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
222 then the MANAGE mode is assumed.
223 Anything other than these will cause the
227 .SH Options that are not mode-specific are:
230 .BR \-h ", " \-\-help
231 Display general help message or, after one of the above options, a
232 mode-specific help message.
236 Display more detailed help about command line parsing and some commonly
240 .BR \-V ", " \-\-version
241 Print version information for mdadm.
244 .BR \-v ", " \-\-verbose
245 Be more verbose about what is happening. This can be used twice to be
247 The extra verbosity currently only affects
248 .B \-\-detail \-\-scan
250 .BR "\-\-examine \-\-scan" .
253 .BR \-q ", " \-\-quiet
254 Avoid printing purely informative messages. With this,
256 will be silent unless there is something really important to report.
260 .BR \-f ", " \-\-force
261 Be more forceful about certain operations. See the various modes for
262 the exact meaning of this option in different contexts.
265 .BR \-c ", " \-\-config=
266 Specify the config file. Default is to use
267 .BR /etc/mdadm.conf ,
268 or if that is missing then
269 .BR /etc/mdadm/mdadm.conf .
270 If the config file given is
272 then nothing will be read, but
274 will act as though the config file contained exactly
275 .B "DEVICE partitions containers"
278 to find a list of devices to scan, and
280 to find a list of containers to examine.
283 is given for the config file, then
285 will act as though the config file were empty.
288 .BR \-s ", " \-\-scan
291 for missing information.
292 In general, this option gives
294 permission to get any missing information (like component devices,
295 array devices, array identities, and alert destination) from the
296 configuration file (see previous option);
297 one exception is MISC mode when using
303 says to get a list of array devices from
307 .BR \-e ", " \-\-metadata=
308 Declare the style of RAID metadata (superblock) to be used. The
309 default is {DEFAULT_METADATA} for
311 and to guess for other operations.
312 The default can be overridden by setting the
321 .ie '{DEFAULT_METADATA}'0.90'
322 .IP "0, 0.90, default"
325 Use the original 0.90 format superblock. This format limits arrays to
326 28 component devices and limits component devices of levels 1 and
327 greater to 2 terabytes. It is also possible for there to be confusion
328 about whether the superblock applies to a whole device or just the
329 last partition, if that partition starts on a 64K boundary.
330 .ie '{DEFAULT_METADATA}'0.90'
331 .IP "1, 1.0, 1.1, 1.2"
333 .IP "1, 1.0, 1.1, 1.2 default"
334 Use the new version-1 format superblock. This has fewer restrictions.
335 It can easily be moved between hosts with different endian-ness, and a
336 recovery operation can be checkpointed and restarted. The different
337 sub-versions store the superblock at different locations on the
338 device, either at the end (for 1.0), at the start (for 1.1) or 4K from
339 the start (for 1.2). "1" is equivalent to "1.2" (the commonly
340 preferred 1.x format).
341 'if '{DEFAULT_METADATA}'1.2' "default" is equivalent to "1.2".
343 Use the "Industry Standard" DDF (Disk Data Format) format defined by
345 When creating a DDF array a
347 will be created, and normal arrays can be created in that container.
349 Use the Intel(R) Matrix Storage Manager metadata format. This creates a
351 which is managed in a similar manner to DDF, and is supported by an
352 option-rom on some platforms:
354 .B http://www.intel.com/design/chipsets/matrixstorage_sb.htm
360 This will override any
362 setting in the config file and provides the identity of the host which
363 should be considered the home for any arrays.
365 When creating an array, the
367 will be recorded in the metadata. For version-1 superblocks, it will
368 be prefixed to the array name. For version-0.90 superblocks, part of
369 the SHA1 hash of the hostname will be stored in the later half of the
372 When reporting information about an array, any array which is tagged
373 for the given homehost will be reported as such.
375 When using Auto-Assemble, only arrays tagged for the given homehost
376 will be allowed to use 'local' names (i.e. not ending in '_' followed
377 by a digit string). See below under
378 .BR "Auto Assembly" .
384 needs to print the name for a device it normally finds the name in
386 which refers to the device and is shortest. When a path component is
390 will prefer a longer name if it contains that component. For example
391 .B \-\-prefer=by-uuid
392 will prefer a name in a subdirectory of
397 This functionality is currently only provided by
402 .SH For create, build, or grow:
405 .BR \-n ", " \-\-raid\-devices=
406 Specify the number of active devices in the array. This, plus the
407 number of spare devices (see below) must equal the number of
409 (including "\fBmissing\fP" devices)
410 that are listed on the command line for
412 Setting a value of 1 is probably
413 a mistake and so requires that
415 be specified first. A value of 1 will then be allowed for linear,
416 multipath, RAID0 and RAID1. It is never allowed for RAID4, RAID5 or RAID6.
