written to stdout.  This is useful with --scan which
              will only continue monitoring if a mail address or alert program is  found  in  the
              config file.

       -i, --pid-file
              When  mdadm  is  running in daemon mode, write the pid of the daemon process to the
              specified file, instead of printing it on standard output.

       -1, --oneshot
              Check arrays only once.  This will generate NewArray events and more  significantly
              DegradedArray and SparesMissing events.  Running
                      mdadm --monitor --scan -1
              from a cron script will ensure regular notification of any degraded arrays.

       -t, --test
              Generate  a  TestMessage  alert  for every array found at startup.  This alert gets
              mailed and passed to the alert program.  This can be used for  testing  that  alert
              message do get through successfully.

       --no-sharing
              This  inhibits  the functionality for moving spares between arrays.  Only one moni-
              toring process started with --scan but without this flag is allowed, otherwise  the
              two could interfere with each other.

ASSEMBLE MODE
       Usage: mdadm --assemble md-device options-and-component-devices...

       Usage: mdadm --assemble --scan md-devices-and-options...

       Usage: mdadm --assemble --scan options...

       This  usage  assembles one or more RAID arrays from pre-existing components.  For each ar-
       ray, mdadm needs to know the md device, the identity of the array, and a number of  compo-
       nent-devices.  These can be found in a number of ways.

       In  the  first usage example (without the --scan) the first device given is the md device.
       In the second usage example, all devices listed are treated as md devices and assembly  is
       attempted.   In  the third (where no devices are listed) all md devices that are listed in
       the configuration file are assembled.  If no arrays are  described  by  the  configuration
       file, then any arrays that can be found on unused devices will be assembled.

       If  precisely  one  device  is  listed, but --scan is not given, then mdadm acts as though
       --scan was given and identity information is extracted from the configuration file.

       The identity can be given with the --uuid option, the --name option, or the  --super-minor
       option,  will be taken from the md-device record in the config file, or will be taken from
       the super block of the first component-device listed on the command line.

       Devices can be given on the --assemble command line or in the config file.   Only  devices
       which  have  an md superblock which contains the right identity will be considered for any
       array.

       The config file is only used if explicitly named with --config or requested with (a possi-
       bly  implicit)  --scan.   In  the  later case, /etc/mdadm/mdadm.conf or /etc/mdadm.conf is
       used.

       If --scan is not given, then the config file will only be used to find the identity of  md
       arrays.

       Normally  the array will be started after it is assembled.  However if --scan is not given
       and not all expected drives were listed, then the array is not started (to  guard  against
       usage  errors).   To insist that the array be started in this case (as may work for RAID1,
       4, 5, 6, or 10), give the --run flag.

       If udev is active, mdadm does not create any entries in /dev but leaves that to udev.   It
       does  record  information  in  /run/mdadm/map  which will allow udev to choose the correct
       name.

       If mdadm detects that udev is not configured, it will create the devices in /dev itself.

       In Linux kernels prior to version 2.6.28 there were two distinctly different types  of  md
       devices  that  could be created: one that could be partitioned using standard partitioning
       tools and one that could not.  Since 2.6.28 that distinction is no longer relevant as both
       type  of  devices can be partitioned.  mdadm will normally create the type that originally
       could not be partitioned as it has a well defined major number (9).

       Prior to 2.6.28, it is important that mdadm chooses the correct type of  array  device  to
       use.   This  can be controlled with the --auto option.  In particular, a value of "mdp" or
       "part" or "p" tells mdadm to use a partitionable device rather than the default.

       In the no-udev case, the value given to --auto can be suffixed by a  number.   This  tells
       mdadm to create that number of partition devices rather than the default of 4.

       The  value  given to --auto can also be given in the configuration file as a word starting
       auto= on the ARRAY line for the relevant array.

   Auto Assembly
       When --assemble is used with --scan and no devices are listed, mdadm will first attempt to
       assemble all the arrays listed in the config file.

       If  no  arrays  are  listed  in the config (other than those marked <ignore>) it will look
       through the available devices for possible arrays and will try to assemble  anything  that
       it  finds.   Arrays  which are tagged as belonging to the given homehost will be assembled
       and started normally.  Arrays which do not obviously belong to this host are  given  names
       that are expected not to conflict with anything local, and are started "read-auto" so that
       nothing is written to any device until the array is written to. i.e.  automatic resync etc
       is delayed.

       If  mdadm  finds a consistent set of devices that look like they should comprise an array,
       and if the superblock is tagged as belonging to the given home host, it will automatically
       choose  a device name and try to assemble the array.  If the array uses version-0.90 meta-
       data, then the minor number as recorded in the superblock is used  to  create  a  name  in
       /dev/md/  so  for  example /dev/md/3.  If the array uses version-1 metadata, then the name
       from the superblock is used to similarly create a name in /dev/md/ (the name will have any
       'host' prefix stripped first).

