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/memory-and-storage/ssd-software/intel-virtual-raid-on-cpu-intel-vroc.html
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.
841 .BR \-\-backup\-file=
844 is used to increase the number of raid devices in a RAID5 or RAID6 if
845 there are no spare devices available, or to shrink, change RAID level
846 or layout. See the GROW MODE section below on RAID\-DEVICES CHANGES.
847 The file must be stored on a separate device, not on the RAID array
852 Arrays with 1.x metadata can leave a gap between the start of the
853 device and the start of array data. This gap can be used for various
854 metadata. The start of data is known as the
856 Normally an appropriate data offset is computed automatically.
857 However it can be useful to set it explicitly such as when re-creating
858 an array which was originally created using a different version of
860 which computed a different offset.
862 Setting the offset explicitly over-rides the default. The value given
863 is in Kilobytes unless a suffix of 'K', 'M', 'G' or 'T' is used to explicitly
864 indicate Kilobytes, Megabytes, Gigabytes or Terabytes respectively.
868 can also be used with
870 for some RAID levels (initially on RAID10). This allows the
871 data\-offset to be changed as part of the reshape process. When the
872 data offset is changed, no backup file is required as the difference
873 in offsets is used to provide the same functionality.
875 When the new offset is earlier than the old offset, the number of
876 devices in the array cannot shrink. When it is after the old offset,
877 the number of devices in the array cannot increase.
879 When creating an array,
883 In the case each member device is expected to have an offset appended
884 to the name, separated by a colon. This makes it possible to recreate
885 exactly an array which has varying data offsets (as can happen when
886 different versions of
888 are used to add different devices).
892 This option is complementary to the
893 .B \-\-freeze-reshape
894 option for assembly. It is needed when
896 operation is interrupted and it is not restarted automatically due to
897 .B \-\-freeze-reshape
898 usage during array assembly. This option is used together with
902 ) command and device for a pending reshape to be continued.
903 All parameters required for reshape continuation will be read from array metadata.
907 .BR \-\-backup\-file=
908 option to be set, continuation option will require to have exactly the same
909 backup file given as well.
911 Any other parameter passed together with
913 option will be ignored.
916 .BR \-N ", " \-\-name=
919 for the array. This is currently only effective when creating an
920 array with a version-1 superblock, or an array in a DDF container.
921 The name is a simple textual string that can be used to identify array
922 components when assembling. If name is needed but not specified, it
923 is taken from the basename of the device that is being created.
935 run the array, even if some of the components
936 appear to be active in another array or filesystem. Normally
938 will ask for confirmation before including such components in an
939 array. This option causes that question to be suppressed.
942 .BR \-f ", " \-\-force
945 accept the geometry and layout specified without question. Normally
947 will not allow the creation of an array with only one device, and will try
948 to create a RAID5 array with one missing drive (as this makes the
949 initial resync work faster). With
952 will not try to be so clever.
955 .BR \-o ", " \-\-readonly
958 rather than read-write as normal. No writes will be allowed to the
959 array, and no resync, recovery, or reshape will be started. It works with
960 Create, Assemble, Manage and Misc mode.
963 .BR \-a ", " "\-\-auto{=yes,md,mdp,part,p}{NN}"
964 Instruct mdadm how to create the device file if needed, possibly allocating
965 an unused minor number. "md" causes a non-partitionable array
966 to be used (though since Linux 2.6.28, these array devices are in fact
967 partitionable). "mdp", "part" or "p" causes a partitionable array (2.6 and
968 later) to be used. "yes" requires the named md device to have
969 a 'standard' format, and the type and minor number will be determined
970 from this. With mdadm 3.0, device creation is normally left up to
972 so this option is unlikely to be needed.
973 See DEVICE NAMES below.
975 The argument can also come immediately after
980 is not given on the command line or in the config file, then
986 is also given, then any
988 entries in the config file will override the
990 instruction given on the command line.
992 For partitionable arrays,
994 will create the device file for the whole array and for the first 4
995 partitions. A different number of partitions can be specified at the
996 end of this option (e.g.
998 If the device name ends with a digit, the partition names add a 'p',
1000 .IR /dev/md/home1p3 .
1001 If there is no trailing digit, then the partition names just have a
1003 .IR /dev/md/scratch3 .
1005 If the md device name is in a 'standard' format as described in DEVICE
1006 NAMES, then it will be created, if necessary, with the appropriate
1007 device number based on that name. If the device name is not in one of these
1008 formats, then an unused device number will be allocated. The device
1009 number will be considered unused if there is no active array for that
1010 number, and there is no entry in /dev for that number and with a
1011 non-standard name. Names that are not in 'standard' format are only
1012 allowed in "/dev/md/".
1014 This is meaningful with
1020 .BR \-a ", " "\-\-add"
1021 This option can be used in Grow mode in two cases.
1023 If the target array is a Linear array, then
1025 can be used to add one or more devices to the array. They
1026 are simply catenated on to the end of the array. Once added, the
1027 devices cannot be removed.
1031 option is being used to increase the number of devices in an array,
1034 can be used to add some extra devices to be included in the array.
1035 In most cases this is not needed as the extra devices can be added as
1036 spares first, and then the number of raid disks can be changed.
1037 However, for RAID0 it is not possible to add spares. So to increase
1038 the number of devices in a RAID0, it is necessary to set the new
1039 number of devices, and to add the new devices, in the same command.
1043 Only works when the array is created for a clustered environment. It specifies
1044 the maximum number of nodes in the cluster that will use this device
1045 simultaneously. If not specified, this defaults to 4.
1048 .BR \-\-write-journal
1049 Specify journal device for the RAID-4/5/6 array. The journal device
1050 should be an SSD with a reasonable lifetime.
1053 .BR \-k ", " \-\-consistency\-policy=
1054 Specify how the array maintains consistency in the case of an unexpected shutdown.
1055 Only relevant for RAID levels with redundancy.
1056 Currently supported options are:
1061 Full resync is performed and all redundancy is regenerated when the array is
1062 started after an unclean shutdown.
1066 Resync assisted by a write-intent bitmap. Implicitly selected when using
1071 For RAID levels 4/5/6, the journal device is used to log transactions and replay
1072 after an unclean shutdown. Implicitly selected when using
1073 .BR \-\-write\-journal .
1077 For RAID5 only, Partial Parity Log is used to close the write hole and
1078 eliminate resync. PPL is stored in the metadata region of RAID member drives,
1079 no additional journal drive is needed.
1082 Can be used with \-\-grow to change the consistency policy of an active array
1083 in some cases. See CONSISTENCY POLICY CHANGES below.
1090 .BR \-u ", " \-\-uuid=
1091 uuid of array to assemble. Devices which don't have this uuid are
1095 .BR \-m ", " \-\-super\-minor=
1096 Minor number of device that array was created for. Devices which
1097 don't have this minor number are excluded. If you create an array as
1098 /dev/md1, then all superblocks will contain the minor number 1, even if
1099 the array is later assembled as /dev/md2.
1101 Giving the literal word "dev" for
1105 to use the minor number of the md device that is being assembled.
1106 e.g. when assembling
1108 .B \-\-super\-minor=dev
1109 will look for super blocks with a minor number of 0.
1112 is only relevant for v0.90 metadata, and should not normally be used.
1118 .BR \-N ", " \-\-name=
1119 Specify the name of the array to assemble. This must be the name
1120 that was specified when creating the array. It must either match
1121 the name stored in the superblock exactly, or it must match
1124 prefixed to the start of the given name.
