Provided by: mdadm_3.2.5-5ubuntu4.4_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.

              Set  first  character  of  argv[0]  to  @  to  indicate  mdadm  was  launched  from
              initrd/initramfs and should not be shutdown by  systemd  as  part  of  the  regular
              shutdown  process.  This  option is normally only used by the system's initscripts.
              Please see here for more details on how systemd handled argv[0]:


       -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.

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

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

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  described  in
              the  next  point.   If  that  fails  or the device was never part of the array, the
              device is added as a hot-spare.  If the array  is  degraded,  it  will  immediately
              start to 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 (/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  /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 /run/mdadm/map.  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 > /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

         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.


       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).