2 .\" Copyright Neil Brown and others.
3 .\" This program is free software; you can redistribute it and/or modify
4 .\" it under the terms of the GNU General Public License as published by
5 .\" the Free Software Foundation; either version 2 of the License, or
6 .\" (at your option) any later version.
7 .\" See file COPYING in distribution for details.
10 mdadm \- manage MD devices
16 .BI mdadm " [mode] <raiddevice> [options] <component-devices>"
19 RAID devices are virtual devices created from two or more
20 real block devices. This allows multiple devices (typically disk
21 drives or partitions thereof) to be combined into a single device to
22 hold (for example) a single filesystem.
23 Some RAID levels include redundancy and so can survive some degree of
26 Linux Software RAID devices are implemented through the md (Multiple
27 Devices) device driver.
29 Currently, Linux supports
46 is not a Software RAID mechanism, but does involve
48 each device is a path to one common physical storage device.
49 New installations should not use md/multipath as it is not well
50 supported and has no ongoing development. Use the Device Mapper based
51 multipath-tools instead.
54 is also not true RAID, and it only involves one device. It
55 provides a layer over a true device that can be used to inject faults.
60 is a collection of devices that are
61 managed as a set. This is similar to the set of devices connected to
62 a hardware RAID controller. The set of devices may contain a number
63 of different RAID arrays each utilising some (or all) of the blocks from a
64 number of the devices in the set. For example, two devices in a 5-device set
65 might form a RAID1 using the whole devices. The remaining three might
66 have a RAID5 over the first half of each device, and a RAID0 over the
71 there is one set of metadata that describes all of
72 the arrays in the container. So when
76 device, the device just represents the metadata. Other normal arrays (RAID1
77 etc) can be created inside the container.
80 mdadm has several major modes of operation:
83 Assemble the components of a previously created
84 array into an active array. Components can be explicitly given
85 or can be searched for.
87 checks that the components
88 do form a bona fide array, and can, on request, fiddle superblock
89 information so as to assemble a faulty array.
93 Build an array that doesn't have per-device metadata (superblocks). For these
96 cannot differentiate between initial creation and subsequent assembly
97 of an array. It also cannot perform any checks that appropriate
98 components have been requested. Because of this, the
100 mode should only be used together with a complete understanding of
105 Create a new array with per-device metadata (superblocks).
106 Appropriate metadata is written to each device, and then the array
107 comprising those devices is activated. A 'resync' process is started
108 to make sure that the array is consistent (e.g. both sides of a mirror
109 contain the same data) but the content of the device is left otherwise
111 The array can be used as soon as it has been created. There is no
112 need to wait for the initial resync to finish.
115 .B "Follow or Monitor"
116 Monitor one or more md devices and act on any state changes. This is
117 only meaningful for RAID1, 4, 5, 6, 10 or multipath arrays, as
118 only these have interesting state. RAID0 or Linear never have
119 missing, spare, or failed drives, so there is nothing to monitor.
123 Grow (or shrink) an array, or otherwise reshape it in some way.
124 Currently supported growth options including changing the active size
125 of component devices and changing the number of active devices in
126 Linear and RAID levels 0/1/4/5/6,
127 changing the RAID level between 0, 1, 5, and 6, and between 0 and 10,
128 changing the chunk size and layout for RAID 0,4,5,6,10 as well as adding or
129 removing a write-intent bitmap and changing the array's consistency policy.
132 .B "Incremental Assembly"
133 Add a single device to an appropriate array. If the addition of the
134 device makes the array runnable, the array will be started.
135 This provides a convenient interface to a
137 system. As each device is detected,
139 has a chance to include it in some array as appropriate.
142 flag is passed in we will remove the device from any active array
143 instead of adding it.
149 in this mode, then any arrays within that container will be assembled
154 This is for doing things to specific components of an array such as
155 adding new spares and removing faulty devices.
159 This is an 'everything else' mode that supports operations on active
160 arrays, operations on component devices such as erasing old superblocks, and
161 information-gathering operations.
162 .\"This mode allows operations on independent devices such as examine MD
163 .\"superblocks, erasing old superblocks and stopping active arrays.
167 This mode does not act on a specific device or array, but rather it
168 requests the Linux Kernel to activate any auto-detected arrays.
171 .SH Options for selecting a mode are:
174 .BR \-A ", " \-\-assemble
175 Assemble a pre-existing array.
178 .BR \-B ", " \-\-build
179 Build a legacy array without superblocks.
182 .BR \-C ", " \-\-create
186 .BR \-F ", " \-\-follow ", " \-\-monitor
192 .BR \-G ", " \-\-grow
193 Change the size or shape of an active array.
196 .BR \-I ", " \-\-incremental
197 Add/remove a single device to/from an appropriate array, and possibly start the array.
201 Request that the kernel starts any auto-detected arrays. This can only
204 is compiled into the kernel \(em not if it is a module.
205 Arrays can be auto-detected by the kernel if all the components are in
206 primary MS-DOS partitions with partition type
208 and all use v0.90 metadata.
209 In-kernel autodetect is not recommended for new installations. Using
211 to detect and assemble arrays \(em possibly in an
213 \(em is substantially more flexible and should be preferred.
216 If a device is given before any options, or if the first option is
225 then the MANAGE mode is assumed.
226 Anything other than these will cause the
230 .SH Options that are not mode-specific are:
233 .BR \-h ", " \-\-help
234 Display a general help message or, after one of the above options, a
235 mode-specific help message.
239 Display more detailed help about command-line parsing and some commonly
243 .BR \-V ", " \-\-version
244 Print version information for mdadm.
247 .BR \-v ", " \-\-verbose
248 Be more verbose about what is happening. This can be used twice to be
250 The extra verbosity currently only affects
251 .B \-\-detail \-\-scan
253 .BR "\-\-examine \-\-scan" .
256 .BR \-q ", " \-\-quiet
257 Avoid printing purely informative messages. With this,
259 will be silent unless there is something really important to report.
263 .BR \-f ", " \-\-force
264 Be more forceful about certain operations. See the various modes for
265 the exact meaning of this option in different contexts.
268 .BR \-c ", " \-\-config=
269 Specify the config file or directory. If not specified, the default config file
270 and default conf.d directory will be used. See
274 If the config file given is
276 then nothing will be read, but
278 will act as though the config file contained exactly
280 .B " DEVICE partitions containers"
284 to find a list of devices to scan, and
286 to find a list of containers to examine.
289 is given for the config file, then
291 will act as though the config file were empty.
293 If the name given is of a directory, then
295 will collect all the files contained in the directory with a name ending
298 sort them lexically, and process all of those files as config files.
301 .BR \-s ", " \-\-scan
304 for missing information.
305 In general, this option gives
307 permission to get any missing information (like component devices,
308 array devices, array identities, and alert destination) from the
309 configuration file (see previous option);
310 one exception is MISC mode when using
316 says to get a list of array devices from
320 .BR \-e ", " \-\-metadata=
321 Declare the style of RAID metadata (superblock) to be used. The
322 default is {DEFAULT_METADATA} for
324 and to guess for other operations.
325 The default can be overridden by setting the
334 .ie '{DEFAULT_METADATA}'0.90'
335 .IP "0, 0.90, default"
338 Use the original 0.90 format superblock. This format limits arrays to
339 28 component devices and limits component devices of levels 1 and
340 greater to 2 terabytes. It is also possible for there to be confusion
341 about whether the superblock applies to a whole device or just the
342 last partition, if that partition starts on a 64K boundary.
343 .ie '{DEFAULT_METADATA}'0.90'
344 .IP "1, 1.0, 1.1, 1.2"
346 .IP "1, 1.0, 1.1, 1.2 default"
347 Use the new version-1 format superblock. This has fewer restrictions.
348 It can easily be moved between hosts with different endian-ness, and a
349 recovery operation can be checkpointed and restarted. The different
350 sub-versions store the superblock at different locations on the
351 device, either at the end (for 1.0), at the start (for 1.1) or 4K from
352 the start (for 1.2). "1" is equivalent to "1.2" (the commonly
353 preferred 1.x format).
354 'if '{DEFAULT_METADATA}'1.2' "default" is equivalent to "1.2".
356 Use the "Industry Standard" DDF (Disk Data Format) format defined by
358 When creating a DDF array a
360 will be created, and normal arrays can be created in that container.
362 Use the Intel(R) Matrix Storage Manager metadata format. This creates a
364 which is managed in a similar manner to DDF, and is supported by an
365 option-rom on some platforms:
367 .B https://www.intel.com/content/www/us/en/support/products/122484
373 This will override any
375 setting in the config file and provides the identity of the host which
376 should be considered the home for any arrays.
378 When creating an array, the
380 will be recorded in the metadata. For version-1 superblocks, it will
381 be prefixed to the array name. For version-0.90 superblocks, part of
382 the SHA1 hash of the hostname will be stored in the latter half of the
385 When reporting information about an array, any array which is tagged
386 for the given homehost will be reported as such.
388 When using Auto-Assemble, only arrays tagged for the given homehost
389 will be allowed to use 'local' names (i.e. not ending in '_' followed
390 by a digit string). See below under
391 .BR "Auto-Assembly" .
393 The special name "\fBany\fP" can be used as a wild card. If an array
396 then the name "\fBany\fP" will be stored in the array and it can be
397 assembled in the same way on any host. If an array is assembled with
398 this option, then the homehost recorded on the array will be ignored.
404 needs to print the name for a device it normally finds the name in
406 which refers to the device and is the shortest. When a path component is
410 will prefer a longer name if it contains that component. For example
411 .B \-\-prefer=by-uuid
412 will prefer a name in a subdirectory of
417 This functionality is currently only provided by
423 .B \-\-home\-cluster=
424 specifies the cluster name for the md device. The md device can be assembled
425 only on the cluster which matches the name specified. If this option is not
426 provided, mdadm tries to detect the cluster name automatically.
428 .SH For create, build, or grow:
431 .BR \-n ", " \-\-raid\-devices=
432 Specify the number of active devices in the array. This, plus the
433 number of spare devices (see below) must equal the number of
435 (including "\fBmissing\fP" devices)
436 that are listed on the command line for
438 Setting a value of 1 is probably
439 a mistake and so requires that
441 be specified first. A value of 1 will then be allowed for linear,
442 multipath, RAID0 and RAID1. It is never allowed for RAID4, RAID5 or RAID6.
444 This number can only be changed using
446 for RAID1, RAID4, RAID5 and RAID6 arrays, and only on kernels which provide
447 the necessary support.
450 .BR \-x ", " \-\-spare\-devices=
451 Specify the number of spare (eXtra) devices in the initial array.
452 Spares can also be added
453 and removed later. The number of component devices listed
454 on the command line must equal the number of RAID devices plus the
455 number of spare devices.
458 .BR \-z ", " \-\-size=
459 Amount (in Kilobytes) of space to use from each drive in RAID levels 1/4/5/6/10
460 and for RAID 0 on external metadata.
