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, as well as adding or
129 removing a write-intent bitmap.
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
221 then the MANAGE mode is assumed.
222 Anything other than these will cause the
226 .SH Options that are not mode-specific are:
229 .BR \-h ", " \-\-help
230 Display general help message or, after one of the above options, a
231 mode-specific help message.
235 Display more detailed help about command line parsing and some commonly
239 .BR \-V ", " \-\-version
240 Print version information for mdadm.
243 .BR \-v ", " \-\-verbose
244 Be more verbose about what is happening. This can be used twice to be
246 The extra verbosity currently only affects
247 .B \-\-detail \-\-scan
249 .BR "\-\-examine \-\-scan" .
252 .BR \-q ", " \-\-quiet
253 Avoid printing purely informative messages. With this,
255 will be silent unless there is something really important to report.
259 Set first character of argv[0] to @ to indicate mdadm was launched
260 from initrd/initramfs and should not be shutdown by systemd as part of
261 the regular shutdown process. This option is normally only used by
262 the system's initscripts. Please see here for more details on how
263 systemd handled argv[0]:
265 .B http://www.freedesktop.org/wiki/Software/systemd/RootStorageDaemons
270 .BR \-f ", " \-\-force
271 Be more forceful about certain operations. See the various modes for
272 the exact meaning of this option in different contexts.
275 .BR \-c ", " \-\-config=
276 Specify the config file. Default is to use
277 .BR /etc/mdadm.conf ,
278 or if that is missing then
279 .BR /etc/mdadm/mdadm.conf .
280 If the config file given is
282 then nothing will be read, but
284 will act as though the config file contained exactly
285 .B "DEVICE partitions containers"
288 to find a list of devices to scan, and
290 to find a list of containers to examine.
293 is given for the config file, then
295 will act as though the config file were empty.
298 .BR \-s ", " \-\-scan
301 for missing information.
302 In general, this option gives
304 permission to get any missing information (like component devices,
305 array devices, array identities, and alert destination) from the
306 configuration file (see previous option);
307 one exception is MISC mode when using
313 says to get a list of array devices from
317 .BR \-e ", " \-\-metadata=
318 Declare the style of RAID metadata (superblock) to be used. The
319 default is {DEFAULT_METADATA} for
321 and to guess for other operations.
322 The default can be overridden by setting the
331 .ie '{DEFAULT_METADATA}'0.90'
332 .IP "0, 0.90, default"
335 Use the original 0.90 format superblock. This format limits arrays to
336 28 component devices and limits component devices of levels 1 and
337 greater to 2 terabytes. It is also possible for there to be confusion
338 about whether the superblock applies to a whole device or just the
339 last partition, if that partition starts on a 64K boundary.
340 .ie '{DEFAULT_METADATA}'0.90'
341 .IP "1, 1.0, 1.1, 1.2"
343 .IP "1, 1.0, 1.1, 1.2 default"
344 Use the new version-1 format superblock. This has fewer restrictions.
345 It can easily be moved between hosts with different endian-ness, and a
346 recovery operation can be checkpointed and restarted. The different
347 sub-versions store the superblock at different locations on the
348 device, either at the end (for 1.0), at the start (for 1.1) or 4K from
349 the start (for 1.2). "1" is equivalent to "1.2" (the commonly
350 preferred 1.x format).
351 'if '{DEFAULT_METADATA}'1.2' "default" is equivalent to "1.2".
353 Use the "Industry Standard" DDF (Disk Data Format) format defined by
355 When creating a DDF array a
357 will be created, and normal arrays can be created in that container.
359 Use the Intel(R) Matrix Storage Manager metadata format. This creates a
361 which is managed in a similar manner to DDF, and is supported by an
362 option-rom on some platforms:
364 .B http://www.intel.com/design/chipsets/matrixstorage_sb.htm
370 This will override any
372 setting in the config file and provides the identity of the host which
373 should be considered the home for any arrays.
375 When creating an array, the
377 will be recorded in the metadata. For version-1 superblocks, it will
378 be prefixed to the array name. For version-0.90 superblocks, part of
379 the SHA1 hash of the hostname will be stored in the later half of the
382 When reporting information about an array, any array which is tagged
383 for the given homehost will be reported as such.
385 When using Auto-Assemble, only arrays tagged for the given homehost
386 will be allowed to use 'local' names (i.e. not ending in '_' followed
387 by a digit string). See below under
388 .BR "Auto Assembly" .
394 needs to print the name for a device it normally finds the name in
396 which refers to the device and is shortest. When a path component is
400 will prefer a longer name if it contains that component. For example
401 .B \-\-prefer=by-uuid
402 will prefer a name in a subdirectory of
407 This functionality is currently only provided by
412 .SH For create, build, or grow:
415 .BR \-n ", " \-\-raid\-devices=
416 Specify the number of active devices in the array. This, plus the
417 number of spare devices (see below) must equal the number of
419 (including "\fBmissing\fP" devices)
420 that are listed on the command line for
422 Setting a value of 1 is probably
423 a mistake and so requires that
425 be specified first. A value of 1 will then be allowed for linear,
426 multipath, RAID0 and RAID1. It is never allowed for RAID4, RAID5 or RAID6.
428 This number can only be changed using
430 for RAID1, RAID4, RAID5 and RAID6 arrays, and only on kernels which provide
431 the necessary support.
434 .BR \-x ", " \-\-spare\-devices=
435 Specify the number of spare (eXtra) devices in the initial array.
436 Spares can also be added
437 and removed later. The number of component devices listed
438 on the command line must equal the number of RAID devices plus the
439 number of spare devices.
442 .BR \-z ", " \-\-size=
443 Amount (in Kibibytes) of space to use from each drive in RAID levels 1/4/5/6.
444 This must be a multiple of the chunk size, and must leave about 128Kb
445 of space at the end of the drive for the RAID superblock.
446 If this is not specified
447 (as it normally is not) the smallest drive (or partition) sets the
448 size, though if there is a variance among the drives of greater than 1%, a warning is
451 A suffix of 'M' or 'G' can be given to indicate Megabytes or
452 Gigabytes respectively.
454 Sometimes a replacement drive can be a little smaller than the
455 original drives though this should be minimised by IDEMA standards.
456 Such a replacement drive will be rejected by
458 To guard against this it can be useful to set the initial size
459 slightly smaller than the smaller device with the aim that it will
460 still be larger than any replacement.
462 This value can be set with
464 for RAID level 1/4/5/6 though
466 based arrays such as those with IMSM metadata may not be able to
468 If the array was created with a size smaller than the currently
469 active drives, the extra space can be accessed using
471 The size can be given as
473 which means to choose the largest size that fits on all current drives.
475 Before reducing the size of the array (with
476 .BR "\-\-grow \-\-size=" )
477 you should make sure that space isn't needed. If the device holds a
478 filesystem, you would need to resize the filesystem to use less space.
480 After reducing the array size you should check that the data stored in
481 the device is still available. If the device holds a filesystem, then
482 an 'fsck' of the filesystem is a minimum requirement. If there are
483 problems the array can be made bigger again with no loss with another
484 .B "\-\-grow \-\-size="
487 This value cannot be used when creating a
489 such as with DDF and IMSM metadata, though it perfectly valid when
490 creating an array inside a container.
493 .BR \-Z ", " \-\-array\-size=
494 This is only meaningful with
496 and its effect is not persistent: when the array is stopped and
497 restarted the default array size will be restored.
499 Setting the array-size causes the array to appear smaller to programs
500 that access the data. This is particularly needed before reshaping an
501 array so that it will be smaller. As the reshape is not reversible,
502 but setting the size with
504 is, it is required that the array size is reduced as appropriate
505 before the number of devices in the array is reduced.
507 Before reducing the size of the array you should make sure that space
508 isn't needed. If the device holds a filesystem, you would need to
509 resize the filesystem to use less space.
511 After reducing the array size you should check that the data stored in
512 the device is still available. If the device holds a filesystem, then
513 an 'fsck' of the filesystem is a minimum requirement. If there are
514 problems the array can be made bigger again with no loss with another
515 .B "\-\-grow \-\-array\-size="
518 A suffix of 'M' or 'G' can be given to indicate Megabytes or
519 Gigabytes respectively.
522 restores the apparent size of the array to be whatever the real
523 amount of available space is.
526 .BR \-c ", " \-\-chunk=
527 Specify chunk size of kibibytes. The default when creating an
528 array is 512KB. To ensure compatibility with earlier versions, the
529 default when Building and array with no persistent metadata is 64KB.
530 This is only meaningful for RAID0, RAID4, RAID5, RAID6, and RAID10.
532 RAID4, RAID5, RAID6, and RAID10 require the chunk size to be a power
533 of 2. In any case it must be a multiple of 4KB.