1127 .BR \-f ", " \-\-force
1128 Assemble the array even if the metadata on some devices appears to be
1131 cannot find enough working devices to start the array, but can find
1132 some devices that are recorded as having failed, then it will mark
1133 those devices as working so that the array can be started. This works only for
1134 native. For external metadata it allows to start dirty degraded RAID 4, 5, 6.
1135 An array which requires
1137 to be started may contain data corruption. Use it carefully.
1140 .BR \-R ", " \-\-run
1141 Attempt to start the array even if fewer drives were given than were
1142 present last time the array was active. Normally if not all the
1143 expected drives are found and
1145 is not used, then the array will be assembled but not started.
1148 an attempt will be made to start it anyway.
1152 This is the reverse of
1154 in that it inhibits the startup of array unless all expected drives
1155 are present. This is only needed with
1157 and can be used if the physical connections to devices are
1158 not as reliable as you would like.
1161 .BR \-a ", " "\-\-auto{=no,yes,md,mdp,part}"
1162 See this option under Create and Build options.
1165 .BR \-b ", " \-\-bitmap=
1166 Specify the bitmap file that was given when the array was created. If
1169 bitmap, there is no need to specify this when assembling the array.
1172 .BR \-\-backup\-file=
1175 was used while reshaping an array (e.g. changing number of devices or
1176 chunk size) and the system crashed during the critical section, then the same
1178 must be presented to
1180 to allow possibly corrupted data to be restored, and the reshape
1184 .BR \-\-invalid\-backup
1185 If the file needed for the above option is not available for any
1186 reason an empty file can be given together with this option to
1187 indicate that the backup file is invalid. In this case the data that
1188 was being rearranged at the time of the crash could be irrecoverably
1189 lost, but the rest of the array may still be recoverable. This option
1190 should only be used as a last resort if there is no way to recover the
1195 .BR \-U ", " \-\-update=
1196 Update the superblock on each device while assembling the array. The
1197 argument given to this flag can be one of
1213 .BR layout\-original ,
1214 .BR layout\-alternate ,
1215 .BR layout\-unspecified ,
1222 option will adjust the superblock of an array what was created on a Sparc
1223 machine running a patched 2.2 Linux kernel. This kernel got the
1224 alignment of part of the superblock wrong. You can use the
1225 .B "\-\-examine \-\-sparc2.2"
1228 to see what effect this would have.
1232 option will update the
1233 .B "preferred minor"
1234 field on each superblock to match the minor number of the array being
1236 This can be useful if
1238 reports a different "Preferred Minor" to
1240 In some cases this update will be performed automatically
1241 by the kernel driver. In particular, the update happens automatically
1242 at the first write to an array with redundancy (RAID level 1 or
1243 greater) on a 2.6 (or later) kernel.
1247 option will change the uuid of the array. If a UUID is given with the
1249 option that UUID will be used as a new UUID and will
1251 be used to help identify the devices in the array.
1254 is given, a random UUID is chosen.
1258 option will change the
1260 of the array as stored in the superblock. This is only supported for
1261 version-1 superblocks.
1265 option will change the
1267 of the array as stored in the bitmap superblock. This option only
1268 works for a clustered environment.
1272 option will change the
1274 as recorded in the superblock. For version-0 superblocks, this is the
1275 same as updating the UUID.
1276 For version-1 superblocks, this involves updating the name.
1280 option will change the cluster name as recorded in the superblock and
1281 bitmap. This option only works for a clustered environment.
1285 option will cause the array to be marked
1287 meaning that any redundancy in the array (e.g. parity for RAID5,
1288 copies for RAID1) may be incorrect. This will cause the RAID system
1289 to perform a "resync" pass to make sure that all redundant information
1294 option allows arrays to be moved between machines with different
1295 byte-order, such as from a big-endian machine like a Sparc or some
1296 MIPS machines, to a little-endian x86_64 machine.
1297 When assembling such an array for the first time after a move, giving
1298 .B "\-\-update=byteorder"
1301 to expect superblocks to have their byteorder reversed, and will
1302 correct that order before assembling the array. This is only valid
1303 with original (Version 0.90) superblocks.
1307 option will correct the summaries in the superblock. That is the
1308 counts of total, working, active, failed, and spare devices.
1312 option will rarely be of use. It applies to version 1.1 and 1.2 metadata
1313 only (where the metadata is at the start of the device) and is only
1314 useful when the component device has changed size (typically become
1315 larger). The version 1 metadata records the amount of the device that
1316 can be used to store data, so if a device in a version 1.1 or 1.2
1317 array becomes larger, the metadata will still be visible, but the
1318 extra space will not. In this case it might be useful to assemble the
1320 .BR \-\-update=devicesize .
1323 to determine the maximum usable amount of space on each device and
1324 update the relevant field in the metadata.
1328 option only works on v0.90 metadata arrays and will convert them to
1329 v1.0 metadata. The array must not be dirty (i.e. it must not need a
1330 sync) and it must not have a write-intent bitmap.
1332 The old metadata will remain on the devices, but will appear older
1333 than the new metadata and so will usually be ignored. The old metadata
1334 (or indeed the new metadata) can be removed by giving the appropriate
1337 .BR \-\-zero\-superblock .
1341 option can be used when an array has an internal bitmap which is
1342 corrupt in some way so that assembling the array normally fails. It
1343 will cause any internal bitmap to be ignored.
1347 option will reserve space in each device for a bad block list. This
1348 will be 4K in size and positioned near the end of any free space
1349 between the superblock and the data.
1353 option will cause any reservation of space for a bad block list to be
1354 removed. If the bad block list contains entries, this will fail, as
1355 removing the list could cause data corruption.
1359 option will enable PPL for a RAID5 array and reserve space for PPL on each
1360 device. There must be enough free space between the data and superblock and a
1361 write-intent bitmap or journal must not be used.
1365 option will disable PPL in the superblock.
1370 .B layout\-alternate
1371 options are for RAID0 arrays with non-uniform devices size that were in
1372 use before Linux 5.4. If the array was being used with Linux 3.13 or
1373 earlier, then to assemble the array on a new kernel,
1374 .B \-\-update=layout\-original
1375 must be given. If the array was created and used with a kernel from Linux 3.14 to
1377 .B \-\-update=layout\-alternate
1378 must be given. This only needs to be given once. Subsequent assembly of the array
1379 will happen normally.
1380 For more information, see
1384 .B layout\-unspecified
1385 option reverts the effect of
1388 .B layout\-alternate
1389 and allows the array to be again used on a kernel prior to Linux 5.3.
1390 This option should be used with great caution.
1393 .BR \-\-freeze\-reshape
1394 This option is intended to be used in start-up scripts during the initrd boot phase.
1395 When the array under reshape is assembled during the initrd phase, this option
1396 stops the reshape after the reshape-critical section has been restored. This happens
1397 before the file system pivot operation and avoids loss of filesystem context.
1398 Losing file system context would cause reshape to be broken.
1400 Reshape can be continued later using the
1402 option for the grow command.
1404 .SH For Manage mode:
1407 .BR \-t ", " \-\-test
1408 Unless a more serious error occurred,
1410 will exit with a status of 2 if no changes were made to the array and
1411 0 if at least one change was made.
1412 This can be useful when an indirect specifier such as
1417 is used in requesting an operation on the array.
1419 will report failure if these specifiers didn't find any match.
1422 .BR \-a ", " \-\-add
1423 hot-add listed devices.