       This  behaviour  can  be  modified  by the AUTO line in the mdadm.conf configuration file.
       This line can indicate that specific metadata type should, or should not, be automatically
       assembled.  If an array is found which is not listed in mdadm.conf and has a metadata for-
       mat that is denied by the AUTO line, then it will not be assembled.   The  AUTO  line  can
       also request that all arrays identified as being for this homehost should be assembled re-
       gardless of their metadata type.  See mdadm.conf(5) for further details.

       Note: Auto assembly cannot be used for assembling and activating some arrays which are un-
       dergoing reshape.  In particular as the backup-file cannot be given, any reshape which re-
       quires a backup-file to continue cannot be started by auto assembly.  An  array  which  is
       growing  to  more devices and has passed the critical section can be assembled using auto-
       assembly.

BUILD MODE
       Usage: mdadm --build md-device --chunk=X --level=Y --raid-devices=Z devices

       This usage is similar to --create.  The difference is that it creates an array  without  a
       superblock.  With these arrays there is no difference between initially creating the array
       and subsequently assembling the array, except that hopefully there is useful data there in
       the second case.

       The  level  may  raid0,  linear, raid1, raid10, multipath, or faulty, or one of their syn-
       onyms.  All devices must be listed and the array will be started once complete.   It  will
       often be appropriate to use --assume-clean with levels raid1 or raid10.

CREATE MODE
       Usage: mdadm --create md-device --chunk=X --level=Y
                   --raid-devices=Z devices

       This  usage  will  initialise a new md array, associate some devices with it, and activate
       the array.

       The named device will normally not exist when mdadm --create is run, but will  be  created
       by udev once the array becomes active.

       The  max length md-device name is limited to 32 characters.  Different metadata types have
       more strict limitation (like IMSM where only 16 characters are allowed).  For that reason,
       long name could be truncated or rejected, it depends on metadata policy.

       As devices are added, they are checked to see if they contain RAID superblocks or filesys-
       tems.  They are also checked to see if the variance in device size exceeds 1%.

       If any discrepancy is found, the array will not automatically be run, though the  presence
       of a --run can override this caution.

       To  create  a  "degraded"  array  in  which some devices are missing, simply give the word
       "missing" in place of a device name.  This will cause mdadm  to  leave  the  corresponding
       slot  in  the  array empty.  For a RAID4 or RAID5 array at most one slot can be "missing";
       for a RAID6 array at most two slots.  For a RAID1 array, only one real device needs to  be
       given.  All of the others can be "missing".

       When  creating a RAID5 array, mdadm will automatically create a degraded array with an ex-
       tra spare drive.  This is because building the spare into a degraded array is  in  general
       faster  than  resyncing  the parity on a non-degraded, but not clean, array.  This feature
       can be overridden with the --force option.

       When creating an array with version-1 metadata a name for the array is required.  If  this
       is  not given with the --name option, mdadm will choose a name based on the last component
       of the name of the device being created.  So if /dev/md3 is being created, then the name 3
       will be chosen.  If /dev/md/home is being created, then the name home will be used.

       When  creating  a partition based array, using mdadm with version-1.x metadata, the parti-
       tion type should be set to 0xDA (non fs-data).  This type  selection  allows  for  greater
       precision since using any other [RAID auto-detect (0xFD) or a GNU/Linux partition (0x83)],
       might create problems in the event of array recovery through a live cdrom.

       A new array will normally get a randomly assigned 128bit UUID which is very likely  to  be
       unique.   If  you  have a specific need, you can choose a UUID for the array by giving the
       --uuid= option.  Be warned that creating two arrays with the same UUID  is  a  recipe  for
       disaster.   Also,  using  --uuid=  when  creating a v0.90 array will silently override any
       --homehost= setting.

       If the array type supports a write-intent bitmap, and if the devices in the  array  exceed
       100G  is  size,  an  internal  write-intent bitmap will automatically be added unless some
       other option is explicitly requested with the --bitmap option or a  different  consistency
       policy  is  selected  with the --consistency-policy option. In any case space for a bitmap
       will be reserved so that one can be added later with --grow --bitmap=internal.

       If the metadata type supports it (currently only 1.x and IMSM metadata), space will be al-
       located  to  store  a  bad  block  list.   This allows a modest number of bad blocks to be
       recorded, allowing the drive to remain in service while only partially functional.

       When creating an array within a CONTAINER mdadm can be given either the list of devices to
       use,  or  simply  the name of the container.  The former case gives control over which de-
       vices in the container will be used for the array.  The latter case allows mdadm to  auto-
       matically choose which devices to use based on how much spare space is available.

       The General Management options that are valid with --create are:

       --run  insist on running the array even if some devices look like they might be in use.

       --readonly
              start the array in readonly mode.

MANAGE MODE
       Usage: mdadm device options... devices...

