Provided by: mdadm_3.2.3-2ubuntu1_amd64 bug


       mdadm - manage MD devices aka Linux Software RAID


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


       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
       single  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

       Currently,  Linux  supports LINEAR md devices, RAID0 (striping), RAID1 (mirroring), RAID4,

       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/multipath 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
       metadata.  Other normal arrays (RAID1 etc) can be created inside the container.


       mdadm has several major modes of operation:

              Assemble  the  components  of  a  previously  created  array  into an active array.
              Components can be explicitly given or can be searched for.  mdadm checks  that  the
              components  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
              components  have  been  requested.   Because of this, the Build mode should only be
              used together 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
              otherwise 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
              meaningful 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
              supported  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, as well as  adding  or  removing  a  write-
              intent bitmap.

       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
              interface  to a hot-plug system.  As each device is detected, mdadm has a chance to
              include 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
              container 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,
              operations on component devices such as erasing old  superblocks,  and  information
              gathering operations.

              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 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

              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  --add,  --fail,  or
       --remove,  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.

              Display  more  detailed  help  about  command  line  parsing and some commonly used

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

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

       -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.  Default is to use /etc/mdadm/mdadm.conf, or  if  that  is
              missing, then /etc/mdadm.conf.  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

       -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,
              array 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
              setting 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:


              This will override any HOMEHOST  setting  in  the  config  file  and  provides  the
              identity 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
              version-1 superblocks, it will be prefixed to the  array  name.   For  version-0.90
              superblocks, 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
              below under Auto Assembly.

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
              arrays, 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 Kibibytes) 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.  If this is not specified (as it normally
              is not) the smallest drive (or partition) sets the  size,  though  if  there  is  a
              variance among the drives of greater than 1%, a warning is issued.

              A  suffix  of  'M'  or  'G'  can  be  given  to  indicate  Megabytes  or  Gigabytes

              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  CONTAINER  based
              arrays  such  as  those with IMSM metadata 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
              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 --size= command.

              This  value  cannot  be  used  when  creating a CONTAINER such as with DDF and IMSM
              metadata, 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
              array 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  'M'  or  'G'  can  be  given  to  indicate  Megabytes  or  Gigabytes
              respectively.   A  value  of  max  restores  the  apparent  size of the array to be
              whatever the real amount of available space is.

       -c, --chunk=
              Specify chunk size of kibibytes.  The default when creating an array is 512KB.   To
              ensure  compatibility  with  earlier  versions, the default when Building and 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  'M'  or  'G'  can  be  given  to  indicate  Megabytes  or  Gigabytes

              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
              highlights  the different meaning for Linear as compared to other RAID levels.  The
              default is 64K if a kernel earlier than 2.6.16 is  in  use,  and  is  0K  (i.e.  no
              rounding) 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

       -p, --layout=
              This option configures the fine details of data layout for RAID5, RAID6, and RAID10
              arrays, and controls the failure modes for faulty.

              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
              parity-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
              provide 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-asymmetric-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
              relevant  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.

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

              'n'  signals  'near'  copies.   Multiple  copies  of  one data block are at similar
              offsets 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
              useful.   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).

              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-
              striping) 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.

              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.

              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.

              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  'M'  or  'G'  can  be  given  to  indicate  Megabytes  or  Gigabytes

       -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.

              Specify  that  write-behind  mode  should be enabled (valid for RAID1 only).  If an
              argument 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

              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
              normally 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
              automatic resync.

              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.

              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.

       -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

       -f, --force
              Insist that mdadm accept  the  geometry  and  layout  specified  without  question.
              Normally  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.

       -a, --auto{=yes,md,mdp,part,p}{NN}
              Instruct  mdadm  how  to  create  the device file if needed, possibly allocating an
              unused 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
              determined 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.

              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
              number  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
              array.  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.

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
              superblocks 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
              specified  when  creating  the  array.  It must either match the name stored in the
              superblock 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.  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.

              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.

              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.

              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
              invalid.  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, homehost, resync,
              byteorder, devicesize, no-bitmap, 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
              --examine 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 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
              superblocks, this involves updating the name.

              The resync option will cause  the  array  to  be  marked  dirty  meaning  that  any
              redundancy 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.  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

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

              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
              after 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.

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
              specifiers didn't find any match.

       -a, --add
              hot-add listed devices.  If a device appears to have  recently  been  part  of  the
              array (possibly it failed or was removed) the device is re-added as describe 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
              rebuild data onto that spare.

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

              re-add  a  device  that was previous 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
              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 --re-add can be accompanied by --update=devicesize.  See  the  description  of
              this option when used in Assemble mode for an explanation of its 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

       -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  and  detached 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.  This will only succeed for
              devices that are spares or have already been marked as failed.

       -f, --fail
              mark listed devices as faulty.  As well as the name of  a  device  file,  the  word
              detached  can be given.  This will cause any device that has been detached from the
              system to be marked as failed.  It can then be removed.

              same as --fail.

              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
              reading from these devices if possible.

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

       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.
       Several 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
       (superblocks) 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.

              Print  details  of  the platform's RAID capabilities (firmware / hardware topology)
              for a given metadata format.

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

       -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.

              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
              incompatibly  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

       -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.

       -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.

              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.

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

              If  the  device  is  a  container and the argument to --update-subarray specifies a
              subarray 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.