1424 If a device appears to have recently been part of the array
1425 (possibly it failed or was removed) the device is re\-added as described
1427 If that fails or the device was never part of the array, the device is
1428 added as a hot-spare.
1429 If the array is degraded, it will immediately start to rebuild data
1432 Note that this and the following options are only meaningful on array
1433 with redundancy. They don't apply to RAID0 or Linear.
1437 re\-add a device that was previously removed from an array.
1438 If the metadata on the device reports that it is a member of the
1439 array, and the slot that it used is still vacant, then the device will
1440 be added back to the array in the same position. This will normally
1441 cause the data for that device to be recovered. However, based on the
1442 event count on the device, the recovery may only require sections that
1443 are flagged by a write-intent bitmap to be recovered or may not require
1444 any recovery at all.
1446 When used on an array that has no metadata (i.e. it was built with
1448 it will be assumed that bitmap-based recovery is enough to make the
1449 device fully consistent with the array.
1452 can also be accompanied by
1453 .BR \-\-update=devicesize ,
1454 .BR \-\-update=bbl ", or"
1455 .BR \-\-update=no\-bbl .
1456 See descriptions of these options when used in Assemble mode for an
1457 explanation of their use.
1459 If the device name given is
1463 will try to find any device that looks like it should be
1464 part of the array but isn't and will try to re\-add all such devices.
1466 If the device name given is
1470 will find all devices in the array that are marked
1472 remove them and attempt to immediately re\-add them. This can be
1473 useful if you are certain that the reason for failure has been
1478 Add a device as a spare. This is similar to
1480 except that it does not attempt
1482 first. The device will be added as a spare even if it looks like it
1483 could be a recent member of the array.
1486 .BR \-r ", " \-\-remove
1487 remove listed devices. They must not be active. i.e. they should
1488 be failed or spare devices.
1490 As well as the name of a device file
1500 The first causes all failed devices to be removed. The second causes
1501 any device which is no longer connected to the system (i.e an 'open'
1505 The third will remove a set as described below under
1509 .BR \-f ", " \-\-fail
1510 Mark listed devices as faulty.
1511 As well as the name of a device file, the word
1515 can be given. The former will cause any device that has been detached from
1516 the system to be marked as failed. It can then be removed.
1518 For RAID10 arrays where the number of copies evenly divides the number
1519 of devices, the devices can be conceptually divided into sets where
1520 each set contains a single complete copy of the data on the array.
1521 Sometimes a RAID10 array will be configured so that these sets are on
1522 separate controllers. In this case, all the devices in one set can be
1523 failed by giving a name like
1529 The appropriate set names are reported by
1539 Mark listed devices as requiring replacement. As soon as a spare is
1540 available, it will be rebuilt and will replace the marked device.
1541 This is similar to marking a device as faulty, but the device remains
1542 in service during the recovery process to increase resilience against
1543 multiple failures. When the replacement process finishes, the
1544 replaced device will be marked as faulty.
1548 This can follow a list of
1550 devices. The devices listed after
1552 will preferentially be used to replace the devices listed after
1554 These devices must already be spare devices in the array.
1557 .BR \-\-write\-mostly
1558 Subsequent devices that are added or re\-added will have the 'write-mostly'
1559 flag set. This is only valid for RAID1 and means that the 'md' driver
1560 will avoid reading from these devices if possible.
1563 Subsequent devices that are added or re\-added will have the 'write-mostly'
1566 .BR \-\-cluster\-confirm
1567 Confirm the existence of the device. This is issued in response to an \-\-add
1568 request by a node in a cluster. When a node adds a device it sends a message
1569 to all nodes in the cluster to look for a device with a UUID. This translates
1570 to a udev notification with the UUID of the device to be added and the slot
1571 number. The receiving node must acknowledge this message
1572 with \-\-cluster\-confirm. Valid arguments are <slot>:<devicename> in case
1573 the device is found or <slot>:missing in case the device is not found.
1577 Add a journal to an existing array, or recreate journal for a RAID-4/5/6 array
1578 that lost a journal device. To avoid interrupting ongoing write operations,
1580 only works for array in Read-Only state.
1584 Subsequent devices that are added or re\-added will have
1585 the 'failfast' flag set. This is only valid for RAID1 and RAID10 and
1586 means that the 'md' driver will avoid long timeouts on error handling
1590 Subsequent devices that are re\-added will be re\-added without
1591 the 'failfast' flag set.
1594 Each of these options requires that the first device listed is the array
1595 to be acted upon, and the remainder are component devices to be added,
1596 removed, marked as faulty, etc. Several different operations can be
1597 specified for different devices, e.g.
1599 mdadm /dev/md0 \-\-add /dev/sda1 \-\-fail /dev/sdb1 \-\-remove /dev/sdb1
1601 Each operation applies to all devices listed until the next
1604 If an array is using a write-intent bitmap, then devices which have
1605 been removed can be re\-added in a way that avoids a full
1606 reconstruction but instead just updates the blocks that have changed
1607 since the device was removed. For arrays with persistent metadata
1608 (superblocks) this is done automatically. For arrays created with
1610 mdadm needs to be told that this device we removed recently with
1613 Devices can only be removed from an array if they are not in active
1614 use, i.e. that must be spares or failed devices. To remove an active
1615 device, it must first be marked as
1621 .BR \-Q ", " \-\-query
1622 Examine a device to see
1623 (1) if it is an md device and (2) if it is a component of an md
1625 Information about what is discovered is presented.
1628 .BR \-D ", " \-\-detail
1629 Print details of one or more md devices.
1632 .BR \-\-detail\-platform
1633 Print details of the platform's RAID capabilities (firmware / hardware
1634 topology) for a given metadata format. If used without an argument, mdadm
1635 will scan all controllers looking for their capabilities. Otherwise, mdadm
1636 will only look at the controller specified by the argument in the form of an
1637 absolute filepath or a link, e.g.
1638 .IR /sys/devices/pci0000:00/0000:00:1f.2 .
1641 .BR \-Y ", " \-\-export
1644 .BR \-\-detail-platform ,
1648 output will be formatted as
1650 pairs for easy import into the environment.
1656 indicates whether an array was started
1658 or not, which may include a reason
1659 .RB ( unsafe ", " nothing ", " no ).
1662 indicates if the array is expected on this host
1664 or seems to be from elsewhere
1668 .BR \-E ", " \-\-examine
1669 Print contents of the metadata stored on the named device(s).
1670 Note the contrast between
1675 applies to devices which are components of an array, while
1677 applies to a whole array which is currently active.
1680 If an array was created on a SPARC machine with a 2.2 Linux kernel
1681 patched with RAID support, the superblock will have been created
1682 incorrectly, or at least incompatibly with 2.4 and later kernels.
1687 will fix the superblock before displaying it. If this appears to do
1688 the right thing, then the array can be successfully assembled using
1689 .BR "\-\-assemble \-\-update=sparc2.2" .
1692 .BR \-X ", " \-\-examine\-bitmap
1693 Report information about a bitmap file.
1694 The argument is either an external bitmap file or an array component
1695 in case of an internal bitmap. Note that running this on an array
1698 does not report the bitmap for that array.
1701 .B \-\-examine\-badblocks
1702 List the bad-blocks recorded for the device, if a bad-blocks list has
1703 been configured. Currently only
1707 metadata support bad-blocks lists.
