table of contents
- NAME
- SYNOPSIS
- DESCRIPTION
- MODES
- OPTIONS
- Options for selecting a mode are:
- Options that are not mode-specific are:
- For create, build, or grow:
- For assemble:
- For Manage mode:
- For Misc mode:
- For Incremental Assembly mode:
- For Monitor mode:
- ASSEMBLE MODE
- BUILD MODE
- CREATE MODE
- MANAGE MODE
- MISC MODE
- MONITOR MODE
- GROW MODE
- INCREMENTAL MODE
- ENVIRONMENT
- EXAMPLES
- FILES
- DEVICE NAMES
- NOTE
- SEE ALSO
MDADM(8) | System Manager's Manual | MDADM(8) |
NAME¶
mdadm - manage MD devices aka Linux Software RAIDSYNOPSIS¶
mdadm [mode] <raiddevice> [options] <component-devices>DESCRIPTION¶
RAID devices are virtual devices created from two or more real block devices. This allows multiple devices (typically disk drives or partitions thereof) to be combined into a single device to hold (for example) a single filesystem. Some RAID levels include redundancy and so can survive some degree of device failure.MODES¶
mdadm has several major modes of operation:- Assemble
- 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.
- 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.
- Auto-detect
- This mode does not act on a specific device or array, but rather it requests the Linux Kernel to activate any auto-detected arrays.
OPTIONS¶
Options for selecting a mode are:¶
- -A, --assemble
- Assemble a pre-existing array.
- -B, --build
- Build a legacy array without superblocks.
- -C, --create
- Create a new array.
- -F, --follow, --monitor
- Select Monitor mode.
- -G, --grow
- Change the size or shape of an active array.
- -I, --incremental
- Add/remove a single device to/from an appropriate array,
and possibly start the array.
- --auto-detect
- Request that the kernel starts any auto-detected arrays.
This can only work if md is compiled into the kernel — not if
it is a module. Arrays can be auto-detected by the kernel if all the
components are in primary MS-DOS partitions with partition type FD,
and all use v0.90 metadata. In-kernel autodetect is not recommended for
new installations. Using mdadm to detect and assemble arrays
— possibly in an initrd — is substantially more
flexible and should be preferred.
Options that are not mode-specific are:¶
- -h, --help
- Display general help message or, after one of the above
options, a mode-specific help message.
- --help-options
- Display more detailed help about command line parsing and
some commonly used 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
report.
- --offroot
- 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 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.
- 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:
- --homehost=
- 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.
- --prefer=
- When mdadm needs to print the name for a device it
normally finds the name in /dev which refers to the device and is
shortest. When a path component is given with --prefer mdadm
will prefer a longer name if it contains that component. For example
--prefer=by-uuid will prefer a name in a subdirectory of
/dev called by-uuid.
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.
- -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.
- -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.
- -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.
- --rounding=
- Specify rounding factor for a Linear array. The size of
each component will be rounded down to a multiple of this size. This is a
synonym for --chunk but 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.
- -p, --layout=
- This option configures the fine details of data layout for
RAID5, RAID6, and RAID10 arrays, and controls the failure modes for
faulty.
- --parity=
- same as --layout (thus explaining the p of
-p).
- -b, --bitmap=
- Specify a file to store a write-intent bitmap in. The file
should not exist unless --force is also given. The same file should
be provided when assembling the array. If the word internal is
given, then the bitmap is stored with the metadata on the array, and so is
replicated on all devices. If the word none is given with
--grow mode, then any bitmap that is present is removed.
- --bitmap-chunk=
- Set the chunksize of the bitmap. Each bit corresponds to
that many Kilobytes of storage. When using a file based bitmap, the
default is to use the smallest size that is at-least 4 and requires no
more than 2^21 chunks. When using an internal bitmap, the chunksize
defaults to 64Meg, or larger if necessary to fit the bitmap into the
available space.
- -W, --write-mostly
- subsequent devices listed in a --build,
--create, or --add command will be flagged as
'write-mostly'. This is valid for RAID1 only and means that the 'md'
driver will avoid reading from these devices if at all possible. This can
be useful if mirroring over a slow link.
- --write-behind=
- Specify that write-behind mode should be enabled (valid for
RAID1 only). If an 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.