418 This number can only be changed using
420 for RAID1, RAID4, RAID5 and RAID6 arrays, and only on kernels which provide
421 the necessary support.
424 .BR \-x ", " \-\-spare\-devices=
425 Specify the number of spare (eXtra) devices in the initial array.
426 Spares can also be added
427 and removed later. The number of component devices listed
428 on the command line must equal the number of RAID devices plus the
429 number of spare devices.
432 .BR \-z ", " \-\-size=
433 Amount (in Kibibytes) of space to use from each drive in RAID levels 1/4/5/6.
434 This must be a multiple of the chunk size, and must leave about 128Kb
435 of space at the end of the drive for the RAID superblock.
436 If this is not specified
437 (as it normally is not) the smallest drive (or partition) sets the
438 size, though if there is a variance among the drives of greater than 1%, a warning is
441 A suffix of 'M' or 'G' can be given to indicate Megabytes or
442 Gigabytes respectively.
444 Sometimes a replacement drive can be a little smaller than the
445 original drives though this should be minimised by IDEMA standards.
446 Such a replacement drive will be rejected by
448 To guard against this it can be useful to set the initial size
449 slightly smaller than the smaller device with the aim that it will
450 still be larger than any replacement.
452 This value can be set with
454 for RAID level 1/4/5/6 though
456 based arrays such as those with IMSM metadata may not be able to
458 If the array was created with a size smaller than the currently
459 active drives, the extra space can be accessed using
461 The size can be given as
463 which means to choose the largest size that fits on all current drives.
465 Before reducing the size of the array (with
466 .BR "\-\-grow \-\-size=" )
467 you should make sure that space isn't needed. If the device holds a
468 filesystem, you would need to resize the filesystem to use less space.
470 After reducing the array size you should check that the data stored in
471 the device is still available. If the device holds a filesystem, then
472 an 'fsck' of the filesystem is a minimum requirement. If there are
473 problems the array can be made bigger again with no loss with another
474 .B "\-\-grow \-\-size="
477 This value cannot be used when creating a
479 such as with DDF and IMSM metadata, though it perfectly valid when
480 creating an array inside a container.
483 .BR \-Z ", " \-\-array\-size=
484 This is only meaningful with
486 and its effect is not persistent: when the array is stopped and
487 restarted the default array size will be restored.
489 Setting the array-size causes the array to appear smaller to programs
490 that access the data. This is particularly needed before reshaping an
491 array so that it will be smaller. As the reshape is not reversible,
492 but setting the size with
494 is, it is required that the array size is reduced as appropriate
495 before the number of devices in the array is reduced.
497 Before reducing the size of the array you should make sure that space
498 isn't needed. If the device holds a filesystem, you would need to
499 resize the filesystem to use less space.
501 After reducing the array size you should check that the data stored in
502 the device is still available. If the device holds a filesystem, then
503 an 'fsck' of the filesystem is a minimum requirement. If there are
504 problems the array can be made bigger again with no loss with another
505 .B "\-\-grow \-\-array\-size="
508 A suffix of 'M' or 'G' can be given to indicate Megabytes or
509 Gigabytes respectively.
512 restores the apparent size of the array to be whatever the real
513 amount of available space is.
516 .BR \-c ", " \-\-chunk=
517 Specify chunk size of kibibytes. The default when creating an
518 array is 512KB. To ensure compatibility with earlier versions, the
519 default when Building and array with no persistent metadata is 64KB.
520 This is only meaningful for RAID0, RAID4, RAID5, RAID6, and RAID10.
522 RAID4, RAID5, RAID6, and RAID10 require the chunk size to be a power
523 of 2. In any case it must be a multiple of 4KB.
525 A suffix of 'M' or 'G' can be given to indicate Megabytes or
526 Gigabytes respectively.
530 Specify rounding factor for a Linear array. The size of each
531 component will be rounded down to a multiple of this size.
532 This is a synonym for
534 but highlights the different meaning for Linear as compared to other
535 RAID levels. The default is 64K if a kernel earlier than 2.6.16 is in
536 use, and is 0K (i.e. no rounding) in later kernels.
539 .BR \-l ", " \-\-level=
540 Set RAID level. When used with
542 options are: linear, raid0, 0, stripe, raid1, 1, mirror, raid4, 4,
543 raid5, 5, raid6, 6, raid10, 10, multipath, mp, faulty, container.