535 A suffix of 'M' or 'G' can be given to indicate Megabytes or
536 Gigabytes respectively.
540 Specify rounding factor for a Linear array. The size of each
541 component will be rounded down to a multiple of this size.
542 This is a synonym for
544 but highlights the different meaning for Linear as compared to other
545 RAID levels. The default is 64K if a kernel earlier than 2.6.16 is in
546 use, and is 0K (i.e. no rounding) in later kernels.
549 .BR \-l ", " \-\-level=
550 Set RAID level. When used with
552 options are: linear, raid0, 0, stripe, raid1, 1, mirror, raid4, 4,
553 raid5, 5, raid6, 6, raid10, 10, multipath, mp, faulty, container.
554 Obviously some of these are synonymous.
558 metadata type is requested, only the
560 level is permitted, and it does not need to be explicitly given.
564 only linear, stripe, raid0, 0, raid1, multipath, mp, and faulty are valid.
568 to change the RAID level in some cases. See LEVEL CHANGES below.
571 .BR \-p ", " \-\-layout=
572 This option configures the fine details of data layout for RAID5, RAID6,
573 and RAID10 arrays, and controls the failure modes for
576 The layout of the RAID5 parity block can be one of
577 .BR left\-asymmetric ,
578 .BR left\-symmetric ,
579 .BR right\-asymmetric ,
580 .BR right\-symmetric ,
581 .BR la ", " ra ", " ls ", " rs .
583 .BR left\-symmetric .
585 It is also possible to cause RAID5 to use a RAID4-like layout by
591 Finally for RAID5 there are DDF\-compatible layouts,
592 .BR ddf\-zero\-restart ,
593 .BR ddf\-N\-restart ,
595 .BR ddf\-N\-continue .
597 These same layouts are available for RAID6. There are also 4 layouts
598 that will provide an intermediate stage for converting between RAID5
599 and RAID6. These provide a layout which is identical to the
600 corresponding RAID5 layout on the first N\-1 devices, and has the 'Q'
601 syndrome (the second 'parity' block used by RAID6) on the last device.
603 .BR left\-symmetric\-6 ,
604 .BR right\-symmetric\-6 ,
605 .BR left\-asymmetric\-6 ,
606 .BR right\-asymmetric\-6 ,
608 .BR parity\-first\-6 .
610 When setting the failure mode for level
613 .BR write\-transient ", " wt ,
614 .BR read\-transient ", " rt ,
615 .BR write\-persistent ", " wp ,
616 .BR read\-persistent ", " rp ,
618 .BR read\-fixable ", " rf ,
619 .BR clear ", " flush ", " none .
621 Each failure mode can be followed by a number, which is used as a period
622 between fault generation. Without a number, the fault is generated
623 once on the first relevant request. With a number, the fault will be
624 generated after that many requests, and will continue to be generated
625 every time the period elapses.
627 Multiple failure modes can be current simultaneously by using the
629 option to set subsequent failure modes.
631 "clear" or "none" will remove any pending or periodic failure modes,
632 and "flush" will clear any persistent faults.
634 Finally, the layout options for RAID10 are one of 'n', 'o' or 'f' followed
635 by a small number. The default is 'n2'. The supported options are:
638 signals 'near' copies. Multiple copies of one data block are at
639 similar offsets in different devices.
642 signals 'offset' copies. Rather than the chunks being duplicated
643 within a stripe, whole stripes are duplicated but are rotated by one
644 device so duplicate blocks are on different devices. Thus subsequent
645 copies of a block are in the next drive, and are one chunk further
650 (multiple copies have very different offsets).
651 See md(4) for more detail about 'near', 'offset', and 'far'.
653 The number is the number of copies of each datablock. 2 is normal, 3
654 can be useful. This number can be at most equal to the number of
655 devices in the array. It does not need to divide evenly into that
656 number (e.g. it is perfectly legal to have an 'n2' layout for an array
657 with an odd number of devices).
659 When an array is converted between RAID5 and RAID6 an intermediate
660 RAID6 layout is used in which the second parity block (Q) is always on
661 the last device. To convert a RAID5 to RAID6 and leave it in this new
662 layout (which does not require re-striping) use
663 .BR \-\-layout=preserve .
664 This will try to avoid any restriping.
666 The converse of this is
667 .B \-\-layout=normalise
668 which will change a non-standard RAID6 layout into a more standard
675 (thus explaining the p of
679 .BR \-b ", " \-\-bitmap=
680 Specify a file to store a write-intent bitmap in. The file should not
683 is also given. The same file should be provided
684 when assembling the array. If the word
686 is given, then the bitmap is stored with the metadata on the array,
687 and so is replicated on all devices. If the word
691 mode, then any bitmap that is present is removed.
693 To help catch typing errors, the filename must contain at least one
694 slash ('/') if it is a real file (not 'internal' or 'none').
696 Note: external bitmaps are only known to work on ext2 and ext3.
697 Storing bitmap files on other filesystems may result in serious problems.
700 .BR \-\-bitmap\-chunk=
701 Set the chunksize of the bitmap. Each bit corresponds to that many
702 Kilobytes of storage.
703 When using a file based bitmap, the default is to use the smallest
704 size that is at-least 4 and requires no more than 2^21 chunks.
707 bitmap, the chunksize defaults to 64Meg, or larger if necessary to
708 fit the bitmap into the available space.
710 A suffix of 'M' or 'G' can be given to indicate Megabytes or
711 Gigabytes respectively.
714 .BR \-W ", " \-\-write\-mostly
715 subsequent devices listed in a
720 command will be flagged as 'write-mostly'. This is valid for RAID1
721 only and means that the 'md' driver will avoid reading from these
722 devices if at all possible. This can be useful if mirroring over a
726 .BR \-\-write\-behind=
727 Specify that write-behind mode should be enabled (valid for RAID1
728 only). If an argument is specified, it will set the maximum number
729 of outstanding writes allowed. The default value is 256.
730 A write-intent bitmap is required in order to use write-behind
731 mode, and write-behind is only attempted on drives marked as
735 .BR \-\-assume\-clean
738 that the array pre-existed and is known to be clean. It can be useful
739 when trying to recover from a major failure as you can be sure that no
740 data will be affected unless you actually write to the array. It can
741 also be used when creating a RAID1 or RAID10 if you want to avoid the
742 initial resync, however this practice \(em while normally safe \(em is not
743 recommended. Use this only if you really know what you are doing.
745 When the devices that will be part of a new array were filled
746 with zeros before creation the operator knows the array is
747 actually clean. If that is the case, such as after running
748 badblocks, this argument can be used to tell mdadm the
749 facts the operator knows.
751 When an array is resized to a larger size with
752 .B "\-\-grow \-\-size="
753 the new space is normally resynced in that same way that the whole
754 array is resynced at creation. From Linux version 3.0,
756 can be used with that command to avoid the automatic resync.
759 .BR \-\-backup\-file=
762 is used to increase the number of raid-devices in a RAID5 or RAID6 if
763 there are no spare devices available, or to shrink, change RAID level
764 or layout. See the GROW MODE section below on RAID\-DEVICES CHANGES.
765 The file must be stored on a separate device, not on the RAID array
770 Arrays with 1.x metadata can leave a gap between the start of the
771 device and the start of array data. This gap can be used for various
772 metadata. The start of data is known as the
774 Normally an appropriate data offset is computed automatically.
775 However it can be useful to set it explicitly such as when re-creating
776 an array which was originally created using a different version of
778 which computed a different offset.
780 Setting the offset explicitly over-rides the default. The value given
781 is in Kilobytes unless an 'M' or 'G' suffix is given.
785 can also be used with
787 for some RAID levels (initially on RAID10). This allows the
788 data\-offset to be changed as part of the reshape process. When the
789 data offset is changed, no backup file is required as the difference
790 in offsets is used to provide the same functionality.
792 When the new offset is earlier than the old offset, the number of
793 devices in the array cannot shrink. When it is after the old offset,
794 the number of devices in the array cannot increase.
796 When creating an array,
800 In the case each member device is expected to have a offset appended
801 to the name, separated by a colon. This makes it possible to recreate
802 exactly an array which has varying data offsets (as can happen when
803 different versions of
805 are used to add different devices).
809 This option is complementary to the
810 .B \-\-freeze-reshape
811 option for assembly. It is needed when
813 operation is interrupted and it is not restarted automatically due to
814 .B \-\-freeze-reshape
815 usage during array assembly. This option is used together with
819 ) command and device for a pending reshape to be continued.