461 This must be a multiple of the chunk size, and must leave about 128Kb
462 of space at the end of the drive for the RAID superblock.
463 If this is not specified
464 (as it normally is not) the smallest drive (or partition) sets the
465 size, though if there is a variance among the drives of greater than 1%, a warning is
468 A suffix of 'K', 'M', 'G' or 'T' can be given to indicate Kilobytes,
469 Megabytes, Gigabytes or Terabytes respectively.
471 Sometimes a replacement drive can be a little smaller than the
472 original drives though this should be minimised by IDEMA standards.
473 Such a replacement drive will be rejected by
475 To guard against this it can be useful to set the initial size
476 slightly smaller than the smaller device with the aim that it will
477 still be larger than any replacement.
479 This option can be used with
481 for determining the initial size of an array. For external metadata,
482 it can be used on a volume, but not on a container itself.
483 Setting the initial size of
485 array is only valid for external metadata.
487 This value can be set with
489 for RAID level 1/4/5/6/10 though
490 DDF arrays may not be able to support this.
491 RAID 0 array size cannot be changed.
492 If the array was created with a size smaller than the currently
493 active drives, the extra space can be accessed using
495 The size can be given as
497 which means to choose the largest size that fits on all current drives.
499 Before reducing the size of the array (with
500 .BR "\-\-grow \-\-size=" )
501 you should make sure that space isn't needed. If the device holds a
502 filesystem, you would need to resize the filesystem to use less space.
504 After reducing the array size you should check that the data stored in
505 the device is still available. If the device holds a filesystem, then
506 an 'fsck' of the filesystem is a minimum requirement. If there are
507 problems the array can be made bigger again with no loss with another
508 .B "\-\-grow \-\-size="
512 .BR \-Z ", " \-\-array\-size=
513 This is only meaningful with
515 and its effect is not persistent: when the array is stopped and
516 restarted the default array size will be restored.
518 Setting the array-size causes the array to appear smaller to programs
519 that access the data. This is particularly needed before reshaping an
520 array so that it will be smaller. As the reshape is not reversible,
521 but setting the size with
523 is, it is required that the array size is reduced as appropriate
524 before the number of devices in the array is reduced.
526 Before reducing the size of the array you should make sure that space
527 isn't needed. If the device holds a filesystem, you would need to
528 resize the filesystem to use less space.
530 After reducing the array size you should check that the data stored in
531 the device is still available. If the device holds a filesystem, then
532 an 'fsck' of the filesystem is a minimum requirement. If there are
533 problems the array can be made bigger again with no loss with another
534 .B "\-\-grow \-\-array\-size="
537 A suffix of 'K', 'M', 'G' or 'T' can be given to indicate Kilobytes,
538 Megabytes, Gigabytes or Terabytes respectively.
541 restores the apparent size of the array to be whatever the real
542 amount of available space is.
544 Clustered arrays do not support this parameter yet.
547 .BR \-c ", " \-\-chunk=
548 Specify chunk size in kilobytes. The default when creating an
549 array is 512KB. To ensure compatibility with earlier versions, the
550 default when building an array with no persistent metadata is 64KB.
551 This is only meaningful for RAID0, RAID4, RAID5, RAID6, and RAID10.
553 RAID4, RAID5, RAID6, and RAID10 require the chunk size to be a power
554 of 2, with minimal chunk size being 4KB.
556 A suffix of 'K', 'M', 'G' or 'T' can be given to indicate Kilobytes,
557 Megabytes, Gigabytes or Terabytes respectively.
561 Specify the rounding factor for a Linear array. The size of each
562 component will be rounded down to a multiple of this size.
563 This is a synonym for
565 but highlights the different meaning for Linear as compared to other
566 RAID levels. The default is 64K if a kernel earlier than 2.6.16 is in
567 use, and is 0K (i.e. no rounding) in later kernels.
570 .BR \-l ", " \-\-level=
571 Set RAID level. When used with
573 options are: linear, raid0, 0, stripe, raid1, 1, mirror, raid4, 4,
574 raid5, 5, raid6, 6, raid10, 10, multipath, mp, faulty, container.
575 Obviously some of these are synonymous.
579 metadata type is requested, only the
581 level is permitted, and it does not need to be explicitly given.
585 only linear, stripe, raid0, 0, raid1, multipath, mp, and faulty are valid.
589 to change the RAID level in some cases. See LEVEL CHANGES below.
592 .BR \-p ", " \-\-layout=
593 This option configures the fine details of data layout for RAID5, RAID6,
594 and RAID10 arrays, and controls the failure modes for
596 It can also be used for working around a kernel bug with RAID0, but generally
597 doesn't need to be used explicitly.
599 The layout of the RAID5 parity block can be one of
600 .BR left\-asymmetric ,
601 .BR left\-symmetric ,
602 .BR right\-asymmetric ,
603 .BR right\-symmetric ,
604 .BR la ", " ra ", " ls ", " rs .
606 .BR left\-symmetric .
608 It is also possible to cause RAID5 to use a RAID4-like layout by
614 Finally for RAID5 there are DDF\-compatible layouts,
615 .BR ddf\-zero\-restart ,
616 .BR ddf\-N\-restart ,
618 .BR ddf\-N\-continue .
620 These same layouts are available for RAID6. There are also 4 layouts
621 that will provide an intermediate stage for converting between RAID5
622 and RAID6. These provide a layout which is identical to the
623 corresponding RAID5 layout on the first N\-1 devices, and has the 'Q'
624 syndrome (the second 'parity' block used by RAID6) on the last device.
626 .BR left\-symmetric\-6 ,
627 .BR right\-symmetric\-6 ,
628 .BR left\-asymmetric\-6 ,
629 .BR right\-asymmetric\-6 ,
631 .BR parity\-first\-6 .
633 When setting the failure mode for level
636 .BR write\-transient ", " wt ,
637 .BR read\-transient ", " rt ,
638 .BR write\-persistent ", " wp ,
639 .BR read\-persistent ", " rp ,
641 .BR read\-fixable ", " rf ,
642 .BR clear ", " flush ", " none .
644 Each failure mode can be followed by a number, which is used as a period
645 between fault generation. Without a number, the fault is generated
646 once on the first relevant request. With a number, the fault will be
647 generated after that many requests, and will continue to be generated
648 every time the period elapses.
650 Multiple failure modes can be current simultaneously by using the
652 option to set subsequent failure modes.
654 "clear" or "none" will remove any pending or periodic failure modes,
655 and "flush" will clear any persistent faults.
657 The layout options for RAID10 are one of 'n', 'o' or 'f' followed
658 by a small number signifying the number of copies of each datablock.
659 The default is 'n2'. The supported options are:
662 signals 'near' copies. Multiple copies of one data block are at
663 similar offsets in different devices.
666 signals 'offset' copies. Rather than the chunks being duplicated
667 within a stripe, whole stripes are duplicated but are rotated by one
668 device so duplicate blocks are on different devices. Thus subsequent
669 copies of a block are in the next drive, and are one chunk further
674 (multiple copies have very different offsets).
675 See md(4) for more detail about 'near', 'offset', and 'far'.
677 As for the number of copies of each data block, 2 is normal, 3
678 can be useful. This number can be at most equal to the number of
679 devices in the array. It does not need to divide evenly into that
680 number (e.g. it is perfectly legal to have an 'n2' layout for an array
681 with an odd number of devices).
683 A bug introduced in Linux 3.14 means that RAID0 arrays
684 .B "with devices of differing sizes"
685 started using a different layout. This could lead to
686 data corruption. Since Linux 5.4 (and various stable releases that received
687 backports), the kernel will not accept such an array unless
688 a layout is explicitly set. It can be set to
692 When creating a new array,
696 by default, so the layout does not normally need to be set.
697 An array created for either
701 will not be recognized by an (unpatched) kernel prior to 5.4. To create
702 a RAID0 array with devices of differing sizes that can be used on an
703 older kernel, you can set the layout to
705 This will use whichever layout the running kernel supports, so the data
706 on the array may become corrupt when changing kernel from pre-3.14 to a
709 When an array is converted between RAID5 and RAID6 an intermediate
710 RAID6 layout is used in which the second parity block (Q) is always on
711 the last device. To convert a RAID5 to RAID6 and leave it in this new
712 layout (which does not require re-striping) use
713 .BR \-\-layout=preserve .
714 This will try to avoid any restriping.
716 The converse of this is
717 .B \-\-layout=normalise
718 which will change a non-standard RAID6 layout into a more standard
725 (thus explaining the p of
729 .BR \-b ", " \-\-bitmap=
730 Specify a file to store a write-intent bitmap in. The file should not
733 is also given. The same file should be provided
734 when assembling the array. If the word
736 is given, then the bitmap is stored with the metadata on the array,
737 and so is replicated on all devices. If the word
741 mode, then any bitmap that is present is removed. If the word
743 is given, the array is created for a clustered environment. One bitmap
744 is created for each node as defined by the
746 parameter and are stored internally.
748 To help catch typing errors, the filename must contain at least one
749 slash ('/') if it is a real file (not 'internal' or 'none').
751 Note: external bitmaps are only known to work on ext2 and ext3.
752 Storing bitmap files on other filesystems may result in serious problems.
754 When creating an array on devices which are 100G or larger,
756 automatically adds an internal bitmap as it will usually be
757 beneficial. This can be suppressed with
759 or by selecting a different consistency policy with
760 .BR \-\-consistency\-policy .
763 .BR \-\-bitmap\-chunk=
764 Set the chunk size of the bitmap. Each bit corresponds to that many
765 Kilobytes of storage.
766 When using a file-based bitmap, the default is to use the smallest
767 size that is at least 4 and requires no more than 2^21 chunks.
770 bitmap, the chunk size defaults to 64Meg, or larger if necessary to
771 fit the bitmap into the available space.
773 A suffix of 'K', 'M', 'G' or 'T' can be given to indicate Kilobytes,
774 Megabytes, Gigabytes or Terabytes respectively.
777 .BR \-W ", " \-\-write\-mostly
778 subsequent devices listed in a
783 command will be flagged as 'write\-mostly'. This is valid for RAID1
784 only and means that the 'md' driver will avoid reading from these
785 devices if at all possible. This can be useful if mirroring over a
789 .BR \-\-write\-behind=
790 Specify that write-behind mode should be enabled (valid for RAID1
791 only). If an argument is specified, it will set the maximum number
792 of outstanding writes allowed. The default value is 256.
793 A write-intent bitmap is required in order to use write-behind
794 mode, and write-behind is only attempted on drives marked as
799 subsequent devices listed in a
803 command will be flagged as 'failfast'. This is valid for RAID1 and
804 RAID10 only. IO requests to these devices will be encouraged to fail
805 quickly rather than cause long delays due to error handling. Also no
806 attempt is made to repair a read error on these devices.
808 If an array becomes degraded so that the 'failfast' device is the only
809 usable device, the 'failfast' flag will then be ignored and extended
810 delays will be preferred to complete failure.
