Provided by: mdadm_3.1.4-1+8efb9d1ubuntu6_i386 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 driver.

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

       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 RAID levels 1/4/5/6, changing the RAID level between
              1, 5, and 6, changing the chunk size and layout  for  RAID5  and
              RAID5, 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


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 array.

              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 options.

       -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 --scan.

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

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

       -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 empty.

       -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.

              1, 1.0, 1.1, 1.2 default
                     Use the new version-1 format superblock.   This  has  few
                     restrictions.    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  "1.0".
                     "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

              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


              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

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.

              This  value  can  be set with --grow for RAID level 1/4/5/6.  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.

              This  value  can not be used with CONTAINER metadata such as DDF
              and IMSM.

       -Z, --array-size=
              This is only meaningful  with  --grow  and  its  effect  is  not
              persistent:  when  the array is stopped an 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

       -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.

              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 below.

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

              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 possibly 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,

              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

              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

              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

              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.

       -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 write-mostly.

              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

              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.

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

       --array-size=, -Z
              Set the size of the array which is seen by users of  the  device
              such  as  filesystems.  This can be less that the real size, but
              never greater.  The size set this way does  not  persist  across
              restarts of the array.

              This  is  most  useful  when reducing the number of devices in a
              RAID5 or RAID6.   Such  arrays  require  the  array-size  to  be
              reduced  before a reshape can be performed that reduces the real

              A value of max restores the apparent size of  the  array  to  be
              whatever the real amount of available space is.

       -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 suppressed.

       -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

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

              If  the md device name is in a 'standard' format as described in
              DEVICE NAMES, then it will be created, if  necessary,  with  the
              appropriate  device  number  based  on that name.  If the device
              name is not in one of these formats, then a unused device 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

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

              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 to grow the number of raid-devices  in
              a  RAID5,  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.

       -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,
              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)

              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

              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)

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

              The devicesize 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 metadata.

For Manage mode:

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

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

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

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

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

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

       -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

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

       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 --update=sparc2.2.

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

       -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

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

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

For Incremental Assembly mode:

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

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

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

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

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 change.

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

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

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

       -1, --oneshot
              Check  arrays only once.  This will generate NewArray events and
              more  significantly  DegradedArray  and  SparesMissing   events.
                      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


       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 not arrays are described  by  the
       configuration file, then any arrays that can be found on unused devices
       will be assembled.

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

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

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

       The  config  file  is  only  used  if explicitly named with --config or
       requested with (a  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 arrays.

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

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

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

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

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

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

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

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

       In  no array at 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

       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.


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

       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

              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

              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


       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  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 monitored.

       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:

                  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: Info)

                  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
                  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  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.


       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,
       including restructuring a RAID5 array to have more active devices.

       Currently the only support available is to

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

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

           change the chunk-size and layout of RAID5 and RAID6.

           convert between RAID1 and RAID5, and between RAID5 and RAID6.

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

       GROW mode is not currently supported for CONTAINERS  or  arrays  inside

       Normally  when  an array is built the "size" it 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

       Note that when an array changes size, any filesystem that may be stored
       in  the  array  will  not  automatically  grow  to  use the space.  The
       filesystem will need to be explicitly told to use the extra space.

       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  it  complete  a  new  bitmap  can  be

       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

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

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

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

       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.  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

       When relocating the first few stripes on a RAID5, 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.  This backup is normally 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.  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

       Changing  the RAID level of any array happens instantaneously.  However
       in the RAID 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  accomplish.   So  while  the  level
       change is instant, the accompanying layout change can take quite a long

       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.

       If the reshape is interrupted for any reason, this backup file must  be
       make  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 only add devices to an array which were previously
       working (active or spare) parts of that array.  It does  not  currently
       support automatic inclusion of a new drive as a spare in some array.

       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 request 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 is

              mdadm keeps a list of arrays that it has partially assembled  in
              /var/run/mdadm/map   (or  /var/run/  if  the  directory
              doesn't exist.  Or maybe even  /dev/   If  no  array
              exists  which matches the metadata on the new device, mdadm must
              choose a device name and unit number.  It does this based on any
              name  given  in mdadm.conf or any name information stored in the
              metadata.  If this name suggests a unit number, that number will
              be  used, otherwise a free unit number will be chosen.  Normally
              mdadm will prefer to create a partitionable  array,  however  if
              the  CREATE line in mdadm.conf suggests that a non-partitionable
              array is preferred, that will be honoured.

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

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

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

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


       This  section  describes  environment  variables  that affect how mdadm

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

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


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

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

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

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

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

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

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

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

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

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

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

         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

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

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

         mdadm --help
       Provide general help.


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

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

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


       mdadm understand two sorts of names for array devices.

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

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

       When mdadm chooses device names  during  auto-assembly  or  incremental
       assembly,  it  will sometimes add a small sequence number to the end of
       the name to avoid conflicted between multiple arrays that have the same
       name.  If mdadm can reasonably determine that the array really is meant
       for this host, either by a hostname in the metadata, or by the presence
       of  the  array in /etc/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

       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 possible.


       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 Ostergaard'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).