       This  usage  will allow individual devices in an array to be failed, removed or added.  It
       is possible to perform multiple operations with on command.  For example:
         mdadm /dev/md0 -f /dev/hda1 -r /dev/hda1 -a /dev/hda1
       will firstly mark /dev/hda1 as faulty in /dev/md0 and will then remove it from  the  array
       and  finally  add  it  back in as a spare.  However only one md array can be affected by a
       single command.

       When a device is added to an active array, mdadm checks to see if it has  metadata  on  it
       which  suggests  that  it  was  recently  a  member of the array.  If it does, it tries to
       "re-add" the device.  If there have been no changes since the device was  removed,  or  if
       the  array  has a write-intent bitmap which has recorded whatever changes there were, then
       the device will immediately become a full  member  of  the  array  and  those  differences
       recorded in the bitmap will be resolved.

MISC MODE
       Usage: mdadm options ...  devices ...

       MISC  mode includes a number of distinct operations that operate on distinct devices.  The
       operations are:

       --query
              The device is examined to see if it is (1) an active md array, or (2)  a  component
              of an md array.  The information discovered is reported.

       --detail
              The  device  should be an active md device.  mdadm will display a detailed descrip-
              tion of the array.  --brief or --scan will cause the output to be less detailed and
              the  format  to  be suitable for inclusion in mdadm.conf.  The exit status of mdadm
              will normally be 0 unless mdadm failed to get  useful  information  about  the  de-
              vice(s); however, if the --test option is given, then the exit status will be:

              0      The array is functioning normally.

              1      The array has at least one failed device.

              2      The array has multiple failed devices such that it is unusable.

              4      There was an error while trying to get information about the device.

       --detail-platform
              Print  detail  of  the platform's RAID capabilities (firmware / hardware topology).
              If the metadata is specified with -e or --metadata= then the return status will be:

              0      metadata successfully enumerated its platform components on this system

              1      metadata is platform independent

              2      metadata failed to find its platform components on this system

       --update-subarray=
              If the device is a container and the argument to --update-subarray specifies a sub-
              array  in  the  container, then attempt to update the given superblock field in the
              subarray.  Similar to updating an array in "assemble" mode, the field to update  is
              selected  by  -U  or --update= option. The supported options are name, ppl, no-ppl,
              bitmap and no-bitmap.

              The name option updates the subarray name in the metadata, it may  not  affect  the
              device node name or the device node symlink until the subarray is re-assembled.  If
              updating name would change the  UUID  of  an  active  subarray  this  operation  is
              blocked, and the command will end in an error.

              The  ppl  and no-ppl options enable and disable PPL in the metadata. Currently sup-
              ported only for IMSM subarrays.

              The bitmap and no-bitmap options enable and  disable  write-intent  bitmap  in  the
              metadata. Currently supported only for IMSM subarrays.

       --examine
              The device should be a component of an md array.  mdadm will read the md superblock
              of the device and display the contents.  If --brief or --scan is given, then multi-
              ple  devices that are components of the one array are grouped together and reported
              in a single entry suitable for inclusion in mdadm.conf.

              Having --scan without listing any devices will cause all devices listed in the con-
              fig file to be examined.

       --dump=directory
              If  the  device contains RAID metadata, a file will be created in the directory and
              the metadata will be written to it.  The file will be the same size as  the  device
              and  have the metadata written in the file at the same locate that it exists in the
              device.  However the file will be "sparse" so that  only  those  blocks  containing
              metadata will be allocated. The total space used will be small.

              The  file name used in the directory will be the base name of the device.   Further
              if any links appear in /dev/disk/by-id which point to the device, then  hard  links
              to the file will be created in directory based on these by-id names.

              Multiple devices can be listed and their metadata will all be stored in the one di-
              rectory.

       --restore=directory
              This is the reverse of --dump.  mdadm will locate a file in the directory that  has
              a  name  appropriate for the given device and will restore metadata from it.  Names
              that match /dev/disk/by-id names are preferred, however if two of  those  refer  to
              different files, mdadm will not choose between them but will abort the operation.

              If  a  file  name is given instead of a directory then mdadm will restore from that
              file to a single device, always provided the size of the file matches that  of  the
              device, and the file contains valid metadata.

       --stop The  devices  should be active md arrays which will be deactivated, as long as they
              are not currently in use.

       --run  This will fully activate a partially assembled md array.

       --readonly
              This will mark an active array as read-only, providing that it is not currently be-
              ing used.

       --readwrite
              This will change a readonly array back to being read/write.

       --scan For  all operations except --examine, --scan will cause the operation to be applied
              to all arrays listed in /proc/mdstat.  For --examine,  --scan  causes  all  devices
              listed in the config file to be examined.

       -b, --brief
              Be  less  verbose.   This  is used with --detail and --examine.  Using --brief with
              --verbose gives an intermediate level of verbosity.

MONITOR MODE
       Usage: mdadm --monitor options... devices...

       This usage causes mdadm to periodically poll a number of md arrays and to  report  on  any
       events  noticed.   mdadm  will  never  exit  once  it  decides that there are arrays to be
       checked, so it should normally be run in the background.