812 The 'failfast' flag is appropriate for storage arrays which have a
813 low probability of true failure, but which may sometimes
814 cause unacceptable delays due to internal maintenance functions.
817 .BR \-\-assume\-clean
820 that the array pre-existed and is known to be clean. It can be useful
821 when trying to recover from a major failure as you can be sure that no
822 data will be affected unless you actually write to the array. It can
823 also be used when creating a RAID1 or RAID10 if you want to avoid the
824 initial resync, however this practice \(em while normally safe \(em is not
825 recommended. Use this only if you really know what you are doing.
827 When the devices that will be part of a new array were filled
828 with zeros before creation the operator knows the array is
829 actually clean. If that is the case, such as after running
830 badblocks, this argument can be used to tell mdadm the
831 facts the operator knows.
833 When an array is resized to a larger size with
834 .B "\-\-grow \-\-size="
835 the new space is normally resynced in that same way that the whole
836 array is resynced at creation. From Linux version 3.0,
838 can be used with that command to avoid the automatic resync.
842 When creating an array, send write zeroes requests to all the block
843 devices. This should zero the data area on all disks such that the
844 initial sync is not necessary and, if successfull, will behave
849 This is intended for use with devices that have hardware offload for
850 zeroing, but despite this zeroing can still take several minutes for
851 large disks. Thus a message is printed before and after zeroing and
852 each disk is zeroed in parallel with the others.
854 This is only meaningful with --create.
857 .BR \-\-backup\-file=
860 is used to increase the number of raid devices in a RAID5 or RAID6 if
861 there are no spare devices available, or to shrink, change RAID level
862 or layout. See the GROW MODE section below on RAID\-DEVICES CHANGES.
863 The file must be stored on a separate device, not on the RAID array
868 Arrays with 1.x metadata can leave a gap between the start of the
869 device and the start of array data. This gap can be used for various
870 metadata. The start of data is known as the
872 Normally an appropriate data offset is computed automatically.
873 However it can be useful to set it explicitly such as when re-creating
874 an array which was originally created using a different version of
876 which computed a different offset.
878 Setting the offset explicitly over-rides the default. The value given
879 is in Kilobytes unless a suffix of 'K', 'M', 'G' or 'T' is used to explicitly
880 indicate Kilobytes, Megabytes, Gigabytes or Terabytes respectively.
884 can also be used with
886 for some RAID levels (initially on RAID10). This allows the
887 data\-offset to be changed as part of the reshape process. When the
888 data offset is changed, no backup file is required as the difference
889 in offsets is used to provide the same functionality.
891 When the new offset is earlier than the old offset, the number of
892 devices in the array cannot shrink. When it is after the old offset,
893 the number of devices in the array cannot increase.
895 When creating an array,
899 In the case each member device is expected to have an offset appended
900 to the name, separated by a colon. This makes it possible to recreate
901 exactly an array which has varying data offsets (as can happen when
902 different versions of
904 are used to add different devices).
908 This option is complementary to the
909 .B \-\-freeze-reshape
910 option for assembly. It is needed when
912 operation is interrupted and it is not restarted automatically due to
913 .B \-\-freeze-reshape
914 usage during array assembly. This option is used together with
918 ) command and device for a pending reshape to be continued.
919 All parameters required for reshape continuation will be read from array metadata.
923 .BR \-\-backup\-file=
924 option to be set, continuation option will require to have exactly the same
925 backup file given as well.
927 Any other parameter passed together with
929 option will be ignored.
932 .BR \-N ", " \-\-name=
935 for the array. It must be
936 .BR "POSIX PORTABLE NAME"
937 compatible and cannot be longer than 32 chars. This is effective when creating an array
938 with a v1 metadata, or an external array.
940 If name is needed but not specified, it is taken from the basename of the device
941 that is being created. See
948 run the array, even if some of the components
949 appear to be active in another array or filesystem. Normally
951 will ask for confirmation before including such components in an
952 array. This option causes that question to be suppressed.
955 .BR \-f ", " \-\-force
958 accept the geometry and layout specified without question. Normally
960 will not allow the creation of an array with only one device, and will try
961 to create a RAID5 array with one missing drive (as this makes the
962 initial resync work faster). With
965 will not try to be so clever.
968 .BR \-o ", " \-\-readonly
971 rather than read-write as normal. No writes will be allowed to the
972 array, and no resync, recovery, or reshape will be started. It works with
973 Create, Assemble, Manage and Misc mode.
976 .BR \-a ", " "\-\-auto{=yes,md,mdp,part,p}{NN}"
977 Instruct mdadm how to create the device file if needed, possibly allocating
978 an unused minor number. "md" causes a non-partitionable array
979 to be used (though since Linux 2.6.28, these array devices are in fact
980 partitionable). "mdp", "part" or "p" causes a partitionable array (2.6 and
981 later) to be used. "yes" requires the named md device to have
982 a 'standard' format, and the type and minor number will be determined
983 from this. With mdadm 3.0, device creation is normally left up to
985 so this option is unlikely to be needed.
986 See DEVICE NAMES below.
988 The argument can also come immediately after
993 is not given on the command line or in the config file, then
999 is also given, then any
1001 entries in the config file will override the
1003 instruction given on the command line.
1005 For partitionable arrays,
1007 will create the device file for the whole array and for the first 4
1008 partitions. A different number of partitions can be specified at the
1009 end of this option (e.g.
1011 If the device name ends with a digit, the partition names add a 'p',
1013 .IR /dev/md/home1p3 .
1014 If there is no trailing digit, then the partition names just have a
1016 .IR /dev/md/scratch3 .
1018 If the md device name is in a 'standard' format as described in DEVICE
1019 NAMES, then it will be created, if necessary, with the appropriate
1020 device number based on that name. If the device name is not in one of these
1021 formats, then an unused device number will be allocated. The device
1022 number will be considered unused if there is no active array for that
1023 number, and there is no entry in /dev for that number and with a
1024 non-standard name. Names that are not in 'standard' format are only
1025 allowed in "/dev/md/".
1027 This is meaningful with
1033 .BR \-a ", " "\-\-add"
1034 This option can be used in Grow mode in two cases.
1036 If the target array is a Linear array, then
1038 can be used to add one or more devices to the array. They
1039 are simply catenated on to the end of the array. Once added, the
1040 devices cannot be removed.
1044 option is being used to increase the number of devices in an array,
1047 can be used to add some extra devices to be included in the array.
1048 In most cases this is not needed as the extra devices can be added as
1049 spares first, and then the number of raid disks can be changed.
1050 However, for RAID0 it is not possible to add spares. So to increase
1051 the number of devices in a RAID0, it is necessary to set the new
1052 number of devices, and to add the new devices, in the same command.
1056 Only works when the array is created for a clustered environment. It specifies
1057 the maximum number of nodes in the cluster that will use this device
1058 simultaneously. If not specified, this defaults to 4.
1061 .BR \-\-write-journal
1062 Specify journal device for the RAID-4/5/6 array. The journal device
1063 should be an SSD with a reasonable lifetime.
1066 .BR \-k ", " \-\-consistency\-policy=
1067 Specify how the array maintains consistency in the case of an unexpected shutdown.
1068 Only relevant for RAID levels with redundancy.
1069 Currently supported options are:
1074 Full resync is performed and all redundancy is regenerated when the array is
1075 started after an unclean shutdown.
1079 Resync assisted by a write-intent bitmap. Implicitly selected when using
1084 For RAID levels 4/5/6, the journal device is used to log transactions and replay
1085 after an unclean shutdown. Implicitly selected when using
1086 .BR \-\-write\-journal .
1090 For RAID5 only, Partial Parity Log is used to close the write hole and
1091 eliminate resync. PPL is stored in the metadata region of RAID member drives,
1092 no additional journal drive is needed.
1095 Can be used with \-\-grow to change the consistency policy of an active array
1096 in some cases. See CONSISTENCY POLICY CHANGES below.
1103 .BR \-u ", " \-\-uuid=
1104 uuid of array to assemble. Devices which don't have this uuid are
1108 .BR \-m ", " \-\-super\-minor=
1109 Minor number of device that array was created for. Devices which
1110 don't have this minor number are excluded. If you create an array as
1111 /dev/md1, then all superblocks will contain the minor number 1, even if
1112 the array is later assembled as /dev/md2.
1114 Giving the literal word "dev" for
1118 to use the minor number of the md device that is being assembled.
1119 e.g. when assembling
1121 .B \-\-super\-minor=dev
1122 will look for super blocks with a minor number of 0.
1125 is only relevant for v0.90 metadata, and should not normally be used.
1131 .BR \-N ", " \-\-name=
1132 Specify the name of the array to assemble. It must be
1133 .BR "POSIX PORTABLE NAME"
1134 compatible and cannot be longer than 32 chars. This must be the name
1135 that was specified when creating the array. It must either match
1136 the name stored in the superblock exactly, or it must match
1139 prefixed to the start of the given name.
1142 .BR \-f ", " \-\-force
1143 Assemble the array even if the metadata on some devices appears to be
1146 cannot find enough working devices to start the array, but can find
1147 some devices that are recorded as having failed, then it will mark
1148 those devices as working so that the array can be started. This works only for
1149 native. For external metadata it allows to start dirty degraded RAID 4, 5, 6.
1150 An array which requires
1152 to be started may contain data corruption. Use it carefully.
1155 .BR \-R ", " \-\-run
1156 Attempt to start the array even if fewer drives were given than were
1157 present last time the array was active. Normally if not all the
1158 expected drives are found and
1160 is not used, then the array will be assembled but not started.
1163 an attempt will be made to start it anyway.
1167 This is the reverse of
1169 in that it inhibits the startup of array unless all expected drives
1170 are present. This is only needed with
1172 and can be used if the physical connections to devices are
1173 not as reliable as you would like.
1176 .BR \-a ", " "\-\-auto{=no,yes,md,mdp,part}"
1177 See this option under Create and Build options.
1180 .BR \-b ", " \-\-bitmap=
1181 Specify the bitmap file that was given when the array was created. If
1184 bitmap, there is no need to specify this when assembling the array.
1187 .BR \-\-backup\-file=
1190 was used while reshaping an array (e.g. changing number of devices or
1191 chunk size) and the system crashed during the critical section, then the same
1193 must be presented to
1195 to allow possibly corrupted data to be restored, and the reshape
1199 .BR \-\-invalid\-backup
1200 If the file needed for the above option is not available for any
1201 reason an empty file can be given together with this option to
1202 indicate that the backup file is invalid. In this case the data that
1203 was being rearranged at the time of the crash could be irrecoverably
1204 lost, but the rest of the array may still be recoverable. This option
1205 should only be used as a last resort if there is no way to recover the
1210 .BR \-U ", " \-\-update=
1211 Update the superblock on each device while assembling the array. The
1212 argument given to this flag can be one of
1228 .BR layout\-original ,
1229 .BR layout\-alternate ,
1230 .BR layout\-unspecified ,
1237 option will adjust the superblock of an array what was created on a Sparc
1238 machine running a patched 2.2 Linux kernel. This kernel got the
1239 alignment of part of the superblock wrong. You can use the
1240 .B "\-\-examine \-\-sparc2.2"
1243 to see what effect this would have.