820 All parameters required for reshape continuation will be read from array metadata.
824 .BR \-\-backup\-file=
825 option to be set, continuation option will require to have exactly the same
826 backup file given as well.
828 Any other parameter passed together with
830 option will be ignored.
833 .BR \-N ", " \-\-name=
836 for the array. This is currently only effective when creating an
837 array with a version-1 superblock, or an array in a DDF container.
838 The name is a simple textual string that can be used to identify array
839 components when assembling. If name is needed but not specified, it
840 is taken from the basename of the device that is being created.
852 run the array, even if some of the components
853 appear to be active in another array or filesystem. Normally
855 will ask for confirmation before including such components in an
856 array. This option causes that question to be suppressed.
859 .BR \-f ", " \-\-force
862 accept the geometry and layout specified without question. Normally
864 will not allow creation of an array with only one device, and will try
865 to create a RAID5 array with one missing drive (as this makes the
866 initial resync work faster). With
869 will not try to be so clever.
872 .BR \-o ", " \-\-readonly
875 rather than read-write as normal. No writes will be allowed to the
876 array, and no resync, recovery, or reshape will be started.
879 .BR \-a ", " "\-\-auto{=yes,md,mdp,part,p}{NN}"
880 Instruct mdadm how to create the device file if needed, possibly allocating
881 an unused minor number. "md" causes a non-partitionable array
882 to be used (though since Linux 2.6.28, these array devices are in fact
883 partitionable). "mdp", "part" or "p" causes a partitionable array (2.6 and
884 later) to be used. "yes" requires the named md device to have
885 a 'standard' format, and the type and minor number will be determined
886 from this. With mdadm 3.0, device creation is normally left up to
888 so this option is unlikely to be needed.
889 See DEVICE NAMES below.
891 The argument can also come immediately after
896 is not given on the command line or in the config file, then
902 is also given, then any
904 entries in the config file will override the
906 instruction given on the command line.
908 For partitionable arrays,
910 will create the device file for the whole array and for the first 4
911 partitions. A different number of partitions can be specified at the
912 end of this option (e.g.
914 If the device name ends with a digit, the partition names add a 'p',
916 .IR /dev/md/home1p3 .
917 If there is no trailing digit, then the partition names just have a
919 .IR /dev/md/scratch3 .
921 If the md device name is in a 'standard' format as described in DEVICE
922 NAMES, then it will be created, if necessary, with the appropriate
923 device number based on that name. If the device name is not in one of these
924 formats, then a unused device number will be allocated. The device
925 number will be considered unused if there is no active array for that
926 number, and there is no entry in /dev for that number and with a
927 non-standard name. Names that are not in 'standard' format are only
928 allowed in "/dev/md/".
930 This is meaningful with
936 .BR \-a ", " "\-\-add"
937 This option can be used in Grow mode in two cases.
939 If the target array is a Linear array, then
941 can be used to add one or more devices to the array. They
942 are simply catenated on to the end of the array. Once added, the
943 devices cannot be removed.
947 option is being used to increase the number of devices in an array,
950 can be used to add some extra devices to be included in the array.
951 In most cases this is not needed as the extra devices can be added as
952 spares first, and then the number of raid-disks can be changed.
953 However for RAID0, it is not possible to add spares. So to increase
954 the number of devices in a RAID0, it is necessary to set the new
955 number of devices, and to add the new devices, in the same command.
960 .BR \-u ", " \-\-uuid=
961 uuid of array to assemble. Devices which don't have this uuid are
965 .BR \-m ", " \-\-super\-minor=
966 Minor number of device that array was created for. Devices which
967 don't have this minor number are excluded. If you create an array as
968 /dev/md1, then all superblocks will contain the minor number 1, even if
969 the array is later assembled as /dev/md2.
971 Giving the literal word "dev" for
975 to use the minor number of the md device that is being assembled.
978 .B \-\-super\-minor=dev
979 will look for super blocks with a minor number of 0.
982 is only relevant for v0.90 metadata, and should not normally be used.
988 .BR \-N ", " \-\-name=
989 Specify the name of the array to assemble. This must be the name
990 that was specified when creating the array. It must either match
991 the name stored in the superblock exactly, or it must match
994 prefixed to the start of the given name.
997 .BR \-f ", " \-\-force
998 Assemble the array even if the metadata on some devices appears to be
1001 cannot find enough working devices to start the array, but can find
1002 some devices that are recorded as having failed, then it will mark
1003 those devices as working so that the array can be started.
1004 An array which requires
1006 to be started may contain data corruption. Use it carefully.
1009 .BR \-R ", " \-\-run
1010 Attempt to start the array even if fewer drives were given than were
1011 present last time the array was active. Normally if not all the
1012 expected drives are found and
1014 is not used, then the array will be assembled but not started.
1017 an attempt will be made to start it anyway.
1021 This is the reverse of
1023 in that it inhibits the startup of array unless all expected drives
1024 are present. This is only needed with
1026 and can be used if the physical connections to devices are
1027 not as reliable as you would like.
1030 .BR \-a ", " "\-\-auto{=no,yes,md,mdp,part}"
1031 See this option under Create and Build options.
1034 .BR \-b ", " \-\-bitmap=
1035 Specify the bitmap file that was given when the array was created. If
1038 bitmap, there is no need to specify this when assembling the array.
1041 .BR \-\-backup\-file=
1044 was used while reshaping an array (e.g. changing number of devices or
1045 chunk size) and the system crashed during the critical section, then the same
1047 must be presented to
1049 to allow possibly corrupted data to be restored, and the reshape
1053 .BR \-\-invalid\-backup
1054 If the file needed for the above option is not available for any
1055 reason an empty file can be given together with this option to
1056 indicate that the backup file is invalid. In this case the data that
1057 was being rearranged at the time of the crash could be irrecoverably
1058 lost, but the rest of the array may still be recoverable. This option
1059 should only be used as a last resort if there is no way to recover the
1064 .BR \-U ", " \-\-update=
1065 Update the superblock on each device while assembling the array. The
1066 argument given to this flag can be one of
1083 option will adjust the superblock of an array what was created on a Sparc
1084 machine running a patched 2.2 Linux kernel. This kernel got the
1085 alignment of part of the superblock wrong. You can use the
1086 .B "\-\-examine \-\-sparc2.2"
1089 to see what effect this would have.
1093 option will update the
1094 .B "preferred minor"
1095 field on each superblock to match the minor number of the array being
1097 This can be useful if
1099 reports a different "Preferred Minor" to
1101 In some cases this update will be performed automatically
1102 by the kernel driver. In particular the update happens automatically
1103 at the first write to an array with redundancy (RAID level 1 or
1104 greater) on a 2.6 (or later) kernel.
1108 option will change the uuid of the array. If a UUID is given with the
1110 option that UUID will be used as a new UUID and will
1112 be used to help identify the devices in the array.
1115 is given, a random UUID is chosen.
1119 option will change the
1121 of the array as stored in the superblock. This is only supported for
1122 version-1 superblocks.
1126 option will change the
1128 as recorded in the superblock. For version-0 superblocks, this is the
1129 same as updating the UUID.
1130 For version-1 superblocks, this involves updating the name.
1134 option will cause the array to be marked
1136 meaning that any redundancy in the array (e.g. parity for RAID5,
1137 copies for RAID1) may be incorrect. This will cause the RAID system
1138 to perform a "resync" pass to make sure that all redundant information
1143 option allows arrays to be moved between machines with different
1145 When assembling such an array for the first time after a move, giving
1146 .B "\-\-update=byteorder"
1149 to expect superblocks to have their byteorder reversed, and will
1150 correct that order before assembling the array. This is only valid
1151 with original (Version 0.90) superblocks.
1155 option will correct the summaries in the superblock. That is the
1156 counts of total, working, active, failed, and spare devices.
1160 option will rarely be of use. It applies to version 1.1 and 1.2 metadata
1161 only (where the metadata is at the start of the device) and is only
1162 useful when the component device has changed size (typically become
1163 larger). The version 1 metadata records the amount of the device that
1164 can be used to store data, so if a device in a version 1.1 or 1.2
1165 array becomes larger, the metadata will still be visible, but the
1166 extra space will not. In this case it might be useful to assemble the
1168 .BR \-\-update=devicesize .
1171 to determine the maximum usable amount of space on each device and
1172 update the relevant field in the metadata.
1176 option can be used when an array has an internal bitmap which is
1177 corrupt in some way so that assembling the array normally fails. It
1178 will cause any internal bitmap to be ignored.
1182 option will reserve space in each device for a bad block list. This
1183 will be 4K in size and positioned near the end of any free space
1184 between the superblock and the data.