- --assume-clean
- Tell mdadm that the array pre-existed and is known to be clean. It can be useful when trying to recover from a major failure as you can be sure that no data will be affected unless you actually write to the array. It can also be used when creating a RAID1 or RAID10 if you want to avoid the initial resync, however this practice — while normally safe — is not recommended. Use this only if you really know what you are doing.
- When the devices that will be part of a new array were filled with zeros before creation the operator knows the array is actually clean. If that is the case, such as after running badblocks, this argument can be used to tell mdadm the facts the operator knows.
- When an array is resized to a larger size with --grow
--size= the new space is 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.
- --backup-file=
- This is needed when --grow is used to increase the
number of raid-devices in a RAID5 or RAID6 if there are no spare devices
available, or to shrink, change RAID level or layout. See the GROW MODE
section below on RAID-DEVICES CHANGES. The file must be stored on a
separate device, not on the RAID array being reshaped.
- --continue
- This option is complementary to the --freeze-reshape option for assembly. It is needed when --grow operation is interrupted and it is not restarted automatically due to --freeze-reshape usage during array assembly. This option is used together with -G , ( --grow ) command and device for a pending reshape to be continued. All parameters required for reshape continuation will be read from array metadata. If initial --grow command had required --backup-file= option to be set, continuation option will require to have exactly the same backup file given as well.
- Any other parameter passed together with --continue
option will be ignored.
- -N, --name=
- Set a name for the array. This is currently only
effective when creating an array with a version-1 superblock, or an array
in a DDF container. The name is a simple textual string that can be used
to identify array components when assembling. If name is needed but not
specified, it is taken from the basename of the device that is being
created. e.g. when creating /dev/md/home the name will
default to home.
- -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.
- -a, --add
- This option can be used in Grow mode in two cases.
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.
- -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.
- --no-degraded
- This is the reverse of --run in that it inhibits the
startup of array unless all expected drives are present. This is only
needed with --scan, and can be used if the physical connections to
devices are not as reliable as you would like.
- -a, --auto{=no,yes,md,mdp,part}
- See this option under Create and Build options.
- -b, --bitmap=
- Specify the bitmap file that was given when the array was
created. If an array has an internal bitmap, there is no need to
specify this when assembling the array.
- --backup-file=
- If --backup-file was used while reshaping an array
(e.g. changing number of devices or chunk size) and the system crashed
during the critical section, then the same --backup-file must be
presented to --assemble to allow possibly corrupted data to be
restored, and the reshape to be completed.
- --invalid-backup
- If the file needed for the above option is not available
for any reason an empty file can be given together with this option to
indicate that the backup file is 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.
- --freeze-reshape
- Option is intended to be used in start-up scripts during
initrd boot phase. When array under reshape is assembled during initrd
phase, this option stops reshape 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.
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.
- --re-add
- 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.
- -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.
- --set-faulty
- same as --fail.
- --write-mostly
- Subsequent devices that are added or re-added will have the 'write-mostly' flag set. This is only valid for RAID1 and means that the 'md' driver will avoid reading from these devices if possible.
- --readwrite
- Subsequent devices that are added or re-added will have the
'write-mostly' flag cleared.
mdadm /dev/md0 --add /dev/sda1 --fail /dev/sdb1 --remove /dev/sdb1
Each operation applies to all devices listed until the next operation.
For Misc mode:¶
- -Q, --query
- Examine a device to see (1) if it is an md device and (2)
if it is a component of an md array. Information about what is discovered
is presented.
- -D, --detail
- Print details of one or more md devices.
- --detail-platform
- Print details of the platform's RAID capabilities (firmware
/ hardware topology) for a given metadata format.
- -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.
- --sparc2.2
- If an array was created on a SPARC machine with a 2.2 Linux
kernel patched with RAID support, the superblock will have been created
incorrectly, or at least 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.
- --zero-superblock
- If the device contains a valid md superblock, the block is
overwritten with zeros. With --force the block where the superblock
would be is overwritten even if it doesn't appear to be valid.
- --kill-subarray=
- 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.
- --update-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.
- --wait-clean
- 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.