1247 option will update the
1248 .B "preferred minor"
1249 field on each superblock to match the minor number of the array being
1251 This can be useful if
1253 reports a different "Preferred Minor" to
1255 In some cases this update will be performed automatically
1256 by the kernel driver. In particular, the update happens automatically
1257 at the first write to an array with redundancy (RAID level 1 or
1258 greater) on a 2.6 (or later) kernel.
1262 option will change the uuid of the array. If a UUID is given with the
1264 option that UUID will be used as a new UUID and will
1266 be used to help identify the devices in the array.
1269 is given, a random UUID is chosen.
1273 option will change the
1275 of the array as stored in the superblock. This is only supported for
1276 version-1 superblocks.
1280 option will change the
1282 of the array as stored in the bitmap superblock. This option only
1283 works for a clustered environment.
1287 option will change the
1289 as recorded in the superblock. For version-0 superblocks, this is the
1290 same as updating the UUID.
1291 For version-1 superblocks, this involves updating the name.
1295 option will change the cluster name as recorded in the superblock and
1296 bitmap. This option only works for a clustered environment.
1300 option will cause the array to be marked
1302 meaning that any redundancy in the array (e.g. parity for RAID5,
1303 copies for RAID1) may be incorrect. This will cause the RAID system
1304 to perform a "resync" pass to make sure that all redundant information
1309 option allows arrays to be moved between machines with different
1310 byte-order, such as from a big-endian machine like a Sparc or some
1311 MIPS machines, to a little-endian x86_64 machine.
1312 When assembling such an array for the first time after a move, giving
1313 .B "\-\-update=byteorder"
1316 to expect superblocks to have their byteorder reversed, and will
1317 correct that order before assembling the array. This is only valid
1318 with original (Version 0.90) superblocks.
1322 option will correct the summaries in the superblock. That is the
1323 counts of total, working, active, failed, and spare devices.
1327 option will rarely be of use. It applies to version 1.1 and 1.2 metadata
1328 only (where the metadata is at the start of the device) and is only
1329 useful when the component device has changed size (typically become
1330 larger). The version 1 metadata records the amount of the device that
1331 can be used to store data, so if a device in a version 1.1 or 1.2
1332 array becomes larger, the metadata will still be visible, but the
1333 extra space will not. In this case it might be useful to assemble the
1335 .BR \-\-update=devicesize .
1338 to determine the maximum usable amount of space on each device and
1339 update the relevant field in the metadata.
1343 option only works on v0.90 metadata arrays and will convert them to
1344 v1.0 metadata. The array must not be dirty (i.e. it must not need a
1345 sync) and it must not have a write-intent bitmap.
1347 The old metadata will remain on the devices, but will appear older
1348 than the new metadata and so will usually be ignored. The old metadata
1349 (or indeed the new metadata) can be removed by giving the appropriate
1352 .BR \-\-zero\-superblock .
1356 option can be used when an array has an internal bitmap which is
1357 corrupt in some way so that assembling the array normally fails. It
1358 will cause any internal bitmap to be ignored.
1362 option will reserve space in each device for a bad block list. This
1363 will be 4K in size and positioned near the end of any free space
1364 between the superblock and the data.
1368 option will cause any reservation of space for a bad block list to be
1369 removed. If the bad block list contains entries, this will fail, as
1370 removing the list could cause data corruption.
1374 option will enable PPL for a RAID5 array and reserve space for PPL on each
1375 device. There must be enough free space between the data and superblock and a
1376 write-intent bitmap or journal must not be used.
1380 option will disable PPL in the superblock.
1385 .B layout\-alternate
1386 options are for RAID0 arrays with non-uniform devices size that were in
1387 use before Linux 5.4. If the array was being used with Linux 3.13 or
1388 earlier, then to assemble the array on a new kernel,
1389 .B \-\-update=layout\-original
1390 must be given. If the array was created and used with a kernel from Linux 3.14 to
1392 .B \-\-update=layout\-alternate
1393 must be given. This only needs to be given once. Subsequent assembly of the array
1394 will happen normally.
1395 For more information, see
1399 .B layout\-unspecified
1400 option reverts the effect of
1403 .B layout\-alternate
1404 and allows the array to be again used on a kernel prior to Linux 5.3.
1405 This option should be used with great caution.
1408 .BR \-\-freeze\-reshape
1409 This option is intended to be used in start-up scripts during the initrd boot phase.
1410 When the array under reshape is assembled during the initrd phase, this option
1411 stops the reshape after the reshape-critical section has been restored. This happens
1412 before the file system pivot operation and avoids loss of filesystem context.
1413 Losing file system context would cause reshape to be broken.
1415 Reshape can be continued later using the
1417 option for the grow command.
1419 .SH For Manage mode:
1422 .BR \-t ", " \-\-test
1423 Unless a more serious error occurred,
1425 will exit with a status of 2 if no changes were made to the array and
1426 0 if at least one change was made.
1427 This can be useful when an indirect specifier such as
1432 is used in requesting an operation on the array.
1434 will report failure if these specifiers didn't find any match.
1437 .BR \-a ", " \-\-add
1438 hot-add listed devices.
1439 If a device appears to have recently been part of the array
1440 (possibly it failed or was removed) the device is re\-added as described
1442 If that fails or the device was never part of the array, the device is
1443 added as a hot-spare.
1444 If the array is degraded, it will immediately start to rebuild data
1447 Note that this and the following options are only meaningful on array
1448 with redundancy. They don't apply to RAID0 or Linear.
1452 re\-add a device that was previously removed from an array.
1453 If the metadata on the device reports that it is a member of the
1454 array, and the slot that it used is still vacant, then the device will
1455 be added back to the array in the same position. This will normally
1456 cause the data for that device to be recovered. However, based on the
1457 event count on the device, the recovery may only require sections that
1458 are flagged by a write-intent bitmap to be recovered or may not require
1459 any recovery at all.
1461 When used on an array that has no metadata (i.e. it was built with
1463 it will be assumed that bitmap-based recovery is enough to make the
1464 device fully consistent with the array.
1467 can also be accompanied by
1468 .BR \-\-update=devicesize ,
1469 .BR \-\-update=bbl ", or"
1470 .BR \-\-update=no\-bbl .
1471 See descriptions of these options when used in Assemble mode for an
1472 explanation of their use.
1474 If the device name given is
1478 will try to find any device that looks like it should be
1479 part of the array but isn't and will try to re\-add all such devices.
1481 If the device name given is
1485 will find all devices in the array that are marked
1487 remove them and attempt to immediately re\-add them. This can be
1488 useful if you are certain that the reason for failure has been
1493 Add a device as a spare. This is similar to
1495 except that it does not attempt
1497 first. The device will be added as a spare even if it looks like it
1498 could be a recent member of the array.
1501 .BR \-r ", " \-\-remove
1502 remove listed devices. They must not be active. i.e. they should
1503 be failed or spare devices.
1505 As well as the name of a device file
1515 The first causes all failed devices to be removed. The second causes
1516 any device which is no longer connected to the system (i.e an 'open'
1520 The third will remove a set as described below under
1524 .BR \-f ", " \-\-fail
1525 Mark listed devices as faulty.
1526 As well as the name of a device file, the word
1530 can be given. The former will cause any device that has been detached from
1531 the system to be marked as failed. It can then be removed.
1533 For RAID10 arrays where the number of copies evenly divides the number
1534 of devices, the devices can be conceptually divided into sets where
1535 each set contains a single complete copy of the data on the array.
1536 Sometimes a RAID10 array will be configured so that these sets are on
1537 separate controllers. In this case, all the devices in one set can be
1538 failed by giving a name like
1544 The appropriate set names are reported by
1554 Mark listed devices as requiring replacement. As soon as a spare is
1555 available, it will be rebuilt and will replace the marked device.
1556 This is similar to marking a device as faulty, but the device remains
1557 in service during the recovery process to increase resilience against
1558 multiple failures. When the replacement process finishes, the
1559 replaced device will be marked as faulty.
1563 This can follow a list of
1565 devices. The devices listed after
1567 will preferentially be used to replace the devices listed after
1569 These devices must already be spare devices in the array.
1572 .BR \-\-write\-mostly
1573 Subsequent devices that are added or re\-added will have the 'write-mostly'
1574 flag set. This is only valid for RAID1 and means that the 'md' driver
1575 will avoid reading from these devices if possible.
1578 Subsequent devices that are added or re\-added will have the 'write-mostly'
1581 .BR \-\-cluster\-confirm
1582 Confirm the existence of the device. This is issued in response to an \-\-add
1583 request by a node in a cluster. When a node adds a device it sends a message
1584 to all nodes in the cluster to look for a device with a UUID. This translates
1585 to a udev notification with the UUID of the device to be added and the slot
1586 number. The receiving node must acknowledge this message
1587 with \-\-cluster\-confirm. Valid arguments are <slot>:<devicename> in case
1588 the device is found or <slot>:missing in case the device is not found.
1592 Add a journal to an existing array, or recreate journal for a RAID-4/5/6 array
1593 that lost a journal device. To avoid interrupting ongoing write operations,
1595 only works for array in Read-Only state.
1599 Subsequent devices that are added or re\-added will have
1600 the 'failfast' flag set. This is only valid for RAID1 and RAID10 and
1601 means that the 'md' driver will avoid long timeouts on error handling
1605 Subsequent devices that are re\-added will be re\-added without
1606 the 'failfast' flag set.
1609 Each of these options requires that the first device listed is the array
1610 to be acted upon, and the remainder are component devices to be added,
1611 removed, marked as faulty, etc. Several different operations can be
1612 specified for different devices, e.g.
1614 mdadm /dev/md0 \-\-add /dev/sda1 \-\-fail /dev/sdb1 \-\-remove /dev/sdb1
1616 Each operation applies to all devices listed until the next
1619 If an array is using a write-intent bitmap, then devices which have
1620 been removed can be re\-added in a way that avoids a full
1621 reconstruction but instead just updates the blocks that have changed
1622 since the device was removed. For arrays with persistent metadata
1623 (superblocks) this is done automatically. For arrays created with
1625 mdadm needs to be told that this device we removed recently with
1628 Devices can only be removed from an array if they are not in active
1629 use, i.e. that must be spares or failed devices. To remove an active
1630 device, it must first be marked as
1636 .BR \-Q ", " \-\-query
1637 Examine a device to see
1638 (1) if it is an md device and (2) if it is a component of an md
1640 Information about what is discovered is presented.
1643 .BR \-D ", " \-\-detail
1644 Print details of one or more md devices.
1647 .BR \-\-detail\-platform
1648 Print details of the platform's RAID capabilities (firmware / hardware
1649 topology) for a given metadata format. If used without an argument, mdadm
1650 will scan all controllers looking for their capabilities. Otherwise, mdadm
1651 will only look at the controller specified by the argument in the form of an
1652 absolute filepath or a link, e.g.