1710 .BI \-\-dump= directory
1712 .BI \-\-restore= directory
1713 Save metadata from lists devices, or restore metadata to listed devices.
1716 .BR \-R ", " \-\-run
1717 start a partially assembled array. If
1719 did not find enough devices to fully start the array, it might leaving
1720 it partially assembled. If you wish, you can then use
1722 to start the array in degraded mode.
1725 .BR \-S ", " \-\-stop
1726 deactivate array, releasing all resources.
1729 .BR \-o ", " \-\-readonly
1730 mark array as readonly.
1733 .BR \-w ", " \-\-readwrite
1734 mark array as readwrite.
1737 .B \-\-zero\-superblock
1738 If the device contains a valid md superblock, the block is
1739 overwritten with zeros. With
1741 the block where the superblock would be is overwritten even if it
1742 doesn't appear to be valid.
1745 Be careful when calling \-\-zero\-superblock with clustered raid. Make sure
1746 the array isn't used or assembled in another cluster node before executing it.
1749 .B \-\-kill\-subarray=
1750 If the device is a container and the argument to \-\-kill\-subarray
1751 specifies an inactive subarray in the container, then the subarray is
1752 deleted. Deleting all subarrays will leave an 'empty-container' or
1753 spare superblock on the drives. See
1754 .B \-\-zero\-superblock
1756 removing a superblock. Note that some formats depend on the subarray
1757 index for generating a UUID, this command will fail if it would change
1758 the UUID of an active subarray.
1761 .B \-\-update\-subarray=
1762 If the device is a container and the argument to \-\-update\-subarray
1763 specifies a subarray in the container, then attempt to update the given
1764 superblock field in the subarray. See below in
1769 .BR \-t ", " \-\-test
1774 is set to reflect the status of the device. See below in
1779 .BR \-W ", " \-\-wait
1780 For each md device given, wait for any resync, recovery, or reshape
1781 activity to finish before returning.
1783 will return with success if it actually waited for every device
1784 listed, otherwise it will return failure.
1788 For each md device given, or each device in /proc/mdstat if
1790 is given, arrange for the array to be marked clean as soon as possible.
1792 will return with success if the array uses external metadata and we
1793 successfully waited. For native arrays, this returns immediately as the
1794 kernel handles dirty-clean transitions at shutdown. No action is taken
1795 if safe-mode handling is disabled.
1799 Set the "sync_action" for all md devices given to one of
1806 will abort any currently running action though some actions will
1807 automatically restart.
1810 will abort any current action and ensure no other action starts
1820 .BR "SCRUBBING AND MISMATCHES" .
1822 .SH For Incremental Assembly mode:
1824 .BR \-\-rebuild\-map ", " \-r
1825 Rebuild the map file
1829 uses to help track which arrays are currently being assembled.
1832 .BR \-\-run ", " \-R
1833 Run any array assembled as soon as a minimal number of devices is
1834 available, rather than waiting until all expected devices are present.
1837 .BR \-\-scan ", " \-s
1838 Only meaningful with
1842 file for arrays that are being incrementally assembled and will try to
1843 start any that are not already started. If any such array is listed
1846 as requiring an external bitmap, that bitmap will be attached first.
1849 .BR \-\-fail ", " \-f
1850 This allows the hot-plug system to remove devices that have fully disappeared
1851 from the kernel. It will first fail and then remove the device from any
1852 array it belongs to.
1853 The device name given should be a kernel device name such as "sda",
1859 Only used with \-\-fail. The 'path' given will be recorded so that if
1860 a new device appears at the same location it can be automatically
1861 added to the same array. This allows the failed device to be
1862 automatically replaced by a new device without metadata if it appears
1863 at specified path. This option is normally only set by an
1867 .SH For Monitor mode:
1869 .BR \-m ", " \-\-mail
1870 Give a mail address to send alerts to.
1873 .BR \-p ", " \-\-program ", " \-\-alert
1874 Give a program to be run whenever an event is detected.
1877 .BR \-y ", " \-\-syslog
1878 Cause all events to be reported through 'syslog'. The messages have
1879 facility of 'daemon' and varying priorities.
1882 .BR \-d ", " \-\-delay
1883 Give a delay in seconds.
1885 polls the md arrays and then waits this many seconds before polling
1886 again. The default is 60 seconds. Since 2.6.16, there is no need to
1887 reduce this as the kernel alerts
1889 immediately when there is any change.
1892 .BR \-r ", " \-\-increment
1893 Give a percentage increment.
1895 will generate RebuildNN events with the given percentage increment.
1898 .BR \-f ", " \-\-daemonise
1901 to run as a background daemon if it decides to monitor anything. This
1902 causes it to fork and run in the child, and to disconnect from the
1903 terminal. The process id of the child is written to stdout.
1906 which will only continue monitoring if a mail address or alert program
1907 is found in the config file.
1910 .BR \-i ", " \-\-pid\-file
1913 is running in daemon mode, write the pid of the daemon process to
1914 the specified file, instead of printing it on standard output.
1917 .BR \-1 ", " \-\-oneshot
1918 Check arrays only once. This will generate
1920 events and more significantly
1926 .B " mdadm \-\-monitor \-\-scan \-1"
1928 from a cron script will ensure regular notification of any degraded arrays.
1931 .BR \-t ", " \-\-test
1934 alert for every array found at startup. This alert gets mailed and
1935 passed to the alert program. This can be used for testing that alert
1936 message do get through successfully.
1940 This inhibits the functionality for moving spares between arrays.
1941 Only one monitoring process started with
1943 but without this flag is allowed, otherwise the two could interfere
1950 .B mdadm \-\-assemble
1951 .I md-device options-and-component-devices...
1954 .B mdadm \-\-assemble \-\-scan
1955 .I md-devices-and-options...
1958 .B mdadm \-\-assemble \-\-scan
1962 This usage assembles one or more RAID arrays from pre-existing components.
1963 For each array, mdadm needs to know the md device, the identity of the
1964 array, and the number of component devices. These can be found in a number of ways.
1966 In the first usage example (without the
1968 the first device given is the md device.
1969 In the second usage example, all devices listed are treated as md
1970 devices and assembly is attempted.
1971 In the third (where no devices are listed) all md devices that are
1972 listed in the configuration file are assembled. If no arrays are
1973 described by the configuration file, then any arrays that
1974 can be found on unused devices will be assembled.
1976 If precisely one device is listed, but
1982 was given and identity information is extracted from the configuration file.
1984 The identity can be given with the
1990 option, will be taken from the md-device record in the config file, or
1991 will be taken from the super block of the first component-device
1992 listed on the command line.
1994 Devices can be given on the
1996 command line or in the config file. Only devices which have an md
1997 superblock which contains the right identity will be considered for
2000 The config file is only used if explicitly named with
2002 or requested with (a possibly implicit)
2004 In the latter case, the default config file is used. See
2010 is not given, then the config file will only be used to find the
2011 identity of md arrays.
2013 Normally the array will be started after it is assembled. However if
2015 is not given and not all expected drives were listed, then the array
2016 is not started (to guard against usage errors). To insist that the
2017 array be started in this case (as may work for RAID1, 4, 5, 6, or 10),
2026 does not create any entries in
2030 It does record information in
2034 to choose the correct name.
2038 detects that udev is not configured, it will create the devices in
2042 In Linux kernels prior to version 2.6.28 there were two distinct
2043 types of md devices that could be created: one that could be
2044 partitioned using standard partitioning tools and one that could not.
2045 Since 2.6.28 that distinction is no longer relevant as both types of
2046 devices can be partitioned.
2048 will normally create the type that originally could not be partitioned
2049 as it has a well-defined major number (9).