       As well as reporting events, mdadm may move a spare drive from one  array  to  another  if
       they are in the same spare-group or domain and if the destination array has a failed drive
       but no spares.

       If any devices are listed on the command line, mdadm  will  only  monitor  those  devices.
       Otherwise  all  arrays  listed  in  the configuration file will be monitored.  Further, if
       --scan is given, then any other md devices that appear in /proc/mdstat will also be  moni-
       tored.

       The  result of monitoring the arrays is the generation of events.  These events are passed
       to a separate program (if specified) and may be mailed to a given E-mail address.

       When passing events to a program, the program is run once for each event, and is  given  2
       or 3 command-line arguments: the first is the name of the event (see below), the second is
       the name of the md device which is affected, and the third is the name of a related device
       if relevant (such as a component device that has failed).

       If  --scan  is given, then a program or an E-mail address must be specified on the command
       line or in the config file.  If neither are available, then mdadm will  not  monitor  any-
       thing.   Without  --scan, mdadm will continue monitoring as long as something was found to
       monitor.  If no program or email is given, then each event is reported to stdout.

       The different events are:

           DeviceDisappeared
                  An md array which previously was configured appears to no longer be configured.
                  (syslog priority: Critical)

                  If  mdadm  was  told to monitor an array which is RAID0 or Linear, then it will
                  report DeviceDisappeared with the extra information Wrong-Level.  This  is  be-
                  cause  RAID0  and Linear do not support the device-failed, hot-spare and resync
                  operations which are monitored.

           RebuildStarted
                  An md array started reconstruction (e.g. recovery, resync, reshape, check,  re-
                  pair). (syslog priority: Warning)

           RebuildNN
                  Where  NN  is  a two-digit number (ie. 05, 48). This indicates that rebuild has
                  passed that many percent of the total. The events are generated with fixed  in-
                  crement since 0. Increment size may be specified with a commandline option (de-
                  fault is 20). (syslog priority: Warning)

           RebuildFinished
                  An md array that was rebuilding, isn't any more,  either  because  it  finished
                  normally or was aborted. (syslog priority: Warning)

           Fail   An  active component device of an array has been marked as faulty. (syslog pri-
                  ority: Critical)

           FailSpare
                  A spare component device which was being rebuilt to replace a faulty device has
                  failed. (syslog priority: Critical)

           SpareActive
                  A spare component device which was being rebuilt to replace a faulty device has
                  been successfully rebuilt and has been made active.  (syslog priority: Info)

           NewArray
                  A new md array has been detected in the /proc/mdstat file.   (syslog  priority:
                  Info)

           DegradedArray
                  A  newly  noticed  array appears to be degraded.  This message is not generated
                  when mdadm notices a drive failure which  causes  degradation,  but  only  when
                  mdadm  notices that an array is degraded when it first sees the array.  (syslog
                  priority: Critical)

           MoveSpare
                  A spare drive has been moved from one array in a spare-group or domain  to  an-
                  other to allow a failed drive to be replaced.  (syslog priority: Info)

           SparesMissing
                  If  mdadm  has been told, via the config file, that an array should have a cer-
                  tain number of spare devices, and mdadm detects that it  has  fewer  than  this
                  number  when  it  first sees the array, it will report a SparesMissing message.
                  (syslog priority: Warning)

           TestMessage
                  An array was found at startup, and the --test flag was given.   (syslog  prior-
                  ity: Info)

       Only Fail, FailSpare, DegradedArray, SparesMissing and TestMessage cause Email to be sent.
       All events cause the program to be run.  The program is run with two or  three  arguments:
       the event name, the array device and possibly a second device.

       Each  event  has an associated array device (e.g.  /dev/md1) and possibly a second device.
       For Fail, FailSpare, and SpareActive the second device is the relevant  component  device.
       For MoveSpare the second device is the array that the spare was moved from.

       For  mdadm  to  move spares from one array to another, the different arrays need to be la-
       beled with the same spare-group or the spares must be allowed to migrate through  matching
       POLICY  domains  in the configuration file.  The spare-group name can be any string; it is
       only necessary that different spare groups use different names.

       When mdadm detects that an array in a spare group has fewer active devices than  necessary
       for  the  complete  array, and has no spare devices, it will look for another array in the
       same spare group that has a full complement of working drive and a spare.   It  will  then
       attempt to remove the spare from the second drive and add it to the first.  If the removal
       succeeds but the adding fails, then it is added back to the original array.

       If the spare group for a degraded array is not defined, mdadm will look at  the  rules  of
       spare  migration  specified by POLICY lines in mdadm.conf and then follow similar steps as
       above if a matching spare is found.

GROW MODE
       The GROW mode is used for changing the size or shape of an  active  array.   For  this  to
       work,  the  kernel  must  support the necessary change.  Various types of growth are being
       added during 2.6 development.