- --path=
- Only used with --fail. The 'path' given will be recorded so
that if a new device appears at the same location it can be automatically
added to the same array. This allows the failed device to be automatically
replaced by a new device without 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 change.
- -r, --increment
- Give a percentage increment. mdadm will generate
RebuildNN events with the given percentage increment.
- -f, --daemonise
- Tell mdadm to run as a background daemon if it
decides to monitor anything. This causes it to fork and run in the child,
and to disconnect from the terminal. The process id of the child is
written to stdout. This is useful with --scan which will only
continue monitoring if a mail address or alert program is found in the
config file.
- -i, --pid-file
- When mdadm is running in daemon mode, write the pid
of the daemon process to the specified file, instead of printing it on
standard output.
- -1, --oneshot
- Check arrays only once. This will generate NewArray
events and more significantly DegradedArray and
SparesMissing events. Running
mdadm --monitor --scan -1
from a cron script will ensure regular notification of any degraded arrays.
- -t, --test
- Generate a TestMessage alert for every array found
at startup. This alert gets mailed and passed to the alert program. This
can be used for testing that alert message do get through successfully.
- --no-sharing
- This inhibits the functionality for moving spares between
arrays. Only one monitoring process started with --scan but without
this flag is allowed, otherwise the two could interfere with each other.
ASSEMBLE MODE¶
Usage:
mdadm --assemble md-device
options-and-component-devices...
Usage:
mdadm --assemble --scan md-devices-and-options...
Usage:
mdadm --assemble --scan options...
This usage assembles one or more RAID arrays from pre-existing components. For
each 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.
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.BUILD MODE¶
Usage:
mdadm --build md-device --chunk=X
--level=Y --raid-devices=Z devices
This usage is similar to --create. The difference is that it creates an
array without a superblock. With these arrays there is no difference between
initially creating the array and subsequently assembling the array, except
that hopefully there is useful data there in the second case.
CREATE MODE¶
Usage:
mdadm --create md-device --chunk=X
--level=Y
--raid-devices=Z devices
This usage will initialise a new md array, associate some devices with it, and
activate the array.
- --run
- insist on running the array even if some devices look like
they might be in use.
- --readonly
- start the array readonly — not supported yet.
MANAGE MODE¶
Usage:
mdadm device options... devices...
MISC MODE¶
Usage:
mdadm options ... devices ...
- --query
- The device is examined to see if it is (1) an active md
array, or (2) a component of an md array. The information discovered is
reported.
- --detail
- The device should be an active md device. mdadm will display a detailed 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.
- --detail-platform
- Print detail of the platform's RAID capabilities (firmware / hardware topology). If the metadata is specified with -e or --metadata= then the return status will be:
- 0
- metadata successfully enumerated its platform components on this system
- 1
- metadata is platform independent
- 2
- metadata failed to find its platform components on this system
- --update-subarray=
- If the device is a container and the argument to
--update-subarray specifies a 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.
- --examine
- The device should be a component of an md array.
mdadm will read the md superblock of the device and display the
contents. If --brief or --scan is given, then 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.
- --stop
- The devices should be active md arrays which will be
deactivated, as long as they are not currently in use.
- --run
- This will fully activate a partially assembled md array.
- --readonly
- This will mark an active array as read-only, providing that
it is not currently being used.
- --readwrite
- This will change a readonly array back to being
read/write.
- --scan
- For all operations except --examine, --scan
will cause the operation to be applied to all arrays listed in
/proc/mdstat. For --examine, --scan causes all
devices listed in the config file to be examined.
- -b, --brief
- Be less verbose. This is used with --detail and
--examine. Using --brief with --verbose gives an
intermediate level of verbosity.
MONITOR MODE¶
Usage:
mdadm --monitor options... devices...
This usage causes mdadm to periodically poll a number of md arrays and to
report on any events noticed. mdadm will never exit once it decides
that there are arrays to be checked, so it should normally be run in the
background.