2051 Prior to 2.6.28, it is important that mdadm chooses the correct type
2052 of array device to use. This can be controlled with the
2054 option. In particular, a value of "mdp" or "part" or "p" tells mdadm
2055 to use a partitionable device rather than the default.
2057 In the no-udev case, the value given to
2059 can be suffixed by a number. This tells
2061 to create that number of partition devices rather than the default of 4.
2065 can also be given in the configuration file as a word starting
2067 on the ARRAY line for the relevant array.
2074 and no devices are listed,
2076 will first attempt to assemble all the arrays listed in the config
2079 If no arrays are listed in the config (other than those marked
2081 it will look through the available devices for possible arrays and
2082 will try to assemble anything that it finds. Arrays which are tagged
2083 as belonging to the given homehost will be assembled and started
2084 normally. Arrays which do not obviously belong to this host are given
2085 names that are expected not to conflict with anything local, and are
2086 started "read-auto" so that nothing is written to any device until the
2087 array is written to. i.e. automatic resync etc is delayed.
2091 finds a consistent set of devices that look like they should comprise
2092 an array, and if the superblock is tagged as belonging to the given
2093 home host, it will automatically choose a device name and try to
2094 assemble the array. If the array uses version-0.90 metadata, then the
2096 number as recorded in the superblock is used to create a name in
2100 If the array uses version-1 metadata, then the
2102 from the superblock is used to similarly create a name in
2104 (the name will have any 'host' prefix stripped first).
2106 This behaviour can be modified by the
2110 configuration file. This line can indicate that specific metadata
2111 type should, or should not, be automatically assembled. If an array
2112 is found which is not listed in
2114 and has a metadata format that is denied by the
2116 line, then it will not be assembled.
2119 line can also request that all arrays identified as being for this
2120 homehost should be assembled regardless of their metadata type.
2123 for further details.
2125 Note: Auto-assembly cannot be used for assembling and activating some
2126 arrays which are undergoing reshape. In particular as the
2128 cannot be given, any reshape which requires a backup file to continue
2129 cannot be started by auto-assembly. An array which is growing to more
2130 devices and has passed the critical section can be assembled using
2141 .BI \-\-raid\-devices= Z
2145 This usage is similar to
2147 The difference is that it creates an array without a superblock. With
2148 these arrays there is no difference between initially creating the array and
2149 subsequently assembling the array, except that hopefully there is useful
2150 data there in the second case.
2152 The level may raid0, linear, raid1, raid10, multipath, or faulty, or
2153 one of their synonyms. All devices must be listed and the array will
2154 be started once complete. It will often be appropriate to use
2155 .B \-\-assume\-clean
2156 with levels raid1 or raid10.
2167 .BI \-\-raid\-devices= Z
2171 This usage will initialise a new md array, associate some devices with
2172 it, and activate the array.
2174 The named device will normally not exist when
2175 .I "mdadm \-\-create"
2176 is run, but will be created by
2178 once the array becomes active.
2180 The max length md-device name is limited to 32 characters.
2181 Different metadata types have more strict limitation
2182 (like IMSM where only 16 characters are allowed).
2183 For that reason, long name could be truncated or rejected, it depends on metadata policy.
2185 As devices are added, they are checked to see if they contain RAID
2186 superblocks or filesystems. They are also checked to see if the variance in
2187 device size exceeds 1%.
2189 If any discrepancy is found, the array will not automatically be run, though
2192 can override this caution.
2194 To create a "degraded" array in which some devices are missing, simply
2195 give the word "\fBmissing\fP"
2196 in place of a device name. This will cause
2198 to leave the corresponding slot in the array empty.
2199 For a RAID4 or RAID5 array at most one slot can be
2200 "\fBmissing\fP"; for a RAID6 array at most two slots.
2201 For a RAID1 array, only one real device needs to be given. All of the
2205 When creating a RAID5 array,
2207 will automatically create a degraded array with an extra spare drive.
2208 This is because building the spare into a degraded array is in general
2209 faster than resyncing the parity on a non-degraded, but not clean,
2210 array. This feature can be overridden with the
2214 When creating an array with version-1 metadata a name for the array is
2216 If this is not given with the
2220 will choose a name based on the last component of the name of the
2221 device being created. So if
2223 is being created, then the name
2228 is being created, then the name
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 may not affect the
2417 device node name or the device node symlink until the subarray is
2418 re\-assembled. If updating
2420 would change the UUID of an active subarray this operation is blocked,
2421 and the command will end in an error.
2427 options enable and disable PPL in the metadata. Currently supported only for
2434 options enable and disable write-intent bitmap in the metadata. Currently supported only for
2439 The device should be a component of an md array.
2441 will read the md superblock of the device and display the contents.
2446 is given, then multiple devices that are components of the one array
2447 are grouped together and reported in a single entry suitable
2453 without listing any devices will cause all devices listed in the
2454 config file to be examined.
2457 .BI \-\-dump= directory
2458 If the device contains RAID metadata, a file will be created in the
2460 and the metadata will be written to it. The file will be the same
2461 size as the device and will have the metadata written at the
2462 same location as it exists in the device. However, the file will be "sparse" so
2463 that only those blocks containing metadata will be allocated. The
2464 total space used will be small.
2466 The filename used in the
2468 will be the base name of the device. Further, if any links appear in
2470 which point to the device, then hard links to the file will be created
2477 Multiple devices can be listed and their metadata will all be stored
2478 in the one directory.
2481 .BI \-\-restore= directory
2482 This is the reverse of
2485 will locate a file in the directory that has a name appropriate for
2486 the given device and will restore metadata from it. Names that match
2488 names are preferred, however if two of those refer to different files,
2490 will not choose between them but will abort the operation.
2492 If a file name is given instead of a
2496 will restore from that file to a single device, always provided the
2497 size of the file matches that of the device, and the file contains
2501 The devices should be active md arrays which will be deactivated, as
2502 long as they are not currently in use.
2506 This will fully activate a partially assembled md array.
2510 This will mark an active array as read-only, providing that it is
2511 not currently being used.
2517 array back to being read/write.
2521 For all operations except
2524 will cause the operation to be applied to all arrays listed in
2529 causes all devices listed in the config file to be examined.
2532 .BR \-b ", " \-\-brief
2533 Be less verbose. This is used with
2541 gives an intermediate level of verbosity.
2547 .B mdadm \-\-monitor
2548 .I options... devices...
2553 to periodically poll a number of md arrays and to report on any events
2556 will never exit once it decides that there are arrays to be checked,
2557 so it should normally be run in the background.
2559 As well as reporting events,
2561 may move a spare drive from one array to another if they are in the
2566 and if the destination array has a failed drive but no spares.
2568 If any devices are listed on the command line,
2570 will only monitor those devices, otherwise, all arrays listed in the
2571 configuration file will be monitored. Further, if
2573 is given, then any other md devices that appear in
2575 will also be monitored.
2577 The result of monitoring the arrays is the generation of events.
2578 These events are passed to a separate program (if specified) and may
2579 be mailed to a given E-mail address.
2581 When passing events to a program, the program is run once for each event,
2582 and is given 2 or 3 command-line arguments: the first is the
2583 name of the event (see below), the second is the name of the
2584 md device which is affected, and the third is the name of a related
2585 device if relevant (such as a component device that has failed).
2589 is given, then a program or an E-mail address must be specified on the
2590 command line or in the config file. If neither are available, then
2592 will not monitor anything.