1188 option will cause any reservation of space for a bad block list to be
1189 removed. If the bad block list contains entries, this will fail, as
1190 removing the list could cause data corruption.
1193 .BR \-\-freeze\-reshape
1194 Option is intended to be used in start-up scripts during initrd boot phase.
1195 When array under reshape is assembled during initrd phase, this option
1196 stops reshape after reshape critical section is being restored. This happens
1197 before file system pivot operation and avoids loss of file system context.
1198 Losing file system context would cause reshape to be broken.
1200 Reshape can be continued later using the
1202 option for the grow command.
1204 .SH For Manage mode:
1207 .BR \-t ", " \-\-test
1208 Unless a more serious error occurred,
1210 will exit with a status of 2 if no changes were made to the array and
1211 0 if at least one change was made.
1212 This can be useful when an indirect specifier such as
1217 is used in requesting an operation on the array.
1219 will report failure if these specifiers didn't find any match.
1222 .BR \-a ", " \-\-add
1223 hot-add listed devices.
1224 If a device appears to have recently been part of the array
1225 (possibly it failed or was removed) the device is re\-added as described
1227 If that fails or the device was never part of the array, the device is
1228 added as a hot-spare.
1229 If the array is degraded, it will immediately start to rebuild data
1232 Note that this and the following options are only meaningful on array
1233 with redundancy. They don't apply to RAID0 or Linear.
1237 re\-add a device that was previous removed from an array.
1238 If the metadata on the device reports that it is a member of the
1239 array, and the slot that it used is still vacant, then the device will
1240 be added back to the array in the same position. This will normally
1241 cause the data for that device to be recovered. However based on the
1242 event count on the device, the recovery may only require sections that
1243 are flagged a write-intent bitmap to be recovered or may not require
1244 any recovery at all.
1246 When used on an array that has no metadata (i.e. it was built with
1248 it will be assumed that bitmap-based recovery is enough to make the
1249 device fully consistent with the array.
1251 When used with v1.x metadata,
1253 can be accompanied by
1254 .BR \-\-update=devicesize ,
1255 .BR \-\-update=bbl ", or"
1256 .BR \-\-update=no\-bbl .
1257 See the description of these option when used in Assemble mode for an
1258 explanation of their use.
1260 If the device name given is
1262 then mdadm will try to find any device that looks like it should be
1263 part of the array but isn't and will try to re\-add all such devices.
1266 .BR \-r ", " \-\-remove
1267 remove listed devices. They must not be active. i.e. they should
1268 be failed or spare devices. As well as the name of a device file
1277 The first causes all failed device to be removed. The second causes
1278 any device which is no longer connected to the system (i.e an 'open'
1281 to be removed. This will only succeed for devices that are spares or
1282 have already been marked as failed.
1285 .BR \-f ", " \-\-fail
1286 mark listed devices as faulty.
1287 As well as the name of a device file, the word
1289 can be given. This will cause any device that has been detached from
1290 the system to be marked as failed. It can then be removed.
1298 .BR \-\-write\-mostly
1299 Subsequent devices that are added or re\-added will have the 'write-mostly'
1300 flag set. This is only valid for RAID1 and means that the 'md' driver
1301 will avoid reading from these devices if possible.
1304 Subsequent devices that are added or re\-added will have the 'write-mostly'
1308 Each of these options requires that the first device listed is the array
1309 to be acted upon, and the remainder are component devices to be added,
1310 removed, marked as faulty, etc. Several different operations can be
1311 specified for different devices, e.g.
1313 mdadm /dev/md0 \-\-add /dev/sda1 \-\-fail /dev/sdb1 \-\-remove /dev/sdb1
1315 Each operation applies to all devices listed until the next
1318 If an array is using a write-intent bitmap, then devices which have
1319 been removed can be re\-added in a way that avoids a full
1320 reconstruction but instead just updates the blocks that have changed
1321 since the device was removed. For arrays with persistent metadata
1322 (superblocks) this is done automatically. For arrays created with
1324 mdadm needs to be told that this device we removed recently with
1327 Devices can only be removed from an array if they are not in active
1328 use, i.e. that must be spares or failed devices. To remove an active
1329 device, it must first be marked as
1335 .BR \-Q ", " \-\-query
1336 Examine a device to see
1337 (1) if it is an md device and (2) if it is a component of an md
1339 Information about what is discovered is presented.
1342 .BR \-D ", " \-\-detail
1343 Print details of one or more md devices.
1346 .BR \-\-detail\-platform
1347 Print details of the platform's RAID capabilities (firmware / hardware
1348 topology) for a given metadata format. If used without argument, mdadm
1349 will scan all controllers looking for their capabilities. Otherwise, mdadm
1350 will only look at the controller specified by the argument in form of an
1351 absolute filepath or a link, e.g.
1352 .IR /sys/devices/pci0000:00/0000:00:1f.2 .
1355 .BR \-Y ", " \-\-export
1357 .B \-\-detail , \-\-detail-platform
1360 output will be formatted as
1362 pairs for easy import into the environment.
1365 .BR \-E ", " \-\-examine
1366 Print contents of the metadata stored on the named device(s).
1367 Note the contrast between
1372 applies to devices which are components of an array, while
1374 applies to a whole array which is currently active.
1377 If an array was created on a SPARC machine with a 2.2 Linux kernel
1378 patched with RAID support, the superblock will have been created
1379 incorrectly, or at least incompatibly with 2.4 and later kernels.
1384 will fix the superblock before displaying it. If this appears to do
1385 the right thing, then the array can be successfully assembled using
1386 .BR "\-\-assemble \-\-update=sparc2.2" .
1389 .BR \-X ", " \-\-examine\-bitmap
1390 Report information about a bitmap file.
1391 The argument is either an external bitmap file or an array component
1392 in case of an internal bitmap. Note that running this on an array
1395 does not report the bitmap for that array.
1398 .BR \-R ", " \-\-run
1399 start a partially assembled array. If
1401 did not find enough devices to fully start the array, it might leaving
1402 it partially assembled. If you wish, you can then use
1404 to start the array in degraded mode.
1407 .BR \-S ", " \-\-stop
1408 deactivate array, releasing all resources.
1411 .BR \-o ", " \-\-readonly
1412 mark array as readonly.
1415 .BR \-w ", " \-\-readwrite
1416 mark array as readwrite.
1419 .B \-\-zero\-superblock
1420 If the device contains a valid md superblock, the block is
1421 overwritten with zeros. With
1423 the block where the superblock would be is overwritten even if it
1424 doesn't appear to be valid.
1427 .B \-\-kill\-subarray=
1428 If the device is a container and the argument to \-\-kill\-subarray
1429 specifies an inactive subarray in the container, then the subarray is
1430 deleted. Deleting all subarrays will leave an 'empty-container' or
1431 spare superblock on the drives. See \-\-zero\-superblock for completely
1432 removing a superblock. Note that some formats depend on the subarray
1433 index for generating a UUID, this command will fail if it would change
1434 the UUID of an active subarray.
1437 .B \-\-update\-subarray=
1438 If the device is a container and the argument to \-\-update\-subarray
1439 specifies a subarray in the container, then attempt to update the given
1440 superblock field in the subarray. See below in
1445 .BR \-t ", " \-\-test
1450 is set to reflect the status of the device. See below in
1455 .BR \-W ", " \-\-wait
1456 For each md device given, wait for any resync, recovery, or reshape
1457 activity to finish before returning.
1459 will return with success if it actually waited for every device
1460 listed, otherwise it will return failure.
1464 For each md device given, or each device in /proc/mdstat if
1466 is given, arrange for the array to be marked clean as soon as possible.
1468 will return with success if the array uses external metadata and we
1469 successfully waited. For native arrays this returns immediately as the
1470 kernel handles dirty-clean transitions at shutdown. No action is taken
1471 if safe-mode handling is disabled.
1473 .SH For Incremental Assembly mode:
1475 .BR \-\-rebuild\-map ", " \-r
1476 Rebuild the map file
1480 uses to help track which arrays are currently being assembled.
1483 .BR \-\-run ", " \-R
1484 Run any array assembled as soon as a minimal number of devices are
1485 available, rather than waiting until all expected devices are present.
1488 .BR \-\-scan ", " \-s
1489 Only meaningful with
1493 file for arrays that are being incrementally assembled and will try to
1494 start any that are not already started. If any such array is listed
1497 as requiring an external bitmap, that bitmap will be attached first.
1500 .BR \-\-fail ", " \-f
1501 This allows the hot-plug system to remove devices that have fully disappeared
1502 from the kernel. It will first fail and then remove the device from any
1503 array it belongs to.