       Currently the supported changes include

       o   change the "size" attribute for RAID1, RAID4, RAID5 and RAID6.

       o   increase or decrease the "raid-devices" attribute of RAID0, RAID1, RAID4,  RAID5,  and
           RAID6.

       o   change the chunk-size and layout of RAID0, RAID4, RAID5, RAID6 and RAID10.

       o   convert  between  RAID1  and RAID5, between RAID5 and RAID6, between RAID0, RAID4, and
           RAID5, and between RAID0 and RAID10 (in the near-2 mode).

       o   add a write-intent bitmap to any array which  supports  these  bitmaps,  or  remove  a
           write-intent bitmap from such an array.

       o   change the array's consistency policy.

       Using  GROW  on  containers is currently supported only for Intel's IMSM container format.
       The number of devices in a container can be increased - which affects all  arrays  in  the
       container  - or an array in a container can be converted between levels where those levels
       are supported by the container, and the conversion is on of those listed above.

       Notes:

       o   Intel's native checkpointing doesn't use --backup-file option and  it  is  transparent
           for assembly feature.

       o   Roaming between Windows(R) and Linux systems for IMSM metadata is not supported during
           grow process.

       o   When growing a raid0 device, the new component disk size  (or  external  backup  size)
           should  be larger than LCM(old, new) * chunk-size * 2, where LCM() is the least common
           multiple of the old and new count of component disks, and "* 2" comes  from  the  fact
           that mdadm refuses to use more than half of a spare device for backup space.

   SIZE CHANGES
       Normally  when  an array is built the "size" is taken from the smallest of the drives.  If
       all the small drives in an arrays are, one at a time, removed  and  replaced  with  larger
       drives,  then  you  could have an array of large drives with only a small amount used.  In
       this situation, changing the "size" with "GROW" mode will allow the extra space  to  start
       being  used.   If the size is increased in this way, a "resync" process will start to make
       sure the new parts of the array are synchronised.

       Note that when an array changes size, any filesystem that may be stored in the array  will
       not  automatically grow or shrink to use or vacate the space.  The filesystem will need to
       be explicitly told to use the extra space after growing, or to reduce its  size  prior  to
       shrinking the array.

       Also  the  size  of an array cannot be changed while it has an active bitmap.  If an array
       has a bitmap, it must be removed before the size can be changed. Once the change  is  com-
       plete a new bitmap can be created.

       Note: --grow --size is not yet supported for external file bitmap.

   RAID-DEVICES CHANGES
       A  RAID1  array  can  work with any number of devices from 1 upwards (though 1 is not very
       useful).  There may be times which you want to increase or decrease the number  of  active
       devices.  Note that this is different to hot-add or hot-remove which changes the number of
       inactive devices.

       When reducing the number of devices in a RAID1 array, the slots which are  to  be  removed
       from  the  array  must  already be vacant.  That is, the devices which were in those slots
       must be failed and removed.

       When the number of devices is increased, any hot spares that are present will be activated
       immediately.

       Changing  the  number  of  active  devices in a RAID5 or RAID6 is much more effort.  Every
       block in the array will need to be read and written back to a new location.  From  2.6.17,
       the  Linux  Kernel  is able to increase the number of devices in a RAID5 safely, including
       restarting an interrupted "reshape".  From 2.6.31, the Linux Kernel is able to increase or
       decrease the number of devices in a RAID5 or RAID6.

       From  2.6.35,  the  Linux Kernel is able to convert a RAID0 in to a RAID4 or RAID5.  mdadm
       uses this functionality and the ability to add devices to a RAID4 to allow devices  to  be
       added to a RAID0.  When requested to do this, mdadm will convert the RAID0 to a RAID4, add
       the necessary disks and make the reshape happen, and then convert the RAID4 back to RAID0.

       When decreasing the number of devices, the size of the array will also decrease.  If there
       was  data  in  the array, it could get destroyed and this is not reversible, so you should
       firstly shrink the filesystem on the array to fit within the new size.   To  help  prevent
       accidents,  mdadm requires that the size of the array be decreased first with mdadm --grow
       --array-size.  This is a reversible change which simply makes the end of the  array  inac-
       cessible.   The integrity of any data can then be checked before the non-reversible reduc-
       tion in the number of devices is request.

       When relocating the first few stripes on a RAID5 or RAID6, it is not possible to keep  the
       data on disk completely consistent and crash-proof.  To provide the required safety, mdadm
       disables writes to the array while this "critical section" is reshaped, and takes a backup
       of  the  data  that is in that section.  For grows, this backup may be stored in any spare
       devices that the array has, however it can also be stored in  a  separate  file  specified
       with  the  --backup-file  option,  and is required to be specified for shrinks, RAID level
       changes and layout changes.  If this option is used, and the system does crash during  the
       critical  period, the same file must be passed to --assemble to restore the backup and re-
       assemble the array.  When shrinking rather than growing the array,  the  reshape  is  done
       from  the  end  towards  the beginning, so the "critical section" is at the end of the re-
       shape.