2596 will continue monitoring as long as something was found to monitor. If
2597 no program or email is given, then each event is reported to
2600 The different events are:
2604 .B DeviceDisappeared
2605 An md array which previously was configured appears to no longer be
2606 configured. (syslog priority: Critical)
2610 was told to monitor an array which is RAID0 or Linear, then it will
2612 .B DeviceDisappeared
2613 with the extra information
2615 This is because RAID0 and Linear do not support the device-failed,
2616 hot-spare and resync operations which are monitored.
2620 An md array started reconstruction (e.g. recovery, resync, reshape,
2621 check, repair). (syslog priority: Warning)
2627 is a two-digit number (eg. 05, 48). This indicates that the rebuild
2628 has reached that percentage of the total. The events are generated
2629 at a fixed increment from 0. The increment size may be specified with
2630 a command-line option (the default is 20). (syslog priority: Warning)
2634 An md array that was rebuilding, isn't any more, either because it
2635 finished normally or was aborted. (syslog priority: Warning)
2639 An active component device of an array has been marked as
2640 faulty. (syslog priority: Critical)
2644 A spare component device which was being rebuilt to replace a faulty
2645 device has failed. (syslog priority: Critical)
2649 A spare component device which was being rebuilt to replace a faulty
2650 device has been successfully rebuilt and has been made active.
2651 (syslog priority: Info)
2655 A new md array has been detected in the
2657 file. (syslog priority: Info)
2661 A newly noticed array appears to be degraded. This message is not
2664 notices a drive failure which causes degradation, but only when
2666 notices that an array is degraded when it first sees the array.
2667 (syslog priority: Critical)
2671 A spare drive has been moved from one array in a
2675 to another to allow a failed drive to be replaced.
2676 (syslog priority: Info)
2682 has been told, via the config file, that an array should have a certain
2683 number of spare devices, and
2685 detects that it has fewer than this number when it first sees the
2686 array, it will report a
2689 (syslog priority: Warning)
2693 An array was found at startup, and the
2696 (syslog priority: Info)
2706 cause Email to be sent. All events cause the program to be run.
2707 The program is run with two or three arguments: the event
2708 name, the array device and possibly a second device.
2710 Each event has an associated array device (e.g.
2712 and possibly a second device. For
2717 the second device is the relevant component device.
2720 the second device is the array that the spare was moved from.
2724 to move spares from one array to another, the different arrays need to
2725 be labeled with the same
2727 or the spares must be allowed to migrate through matching POLICY domains
2728 in the configuration file. The
2730 name can be any string; it is only necessary that different spare
2731 groups use different names.
2735 detects that an array in a spare group has fewer active
2736 devices than necessary for the complete array, and has no spare
2737 devices, it will look for another array in the same spare group that
2738 has a full complement of working drives and a spare. It will then
2739 attempt to remove the spare from the second array and add it to the
2741 If the removal succeeds but the adding fails, then it is added back to
2744 If the spare group for a degraded array is not defined,
2746 will look at the rules of spare migration specified by POLICY lines in
2748 and then follow similar steps as above if a matching spare is found.
2751 The GROW mode is used for changing the size or shape of an active
2754 During the kernel 2.6 era the following changes were added:
2756 change the "size" attribute for RAID1, RAID4, RAID5 and RAID6.
2758 increase or decrease the "raid\-devices" attribute of RAID0, RAID1, RAID4,
2761 change the chunk-size and layout of RAID0, RAID4, RAID5, RAID6 and RAID10.
2763 convert between RAID1 and RAID5, between RAID5 and RAID6, between
2764 RAID0, RAID4, and RAID5, and between RAID0 and RAID10 (in the near-2 mode).
2766 add a write-intent bitmap to any array which supports these bitmaps, or
2767 remove a write-intent bitmap from such an array.
2769 change the array's consistency policy.
2772 Using GROW on containers is currently supported only for Intel's IMSM
2773 container format. The number of devices in a container can be
2774 increased - which affects all arrays in the container - or an array
2775 in a container can be converted between levels where those levels are
2776 supported by the container, and the conversion is on of those listed
2782 Intel's native checkpointing doesn't use
2784 option and it is transparent for assembly feature.
2786 Roaming between Windows(R) and Linux systems for IMSM metadata is not
2787 supported during grow process.
2789 When growing a raid0 device, the new component disk size (or external
2790 backup size) should be larger than LCM(old, new) * chunk-size * 2,
2791 where LCM() is the least common multiple of the old and new count of
2792 component disks, and "* 2" comes from the fact that mdadm refuses to
2793 use more than half of a spare device for backup space.
2796 Normally when an array is built the "size" is taken from the smallest
2797 of the drives. If all the small drives in an arrays are, over time,
2798 removed and replaced with larger drives, then you could have an
2799 array of large drives with only a small amount used. In this
2800 situation, changing the "size" with "GROW" mode will allow the extra
2801 space to start being used. If the size is increased in this way, a
2802 "resync" process will start to make sure the new parts of the array
2805 Note that when an array changes size, any filesystem that may be
2806 stored in the array will not automatically grow or shrink to use or
2807 vacate the space. The
2808 filesystem will need to be explicitly told to use the extra space
2809 after growing, or to reduce its size
2811 to shrinking the array.
2813 Also, the size of an array cannot be changed while it has an active
2814 bitmap. If an array has a bitmap, it must be removed before the size
2815 can be changed. Once the change is complete a new bitmap can be created.
2820 is not yet supported for external file bitmap.
2822 .SS RAID\-DEVICES CHANGES
2824 A RAID1 array can work with any number of devices from 1 upwards
2825 (though 1 is not very useful). There may be times which you want to
2826 increase or decrease the number of active devices. Note that this is
2827 different to hot-add or hot-remove which changes the number of
2830 When reducing the number of devices in a RAID1 array, the slots which
2831 are to be removed from the array must already be vacant. That is, the
2832 devices which were in those slots must be failed and removed.
2834 When the number of devices is increased, any hot spares that are
2835 present will be activated immediately.
2837 Changing the number of active devices in a RAID5 or RAID6 is much more
2838 effort. Every block in the array will need to be read and written
2839 back to a new location. From 2.6.17, the Linux Kernel is able to
2840 increase the number of devices in a RAID5 safely, including restarting
2841 an interrupted "reshape". From 2.6.31, the Linux Kernel is able to
2842 increase or decrease the number of devices in a RAID5 or RAID6.
2844 From 2.6.35, the Linux Kernel is able to convert a RAID0 in to a RAID4
2847 uses this functionality and the ability to add
2848 devices to a RAID4 to allow devices to be added to a RAID0. When
2849 requested to do this,
2851 will convert the RAID0 to a RAID4, add the necessary disks and make
2852 the reshape happen, and then convert the RAID4 back to RAID0.
2854 When decreasing the number of devices, the size of the array will also
2855 decrease. If there was data in the array, it could get destroyed and
2856 this is not reversible, so you should firstly shrink the filesystem on
2857 the array to fit within the new size. To help prevent accidents,
2859 requires that the size of the array be decreased first with
2860 .BR "mdadm --grow --array-size" .
2861 This is a reversible change which simply makes the end of the array
2862 inaccessible. The integrity of any data can then be checked before
2863 the non-reversible reduction in the number of devices is request.