1653 .IR /sys/devices/pci0000:00/0000:00:1f.2 .
1656 .BR \-Y ", " \-\-export
1659 .BR \-\-detail-platform ,
1663 output will be formatted as
1665 pairs for easy import into the environment.
1671 indicates whether an array was started
1673 or not, which may include a reason
1674 .RB ( unsafe ", " nothing ", " no ).
1677 indicates if the array is expected on this host
1679 or seems to be from elsewhere
1683 .BR \-E ", " \-\-examine
1684 Print contents of the metadata stored on the named device(s).
1685 Note the contrast between
1690 applies to devices which are components of an array, while
1692 applies to a whole array which is currently active.
1695 If an array was created on a SPARC machine with a 2.2 Linux kernel
1696 patched with RAID support, the superblock will have been created
1697 incorrectly, or at least incompatibly with 2.4 and later kernels.
1702 will fix the superblock before displaying it. If this appears to do
1703 the right thing, then the array can be successfully assembled using
1704 .BR "\-\-assemble \-\-update=sparc2.2" .
1707 .BR \-X ", " \-\-examine\-bitmap
1708 Report information about a bitmap file.
1709 The argument is either an external bitmap file or an array component
1710 in case of an internal bitmap. Note that running this on an array
1713 does not report the bitmap for that array.
1716 .B \-\-examine\-badblocks
1717 List the bad-blocks recorded for the device, if a bad-blocks list has
1718 been configured. Currently only
1722 metadata support bad-blocks lists.
1725 .BI \-\-dump= directory
1727 .BI \-\-restore= directory
1728 Save metadata from lists devices, or restore metadata to listed devices.
1731 .BR \-R ", " \-\-run
1732 start a partially assembled array. If
1734 did not find enough devices to fully start the array, it might leaving
1735 it partially assembled. If you wish, you can then use
1737 to start the array in degraded mode.
1740 .BR \-S ", " \-\-stop
1741 deactivate array, releasing all resources.
1744 .BR \-o ", " \-\-readonly
1745 mark array as readonly.
1748 .BR \-w ", " \-\-readwrite
1749 mark array as readwrite.
1752 .B \-\-zero\-superblock
1753 If the device contains a valid md superblock, the block is
1754 overwritten with zeros. With
1756 the block where the superblock would be is overwritten even if it
1757 doesn't appear to be valid.
1760 Be careful when calling \-\-zero\-superblock with clustered raid. Make sure
1761 the array isn't used or assembled in another cluster node before executing it.
1764 .B \-\-kill\-subarray=
1765 If the device is a container and the argument to \-\-kill\-subarray
1766 specifies an inactive subarray in the container, then the subarray is
1767 deleted. Deleting all subarrays will leave an 'empty-container' or
1768 spare superblock on the drives. See
1769 .B \-\-zero\-superblock
1771 removing a superblock. Note that some formats depend on the subarray
1772 index for generating a UUID, this command will fail if it would change
1773 the UUID of an active subarray.
1776 .B \-\-update\-subarray=
1777 If the device is a container and the argument to \-\-update\-subarray
1778 specifies a subarray in the container, then attempt to update the given
1779 superblock field in the subarray. See below in
1784 .BR \-t ", " \-\-test
1789 is set to reflect the status of the device. See below in
1794 .BR \-W ", " \-\-wait
1795 For each md device given, wait for any resync, recovery, or reshape
1796 activity to finish before returning.
1798 will return with success if it actually waited for every device
1799 listed, otherwise it will return failure.
1803 For each md device given, or each device in /proc/mdstat if
1805 is given, arrange for the array to be marked clean as soon as possible.
1807 will return with success if the array uses external metadata and we
1808 successfully waited. For native arrays, this returns immediately as the
1809 kernel handles dirty-clean transitions at shutdown. No action is taken
1810 if safe-mode handling is disabled.
1814 Set the "sync_action" for all md devices given to one of
1821 will abort any currently running action though some actions will
1822 automatically restart.
1825 will abort any current action and ensure no other action starts
1835 .BR "SCRUBBING AND MISMATCHES" .
1837 .SH For Incremental Assembly mode:
1839 .BR \-\-rebuild\-map ", " \-r
1840 Rebuild the map file
1844 uses to help track which arrays are currently being assembled.
1847 .BR \-\-run ", " \-R
1848 Run any array assembled as soon as a minimal number of devices is
1849 available, rather than waiting until all expected devices are present.
1852 .BR \-\-scan ", " \-s
1853 Only meaningful with
1857 file for arrays that are being incrementally assembled and will try to
1858 start any that are not already started. If any such array is listed
1861 as requiring an external bitmap, that bitmap will be attached first.
1864 .BR \-\-fail ", " \-f
1865 This allows the hot-plug system to remove devices that have fully disappeared
1866 from the kernel. It will first fail and then remove the device from any
1867 array it belongs to.
1868 The device name given should be a kernel device name such as "sda",
1874 Only used with \-\-fail. The 'path' given will be recorded so that if
1875 a new device appears at the same location it can be automatically
1876 added to the same array. This allows the failed device to be
1877 automatically replaced by a new device without metadata if it appears
1878 at specified path. This option is normally only set by an
1882 .SH For Monitor mode:
1884 .BR \-m ", " \-\-mail
1885 Give a mail address to send alerts to.
1888 .BR \-p ", " \-\-program ", " \-\-alert
1889 Give a program to be run whenever an event is detected.
1892 .BR \-y ", " \-\-syslog
1893 Cause all events to be reported through 'syslog'. The messages have
1894 facility of 'daemon' and varying priorities.
1897 .BR \-d ", " \-\-delay
1898 Give a delay in seconds.
1900 polls the md arrays and then waits this many seconds before polling
1901 again. The default is 60 seconds. Since 2.6.16, there is no need to
1902 reduce this as the kernel alerts
1904 immediately when there is any change.
1907 .BR \-r ", " \-\-increment
1908 Give a percentage increment.
1910 will generate RebuildNN events with the given percentage increment.
1913 .BR \-f ", " \-\-daemonise
1916 to run as a background daemon if it decides to monitor anything. This
1917 causes it to fork and run in the child, and to disconnect from the
1918 terminal. The process id of the child is written to stdout.
1921 which will only continue monitoring if a mail address or alert program
1922 is found in the config file.
1925 .BR \-i ", " \-\-pid\-file
1928 is running in daemon mode, write the pid of the daemon process to
1929 the specified file, instead of printing it on standard output.
1932 .BR \-1 ", " \-\-oneshot
1933 Check arrays only once. This will generate
1935 events and more significantly
1941 .B " mdadm \-\-monitor \-\-scan \-1"
1943 from a cron script will ensure regular notification of any degraded arrays.
1946 .BR \-t ", " \-\-test
1949 alert for every array found at startup. This alert gets mailed and
1950 passed to the alert program. This can be used for testing that alert
1951 message do get through successfully.
1955 This inhibits the functionality for moving spares between arrays.
1956 Only one monitoring process started with
1958 but without this flag is allowed, otherwise the two could interfere
1965 .B mdadm \-\-assemble
1966 .I md-device options-and-component-devices...
1969 .B mdadm \-\-assemble \-\-scan
1970 .I md-devices-and-options...
1973 .B mdadm \-\-assemble \-\-scan
1977 This usage assembles one or more RAID arrays from pre-existing components.
1978 For each array, mdadm needs to know the md device, the identity of the
1979 array, and the number of component devices. These can be found in a number of ways.
1981 In the first usage example (without the
1983 the first device given is the md device.
1984 In the second usage example, all devices listed are treated as md
1985 devices and assembly is attempted.
1986 In the third (where no devices are listed) all md devices that are
1987 listed in the configuration file are assembled. If no arrays are
1988 described by the configuration file, then any arrays that
1989 can be found on unused devices will be assembled.
1991 If precisely one device is listed, but
1997 was given and identity information is extracted from the configuration file.
1999 The identity can be given with the
2005 option, will be taken from the md-device record in the config file, or
2006 will be taken from the super block of the first component-device
2007 listed on the command line.
2009 Devices can be given on the
2011 command line or in the config file. Only devices which have an md
2012 superblock which contains the right identity will be considered for
2015 The config file is only used if explicitly named with
2017 or requested with (a possibly implicit)
2019 In the latter case, the default config file is used. See
2025 is not given, then the config file will only be used to find the
2026 identity of md arrays.
2028 Normally the array will be started after it is assembled. However if
2030 is not given and not all expected drives were listed, then the array
2031 is not started (to guard against usage errors). To insist that the
2032 array be started in this case (as may work for RAID1, 4, 5, 6, or 10),
2041 does not create any entries in
2045 It does record information in
2049 to choose the correct name.
2053 detects that udev is not configured, it will create the devices in
2057 In Linux kernels prior to version 2.6.28 there were two distinct
2058 types of md devices that could be created: one that could be
2059 partitioned using standard partitioning tools and one that could not.
2060 Since 2.6.28 that distinction is no longer relevant as both types of
2061 devices can be partitioned.
2063 will normally create the type that originally could not be partitioned
2064 as it has a well-defined major number (9).
2066 Prior to 2.6.28, it is important that mdadm chooses the correct type
2067 of array device to use. This can be controlled with the
2069 option. In particular, a value of "mdp" or "part" or "p" tells mdadm
2070 to use a partitionable device rather than the default.
2072 In the no-udev case, the value given to
2074 can be suffixed by a number. This tells
2076 to create that number of partition devices rather than the default of 4.
2080 can also be given in the configuration file as a word starting
2082 on the ARRAY line for the relevant array.
2089 and no devices are listed,
2091 will first attempt to assemble all the arrays listed in the config
2094 If no arrays are listed in the config (other than those marked
2096 it will look through the available devices for possible arrays and
2097 will try to assemble anything that it finds. Arrays which are tagged
2098 as belonging to the given homehost will be assembled and started
2099 normally. Arrays which do not obviously belong to this host are given
2100 names that are expected not to conflict with anything local, and are
2101 started "read-auto" so that nothing is written to any device until the
2102 array is written to. i.e. automatic resync etc is delayed.
2106 finds a consistent set of devices that look like they should comprise
2107 an array, and if the superblock is tagged as belonging to the given
2108 home host, it will automatically choose a device name and try to
2109 assemble the array. If the array uses version-0.90 metadata, then the
2111 number as recorded in the superblock is used to create a name in
2115 If the array uses version-1 metadata, then the
2117 from the superblock is used to similarly create a name in
2119 (the name will have any 'host' prefix stripped first).
2121 This behaviour can be modified by the
2125 configuration file. This line can indicate that specific metadata
2126 type should, or should not, be automatically assembled. If an array
2127 is found which is not listed in
2129 and has a metadata format that is denied by the
2131 line, then it will not be assembled.
2134 line can also request that all arrays identified as being for this
2135 homehost should be assembled regardless of their metadata type.
2138 for further details.