   LEVEL CHANGES
       Changing the RAID level of any array happens instantaneously.  However  in  the  RAID5  to
       RAID6  case  this  requires  a  non-standard layout of the RAID6 data, and in the RAID6 to
       RAID5 case that non-standard layout is required before the change can be accomplished.  So
       while  the  level  change is instant, the accompanying layout change can take quite a long
       time.  A --backup-file is required.  If the array is not  simultaneously  being  grown  or
       shrunk,  so  that  the  array size will remain the same - for example, reshaping a 3-drive
       RAID5 into a 4-drive RAID6 - the backup file will be used not just for  a  "critical  sec-
       tion" but throughout the reshape operation, as described below under LAYOUT CHANGES.

   CHUNK-SIZE AND LAYOUT CHANGES
       Changing  the chunk-size or layout without also changing the number of devices as the same
       time will involve re-writing all blocks in-place.  To ensure against data loss in the case
       of a crash, a --backup-file must be provided for these changes.  Small sections of the ar-
       ray will be copied to the backup file while they are being rearranged.   This  means  that
       all  the data is copied twice, once to the backup and once to the new layout on the array,
       so this type of reshape will go very slowly.

       If the reshape is interrupted for any reason, this backup file must be made  available  to
       mdadm  --assemble so the array can be reassembled.  Consequently the file cannot be stored
       on the device being reshaped.

   BITMAP CHANGES
       A write-intent bitmap can be added to, or removed from, an active array.  Either  internal
       bitmaps,  or bitmaps stored in a separate file, can be added.  Note that if you add a bit-
       map stored in a file which is in a filesystem that is on the RAID  array  being  affected,
       the system will deadlock.  The bitmap must be on a separate filesystem.

   CONSISTENCY POLICY CHANGES
       The consistency policy of an active array can be changed by using the --consistency-policy
       option in Grow mode. Currently this works only for the ppl and resync policies and  allows
       one to enable or disable the RAID5 Partial Parity Log (PPL).

INCREMENTAL MODE
       Usage:  mdadm  --incremental  [--run] [--quiet] component-device [optional-aliases-for-de-
                   vice]

       Usage: mdadm --incremental --fail component-device

       Usage: mdadm --incremental --rebuild-map

       Usage: mdadm --incremental --run --scan

       This mode is designed to be used in conjunction with a device discovery  system.   As  de-
       vices are found in a system, they can be passed to mdadm --incremental to be conditionally
       added to an appropriate array.

       Conversely, it can also be used with the --fail flag to do  just  the  opposite  and  find
       whatever array a particular device is part of and remove the device from that array.

       If  the  device  passed  is  a  CONTAINER device created by a previous call to mdadm, then
       rather than trying to add that device to an array, all the arrays described by  the  meta-
       data of the container will be started.

       mdadm performs a number of tests to determine if the device is part of an array, and which
       array it should be part of.  If an appropriate array is found, or can  be  created,  mdadm
       adds the device to the array and conditionally starts the array.

       Note  that  mdadm will normally only add devices to an array which were previously working
       (active or spare) parts of that array.  The support for automatic inclusion of a new drive
       as a spare in some array requires a configuration through POLICY in config file.

       The tests that mdadm makes are as follow:

       +      Is  the device permitted by mdadm.conf?  That is, is it listed in a DEVICES line in
              that file.  If DEVICES is absent then the default it to allow  any  device.   Simi-
              larly  if  DEVICES contains the special word partitions then any device is allowed.
              Otherwise the device name given to mdadm, or one of the aliases given, or an  alias
              found in the filesystem, must match one of the names or patterns in a DEVICES line.

              This  is the only context where the aliases are used.  They are usually provided by
              a udev rules mentioning $env{DEVLINKS}.

       +      Does the device have a valid md superblock?  If a specific metadata version is  re-
              quested  with --metadata or -e then only that style of metadata is accepted, other-
              wise mdadm finds any known version of metadata.  If no md metadata  is  found,  the
              device may be still added to an array as a spare if POLICY allows.

       mdadm keeps a list of arrays that it has partially assembled in /run/mdadm/map.  If no ar-
       ray exists which matches the metadata on the new device, mdadm must choose a  device  name
       and  unit number.  It does this based on any name given in mdadm.conf or any name informa-
       tion stored in the metadata.  If this name suggests a unit number,  that  number  will  be
       used, otherwise a free unit number will be chosen.  Normally mdadm will prefer to create a
       partitionable array, however if the CREATE line in mdadm.conf suggests that  a  non-parti-
       tionable array is preferred, that will be honoured.

       If  the array is not found in the config file and its metadata does not identify it as be-
       longing to the "homehost", then mdadm will choose a name for the array  which  is  certain
       not  to conflict with any array which does belong to this host.  It does this be adding an
       underscore and a small number to the name preferred by the metadata.