2865 When relocating the first few stripes on a RAID5 or RAID6, it is not
2866 possible to keep the data on disk completely consistent and
2867 crash-proof. To provide the required safety, mdadm disables writes to
2868 the array while this "critical section" is reshaped, and takes a
2869 backup of the data that is in that section. For grows, this backup may be
2870 stored in any spare devices that the array has, however it can also be
2871 stored in a separate file specified with the
2873 option, and is required to be specified for shrinks, RAID level
2874 changes and layout changes. If this option is used, and the system
2875 does crash during the critical period, the same file must be passed to
2877 to restore the backup and reassemble the array. When shrinking rather
2878 than growing the array, the reshape is done from the end towards the
2879 beginning, so the "critical section" is at the end of the reshape.
2883 Changing the RAID level of any array happens instantaneously. However
2884 in the RAID5 to RAID6 case this requires a non-standard layout of the
2885 RAID6 data, and in the RAID6 to RAID5 case that non-standard layout is
2886 required before the change can be accomplished. So while the level
2887 change is instant, the accompanying layout change can take quite a
2890 is required. If the array is not simultaneously being grown or
2891 shrunk, so that the array size will remain the same - for example,
2892 reshaping a 3-drive RAID5 into a 4-drive RAID6 - the backup file will
2893 be used not just for a "critical section" but throughout the reshape
2894 operation, as described below under LAYOUT CHANGES.
2896 .SS CHUNK-SIZE AND LAYOUT CHANGES
2898 Changing the chunk-size or layout without also changing the number of
2899 devices as the same time will involve re-writing all blocks in-place.
2900 To ensure against data loss in the case of a crash, a
2902 must be provided for these changes. Small sections of the array will
2903 be copied to the backup file while they are being rearranged. This
2904 means that all the data is copied twice, once to the backup and once
2905 to the new layout on the array, so this type of reshape will go very
2908 If the reshape is interrupted for any reason, this backup file must be
2910 .B "mdadm --assemble"
2911 so the array can be reassembled. Consequently, the file cannot be
2912 stored on the device being reshaped.
2917 A write-intent bitmap can be added to, or removed from, an active
2918 array. Either internal bitmaps, or bitmaps stored in a separate file,
2919 can be added. Note that if you add a bitmap stored in a file which is
2920 in a filesystem that is on the RAID array being affected, the system
2921 will deadlock. The bitmap must be on a separate filesystem.
2923 .SS CONSISTENCY POLICY CHANGES
2925 The consistency policy of an active array can be changed by using the
2926 .B \-\-consistency\-policy
2927 option in Grow mode. Currently this works only for the
2931 policies and allows to enable or disable the RAID5 Partial Parity Log (PPL).
2933 .SH INCREMENTAL MODE
2937 .B mdadm \-\-incremental
2941 .RI [ optional-aliases-for-device ]
2944 .B mdadm \-\-incremental \-\-fail
2948 .B mdadm \-\-incremental \-\-rebuild\-map
2951 .B mdadm \-\-incremental \-\-run \-\-scan
2954 This mode is designed to be used in conjunction with a device
2955 discovery system. As devices are found in a system, they can be
2957 .B "mdadm \-\-incremental"
2958 to be conditionally added to an appropriate array.
2960 Conversely, it can also be used with the
2962 flag to do just the opposite and find whatever array a particular device
2963 is part of and remove the device from that array.
2965 If the device passed is a
2967 device created by a previous call to
2969 then rather than trying to add that device to an array, all the arrays
2970 described by the metadata of the container will be started.
2973 performs a number of tests to determine if the device is part of an
2974 array, and which array it should be part of. If an appropriate array
2975 is found, or can be created,
2977 adds the device to the array and conditionally starts the array.
2981 will normally only add devices to an array which were previously working
2982 (active or spare) parts of that array. The support for automatic
2983 inclusion of a new drive as a spare in some array requires
2984 a configuration through POLICY in config file.
2988 makes are as follow:
2990 Is the device permitted by
2992 That is, is it listed in a
2994 line in that file. If
2996 is absent then the default it to allow any device. Similarly if
2998 contains the special word
3000 then any device is allowed. Otherwise the device name given to
3002 or one of the aliases given, or an alias found in the filesystem,
3003 must match one of the names or patterns in a
3007 This is the only context where the aliases are used. They are
3008 usually provided by a
3011 .BR $env{DEVLINKS} .
3014 Does the device have a valid md superblock? If a specific metadata
3015 version is requested with
3019 then only that style of metadata is accepted, otherwise
3021 finds any known version of metadata. If no
3023 metadata is found, the device may be still added to an array
3024 as a spare if POLICY allows.
3028 Does the metadata match an expected array?
3029 The metadata can match in two ways. Either there is an array listed
3032 which identifies the array (either by UUID, by name, by device list,
3033 or by minor-number), or the array was created with a
3039 or on the command line.
3042 is not able to positively identify the array as belonging to the
3043 current host, the device will be rejected.
3048 keeps a list of arrays that it has partially assembled in
3050 If no array exists which matches
3051 the metadata on the new device,
3053 must choose a device name and unit number. It does this based on any
3056 or any name information stored in the metadata. If this name
3057 suggests a unit number, that number will be used, otherwise a free
3058 unit number will be chosen. Normally
3060 will prefer to create a partitionable array, however if the
3064 suggests that a non-partitionable array is preferred, that will be
3067 If the array is not found in the config file and its metadata does not
3068 identify it as belonging to the "homehost", then
3070 will choose a name for the array which is certain not to conflict with
3071 any array which does belong to this host. It does this be adding an
3072 underscore and a small number to the name preferred by the metadata.
3074 Once an appropriate array is found or created and the device is added,
3076 must decide if the array is ready to be started. It will
3077 normally compare the number of available (non-spare) devices to the
3078 number of devices that the metadata suggests need to be active. If
3079 there are at least that many, the array will be started. This means
3080 that if any devices are missing the array will not be restarted.
3086 in which case the array will be run as soon as there are enough
3087 devices present for the data to be accessible. For a RAID1, that
3088 means one device will start the array. For a clean RAID5, the array
3089 will be started as soon as all but one drive is present.
3091 Note that neither of these approaches is really ideal. If it can
3092 be known that all device discovery has completed, then
3096 can be run which will try to start all arrays that are being
3097 incrementally assembled. They are started in "read-auto" mode in
3098 which they are read-only until the first write request. This means
3099 that no metadata updates are made and no attempt at resync or recovery
3100 happens. Further devices that are found before the first write can
3101 still be added safely.
3104 This section describes environment variables that affect how mdadm
3109 Setting this value to 1 will prevent mdadm from automatically launching
3110 mdmon. This variable is intended primarily for debugging mdadm/mdmon.
3116 does not create any device nodes in /dev, but leaves that task to
3120 appears not to be configured, or if this environment variable is set
3123 will create and devices that are needed.
3126 .B MDADM_NO_SYSTEMCTL
3131 is in use it will normally request
3133 to start various background tasks (particularly
3135 rather than forking and running them in the background. This can be
3136 suppressed by setting
3137 .BR MDADM_NO_SYSTEMCTL=1 .
3141 A key value of IMSM metadata is that it allows interoperability with
3142 boot ROMs on Intel platforms, and with other major operating systems.
3145 will only allow an IMSM array to be created or modified if detects
3146 that it is running on an Intel platform which supports IMSM, and
3147 supports the particular configuration of IMSM that is being requested
3148 (some functionality requires newer OROM support).
3150 These checks can be suppressed by setting IMSM_NO_PLATFORM=1 in the
3151 environment. This can be useful for testing or for disaster
3152 recovery. You should be aware that interoperability may be
3153 compromised by setting this value.