1504 The device name given should be a kernel device name such as "sda",
1510 Only used with \-\-fail. The 'path' given will be recorded so that if
1511 a new device appears at the same location it can be automatically
1512 added to the same array. This allows the failed device to be
1513 automatically replaced by a new device without metadata if it appears
1514 at specified path. This option is normally only set by a
1518 .SH For Monitor mode:
1520 .BR \-m ", " \-\-mail
1521 Give a mail address to send alerts to.
1524 .BR \-p ", " \-\-program ", " \-\-alert
1525 Give a program to be run whenever an event is detected.
1528 .BR \-y ", " \-\-syslog
1529 Cause all events to be reported through 'syslog'. The messages have
1530 facility of 'daemon' and varying priorities.
1533 .BR \-d ", " \-\-delay
1534 Give a delay in seconds.
1536 polls the md arrays and then waits this many seconds before polling
1537 again. The default is 60 seconds. Since 2.6.16, there is no need to
1538 reduce this as the kernel alerts
1540 immediately when there is any change.
1543 .BR \-r ", " \-\-increment
1544 Give a percentage increment.
1546 will generate RebuildNN events with the given percentage increment.
1549 .BR \-f ", " \-\-daemonise
1552 to run as a background daemon if it decides to monitor anything. This
1553 causes it to fork and run in the child, and to disconnect from the
1554 terminal. The process id of the child is written to stdout.
1557 which will only continue monitoring if a mail address or alert program
1558 is found in the config file.
1561 .BR \-i ", " \-\-pid\-file
1564 is running in daemon mode, write the pid of the daemon process to
1565 the specified file, instead of printing it on standard output.
1568 .BR \-1 ", " \-\-oneshot
1569 Check arrays only once. This will generate
1571 events and more significantly
1577 .B " mdadm \-\-monitor \-\-scan \-1"
1579 from a cron script will ensure regular notification of any degraded arrays.
1582 .BR \-t ", " \-\-test
1585 alert for every array found at startup. This alert gets mailed and
1586 passed to the alert program. This can be used for testing that alert
1587 message do get through successfully.
1591 This inhibits the functionality for moving spares between arrays.
1592 Only one monitoring process started with
1594 but without this flag is allowed, otherwise the two could interfere
1601 .B mdadm \-\-assemble
1602 .I md-device options-and-component-devices...
1605 .B mdadm \-\-assemble \-\-scan
1606 .I md-devices-and-options...
1609 .B mdadm \-\-assemble \-\-scan
1613 This usage assembles one or more RAID arrays from pre-existing components.
1614 For each array, mdadm needs to know the md device, the identity of the
1615 array, and a number of component-devices. These can be found in a number of ways.
1617 In the first usage example (without the
1619 the first device given is the md device.
1620 In the second usage example, all devices listed are treated as md
1621 devices and assembly is attempted.
1622 In the third (where no devices are listed) all md devices that are
1623 listed in the configuration file are assembled. If no arrays are
1624 described by the configuration file, then any arrays that
1625 can be found on unused devices will be assembled.
1627 If precisely one device is listed, but
1633 was given and identity information is extracted from the configuration file.
1635 The identity can be given with the
1641 option, will be taken from the md-device record in the config file, or
1642 will be taken from the super block of the first component-device
1643 listed on the command line.
1645 Devices can be given on the
1647 command line or in the config file. Only devices which have an md
1648 superblock which contains the right identity will be considered for
1651 The config file is only used if explicitly named with
1653 or requested with (a possibly implicit)
1658 .B /etc/mdadm/mdadm.conf
1663 is not given, then the config file will only be used to find the
1664 identity of md arrays.
1666 Normally the array will be started after it is assembled. However if
1668 is not given and not all expected drives were listed, then the array
1669 is not started (to guard against usage errors). To insist that the
1670 array be started in this case (as may work for RAID1, 4, 5, 6, or 10),
1679 does not create any entries in
1683 It does record information in
1687 to choose the correct name.
1691 detects that udev is not configured, it will create the devices in
1695 In Linux kernels prior to version 2.6.28 there were two distinctly
1696 different types of md devices that could be created: one that could be
1697 partitioned using standard partitioning tools and one that could not.
1698 Since 2.6.28 that distinction is no longer relevant as both type of
1699 devices can be partitioned.
1701 will normally create the type that originally could not be partitioned
1702 as it has a well defined major number (9).
1704 Prior to 2.6.28, it is important that mdadm chooses the correct type
1705 of array device to use. This can be controlled with the
1707 option. In particular, a value of "mdp" or "part" or "p" tells mdadm
1708 to use a partitionable device rather than the default.
1710 In the no-udev case, the value given to
1712 can be suffixed by a number. This tells
1714 to create that number of partition devices rather than the default of 4.
1718 can also be given in the configuration file as a word starting
1720 on the ARRAY line for the relevant array.
1727 and no devices are listed,
1729 will first attempt to assemble all the arrays listed in the config
1732 If no arrays are listed in the config (other than those marked
1734 it will look through the available devices for possible arrays and
1735 will try to assemble anything that it finds. Arrays which are tagged
1736 as belonging to the given homehost will be assembled and started
1737 normally. Arrays which do not obviously belong to this host are given
1738 names that are expected not to conflict with anything local, and are
1739 started "read-auto" so that nothing is written to any device until the
1740 array is written to. i.e. automatic resync etc is delayed.
1744 finds a consistent set of devices that look like they should comprise
1745 an array, and if the superblock is tagged as belonging to the given
1746 home host, it will automatically choose a device name and try to
1747 assemble the array. If the array uses version-0.90 metadata, then the
1749 number as recorded in the superblock is used to create a name in
1753 If the array uses version-1 metadata, then the
1755 from the superblock is used to similarly create a name in
1757 (the name will have any 'host' prefix stripped first).
1759 This behaviour can be modified by the
1763 configuration file. This line can indicate that specific metadata
1764 type should, or should not, be automatically assembled. If an array
1765 is found which is not listed in
1767 and has a metadata format that is denied by the
1769 line, then it will not be assembled.
1772 line can also request that all arrays identified as being for this
1773 homehost should be assembled regardless of their metadata type.
1776 for further details.
1778 Note: Auto assembly cannot be used for assembling and activating some
1779 arrays which are undergoing reshape. In particular as the
1781 cannot be given, any reshape which requires a backup-file to continue
1782 cannot be started by auto assembly. An array which is growing to more
1783 devices and has passed the critical section can be assembled using
1794 .BI \-\-raid\-devices= Z
1798 This usage is similar to
1800 The difference is that it creates an array without a superblock. With
1801 these arrays there is no difference between initially creating the array and
1802 subsequently assembling the array, except that hopefully there is useful
1803 data there in the second case.
1805 The level may raid0, linear, raid1, raid10, multipath, or faulty, or
1806 one of their synonyms. All devices must be listed and the array will
1807 be started once complete. It will often be appropriate to use
1808 .B \-\-assume\-clean
1809 with levels raid1 or raid10.
1820 .BI \-\-raid\-devices= Z
1824 This usage will initialise a new md array, associate some devices with
1825 it, and activate the array.
1827 The named device will normally not exist when
1828 .I "mdadm \-\-create"
1829 is run, but will be created by
1831 once the array becomes active.
1833 As devices are added, they are checked to see if they contain RAID
1834 superblocks or filesystems. They are also checked to see if the variance in
1835 device size exceeds 1%.
1837 If any discrepancy is found, the array will not automatically be run, though
1840 can override this caution.
1842 To create a "degraded" array in which some devices are missing, simply
1843 give the word "\fBmissing\fP"
1844 in place of a device name. This will cause
1846 to leave the corresponding slot in the array empty.
1847 For a RAID4 or RAID5 array at most one slot can be
1848 "\fBmissing\fP"; for a RAID6 array at most two slots.
1849 For a RAID1 array, only one real device needs to be given. All of the
1853 When creating a RAID5 array,
1855 will automatically create a degraded array with an extra spare drive.
1856 This is because building the spare into a degraded array is in general
1857 faster than resyncing the parity on a non-degraded, but not clean,
1858 array. This feature can be overridden with the
1862 When creating an array with version-1 metadata a name for the array is
1864 If this is not given with the
1868 will choose a name based on the last component of the name of the
1869 device being created. So if
1871 is being created, then the name
1876 is being created, then the name
1880 When creating a partition based array, using
1882 with version-1.x metadata, the partition type should be set to
1884 (non fs-data). This type selection allows for greater precision since
1885 using any other [RAID auto-detect (0xFD) or a GNU/Linux partition (0x83)],
1886 might create problems in the event of array recovery through a live cdrom.