       Once an appropriate array is found or created and the device is added, mdadm  must  decide
       if  the  array  is  ready to be started.  It will normally compare the number of available
       (non-spare) devices to the number of devices that the metadata suggests need to be active.
       If  there  are  at least that many, the array will be started.  This means that if any de-
       vices are missing the array will not be restarted.

       As an alternative, --run may be passed to mdadm in which case the array  will  be  run  as
       soon as there are enough devices present for the data to be accessible.  For a RAID1, that
       means one device will start the array.  For a clean RAID5, the array will  be  started  as
       soon as all but one drive is present.

       Note that neither of these approaches is really ideal.  If it can be known that all device
       discovery has completed, then
          mdadm -IRs
       can be run which will try to start all arrays  that  are  being  incrementally  assembled.
       They are started in "read-auto" mode in which they are read-only until the first write re-
       quest.  This means that no metadata updates are made and no attempt at resync or  recovery
       happens.  Further devices that are found before the first write can still be added safely.

ENVIRONMENT
       This section describes environment variables that affect how mdadm operates.

       MDADM_NO_MDMON
              Setting  this  value  to  1  will prevent mdadm from automatically launching mdmon.
              This variable is intended primarily for debugging mdadm/mdmon.

       MDADM_NO_UDEV
              Normally, mdadm does not create any device nodes in /dev, but leaves that  task  to
              udev.  If udev appears not to be configured, or if this environment variable is set
              to '1', the mdadm will create and devices that are needed.

       MDADM_NO_SYSTEMCTL
              If mdadm detects that systemd is in use it will normally request systemd  to  start
              various  background tasks (particularly mdmon) rather than forking and running them
              in the background.  This can be suppressed by setting MDADM_NO_SYSTEMCTL=1.

       IMSM_NO_PLATFORM
              A key value of IMSM metadata is that it allows interoperability with boot  ROMs  on
              Intel  platforms, and with other major operating systems.  Consequently, mdadm will
              only allow an IMSM array to be created or modified if detects that it is running on
              an Intel platform which supports IMSM, and supports the particular configuration of
              IMSM that is being requested (some functionality requires newer OROM support).

              These checks can be suppressed by setting IMSM_NO_PLATFORM=1  in  the  environment.
              This  can be useful for testing or for disaster recovery.  You should be aware that
              interoperability may be compromised by setting this value.

       MDADM_GROW_ALLOW_OLD
              If an array is stopped while it is performing a reshape and that reshape was making
              use of a backup file, then when the array is re-assembled mdadm will sometimes com-
              plain that the backup file is too old.  If this happens and you are certain  it  is
              the  right  backup  file,  you  can  over-ride this check by setting MDADM_GROW_AL-
              LOW_OLD=1 in the environment.

       MDADM_CONF_AUTO
              Any string given in this variable is added to the start of the  AUTO  line  in  the
              config file, or treated as the whole AUTO line if none is given.  It can be used to
              disable certain metadata types when mdadm is called from a boot script.  For  exam-
              ple
                  export MDADM_CONF_AUTO='-ddf -imsm'
              will  make  sure  that mdadm does not automatically assemble any DDF or IMSM arrays
              that are found.  This can be useful on systems configured  to  manage  such  arrays
              with dmraid.

EXAMPLES
         mdadm --query /dev/name-of-device
       This  will find out if a given device is a RAID array, or is part of one, and will provide
       brief information about the device.

         mdadm --assemble --scan
       This will assemble and start all arrays listed in the standard config file.  This  command
       will typically go in a system startup file.

         mdadm --stop --scan
       This  will  shut  down  all  arrays that can be shut down (i.e. are not currently in use).
       This will typically go in a system shutdown script.

         mdadm --follow --scan --delay=120
       If (and only if) there is an Email address or program given in the standard  config  file,
       then monitor the status of all arrays listed in that file by polling them ever 2 minutes.

         mdadm --create /dev/md0 --level=1 --raid-devices=2 /dev/hd[ac]1
       Create /dev/md0 as a RAID1 array consisting of /dev/hda1 and /dev/hdc1.

         echo 'DEVICE /dev/hd*[0-9] /dev/sd*[0-9]' > mdadm.conf
         mdadm --detail --scan >> mdadm.conf
       This  will  create a prototype config file that describes currently active arrays that are
       known to be made from partitions of IDE or SCSI drives.  This file should be reviewed  be-
       fore being used as it may contain unwanted detail.

         echo 'DEVICE /dev/hd[a-z] /dev/sd*[a-z]' > mdadm.conf
         mdadm --examine --scan --config=mdadm.conf >> mdadm.conf
       This  will  find  arrays  which could be assembled from existing IDE and SCSI whole drives
       (not partitions), and store the information in the format of a config file.  This file  is
       very  likely  to contain unwanted detail, particularly the devices= entries.  It should be
       reviewed and edited before being used as an actual config file.

         mdadm --examine --brief --scan --config=partitions
         mdadm -Ebsc partitions
       Create a list of devices by reading /proc/partitions, scan these for RAID superblocks, and
       printout a brief listing of all that were found.