2140 Note: Auto-assembly cannot be used for assembling and activating some
2141 arrays which are undergoing reshape. In particular as the
2143 cannot be given, any reshape which requires a backup file to continue
2144 cannot be started by auto-assembly. An array which is growing to more
2145 devices and has passed the critical section can be assembled using
2156 .BI \-\-raid\-devices= Z
2160 This usage is similar to
2162 The difference is that it creates an array without a superblock. With
2163 these arrays there is no difference between initially creating the array and
2164 subsequently assembling the array, except that hopefully there is useful
2165 data there in the second case.
2167 The level may raid0, linear, raid1, raid10, multipath, or faulty, or
2168 one of their synonyms. All devices must be listed and the array will
2169 be started once complete. It will often be appropriate to use
2170 .B \-\-assume\-clean
2171 with levels raid1 or raid10.
2181 .BI \-\-raid\-devices= Z
2185 This usage will initialize a new md array, associate some devices with
2186 it, and activate the array.
2189 is a new device. This could be standard name or chosen name. For details see:
2192 The named device will normally not exist when
2193 .I "mdadm \-\-create"
2194 is run, but will be created by
2196 once the array becomes active.
2198 The max length md-device name is limited to 32 characters.
2199 Different metadata types have more strict limitation
2200 (like IMSM where only 16 characters are allowed).
2201 For that reason, long name could be truncated or rejected, it depends on metadata policy.
2203 As devices are added, they are checked to see if they contain RAID
2204 superblocks or filesystems. They are also checked to see if the variance in
2205 device size exceeds 1%.
2207 If any discrepancy is found, the array will not automatically be run, though
2210 can override this caution.
2212 To create a "degraded" array in which some devices are missing, simply
2213 give the word "\fBmissing\fP"
2214 in place of a device name. This will cause
2216 to leave the corresponding slot in the array empty.
2217 For a RAID4 or RAID5 array at most one slot can be
2218 "\fBmissing\fP"; for a RAID6 array at most two slots.
2219 For a RAID1 array, only one real device needs to be given. All of the
2223 When creating a RAID5 array,
2225 will automatically create a degraded array with an extra spare drive.
2226 This is because building the spare into a degraded array is in general
2227 faster than resyncing the parity on a non-degraded, but not clean,
2228 array. This feature can be overridden with the
2232 When creating a partition based array, using
2234 with version-1.x metadata, the partition type should be set to
2236 (non fs-data). This type of selection allows for greater precision since
2237 using any other [RAID auto-detect (0xFD) or a GNU/Linux partition (0x83)],
2238 might create problems in the event of array recovery through a live cdrom.
2240 A new array will normally get a randomly assigned 128bit UUID which is
2241 very likely to be unique. If you have a specific need, you can choose
2242 a UUID for the array by giving the
2244 option. Be warned that creating two arrays with the same UUID is a
2245 recipe for disaster. Also, using
2247 when creating a v0.90 array will silently override any
2252 .\"option is given, it is not necessary to list any component devices in this command.
2253 .\"They can be added later, before a
2257 .\"is given, the apparent size of the smallest drive given is used.
2259 If the array type supports a write-intent bitmap, and if the devices
2260 in the array exceed 100G is size, an internal write-intent bitmap
2261 will automatically be added unless some other option is explicitly
2264 option or a different consistency policy is selected with the
2265 .B \-\-consistency\-policy
2266 option. In any case, space for a bitmap will be reserved so that one
2267 can be added later with
2268 .BR "\-\-grow \-\-bitmap=internal" .
2270 If the metadata type supports it (currently only 1.x and IMSM metadata),
2271 space will be allocated to store a bad block list. This allows a modest
2272 number of bad blocks to be recorded, allowing the drive to remain in
2273 service while only partially functional.
2275 When creating an array within a
2278 can be given either the list of devices to use, or simply the name of
2279 the container. The former case gives control over which devices in
2280 the container will be used for the array. The latter case allows
2282 to automatically choose which devices to use based on how much spare
2285 The General Management options that are valid with
2290 insist on running the array even if some devices look like they might
2295 start the array in readonly mode.
2302 .I options... devices...
2305 This usage will allow individual devices in an array to be failed,
2306 removed or added. It is possible to perform multiple operations with
2307 on command. For example:
2309 .B " mdadm /dev/md0 \-f /dev/hda1 \-r /dev/hda1 \-a /dev/hda1"
2315 and will then remove it from the array and finally add it back
2316 in as a spare. However, only one md array can be affected by a single
2319 When a device is added to an active array, mdadm checks to see if it
2320 has metadata on it which suggests that it was recently a member of the
2321 array. If it does, it tries to "re\-add" the device. If there have
2322 been no changes since the device was removed, or if the array has a
2323 write-intent bitmap which has recorded whatever changes there were,
2324 then the device will immediately become a full member of the array and
2325 those differences recorded in the bitmap will be resolved.
2335 MISC mode includes a number of distinct operations that
2336 operate on distinct devices. The operations are:
2339 The device is examined to see if it is
2340 (1) an active md array, or
2341 (2) a component of an md array.
2342 The information discovered is reported.
2346 The device should be an active md device.
2348 will display a detailed description of the array.
2352 will cause the output to be less detailed and the format to be
2353 suitable for inclusion in
2357 will normally be 0 unless
2359 failed to get useful information about the device(s); however, if the
2361 option is given, then the exit status will be:
2365 The array is functioning normally.
2368 The array has at least one failed device.
2371 The array has multiple failed devices such that it is unusable.
2374 There was an error while trying to get information about the device.
2378 .B \-\-detail\-platform
2379 Print detail of the platform's RAID capabilities (firmware / hardware
2380 topology). If the metadata is specified with
2384 then the return status will be:
2388 metadata successfully enumerated its platform components on this system
2391 metadata is platform independent
2394 metadata failed to find its platform components on this system
2398 .B \-\-update\-subarray=
2399 If the device is a container and the argument to \-\-update\-subarray
2400 specifies a subarray in the container, then attempt to update the given
2401 superblock field in the subarray. Similar to updating an array in
2402 "assemble" mode, the field to update is selected by
2406 option. The supported options are
2416 option updates the subarray name in the metadata. It must be
2417 .BR "POSIX PORTABLE NAME"
2418 compatible and cannot be longer than 32 chars. If successes, new value will be respected after
2425 options enable and disable PPL in the metadata. Currently supported only for
2432 options enable and disable write-intent bitmap in the metadata. Currently supported only for
2437 The device should be a component of an md array.
2439 will read the md superblock of the device and display the contents.
2444 is given, then multiple devices that are components of the one array
2445 are grouped together and reported in a single entry suitable
2451 without listing any devices will cause all devices listed in the
2452 config file to be examined.
2455 .BI \-\-dump= directory
2456 If the device contains RAID metadata, a file will be created in the
2458 and the metadata will be written to it. The file will be the same
2459 size as the device and will have the metadata written at the
2460 same location as it exists in the device. However, the file will be "sparse" so
2461 that only those blocks containing metadata will be allocated. The
2462 total space used will be small.
2464 The filename used in the
2466 will be the base name of the device. Further, if any links appear in
2468 which point to the device, then hard links to the file will be created
2475 Multiple devices can be listed and their metadata will all be stored
2476 in the one directory.
2479 .BI \-\-restore= directory
2480 This is the reverse of
2483 will locate a file in the directory that has a name appropriate for
2484 the given device and will restore metadata from it. Names that match
2486 names are preferred, however if two of those refer to different files,
2488 will not choose between them but will abort the operation.
2490 If a file name is given instead of a
2494 will restore from that file to a single device, always provided the
2495 size of the file matches that of the device, and the file contains
2499 The devices should be active md arrays which will be deactivated, as
2500 long as they are not currently in use.
2504 This will fully activate a partially assembled md array.
2508 This will mark an active array as read-only, providing that it is
2509 not currently being used.
2515 array back to being read/write.
2519 For all operations except
2522 will cause the operation to be applied to all arrays listed in
2527 causes all devices listed in the config file to be examined.
2530 .BR \-b ", " \-\-brief
2531 Be less verbose. This is used with
2539 gives an intermediate level of verbosity.
2545 .B mdadm \-\-monitor
2546 .I options... devices...
2549 Monitor option can work in two modes:
2551 system wide mode, follow all md devices based on
2554 follow only specified MD devices in command line.
2558 indicates system wide mode. Option causes the
2560 to track all md devices that appear in
2562 If it is not set, then at least one
2566 Monitor usage causes
2568 to periodically poll a number of md arrays and to report on any events
2573 will work as long as there is an active array with redundancy and it is defined to follow (for
2575 every array is followed).
2577 As well as reporting events,
2579 may move a spare drive from one array to another if they are in the
2584 and if the destination array has a failed drive but no spares.
2586 The result of monitoring the arrays is the generation of events.
2587 These events are passed to a separate program (if specified) and may
2588 be mailed to a given E-mail address.
2590 When passing events to a program, the program is run once for each event,
2591 and is given 2 or 3 command-line arguments: the first is the
2592 name of the event (see below), the second is the name of the
2593 md device which is affected, and the third is the name of a related
2594 device if relevant (such as a component device that has failed).
2602 address must be specified on the
2603 command line or in the config file. If neither are available, then
2605 will not monitor anything.
2606 For devices given directly in command line, without
2610 specified, each event is reported to
2613 Note: For systems where
2615 is configured via systemd,
2616 .B mdmonitor(mdmonitor.service)
2617 should be configured. The service is designed to be primary solution for array monitoring,
2618 it is configured to work in system wide mode.
2619 It is automatically started and stopped according to current state and types of MD arrays in system.
2620 The service may require additional configuration, like
2624 That should be done in
2627 The different events are:
2631 .B DeviceDisappeared
2632 An md array which previously was configured appears to no longer be
2633 configured. (syslog priority: Critical)
2637 was told to monitor an array which is RAID0 or Linear, then it will
2639 .B DeviceDisappeared
2640 with the extra information
2642 This is because RAID0 and Linear do not support the device-failed,
2643 hot-spare and resync operations which are monitored.
2647 An md array started reconstruction (e.g. recovery, resync, reshape,
2648 check, repair). (syslog priority: Warning)
2654 is a two-digit number (eg. 05, 48). This indicates that the rebuild
2655 has reached that percentage of the total. The events are generated
2656 at a fixed increment from 0. The increment size may be specified with
2657 a command-line option (the default is 20). (syslog priority: Warning)
2661 An md array that was rebuilding, isn't any more, either because it
2662 finished normally or was aborted. (syslog priority: Warning)
2666 An active component device of an array has been marked as
2667 faulty. (syslog priority: Critical)
2671 A spare component device which was being rebuilt to replace a faulty
2672 device has failed. (syslog priority: Critical)
2676 A spare component device which was being rebuilt to replace a faulty
2677 device has been successfully rebuilt and has been made active.
2678 (syslog priority: Info)
2682 A new md array has been detected in the
2684 file. (syslog priority: Info)
2688 A newly noticed array appears to be degraded. This message is not
2691 notices a drive failure which causes degradation, but only when
2693 notices that an array is degraded when it first sees the array.
