GNU/Linux man pages
Livre :
Expressions régulières,
Syntaxe et mise en oeuvre :
GNU/Linux |
Debian 6.0.0(Squeeze) |
|
 |
mdadm(8) |
 |
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 CONTAINER.
MULTIPATH is not a Software RAID mechanism, but does involve multiple devices: each device is a path to one common physical storage device. New installations should not use md/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
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. |
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.
−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.
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.
−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.
−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.
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 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: |
http://www.intel.com/design/chipsets/matrixstorage_sb.htm
−−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.
When creating an array, the homehost will be recorded in the metadata. For version-1 superblocks, it will be prefixed to the array name. For version-0.90 superblocks, part of the SHA1 hash of the hostname will be stored in the later half of the UUID.
When reporting information about an array, any array which is tagged for the given homehost will be reported as such.
When using Auto-Assemble, only arrays tagged for the given homehost will be allowed to use ’local’ names (i.e. not ending in ’_’ followed by a digit string). See below under Auto Assembly.
−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 reduced.
−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.
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, none.
Each failure mode can be followed by a number, which is used as a period between fault generation. Without a number, the fault is generated once on the first relevant request. With a number, the fault will be generated after that many requests, and will continue to be generated every time the period elapses.
Multiple failure modes can be current simultaneously by using the −−grow option to set subsequent failure modes.
"clear" or "none" will remove any pending or periodic failure modes, and "flush" will clear any persistent faults.
Finally, the layout options for RAID10 are one of ’n’, ’o’ or ’f’ followed by a small number. The default is ’n2’. The supported options are:
’n’ signals ’near’ copies. Multiple copies of one data block are at similar offsets in different devices.
’o’ signals ’offset’ copies. Rather than the chunks being duplicated within a stripe, whole stripes are duplicated but are rotated by one device so duplicate blocks are on different devices. Thus subsequent copies of a block are in the next drive, and are one chunk further down.
’f’ signals ’far’ copies (multiple copies have very different offsets). See md(4) for more detail about ’near’, ’offset’, and ’far’.
The number is the number of copies of each datablock. 2 is normal, 3 can be useful. This number can be at most equal to the number of devices in the array. It does not need to divide evenly into that number (e.g. it is perfectly legal to have an ’n2’ layout for an array with an odd number of devices).
When an array is converted between RAID5 and RAID6 an intermediate RAID6 layout is used in which the second parity block (Q) is always on the last device. To convert a RAID5 to RAID6 and leave it in this new layout (which does not require re-striping) use −−layout=preserve. This will try to avoid any restriping.
The converse of this is −−layout=normalise which will change a non-standard RAID6 layout into a more standard arrangement.
−−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.
To help catch typing errors, the filename must contain at least one slash (’/’) if it is a real file (not ’internal’ or ’none’).
Note: external bitmaps are only known to work on ext2 and ext3. Storing bitmap files on other filesystems may result in serious problems.
−−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.
−−backup−file=
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 size.
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 line.
For partitionable arrays, mdadm will create the device file for the whole array and for the first 4 partitions. A different number of partitions can be specified at the end of this option (e.g. −−auto=p7). If the device name ends with a digit, the partition names add a ’p’, and a number, e.g. /dev/md/home1p3. If there is no trailing digit, then the partition names just have a number added, e.g. /dev/md/scratch3.
If the md device name is in a ’standard’ format as described in DEVICE NAMES, then it will be created, if necessary, with the appropriate device number based on that name. If the device name is not in one of these formats, then a unused device number will be allocated. The device number will be considered unused if there is no active array for that number, and there is no entry in /dev for that number and with a non-standard name. Names that are not in ’standard’ format are only allowed in "/dev/md/".
−u, −−uuid=
uuid of array to assemble. Devices which don’t have this uuid are excluded
−m, −−super−minor=
Minor number of device that array was created for. Devices which don’t have this minor number are excluded. If you create an array as /dev/md1, then all superblocks will contain the minor number 1, even if the array is later assembled as /dev/md2.
Giving the literal word "dev" for −−super−minor will cause mdadm to use the minor number of the md device that is being assembled. e.g. when assembling /dev/md0, −−super−minor=dev will look for super blocks with a minor number of 0.
−−super−minor is only relevant for v0.90 metadata, and should not normally be used. Using −−uuid is much safer.
−N, −−name=
Specify the name of the array to assemble. This must be the name that was specified when creating the array. It must either match the name stored in the superblock exactly, or it must match with the current homehost prefixed to the start of the given name.
−f, −−force
Assemble the array even if the metadata on some devices appears to be out-of-date. If mdadm cannot find enough working devices to start the array, but can find some devices that are recorded as having failed, then it will mark those devices as working so that the array can be started. An array which requires −−force to be started may contain data corruption. Use it carefully.
−R, −−run
Attempt to start the array even if fewer drives were given than were present last time the array was active. Normally if not all the expected drives are found and −−scan is not used, then the array will be assembled but not started. With −−run an attempt will be made to start it anyway.
−−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 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) kernel.
The uuid option will change the uuid of the array. If a UUID is given with the −−uuid option that UUID will be used as a new UUID and will NOT be used to help identify the devices in the array. If no −−uuid is given, a random UUID is chosen.
The name option will change the name of the array as stored in the superblock. This is only supported for version-1 superblocks.
The homehost option will change the homehost as recorded in the superblock. For version-0 superblocks, this is the same as updating the UUID. For version-1 superblocks, this involves updating the name.
The resync option will cause the array to be marked dirty meaning that any redundancy in the array (e.g. parity for RAID5, copies for RAID1) may be incorrect. This will cause the RAID system to perform a "resync" pass to make sure that all redundant information is correct.
The byteorder option allows arrays to be moved between machines with different byte-order. When assembling such an array for the first time after a move, giving −−update=byteorder will cause mdadm to expect superblocks to have their byteorder reversed, and will correct that order before assembling the array. This is only valid with original (Version 0.90) superblocks.
The summaries option will correct the summaries in the superblock. That is the counts of total, working, active, failed, and spare devices.
The devicesize 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.
−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
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.
−−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.
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.
−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.
−−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.
−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.