         mdadm -Ac partitions -m 0 /dev/md0
       Scan  all  partitions  and devices listed in /proc/partitions and assemble /dev/md0 out of
       all such devices with a RAID superblock with a minor number of 0.

         mdadm --monitor --scan --daemonise > /run/mdadm/mon.pid
       If config file contains a mail address or alert program, run mdadm in  the  background  in
       monitor   mode   monitoring   all   md  devices.   Also  write  pid  of  mdadm  daemon  to
       /run/mdadm/mon.pid.

         mdadm -Iq /dev/somedevice
       Try to incorporate newly discovered device into some array as appropriate.

         mdadm --incremental --rebuild-map --run --scan
       Rebuild the array map from any current arrays, and then start any that can be started.

         mdadm /dev/md4 --fail detached --remove detached
       Any devices which are components of /dev/md4 will be marked as faulty and then remove from
       the array.

         mdadm --grow /dev/md4 --level=6 --backup-file=/root/backup-md4
       The  array  /dev/md4  which  is currently a RAID5 array will be converted to RAID6.  There
       should normally already be a spare drive attached to the array as a RAID6 needs  one  more
       drive than a matching RAID5.

         mdadm --create /dev/md/ddf --metadata=ddf --raid-disks 6 /dev/sd[a-f]
       Create a DDF array over 6 devices.

         mdadm --create /dev/md/home -n3 -l5 -z 30000000 /dev/md/ddf
       Create  a  RAID5  array over any 3 devices in the given DDF set.  Use only 30 gigabytes of
       each device.

         mdadm -A /dev/md/ddf1 /dev/sd[a-f]
       Assemble a pre-exist ddf array.

         mdadm -I /dev/md/ddf1
       Assemble all arrays contained in the ddf array, assigning names as appropriate.

         mdadm --create --help
       Provide help about the Create mode.

         mdadm --config --help
       Provide help about the format of the config file.

         mdadm --help
       Provide general help.

FILES
   /proc/mdstat
       If you're using the /proc filesystem, /proc/mdstat lists all active md devices with infor-
       mation  about them.  mdadm uses this to find arrays when --scan is given in Misc mode, and
       to monitor array reconstruction on Monitor mode.

   /etc/mdadm/mdadm.conf (or /etc/mdadm.conf)
       The config file lists which devices may be scanned to see if they contain MD super  block,
       and  gives  identifying  information (e.g. UUID) about known MD arrays.  See mdadm.conf(5)
       for more details.

   /etc/mdadm/mdadm.conf.d (or /etc/mdadm.conf.d)
       A directory containing configuration files which are read in lexical order.

   /run/mdadm/map
       When --incremental mode is used, this file gets a list of arrays currently being created.

DEVICE NAMES
       mdadm understand two sorts of names for array devices.

       The first is the so-called 'standard' format name, which matches the  names  used  by  the
       kernel and which appear in /proc/mdstat.

       The  second  sort can be freely chosen, but must reside in /dev/md/.  When giving a device
       name to mdadm to create or assemble an array, either full path name such  as  /dev/md0  or
       /dev/md/home can be given, or just the suffix of the second sort of name, such as home can
       be given.

       When mdadm chooses device names during auto-assembly  or  incremental  assembly,  it  will
       sometimes  add  a small sequence number to the end of the name to avoid conflicted between
       multiple arrays that have the same name.  If mdadm can reasonably determine that the array
       really is meant for this host, either by a hostname in the metadata, or by the presence of
       the array in mdadm.conf, then it will leave off the suffix if possible.  Also if the home-
       host  is  specified  as  <ignore> mdadm will only use a suffix if a different array of the
       same name already exists or is listed in the config file.

       The standard names for non-partitioned arrays (the only sort of md array available in  2.4
       and earlier) are of the form

              /dev/mdNN

       where  NN is a number.  The standard names for partitionable arrays (as available from 2.6
       onwards) are of the form:

              /dev/md_dNN

       Partition numbers should be indicated by adding "pMM" to these, thus "/dev/md/d1p2".

       From kernel version 2.6.28 the "non-partitioned array" can actually  be  partitioned.   So
       the  "md_dNN" names are no longer needed, and partitions such as "/dev/mdNNpXX" are possi-
       ble.

       From kernel version 2.6.29 standard names can be non-numeric following the form:

              /dev/md_XXX

       where XXX is any string.  These names are supported by mdadm since  version  3.3  provided
       they are enabled in mdadm.conf.

NOTE
       mdadm was previously known as mdctl.

SEE ALSO
       For further information on mdadm usage, MD and the various levels of RAID, see:

              https://raid.wiki.kernel.org/

       (based upon Jakob Ostergaard's Software-RAID.HOWTO)

       The latest version of mdadm should always be available from

              https://www.kernel.org/pub/linux/utils/raid/mdadm/

       Related man pages:

       mdmon(8), mdadm.conf(5), md(4).

v4.2                                                                                     MDADM(8)

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