2694 (syslog priority: Critical)
2698 A spare drive has been moved from one array in a
2702 to another to allow a failed drive to be replaced.
2703 (syslog priority: Info)
2709 has been told, via the config file, that an array should have a certain
2710 number of spare devices, and
2712 detects that it has fewer than this number when it first sees the
2713 array, it will report a
2716 (syslog priority: Warning)
2720 An array was found at startup, and the
2723 (syslog priority: Info)
2733 cause Email to be sent. All events cause the program to be run.
2734 The program is run with two or three arguments: the event
2735 name, the array device and possibly a second device.
2737 Each event has an associated array device (e.g.
2739 and possibly a second device. For
2744 the second device is the relevant component device.
2747 the second device is the array that the spare was moved from.
2751 to move spares from one array to another, the different arrays need to
2752 be labeled with the same
2754 or the spares must be allowed to migrate through matching POLICY domains
2755 in the configuration file. The
2757 name can be any string; it is only necessary that different spare
2758 groups use different names.
2762 detects that an array in a spare group has fewer active
2763 devices than necessary for the complete array, and has no spare
2764 devices, it will look for another array in the same spare group that
2765 has a full complement of working drives and a spare. It will then
2766 attempt to remove the spare from the second array and add it to the
2768 If the removal succeeds but the adding fails, then it is added back to
2771 If the spare group for a degraded array is not defined,
2773 will look at the rules of spare migration specified by POLICY lines in
2775 and then follow similar steps as above if a matching spare is found.
2778 The GROW mode is used for changing the size or shape of an active
2781 During the kernel 2.6 era the following changes were added:
2783 change the "size" attribute for RAID1, RAID4, RAID5 and RAID6.
2785 increase or decrease the "raid\-devices" attribute of RAID0, RAID1, RAID4,
2788 change the chunk-size and layout of RAID0, RAID4, RAID5, RAID6 and RAID10.
2790 convert between RAID1 and RAID5, between RAID5 and RAID6, between
2791 RAID0, RAID4, and RAID5, and between RAID0 and RAID10 (in the near-2 mode).
2793 add a write-intent bitmap to any array which supports these bitmaps, or
2794 remove a write-intent bitmap from such an array.
2796 change the array's consistency policy.
2799 Using GROW on containers is currently supported only for Intel's IMSM
2800 container format. The number of devices in a container can be
2801 increased - which affects all arrays in the container - or an array
2802 in a container can be converted between levels where those levels are
2803 supported by the container, and the conversion is on of those listed
2809 Intel's native checkpointing doesn't use
2811 option and it is transparent for assembly feature.
2813 Roaming between Windows(R) and Linux systems for IMSM metadata is not
2814 supported during grow process.
2816 When growing a raid0 device, the new component disk size (or external
2817 backup size) should be larger than LCM(old, new) * chunk-size * 2,
2818 where LCM() is the least common multiple of the old and new count of
2819 component disks, and "* 2" comes from the fact that mdadm refuses to
2820 use more than half of a spare device for backup space.
2823 Normally when an array is built the "size" is taken from the smallest
2824 of the drives. If all the small drives in an arrays are, over time,
2825 removed and replaced with larger drives, then you could have an
2826 array of large drives with only a small amount used. In this
2827 situation, changing the "size" with "GROW" mode will allow the extra
2828 space to start being used. If the size is increased in this way, a
2829 "resync" process will start to make sure the new parts of the array
2832 Note that when an array changes size, any filesystem that may be
2833 stored in the array will not automatically grow or shrink to use or
2834 vacate the space. The
2835 filesystem will need to be explicitly told to use the extra space
2836 after growing, or to reduce its size
2838 to shrinking the array.
2840 Also, the size of an array cannot be changed while it has an active
2841 bitmap. If an array has a bitmap, it must be removed before the size
2842 can be changed. Once the change is complete a new bitmap can be created.
2847 is not yet supported for external file bitmap.
2849 .SS RAID\-DEVICES CHANGES
2851 A RAID1 array can work with any number of devices from 1 upwards
2852 (though 1 is not very useful). There may be times which you want to
2853 increase or decrease the number of active devices. Note that this is
2854 different to hot-add or hot-remove which changes the number of
2857 When reducing the number of devices in a RAID1 array, the slots which
2858 are to be removed from the array must already be vacant. That is, the
2859 devices which were in those slots must be failed and removed.
2861 When the number of devices is increased, any hot spares that are
2862 present will be activated immediately.
2864 Changing the number of active devices in a RAID5 or RAID6 is much more
2865 effort. Every block in the array will need to be read and written
2866 back to a new location. From 2.6.17, the Linux Kernel is able to
2867 increase the number of devices in a RAID5 safely, including restarting
2868 an interrupted "reshape". From 2.6.31, the Linux Kernel is able to
2869 increase or decrease the number of devices in a RAID5 or RAID6.
2871 From 2.6.35, the Linux Kernel is able to convert a RAID0 in to a RAID4
2874 uses this functionality and the ability to add
2875 devices to a RAID4 to allow devices to be added to a RAID0. When
2876 requested to do this,
2878 will convert the RAID0 to a RAID4, add the necessary disks and make
2879 the reshape happen, and then convert the RAID4 back to RAID0.
2881 When decreasing the number of devices, the size of the array will also
2882 decrease. If there was data in the array, it could get destroyed and
2883 this is not reversible, so you should firstly shrink the filesystem on
2884 the array to fit within the new size. To help prevent accidents,
2886 requires that the size of the array be decreased first with
2887 .BR "mdadm --grow --array-size" .
2888 This is a reversible change which simply makes the end of the array
2889 inaccessible. The integrity of any data can then be checked before
2890 the non-reversible reduction in the number of devices is request.
2892 When relocating the first few stripes on a RAID5 or RAID6, it is not
2893 possible to keep the data on disk completely consistent and
2894 crash-proof. To provide the required safety, mdadm disables writes to
2895 the array while this "critical section" is reshaped, and takes a
2896 backup of the data that is in that section. For grows, this backup may be
2897 stored in any spare devices that the array has, however it can also be
2898 stored in a separate file specified with the
2900 option, and is required to be specified for shrinks, RAID level
2901 changes and layout changes. If this option is used, and the system
2902 does crash during the critical period, the same file must be passed to
2904 to restore the backup and reassemble the array. When shrinking rather
2905 than growing the array, the reshape is done from the end towards the
2906 beginning, so the "critical section" is at the end of the reshape.
2910 Changing the RAID level of any array happens instantaneously. However
2911 in the RAID5 to RAID6 case this requires a non-standard layout of the
2912 RAID6 data, and in the RAID6 to RAID5 case that non-standard layout is
2913 required before the change can be accomplished. So while the level
2914 change is instant, the accompanying layout change can take quite a
2917 is required. If the array is not simultaneously being grown or
2918 shrunk, so that the array size will remain the same - for example,
2919 reshaping a 3-drive RAID5 into a 4-drive RAID6 - the backup file will
2920 be used not just for a "critical section" but throughout the reshape
2921 operation, as described below under LAYOUT CHANGES.
2923 .SS CHUNK-SIZE AND LAYOUT CHANGES
2925 Changing the chunk-size or layout without also changing the number of
2926 devices as the same time will involve re-writing all blocks in-place.
2927 To ensure against data loss in the case of a crash, a
2929 must be provided for these changes. Small sections of the array will
2930 be copied to the backup file while they are being rearranged. This
2931 means that all the data is copied twice, once to the backup and once
2932 to the new layout on the array, so this type of reshape will go very
2935 If the reshape is interrupted for any reason, this backup file must be
2937 .B "mdadm --assemble"
2938 so the array can be reassembled. Consequently, the file cannot be
2939 stored on the device being reshaped.
2944 A write-intent bitmap can be added to, or removed from, an active
2945 array. Either internal bitmaps, or bitmaps stored in a separate file,
2946 can be added. Note that if you add a bitmap stored in a file which is
2947 in a filesystem that is on the RAID array being affected, the system
2948 will deadlock. The bitmap must be on a separate filesystem.
2950 .SS CONSISTENCY POLICY CHANGES
2952 The consistency policy of an active array can be changed by using the
2953 .B \-\-consistency\-policy
2954 option in Grow mode. Currently this works only for the
2958 policies and allows to enable or disable the RAID5 Partial Parity Log (PPL).
2960 .SH INCREMENTAL MODE
2964 .B mdadm \-\-incremental
2968 .RI [ optional-aliases-for-device ]
2971 .B mdadm \-\-incremental \-\-fail
2975 .B mdadm \-\-incremental \-\-rebuild\-map
2978 .B mdadm \-\-incremental \-\-run \-\-scan
2981 This mode is designed to be used in conjunction with a device
2982 discovery system. As devices are found in a system, they can be
2984 .B "mdadm \-\-incremental"
2985 to be conditionally added to an appropriate array.
2987 Conversely, it can also be used with the
2989 flag to do just the opposite and find whatever array a particular device
2990 is part of and remove the device from that array.
2992 If the device passed is a
2994 device created by a previous call to
2996 then rather than trying to add that device to an array, all the arrays
2997 described by the metadata of the container will be started.
3000 performs a number of tests to determine if the device is part of an
3001 array, and which array it should be part of. If an appropriate array
3002 is found, or can be created,
3004 adds the device to the array and conditionally starts the array.
3008 will normally only add devices to an array which were previously working
3009 (active or spare) parts of that array. The support for automatic
3010 inclusion of a new drive as a spare in some array requires
3011 a configuration through POLICY in config file.
3015 makes are as follow:
3017 Is the device permitted by
3019 That is, is it listed in a
3021 line in that file. If
3023 is absent then the default it to allow any device. Similarly if
3025 contains the special word
3027 then any device is allowed. Otherwise the device name given to
3029 or one of the aliases given, or an alias found in the filesystem,
3030 must match one of the names or patterns in a
3034 This is the only context where the aliases are used. They are
3035 usually provided by a
3038 .BR $env{DEVLINKS} .
3041 Does the device have a valid md superblock? If a specific metadata
3042 version is requested with
3046 then only that style of metadata is accepted, otherwise
3048 finds any known version of metadata. If no
3050 metadata is found, the device may be still added to an array
3051 as a spare if POLICY allows.
3055 Does the metadata match an expected array?
3056 The metadata can match in two ways. Either there is an array listed
3059 which identifies the array (either by UUID, by name, by device list,
3060 or by minor-number), or the array was created with a
3066 or on the command line.
3069 is not able to positively identify the array as belonging to the
3070 current host, the device will be rejected.
3075 keeps a list of arrays that it has partially assembled in
3077 If no array exists which matches
3078 the metadata on the new device,
3080 must choose a device name and unit number. It does this based on any
3083 or any name information stored in the metadata. If this name
3084 suggests a unit number, that number will be used, otherwise a free
3085 unit number will be chosen. Normally
3087 will prefer to create a partitionable array, however if the
3091 suggests that a non-partitionable array is preferred, that will be
3094 If the array is not found in the config file and its metadata does not
3095 identify it as belonging to the "homehost", then
3097 will choose a name for the array which is certain not to conflict with
3098 any array which does belong to this host. It does this be adding an
3099 underscore and a small number to the name preferred by the metadata.