3156 .B MDADM_GROW_ALLOW_OLD
3157 If an array is stopped while it is performing a reshape and that
3158 reshape was making use of a backup file, then when the array is
3161 will sometimes complain that the backup file is too old. If this
3162 happens and you are certain it is the right backup file, you can
3163 over-ride this check by setting
3164 .B MDADM_GROW_ALLOW_OLD=1
3169 Any string given in this variable is added to the start of the
3171 line in the config file, or treated as the whole
3173 line if none is given. It can be used to disable certain metadata
3176 is called from a boot script. For example
3178 .B " export MDADM_CONF_AUTO='-ddf -imsm'
3182 does not automatically assemble any DDF or
3183 IMSM arrays that are found. This can be useful on systems configured
3184 to manage such arrays with
3190 .B " mdadm \-\-query /dev/name-of-device"
3192 This will find out if a given device is a RAID array, or is part of
3193 one, and will provide brief information about the device.
3195 .B " mdadm \-\-assemble \-\-scan"
3197 This will assemble and start all arrays listed in the standard config
3198 file. This command will typically go in a system startup file.
3200 .B " mdadm \-\-stop \-\-scan"
3202 This will shut down all arrays that can be shut down (i.e. are not
3203 currently in use). This will typically go in a system shutdown script.
3205 .B " mdadm \-\-follow \-\-scan \-\-delay=120"
3207 If (and only if) there is an Email address or program given in the
3208 standard config file, then
3209 monitor the status of all arrays listed in that file by
3210 polling them ever 2 minutes.
3212 .B " mdadm \-\-create /dev/md0 \-\-level=1 \-\-raid\-devices=2 /dev/hd[ac]1"
3214 Create /dev/md0 as a RAID1 array consisting of /dev/hda1 and /dev/hdc1.
3217 .B " echo 'DEVICE /dev/hd*[0\-9] /dev/sd*[0\-9]' > mdadm.conf"
3219 .B " mdadm \-\-detail \-\-scan >> mdadm.conf"
3221 This will create a prototype config file that describes currently
3222 active arrays that are known to be made from partitions of IDE or SCSI drives.
3223 This file should be reviewed before being used as it may
3224 contain unwanted detail.
3226 .B " echo 'DEVICE /dev/hd[a\-z] /dev/sd*[a\-z]' > mdadm.conf"
3228 .B " mdadm \-\-examine \-\-scan \-\-config=mdadm.conf >> mdadm.conf"
3230 This will find arrays which could be assembled from existing IDE and
3231 SCSI whole drives (not partitions), and store the information in the
3232 format of a config file.
3233 This file is very likely to contain unwanted detail, particularly
3236 entries. It should be reviewed and edited before being used as an
3239 .B " mdadm \-\-examine \-\-brief \-\-scan \-\-config=partitions"
3241 .B " mdadm \-Ebsc partitions"
3243 Create a list of devices by reading
3244 .BR /proc/partitions ,
3245 scan these for RAID superblocks, and printout a brief listing of all
3248 .B " mdadm \-Ac partitions \-m 0 /dev/md0"
3250 Scan all partitions and devices listed in
3251 .BR /proc/partitions
3254 out of all such devices with a RAID superblock with a minor number of 0.
3256 .B " mdadm \-\-monitor \-\-scan \-\-daemonise > /run/mdadm/mon.pid"
3258 If config file contains a mail address or alert program, run mdadm in
3259 the background in monitor mode monitoring all md devices. Also write
3260 pid of mdadm daemon to
3261 .BR /run/mdadm/mon.pid .
3263 .B " mdadm \-Iq /dev/somedevice"
3265 Try to incorporate newly discovered device into some array as
3268 .B " mdadm \-\-incremental \-\-rebuild\-map \-\-run \-\-scan"
3270 Rebuild the array map from any current arrays, and then start any that
3273 .B " mdadm /dev/md4 --fail detached --remove detached"
3275 Any devices which are components of /dev/md4 will be marked as faulty
3276 and then remove from the array.
3278 .B " mdadm --grow /dev/md4 --level=6 --backup-file=/root/backup-md4"
3282 which is currently a RAID5 array will be converted to RAID6. There
3283 should normally already be a spare drive attached to the array as a
3284 RAID6 needs one more drive than a matching RAID5.
3286 .B " mdadm --create /dev/md/ddf --metadata=ddf --raid-disks 6 /dev/sd[a-f]"
3288 Create a DDF array over 6 devices.
3290 .B " mdadm --create /dev/md/home -n3 -l5 -z 30000000 /dev/md/ddf"
3292 Create a RAID5 array over any 3 devices in the given DDF set. Use
3293 only 30 gigabytes of each device.
3295 .B " mdadm -A /dev/md/ddf1 /dev/sd[a-f]"
3297 Assemble a pre-exist ddf array.
3299 .B " mdadm -I /dev/md/ddf1"
3301 Assemble all arrays contained in the ddf array, assigning names as
3304 .B " mdadm \-\-create \-\-help"
3306 Provide help about the Create mode.
3308 .B " mdadm \-\-config \-\-help"
3310 Provide help about the format of the config file.
3312 .B " mdadm \-\-help"
3314 Provide general help.
3324 lists all active md devices with information about them.
3326 uses this to find arrays when
3328 is given in Misc mode, and to monitor array reconstruction
3331 .SS {CONFFILE} (or {CONFFILE2})
3333 Default config file. See
3337 .SS {CONFFILE}.d (or {CONFFILE2}.d)
3339 Default directory containing configuration files. See
3346 mode is used, this file gets a list of arrays currently being created.
3351 understand two sorts of names for array devices.
3353 The first is the so-called 'standard' format name, which matches the
3354 names used by the kernel and which appear in
3357 The second sort can be freely chosen, but must reside in
3359 When giving a device name to
3361 to create or assemble an array, either full path name such as
3365 can be given, or just the suffix of the second sort of name, such as
3371 chooses device names during auto-assembly or incremental assembly, it
3372 will sometimes add a small sequence number to the end of the name to
3373 avoid conflicted between multiple arrays that have the same name. If
3375 can reasonably determine that the array really is meant for this host,
3376 either by a hostname in the metadata, or by the presence of the array
3379 then it will leave off the suffix if possible.
3380 Also if the homehost is specified as
3383 will only use a suffix if a different array of the same name already
3384 exists or is listed in the config file.
3386 The standard names for non-partitioned arrays (the only sort of md
3387 array available in 2.4 and earlier) are of the form
3391 where NN is a number.
3392 The standard names for partitionable arrays (as available from 2.6
3393 onwards) are of the form:
3397 Partition numbers should be indicated by adding "pMM" to these, thus "/dev/md/d1p2".
3399 From kernel version 2.6.28 the "non-partitioned array" can actually
3400 be partitioned. So the "md_d\fBNN\fP"
3401 names are no longer needed, and
3402 partitions such as "/dev/md\fBNN\fPp\fBXX\fP"
3405 From kernel version 2.6.29 standard names can be non-numeric following
3412 is any string. These names are supported by
3414 since version 3.3 provided they are enabled in
3419 was previously known as
3423 For further information on mdadm usage, MD and the various levels of
3426 .B https://raid.wiki.kernel.org/
3428 (based upon Jakob \(/Ostergaard's Software\-RAID.HOWTO)
3430 The latest version of
3432 should always be available from
3434 .B https://www.kernel.org/pub/linux/utils/raid/mdadm/
projects / thirdparty / mdadm.git / blob