1888 A new array will normally get a randomly assigned 128bit UUID which is
1889 very likely to be unique. If you have a specific need, you can choose
1890 a UUID for the array by giving the
1892 option. Be warned that creating two arrays with the same UUID is a
1893 recipe for disaster. Also, using
1895 when creating a v0.90 array will silently override any
1900 .\"option is given, it is not necessary to list any component-devices in this command.
1901 .\"They can be added later, before a
1905 .\"is given, the apparent size of the smallest drive given is used.
1907 If the metadata type supports it (currently only 1.x metadata), space
1908 will be allocated to store a bad block list. This allows a modest
1909 number of bad blocks to be recorded, allowing the drive to remain in
1910 service while only partially functional.
1912 When creating an array within a
1915 can be given either the list of devices to use, or simply the name of
1916 the container. The former case gives control over which devices in
1917 the container will be used for the array. The latter case allows
1919 to automatically choose which devices to use based on how much spare
1922 The General Management options that are valid with
1927 insist on running the array even if some devices look like they might
1932 start the array readonly \(em not supported yet.
1939 .I options... devices...
1942 This usage will allow individual devices in an array to be failed,
1943 removed or added. It is possible to perform multiple operations with
1944 on command. For example:
1946 .B " mdadm /dev/md0 \-f /dev/hda1 \-r /dev/hda1 \-a /dev/hda1"
1952 and will then remove it from the array and finally add it back
1953 in as a spare. However only one md array can be affected by a single
1956 When a device is added to an active array, mdadm checks to see if it
1957 has metadata on it which suggests that it was recently a member of the
1958 array. If it does, it tries to "re\-add" the device. If there have
1959 been no changes since the device was removed, or if the array has a
1960 write-intent bitmap which has recorded whatever changes there were,
1961 then the device will immediately become a full member of the array and
1962 those differences recorded in the bitmap will be resolved.
1972 MISC mode includes a number of distinct operations that
1973 operate on distinct devices. The operations are:
1976 The device is examined to see if it is
1977 (1) an active md array, or
1978 (2) a component of an md array.
1979 The information discovered is reported.
1983 The device should be an active md device.
1985 will display a detailed description of the array.
1989 will cause the output to be less detailed and the format to be
1990 suitable for inclusion in
1994 will normally be 0 unless
1996 failed to get useful information about the device(s); however, if the
1998 option is given, then the exit status will be:
2002 The array is functioning normally.
2005 The array has at least one failed device.
2008 The array has multiple failed devices such that it is unusable.
2011 There was an error while trying to get information about the device.
2015 .B \-\-detail\-platform
2016 Print detail of the platform's RAID capabilities (firmware / hardware
2017 topology). If the metadata is specified with
2021 then the return status will be:
2025 metadata successfully enumerated its platform components on this system
2028 metadata is platform independent
2031 metadata failed to find its platform components on this system
2035 .B \-\-update\-subarray=
2036 If the device is a container and the argument to \-\-update\-subarray
2037 specifies a subarray in the container, then attempt to update the given
2038 superblock field in the subarray. Similar to updating an array in
2039 "assemble" mode, the field to update is selected by
2043 option. Currently only
2049 option updates the subarray name in the metadata, it may not affect the
2050 device node name or the device node symlink until the subarray is
2051 re\-assembled. If updating
2053 would change the UUID of an active subarray this operation is blocked,
2054 and the command will end in an error.
2058 The device should be a component of an md array.
2060 will read the md superblock of the device and display the contents.
2065 is given, then multiple devices that are components of the one array
2066 are grouped together and reported in a single entry suitable
2072 without listing any devices will cause all devices listed in the
2073 config file to be examined.
2077 The devices should be active md arrays which will be deactivated, as
2078 long as they are not currently in use.
2082 This will fully activate a partially assembled md array.
2086 This will mark an active array as read-only, providing that it is
2087 not currently being used.
2093 array back to being read/write.
2097 For all operations except
2100 will cause the operation to be applied to all arrays listed in
2105 causes all devices listed in the config file to be examined.
2108 .BR \-b ", " \-\-brief
2109 Be less verbose. This is used with
2117 gives an intermediate level of verbosity.
2123 .B mdadm \-\-monitor
2124 .I options... devices...
2129 to periodically poll a number of md arrays and to report on any events
2132 will never exit once it decides that there are arrays to be checked,
2133 so it should normally be run in the background.
2135 As well as reporting events,
2137 may move a spare drive from one array to another if they are in the
2142 and if the destination array has a failed drive but no spares.
2144 If any devices are listed on the command line,
2146 will only monitor those devices. Otherwise all arrays listed in the
2147 configuration file will be monitored. Further, if
2149 is given, then any other md devices that appear in
2151 will also be monitored.
2153 The result of monitoring the arrays is the generation of events.
2154 These events are passed to a separate program (if specified) and may
2155 be mailed to a given E-mail address.
2157 When passing events to a program, the program is run once for each event,
2158 and is given 2 or 3 command-line arguments: the first is the
2159 name of the event (see below), the second is the name of the
2160 md device which is affected, and the third is the name of a related
2161 device if relevant (such as a component device that has failed).
2165 is given, then a program or an E-mail address must be specified on the
2166 command line or in the config file. If neither are available, then
2168 will not monitor anything.
2172 will continue monitoring as long as something was found to monitor. If
2173 no program or email is given, then each event is reported to
2176 The different events are:
2180 .B DeviceDisappeared
2181 An md array which previously was configured appears to no longer be
2182 configured. (syslog priority: Critical)
2186 was told to monitor an array which is RAID0 or Linear, then it will
2188 .B DeviceDisappeared
2189 with the extra information
2191 This is because RAID0 and Linear do not support the device-failed,
2192 hot-spare and resync operations which are monitored.
2196 An md array started reconstruction. (syslog priority: Warning)
2202 is a two-digit number (ie. 05, 48). This indicates that rebuild
2203 has passed that many percent of the total. The events are generated
2204 with fixed increment since 0. Increment size may be specified with
2205 a commandline option (default is 20). (syslog priority: Warning)
2209 An md array that was rebuilding, isn't any more, either because it
2210 finished normally or was aborted. (syslog priority: Warning)
2214 An active component device of an array has been marked as
2215 faulty. (syslog priority: Critical)
2219 A spare component device which was being rebuilt to replace a faulty
2220 device has failed. (syslog priority: Critical)
2224 A spare component device which was being rebuilt to replace a faulty
2225 device has been successfully rebuilt and has been made active.
2226 (syslog priority: Info)
2230 A new md array has been detected in the
2232 file. (syslog priority: Info)
2236 A newly noticed array appears to be degraded. This message is not
2239 notices a drive failure which causes degradation, but only when
2241 notices that an array is degraded when it first sees the array.
2242 (syslog priority: Critical)
2246 A spare drive has been moved from one array in a
2250 to another to allow a failed drive to be replaced.
2251 (syslog priority: Info)
2257 has been told, via the config file, that an array should have a certain
2258 number of spare devices, and
2260 detects that it has fewer than this number when it first sees the
2261 array, it will report a
2264 (syslog priority: Warning)
2268 An array was found at startup, and the
2271 (syslog priority: Info)
2281 cause Email to be sent. All events cause the program to be run.
2282 The program is run with two or three arguments: the event
2283 name, the array device and possibly a second device.
2285 Each event has an associated array device (e.g.
2287 and possibly a second device. For
2292 the second device is the relevant component device.
2295 the second device is the array that the spare was moved from.
2299 to move spares from one array to another, the different arrays need to
2300 be labeled with the same
2302 or the spares must be allowed to migrate through matching POLICY domains
2303 in the configuration file. The
2305 name can be any string; it is only necessary that different spare
2306 groups use different names.
2310 detects that an array in a spare group has fewer active
2311 devices than necessary for the complete array, and has no spare
2312 devices, it will look for another array in the same spare group that
2313 has a full complement of working drive and a spare. It will then
2314 attempt to remove the spare from the second drive and add it to the
2316 If the removal succeeds but the adding fails, then it is added back to
2319 If the spare group for a degraded array is not defined,
2321 will look at the rules of spare migration specified by POLICY lines in
2323 and then follow similar steps as above if a matching spare is found.
2326 The GROW mode is used for changing the size or shape of an active
2328 For this to work, the kernel must support the necessary change.
2329 Various types of growth are being added during 2.6 development.
2331 Currently the supported changes include
2333 change the "size" attribute for RAID1, RAID4, RAID5 and RAID6.
2335 increase or decrease the "raid\-devices" attribute of RAID0, RAID1, RAID4,
2338 change the chunk-size and layout of RAID0, RAID4, RAID5 and RAID6.