              For each md device given, or each  device  in  /proc/mdstat  if  --scan  is  given,
              arrange  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.

For Incremental Assembly mode:

       --rebuild-map, -r
              Rebuild the map file (/var/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
              incrementally 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
              belongs  to.   The  device name given should be a kernel device name such as "sda",
              not a name in /dev.

              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
              metadata  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
              seconds 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

       -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.

              This  inhibits  the  functionality  for  moving  spares  between  arrays.  Only one
              monitoring process started with --scan but without this flag is allowed,  otherwise
              the two could interfere with each other.


       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
       array, mdadm needs to know the md device, the identity of  the  array,  and  a  number  of
       component-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

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

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

       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 /var/run/mdadm/map which will allow udev to choose the  correct

       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
       metadata,  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
       format  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
       regardless 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
       undergoing reshape.  In particular as the backup-file cannot be given, any  reshape  which
       requires  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-


       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
       synonyms.   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.


       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.

       As devices are added, they are  checked  to  see  if  they  contain  RAID  superblocks  or
       filesystems.  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
       extra 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
       partition  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.

       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
       devices  in  the  container  will  be used for the array.  The latter case allows mdadm to
       automatically 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.

              start the array readonly — not supported yet.


       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.


       Usage: mdadm options ...  devices ...

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

              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.

              The device  should  be  an  active  md  device.   mdadm  will  display  a  detailed
              description  of  the  array.   --brief  or  --scan will cause the output to be less
              detailed and the format to be suitable for inclusion in /etc/mdadm/mdadm.conf.  The
              exit  status  of  mdadm  will  normally  be  0  unless  mdadm  failed to get useful
              information about the device(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.

              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

              If the device is a container and the  argument  to  --update-subarray  specifies  a
              subarray 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.  Currently only name is supported.

              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 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
              multiple devices that are components of the one  array  are  grouped  together  and
              reported in a single entry suitable for inclusion in /etc/mdadm/mdadm.conf.

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

       --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.

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

              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.


       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

       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
       anything.  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:

                  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
                  because RAID0 and Linear do not support the device-failed, hot-spare and resync
                  operations which are monitored.

                  An md array started reconstruction. (syslog priority: Warning)

                  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
                  increment  since  0.  Increment size may be specified with a commandline option
                  (default is 20). (syslog priority: Warning)

                  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
                  priority: Critical)

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

                  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)

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

                  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)

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

                  If  mdadm  has  been  told,  via  the  config file, that an array should have a
                  certain 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)

                  An array was found  at  startup,  and  the  --test  flag  was  given.   (syslog
                  priority: 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
       labeled 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.


       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

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

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

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

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

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

       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.   Resizing
       arrays in an IMSM container with --grow --size is not yet supported.

       Grow  functionality  (e.g.  expand  a  number  of raid devices) for Intel's IMSM container
       format has an experimental status. It is guarded  by  the  MDADM_EXPERIMENTAL  environment
       variable  which  must  be  set  to  '1'  for  a  GROW command to succeed.  This is for the
       following reasons:

       1.     Intel's native IMSM check-pointing is not fully tested yet.  This can  causes  IMSM
              incompatibility  during  the  grow  process:  an array which is growing cannot roam
              between Microsoft Windows(R) and Linux systems.

       2.     Interrupting a grow operation is not recommended, because it  has  not  been  fully
              tested for Intel's IMSM container format yet.

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

       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
       complete a new bitmap can be created.

       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

       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
       inaccessible.  The integrity of any data can then be  checked  before  the  non-reversible
       reduction 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
       reassemble  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

       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 "cricital
       section" but throughout the reshape operation, as described below under LAYOUT CHANGES.

       Changing the chunk-size of 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
       array  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.

       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
       bitmap 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.


       Usage: mdadm --incremental [--run] [--quiet] component-device

       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
       devices  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
       metadata 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.   Similar
              if  DEVICES  contains  the  special  word  partitions  then  any device is allowed.
              Otherwise the device name given to mdadm must match one of the names or patterns in
              a DEVICES line.

       +      Does  the  device  have  a  valid md superblock?  If a specific metadata version is
              requested with --metadata or -e then only  that  style  of  metadata  is  accepted,
              otherwise  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  /var/run/mdadm/map  (or
       /var/run/ if the directory doesn't exist.  Or maybe even /dev/  If no
       array 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
       information 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-partitionable 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
       belonging 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
       devices 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
       request.  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.


       This section describes environment variables that affect how mdadm operates.

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

              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 --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
       before 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 > /var/run/mdadm
       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 /var/run/mdadm.

         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.


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

       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.

       When  --incremental mode is used, this file gets a list of arrays currently being created.
       If /var/run/mdadm does not exist as a directory, then /var/run/ is used  instead.
       If  /var/run  is  not available (as may be the case during early boot), /dev/ is
       used on the basis that /dev is usually available very early in boot.


       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
       homehost 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


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


       Partition numbers should be indicated by added "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


       mdadm was previously known as mdctl.

       mdadm is completely separate from the raidtools package, and does not use the /etc/raidtab
       configuration file at all.


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


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

       The latest version of mdadm should always be available from


       Related man pages:

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

       raidtab(5), raid0run(8), raidstop(8), mkraid(8).