- DeviceDisappeared
- An md array which previously was configured appears to no
longer be configured. (syslog priority: Critical)
- RebuildStarted
- An md array started reconstruction. (syslog priority:
Warning)
- RebuildNN
- Where NN is a two-digit number (ie. 05, 48). This
indicates that rebuild has passed that many percent of the total. The
events are generated with fixed increment since 0. Increment size may be
specified with a commandline option (default is 20). (syslog priority:
Warning)
- RebuildFinished
- An md array that was rebuilding, isn't any more, either
because it finished normally or was aborted. (syslog priority: Warning)
- Fail
- An active component device of an array has been marked as
faulty. (syslog priority: Critical)
- FailSpare
- A spare component device which was being rebuilt to replace
a faulty device has failed. (syslog priority: Critical)
- SpareActive
- A spare component device which was being rebuilt to replace
a faulty device has been successfully rebuilt and has been made active.
(syslog priority: Info)
- NewArray
- A new md array has been detected in the /proc/mdstat
file. (syslog priority: Info)
- DegradedArray
- A newly noticed array appears to be degraded. This message
is not generated when mdadm notices a drive failure which causes
degradation, but only when mdadm notices that an array is degraded
when it first sees the array. (syslog priority: Critical)
- MoveSpare
- A spare drive has been moved from one array in a
spare-group or domain to another to allow a failed drive to
be replaced. (syslog priority: Info)
- SparesMissing
- If mdadm has been told, via the config file, that an
array should have a 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)
- TestMessage
- An array was found at startup, and the --test flag was given. (syslog priority: Info)
GROW MODE¶
The GROW mode is used for changing the size or shape of an active array. For this to work, the kernel must support the necessary change. Various types of growth are being added during 2.6 development.- •
- change the "size" attribute for RAID1, RAID4, RAID5 and RAID6.
- •
- increase or decrease the "raid-devices" attribute of RAID0, RAID1, RAID4, RAID5, and RAID6.
- •
- 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.
- 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.
SIZE CHANGES¶
Normally when an array is built the "size" is taken from the smallest of the drives. If all the small drives in an arrays are, one at a time, removed and replaced with larger drives, then you could have an array of large drives with only a small amount used. In this situation, changing the "size" with "GROW" mode will allow the extra space to start being used. If the size is increased in this way, a "resync" process will start to make sure the new parts of the array are synchronised.RAID-DEVICES CHANGES¶
A RAID1 array can work with any number of devices from 1 upwards (though 1 is not very useful). There may be times which you want to increase or decrease the number of active devices. Note that this is different to hot-add or hot-remove which changes the number of inactive devices.LEVEL CHANGES¶
Changing the RAID level of any array happens instantaneously. However in the RAID5 to RAID6 case this requires a non-standard layout of the RAID6 data, and in the RAID6 to RAID5 case that non-standard layout is required before the change can be accomplished. So while the level change is instant, the accompanying layout change can take quite a long time. A --backup-file is required. If the array is not simultaneously being grown or shrunk, so that the array size will remain the same - for example, reshaping a 3-drive RAID5 into a 4-drive RAID6 - the backup file will be used not just for a "cricital section" but throughout the reshape operation, as described below under LAYOUT CHANGES.CHUNK-SIZE AND 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.BITMAP CHANGES¶
A write-intent bitmap can be added to, or removed from, an active array. Either internal bitmaps, or bitmaps stored in a separate file, can be added. Note that if you add a 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.INCREMENTAL MODE¶
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.
- +
- 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.
ENVIRONMENT¶
This section describes environment variables that affect how mdadm operates.- MDADM_NO_MDMON
- Setting this value to 1 will prevent mdadm from
automatically launching mdmon. This variable is intended primarily for
debugging mdadm/mdmon.
- MDADM_NO_UDEV
- Normally, mdadm does not create any device nodes in
/dev, but leaves that task to udev. If udev appears not to
be configured, or if this environment variable is set to '1', the
mdadm will create and devices that are needed.
EXAMPLES¶
mdadm --query /dev/name-of-deviceFILES¶
/proc/mdstat¶
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./etc/mdadm/mdadm.conf¶
The config file lists which devices may be scanned to see if they contain MD super block, and gives identifying information (e.g. UUID) about known MD arrays. See mdadm.conf(5) for more details./run/mdadm/map¶
When --incremental mode is used, this file gets a list of arrays currently being created.DEVICE NAMES¶
mdadm understand two sorts of names for array devices.- /dev/mdNN
- /dev/md_dNN
NOTE¶
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.SEE ALSO¶
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).v3.2.5 |