3101 Once an appropriate array is found or created and the device is added,
3103 must decide if the array is ready to be started. It will
3104 normally compare the number of available (non-spare) devices to the
3105 number of devices that the metadata suggests need to be active. If
3106 there are at least that many, the array will be started. This means
3107 that if any devices are missing the array will not be restarted.
3113 in which case the array will be run as soon as there are enough
3114 devices present for the data to be accessible. For a RAID1, that
3115 means one device will start the array. For a clean RAID5, the array
3116 will be started as soon as all but one drive is present.
3118 Note that neither of these approaches is really ideal. If it can
3119 be known that all device discovery has completed, then
3123 can be run which will try to start all arrays that are being
3124 incrementally assembled. They are started in "read-auto" mode in
3125 which they are read-only until the first write request. This means
3126 that no metadata updates are made and no attempt at resync or recovery
3127 happens. Further devices that are found before the first write can
3128 still be added safely.
3131 This section describes environment variables that affect how mdadm
3136 Setting this value to 1 will prevent mdadm from automatically launching
3137 mdmon. This variable is intended primarily for debugging mdadm/mdmon.
3143 does not create any device nodes in /dev, but leaves that task to
3147 appears not to be configured, or if this environment variable is set
3150 will create and devices that are needed.
3153 .B MDADM_NO_SYSTEMCTL
3158 is in use it will normally request
3160 to start various background tasks (particularly
3162 rather than forking and running them in the background. This can be
3163 suppressed by setting
3164 .BR MDADM_NO_SYSTEMCTL=1 .
3168 A key value of IMSM metadata is that it allows interoperability with
3169 boot ROMs on Intel platforms, and with other major operating systems.
3172 will only allow an IMSM array to be created or modified if detects
3173 that it is running on an Intel platform which supports IMSM, and
3174 supports the particular configuration of IMSM that is being requested
3175 (some functionality requires newer OROM support).
3177 These checks can be suppressed by setting IMSM_NO_PLATFORM=1 in the
3178 environment. This can be useful for testing or for disaster
3179 recovery. You should be aware that interoperability may be
3180 compromised by setting this value.
3182 These change can also be suppressed by adding
3183 .B mdadm.imsm.test=1
3184 to the kernel command line. This makes it easy to test IMSM
3185 code in a virtual machine that doesn't have IMSM virtual hardware.
3188 .B MDADM_GROW_ALLOW_OLD
3189 If an array is stopped while it is performing a reshape and that
3190 reshape was making use of a backup file, then when the array is
3193 will sometimes complain that the backup file is too old. If this
3194 happens and you are certain it is the right backup file, you can
3195 over-ride this check by setting
3196 .B MDADM_GROW_ALLOW_OLD=1
3201 Any string given in this variable is added to the start of the
3203 line in the config file, or treated as the whole
3205 line if none is given. It can be used to disable certain metadata
3208 is called from a boot script. For example
3210 .B " export MDADM_CONF_AUTO='-ddf -imsm'
3214 does not automatically assemble any DDF or
3215 IMSM arrays that are found. This can be useful on systems configured
3216 to manage such arrays with
3222 .B " mdadm \-\-query /dev/name-of-device"
3224 This will find out if a given device is a RAID array, or is part of
3225 one, and will provide brief information about the device.
3227 .B " mdadm \-\-assemble \-\-scan"
3229 This will assemble and start all arrays listed in the standard config
3230 file. This command will typically go in a system startup file.
3232 .B " mdadm \-\-stop \-\-scan"
3234 This will shut down all arrays that can be shut down (i.e. are not
3235 currently in use). This will typically go in a system shutdown script.
3237 .B " mdadm \-\-follow \-\-scan \-\-delay=120"
3239 If (and only if) there is an Email address or program given in the
3240 standard config file, then
3241 monitor the status of all arrays listed in that file by
3242 polling them ever 2 minutes.
3244 .B " mdadm \-\-create /dev/md0 \-\-level=1 \-\-raid\-devices=2 /dev/hd[ac]1"
3246 Create /dev/md0 as a RAID1 array consisting of /dev/hda1 and /dev/hdc1.
3249 .B " echo 'DEVICE /dev/hd*[0\-9] /dev/sd*[0\-9]' > mdadm.conf"
3251 .B " mdadm \-\-detail \-\-scan >> mdadm.conf"
3253 This will create a prototype config file that describes currently
3254 active arrays that are known to be made from partitions of IDE or SCSI drives.
3255 This file should be reviewed before being used as it may
3256 contain unwanted detail.
3258 .B " echo 'DEVICE /dev/hd[a\-z] /dev/sd*[a\-z]' > mdadm.conf"
3260 .B " mdadm \-\-examine \-\-scan \-\-config=mdadm.conf >> mdadm.conf"
3262 This will find arrays which could be assembled from existing IDE and
3263 SCSI whole drives (not partitions), and store the information in the
3264 format of a config file.
3265 This file is very likely to contain unwanted detail, particularly
3268 entries. It should be reviewed and edited before being used as an
3271 .B " mdadm \-\-examine \-\-brief \-\-scan \-\-config=partitions"
3273 .B " mdadm \-Ebsc partitions"
3275 Create a list of devices by reading
3276 .BR /proc/partitions ,
3277 scan these for RAID superblocks, and printout a brief listing of all
3280 .B " mdadm \-Ac partitions \-m 0 /dev/md0"
3282 Scan all partitions and devices listed in
3283 .BR /proc/partitions
3286 out of all such devices with a RAID superblock with a minor number of 0.
3288 .B " mdadm \-\-monitor \-\-scan \-\-daemonise > /run/mdadm/mon.pid"
3290 If config file contains a mail address or alert program, run mdadm in
3291 the background in monitor mode monitoring all md devices. Also write
3292 pid of mdadm daemon to
3293 .BR /run/mdadm/mon.pid .
3295 .B " mdadm \-Iq /dev/somedevice"
3297 Try to incorporate newly discovered device into some array as
3300 .B " mdadm \-\-incremental \-\-rebuild\-map \-\-run \-\-scan"
3302 Rebuild the array map from any current arrays, and then start any that
3305 .B " mdadm /dev/md4 --fail detached --remove detached"
3307 Any devices which are components of /dev/md4 will be marked as faulty
3308 and then remove from the array.
3310 .B " mdadm --grow /dev/md4 --level=6 --backup-file=/root/backup-md4"
3314 which is currently a RAID5 array will be converted to RAID6. There
3315 should normally already be a spare drive attached to the array as a
3316 RAID6 needs one more drive than a matching RAID5.
3318 .B " mdadm --create /dev/md/ddf --metadata=ddf --raid-disks 6 /dev/sd[a-f]"
3320 Create a DDF array over 6 devices.
3322 .B " mdadm --create /dev/md/home -n3 -l5 -z 30000000 /dev/md/ddf"
3324 Create a RAID5 array over any 3 devices in the given DDF set. Use
3325 only 30 gigabytes of each device.
3327 .B " mdadm -A /dev/md/ddf1 /dev/sd[a-f]"
3329 Assemble a pre-exist ddf array.
3331 .B " mdadm -I /dev/md/ddf1"
3333 Assemble all arrays contained in the ddf array, assigning names as
3336 .B " mdadm \-\-create \-\-help"
3338 Provide help about the Create mode.
3340 .B " mdadm \-\-config \-\-help"
3342 Provide help about the format of the config file.
3344 .B " mdadm \-\-help"
3346 Provide general help.
3356 lists all active md devices with information about them.
3358 uses this to find arrays when
3360 is given in Misc mode, and to monitor array reconstruction
3363 .SS {CONFFILE} (or {CONFFILE2})
3365 Default config file. See
3369 .SS {CONFFILE}.d (or {CONFFILE2}.d)
3371 Default directory containing configuration files. See
3378 mode is used, this file gets a list of arrays currently being created.
3380 .SH POSIX PORTABLE NAME
3381 A valid name can only consist of characters "A-Za-z0-9.-_".
3382 The name cannot start with a leading "-" and cannot exceed 255 chars.
3387 understand two sorts of names for array devices.
3389 The first is the so-called 'standard' format name, which matches the
3390 names used by the kernel and which appear in
3393 The second sort can be freely chosen, but must reside in
3395 When giving a device name to
3397 to create or assemble an array, either full path name such as
3401 can be given, or just the suffix of the second sort of name, such as
3405 In every style, raw name must be compatible with
3406 .BR "POSIX PORTABLE NAME"
3407 and has to be no longer than 32 chars.
3411 chooses device names during auto-assembly or incremental assembly, it
3412 will sometimes add a small sequence number to the end of the name to
3413 avoid conflicted between multiple arrays that have the same name. If
3415 can reasonably determine that the array really is meant for this host,
3416 either by a hostname in the metadata, or by the presence of the array
3419 then it will leave off the suffix if possible.
3420 Also if the homehost is specified as
3423 will only use a suffix if a different array of the same name already
3424 exists or is listed in the config file.
3426 The standard names for non-partitioned arrays (the only sort of md
3427 array available in 2.4 and earlier) are of the form
3431 where NN is a number.
3432 The standard names for partitionable arrays (as available from 2.6
3433 onwards) are of the form:
3437 Partition numbers should be indicated by adding "pMM" to these, thus "/dev/md/d1p2".
3439 From kernel version 2.6.28 the "non-partitioned array" can actually
3440 be partitioned. So the "md_d\fBNN\fP"
3441 names are no longer needed, and
3442 partitions such as "/dev/md\fBNN\fPp\fBXX\fP"
3445 From kernel version 2.6.29 standard names can be non-numeric following
3452 is any string. These names are supported by
3454 since version 3.3 provided they are enabled in
3457 .SH UNDERSTANDING OUTPUT
3464 Checkpoint value is reported when array is performing some action including
3465 resync, recovery or reshape. Checkpoints allow resuming action from certain
3466 point if it was interrupted.
3468 Checkpoint is reported as combination of two values: current migration unit
3469 and number of blocks per unit. By multiplying those values and dividing by
3470 array size checkpoint progress percentage can be obtained in relation to
3471 current progress reported in /proc/mdstat. Checkpoint is also related to (and
3472 sometimes based on) sysfs entry sync_completed but depending on action units
3473 may differ. Even if units are the same, it should not be expected that
3474 checkpoint and sync_completed will be exact match nor updated simultaneously.
3478 was previously known as
3482 For further information on mdadm usage, MD and the various levels of
3485 .B https://raid.wiki.kernel.org/
3487 (based upon Jakob \(/Ostergaard's Software\-RAID.HOWTO)
3489 The latest version of
3491 should always be available from
3493 .B https://www.kernel.org/pub/linux/utils/raid/mdadm/
projects / thirdparty / mdadm.git / blob