2340 convert between RAID1 and RAID5, between RAID5 and RAID6, between
2341 RAID0, RAID4, and RAID5, and between RAID0 and RAID10 (in the near-2 mode).
2343 add a write-intent bitmap to any array which supports these bitmaps, or
2344 remove a write-intent bitmap from such an array.
2347 Using GROW on containers is currently supported only for Intel's IMSM
2348 container format. The number of devices in a container can be
2349 increased - which affects all arrays in the container - or an array
2350 in a container can be converted between levels where those levels are
2351 supported by the container, and the conversion is on of those listed
2352 above. Resizing arrays in an IMSM container with
2354 is not yet supported.
2356 Grow functionality (e.g. expand a number of raid devices) for Intel's
2357 IMSM container format has an experimental status. It is guarded by the
2358 .B MDADM_EXPERIMENTAL
2359 environment variable which must be set to '1' for a GROW command to
2361 This is for the following reasons:
2364 Intel's native IMSM check-pointing is not fully tested yet.
2365 This can causes IMSM incompatibility during the grow process: an array
2366 which is growing cannot roam between Microsoft Windows(R) and Linux
2370 Interrupting a grow operation is not recommended, because it
2371 has not been fully tested for Intel's IMSM container format yet.
2374 Note: Intel's native checkpointing doesn't use
2376 option and it is transparent for assembly feature.
2379 Normally when an array is built the "size" is taken from the smallest
2380 of the drives. If all the small drives in an arrays are, one at a
2381 time, removed and replaced with larger drives, then you could have an
2382 array of large drives with only a small amount used. In this
2383 situation, changing the "size" with "GROW" mode will allow the extra
2384 space to start being used. If the size is increased in this way, a
2385 "resync" process will start to make sure the new parts of the array
2388 Note that when an array changes size, any filesystem that may be
2389 stored in the array will not automatically grow or shrink to use or
2390 vacate the space. The
2391 filesystem will need to be explicitly told to use the extra space
2392 after growing, or to reduce its size
2394 to shrinking the array.
2396 Also the size of an array cannot be changed while it has an active
2397 bitmap. If an array has a bitmap, it must be removed before the size
2398 can be changed. Once the change is complete a new bitmap can be created.
2400 .SS RAID\-DEVICES CHANGES
2402 A RAID1 array can work with any number of devices from 1 upwards
2403 (though 1 is not very useful). There may be times which you want to
2404 increase or decrease the number of active devices. Note that this is
2405 different to hot-add or hot-remove which changes the number of
2408 When reducing the number of devices in a RAID1 array, the slots which
2409 are to be removed from the array must already be vacant. That is, the
2410 devices which were in those slots must be failed and removed.
2412 When the number of devices is increased, any hot spares that are
2413 present will be activated immediately.
2415 Changing the number of active devices in a RAID5 or RAID6 is much more
2416 effort. Every block in the array will need to be read and written
2417 back to a new location. From 2.6.17, the Linux Kernel is able to
2418 increase the number of devices in a RAID5 safely, including restarting
2419 an interrupted "reshape". From 2.6.31, the Linux Kernel is able to
2420 increase or decrease the number of devices in a RAID5 or RAID6.
2422 From 2.6.35, the Linux Kernel is able to convert a RAID0 in to a RAID4
2425 uses this functionality and the ability to add
2426 devices to a RAID4 to allow devices to be added to a RAID0. When
2427 requested to do this,
2429 will convert the RAID0 to a RAID4, add the necessary disks and make
2430 the reshape happen, and then convert the RAID4 back to RAID0.
2432 When decreasing the number of devices, the size of the array will also
2433 decrease. If there was data in the array, it could get destroyed and
2434 this is not reversible, so you should firstly shrink the filesystem on
2435 the array to fit within the new size. To help prevent accidents,
2437 requires that the size of the array be decreased first with
2438 .BR "mdadm --grow --array-size" .
2439 This is a reversible change which simply makes the end of the array
2440 inaccessible. The integrity of any data can then be checked before
2441 the non-reversible reduction in the number of devices is request.
2443 When relocating the first few stripes on a RAID5 or RAID6, it is not
2444 possible to keep the data on disk completely consistent and
2445 crash-proof. To provide the required safety, mdadm disables writes to
2446 the array while this "critical section" is reshaped, and takes a
2447 backup of the data that is in that section. For grows, this backup may be
2448 stored in any spare devices that the array has, however it can also be
2449 stored in a separate file specified with the
2451 option, and is required to be specified for shrinks, RAID level
2452 changes and layout changes. If this option is used, and the system
2453 does crash during the critical period, the same file must be passed to
2455 to restore the backup and reassemble the array. When shrinking rather
2456 than growing the array, the reshape is done from the end towards the
2457 beginning, so the "critical section" is at the end of the reshape.
2461 Changing the RAID level of any array happens instantaneously. However
2462 in the RAID5 to RAID6 case this requires a non-standard layout of the
2463 RAID6 data, and in the RAID6 to RAID5 case that non-standard layout is
2464 required before the change can be accomplished. So while the level
2465 change is instant, the accompanying layout change can take quite a
2468 is required. If the array is not simultaneously being grown or
2469 shrunk, so that the array size will remain the same - for example,
2470 reshaping a 3-drive RAID5 into a 4-drive RAID6 - the backup file will
2471 be used not just for a "cricital section" but throughout the reshape
2472 operation, as described below under LAYOUT CHANGES.
2474 .SS CHUNK-SIZE AND LAYOUT CHANGES
2476 Changing the chunk-size of layout without also changing the number of
2477 devices as the same time will involve re-writing all blocks in-place.
2478 To ensure against data loss in the case of a crash, a
2480 must be provided for these changes. Small sections of the array will
2481 be copied to the backup file while they are being rearranged. This
2482 means that all the data is copied twice, once to the backup and once
2483 to the new layout on the array, so this type of reshape will go very
2486 If the reshape is interrupted for any reason, this backup file must be
2488 .B "mdadm --assemble"
2489 so the array can be reassembled. Consequently the file cannot be
2490 stored on the device being reshaped.
2495 A write-intent bitmap can be added to, or removed from, an active
2496 array. Either internal bitmaps, or bitmaps stored in a separate file,
2497 can be added. Note that if you add a bitmap stored in a file which is
2498 in a filesystem that is on the RAID array being affected, the system
2499 will deadlock. The bitmap must be on a separate filesystem.
2501 .SH INCREMENTAL MODE
2505 .B mdadm \-\-incremental
2511 .B mdadm \-\-incremental \-\-fail
2515 .B mdadm \-\-incremental \-\-rebuild\-map
2518 .B mdadm \-\-incremental \-\-run \-\-scan
2521 This mode is designed to be used in conjunction with a device
2522 discovery system. As devices are found in a system, they can be
2524 .B "mdadm \-\-incremental"
2525 to be conditionally added to an appropriate array.
2527 Conversely, it can also be used with the
2529 flag to do just the opposite and find whatever array a particular device
2530 is part of and remove the device from that array.
2532 If the device passed is a
2534 device created by a previous call to
2536 then rather than trying to add that device to an array, all the arrays
2537 described by the metadata of the container will be started.
2540 performs a number of tests to determine if the device is part of an
2541 array, and which array it should be part of. If an appropriate array
2542 is found, or can be created,
2544 adds the device to the array and conditionally starts the array.
2548 will normally only add devices to an array which were previously working
2549 (active or spare) parts of that array. The support for automatic
2550 inclusion of a new drive as a spare in some array requires
2551 a configuration through POLICY in config file.
2555 makes are as follow:
2557 Is the device permitted by
2559 That is, is it listed in a
2561 line in that file. If
2563 is absent then the default it to allow any device. Similar if
2565 contains the special word
2567 then any device is allowed. Otherwise the device name given to
2569 must match one of the names or patterns in a
2574 Does the device have a valid md superblock? If a specific metadata
2575 version is requested with
2579 then only that style of metadata is accepted, otherwise
2581 finds any known version of metadata. If no
2583 metadata is found, the device may be still added to an array
2584 as a spare if POLICY allows.
2588 Does the metadata match an expected array?
2589 The metadata can match in two ways. Either there is an array listed
2592 which identifies the array (either by UUID, by name, by device list,
2593 or by minor-number), or the array was created with a
2599 or on the command line.
2602 is not able to positively identify the array as belonging to the
2603 current host, the device will be rejected.
2608 keeps a list of arrays that it has partially assembled in
2610 If no array exists which matches
2611 the metadata on the new device,
2613 must choose a device name and unit number. It does this based on any
2616 or any name information stored in the metadata. If this name
2617 suggests a unit number, that number will be used, otherwise a free
2618 unit number will be chosen. Normally
2620 will prefer to create a partitionable array, however if the
2624 suggests that a non-partitionable array is preferred, that will be
2627 If the array is not found in the config file and its metadata does not
2628 identify it as belonging to the "homehost", then
2630 will choose a name for the array which is certain not to conflict with
2631 any array which does belong to this host. It does this be adding an
2632 underscore and a small number to the name preferred by the metadata.
2634 Once an appropriate array is found or created and the device is added,
2636 must decide if the array is ready to be started. It will
2637 normally compare the number of available (non-spare) devices to the
2638 number of devices that the metadata suggests need to be active. If
2639 there are at least that many, the array will be started. This means
2640 that if any devices are missing the array will not be restarted.
2646 in which case the array will be run as soon as there are enough
2647 devices present for the data to be accessible. For a RAID1, that
2648 means one device will start the array. For a clean RAID5, the array
2649 will be started as soon as all but one drive is present.
2651 Note that neither of these approaches is really ideal. If it can
2652 be known that all device discovery has completed, then
2656 can be run which will try to start all arrays that are being
2657 incrementally assembled. They are started in "read-auto" mode in
2658 which they are read-only until the first write request. This means
2659 that no metadata updates are made and no attempt at resync or recovery
2660 happens. Further devices that are found before the first write can
2661 still be added safely.
2664 This section describes environment variables that affect how mdadm
2669 Setting this value to 1 will prevent mdadm from automatically launching
2670 mdmon. This variable is intended primarily for debugging mdadm/mdmon.
2676 does not create any device nodes in /dev, but leaves that task to
2680 appears not to be configured, or if this environment variable is set
2683 will create and devices that are needed.
2687 .B " mdadm \-\-query /dev/name-of-device"
2689 This will find out if a given device is a RAID array, or is part of
2690 one, and will provide brief information about the device.
2692 .B " mdadm \-\-assemble \-\-scan"
2694 This will assemble and start all arrays listed in the standard config
2695 file. This command will typically go in a system startup file.
2697 .B " mdadm \-\-stop \-\-scan"
2699 This will shut down all arrays that can be shut down (i.e. are not
2700 currently in use). This will typically go in a system shutdown script.
2702 .B " mdadm \-\-follow \-\-scan \-\-delay=120"
2704 If (and only if) there is an Email address or program given in the
2705 standard config file, then
2706 monitor the status of all arrays listed in that file by
2707 polling them ever 2 minutes.
2709 .B " mdadm \-\-create /dev/md0 \-\-level=1 \-\-raid\-devices=2 /dev/hd[ac]1"
2711 Create /dev/md0 as a RAID1 array consisting of /dev/hda1 and /dev/hdc1.
2714 .B " echo 'DEVICE /dev/hd*[0\-9] /dev/sd*[0\-9]' > mdadm.conf"
2716 .B " mdadm \-\-detail \-\-scan >> mdadm.conf"
2718 This will create a prototype config file that describes currently
2719 active arrays that are known to be made from partitions of IDE or SCSI drives.
2720 This file should be reviewed before being used as it may
2721 contain unwanted detail.
2723 .B " echo 'DEVICE /dev/hd[a\-z] /dev/sd*[a\-z]' > mdadm.conf"
2725 .B " mdadm \-\-examine \-\-scan \-\-config=mdadm.conf >> mdadm.conf"
2727 This will find arrays which could be assembled from existing IDE and
2728 SCSI whole drives (not partitions), and store the information in the
2729 format of a config file.
2730 This file is very likely to contain unwanted detail, particularly
2733 entries. It should be reviewed and edited before being used as an
2736 .B " mdadm \-\-examine \-\-brief \-\-scan \-\-config=partitions"
2738 .B " mdadm \-Ebsc partitions"
2740 Create a list of devices by reading
2741 .BR /proc/partitions ,
2742 scan these for RAID superblocks, and printout a brief listing of all
2745 .B " mdadm \-Ac partitions \-m 0 /dev/md0"
2747 Scan all partitions and devices listed in
2748 .BR /proc/partitions
2751 out of all such devices with a RAID superblock with a minor number of 0.
2753 .B " mdadm \-\-monitor \-\-scan \-\-daemonise > /run/mdadm/mon.pid"
2755 If config file contains a mail address or alert program, run mdadm in
2756 the background in monitor mode monitoring all md devices. Also write
2757 pid of mdadm daemon to
2758 .BR /run/mdadm/mon.pid .
2760 .B " mdadm \-Iq /dev/somedevice"
2762 Try to incorporate newly discovered device into some array as
2765 .B " mdadm \-\-incremental \-\-rebuild\-map \-\-run \-\-scan"
2767 Rebuild the array map from any current arrays, and then start any that
2770 .B " mdadm /dev/md4 --fail detached --remove detached"
2772 Any devices which are components of /dev/md4 will be marked as faulty
2773 and then remove from the array.
2775 .B " mdadm --grow /dev/md4 --level=6 --backup-file=/root/backup-md4"
2779 which is currently a RAID5 array will be converted to RAID6. There
2780 should normally already be a spare drive attached to the array as a
2781 RAID6 needs one more drive than a matching RAID5.
2783 .B " mdadm --create /dev/md/ddf --metadata=ddf --raid-disks 6 /dev/sd[a-f]"
2785 Create a DDF array over 6 devices.
2787 .B " mdadm --create /dev/md/home -n3 -l5 -z 30000000 /dev/md/ddf"
2789 Create a RAID5 array over any 3 devices in the given DDF set. Use
2790 only 30 gigabytes of each device.
2792 .B " mdadm -A /dev/md/ddf1 /dev/sd[a-f]"
2794 Assemble a pre-exist ddf array.
2796 .B " mdadm -I /dev/md/ddf1"
2798 Assemble all arrays contained in the ddf array, assigning names as
2801 .B " mdadm \-\-create \-\-help"
2803 Provide help about the Create mode.
2805 .B " mdadm \-\-config \-\-help"
2807 Provide help about the format of the config file.
2809 .B " mdadm \-\-help"
2811 Provide general help.
2821 lists all active md devices with information about them.
2823 uses this to find arrays when
2825 is given in Misc mode, and to monitor array reconstruction
2830 The config file lists which devices may be scanned to see if
2831 they contain MD super block, and gives identifying information
2832 (e.g. UUID) about known MD arrays. See
2839 mode is used, this file gets a list of arrays currently being created.
2844 understand two sorts of names for array devices.
2846 The first is the so-called 'standard' format name, which matches the
2847 names used by the kernel and which appear in
2850 The second sort can be freely chosen, but must reside in
2852 When giving a device name to
2854 to create or assemble an array, either full path name such as
2858 can be given, or just the suffix of the second sort of name, such as
2864 chooses device names during auto-assembly or incremental assembly, it
2865 will sometimes add a small sequence number to the end of the name to
2866 avoid conflicted between multiple arrays that have the same name. If
2868 can reasonably determine that the array really is meant for this host,
2869 either by a hostname in the metadata, or by the presence of the array
2872 then it will leave off the suffix if possible.
2873 Also if the homehost is specified as
2876 will only use a suffix if a different array of the same name already
2877 exists or is listed in the config file.
2879 The standard names for non-partitioned arrays (the only sort of md
2880 array available in 2.4 and earlier) are of the form
2884 where NN is a number.
2885 The standard names for partitionable arrays (as available from 2.6
2886 onwards) are of the form
2890 Partition numbers should be indicated by added "pMM" to these, thus "/dev/md/d1p2".
2892 From kernel version, 2.6.28 the "non-partitioned array" can actually
2893 be partitioned. So the "md_dNN" names are no longer needed, and
2894 partitions such as "/dev/mdNNpXX" are possible.
2898 was previously known as
2902 is completely separate from the
2904 package, and does not use the
2906 configuration file at all.
2909 For further information on mdadm usage, MD and the various levels of
2912 .B http://raid.wiki.kernel.org/
2914 (based upon Jakob \(/Ostergaard's Software\-RAID.HOWTO)
2916 .\"for new releases of the RAID driver check out:
2919 .\".UR ftp://ftp.kernel.org/pub/linux/kernel/people/mingo/raid-patches
2920 .\"ftp://ftp.kernel.org/pub/linux/kernel/people/mingo/raid-patches
2925 .\".UR http://www.cse.unsw.edu.au/~neilb/patches/linux-stable/
2926 .\"http://www.cse.unsw.edu.au/~neilb/patches/linux-stable/
2929 The latest version of
2931 should always be available from
2933 .B http://www.kernel.org/pub/linux/utils/raid/mdadm/
projects / thirdparty / mdadm.git / blob