544 Obviously some of these are synonymous.
548 metadata type is requested, only the
550 level is permitted, and it does not need to be explicitly given.
554 only linear, stripe, raid0, 0, raid1, multipath, mp, and faulty are valid.
558 to change the RAID level in some cases. See LEVEL CHANGES below.
561 .BR \-p ", " \-\-layout=
562 This option configures the fine details of data layout for RAID5, RAID6,
563 and RAID10 arrays, and controls the failure modes for
566 The layout of the RAID5 parity block can be one of
567 .BR left\-asymmetric ,
568 .BR left\-symmetric ,
569 .BR right\-asymmetric ,
570 .BR right\-symmetric ,
571 .BR la ", " ra ", " ls ", " rs .
573 .BR left\-symmetric .
575 It is also possible to cause RAID5 to use a RAID4-like layout by
581 Finally for RAID5 there are DDF\-compatible layouts,
582 .BR ddf\-zero\-restart ,
583 .BR ddf\-N\-restart ,
585 .BR ddf\-N\-continue .
587 These same layouts are available for RAID6. There are also 4 layouts
588 that will provide an intermediate stage for converting between RAID5
589 and RAID6. These provide a layout which is identical to the
590 corresponding RAID5 layout on the first N\-1 devices, and has the 'Q'
591 syndrome (the second 'parity' block used by RAID6) on the last device.
593 .BR left\-symmetric\-6 ,
594 .BR right\-symmetric\-6 ,
595 .BR left\-asymmetric\-6 ,
596 .BR right\-asymmetric\-6 ,
598 .BR parity\-first\-6 .
600 When setting the failure mode for level
603 .BR write\-transient ", " wt ,
604 .BR read\-transient ", " rt ,
605 .BR write\-persistent ", " wp ,
606 .BR read\-persistent ", " rp ,
608 .BR read\-fixable ", " rf ,
609 .BR clear ", " flush ", " none .
611 Each failure mode can be followed by a number, which is used as a period
612 between fault generation. Without a number, the fault is generated
613 once on the first relevant request. With a number, the fault will be
614 generated after that many requests, and will continue to be generated
615 every time the period elapses.
617 Multiple failure modes can be current simultaneously by using the
619 option to set subsequent failure modes.
621 "clear" or "none" will remove any pending or periodic failure modes,
622 and "flush" will clear any persistent faults.
624 Finally, the layout options for RAID10 are one of 'n', 'o' or 'f' followed
625 by a small number. The default is 'n2'. The supported options are:
628 signals 'near' copies. Multiple copies of one data block are at
629 similar offsets in different devices.
632 signals 'offset' copies. Rather than the chunks being duplicated
633 within a stripe, whole stripes are duplicated but are rotated by one
634 device so duplicate blocks are on different devices. Thus subsequent
635 copies of a block are in the next drive, and are one chunk further
640 (multiple copies have very different offsets).
641 See md(4) for more detail about 'near', 'offset', and 'far'.
643 The number is the number of copies of each datablock. 2 is normal, 3
644 can be useful. This number can be at most equal to the number of
645 devices in the array. It does not need to divide evenly into that
646 number (e.g. it is perfectly legal to have an 'n2' layout for an array
647 with an odd number of devices).
649 When an array is converted between RAID5 and RAID6 an intermediate
650 RAID6 layout is used in which the second parity block (Q) is always on
651 the last device. To convert a RAID5 to RAID6 and leave it in this new
652 layout (which does not require re-striping) use
653 .BR \-\-layout=preserve .
654 This will try to avoid any restriping.
656 The converse of this is
657 .B \-\-layout=normalise
658 which will change a non-standard RAID6 layout into a more standard
665 (thus explaining the p of
669 .BR \-b ", " \-\-bitmap=
670 Specify a file to store a write-intent bitmap in. The file should not
673 is also given. The same file should be provided
674 when assembling the array. If the word
676 is given, then the bitmap is stored with the metadata on the array,
677 and so is replicated on all devices. If the word
681 mode, then any bitmap that is present is removed.
683 To help catch typing errors, the filename must contain at least one
684 slash ('/') if it is a real file (not 'internal' or 'none').
686 Note: external bitmaps are only known to work on ext2 and ext3.
687 Storing bitmap files on other filesystems may result in serious problems.
689 When creating an array on devices which are 100G or larger,
691 automatically adds an internal bitmap as it will usually be
692 beneficial. This can be suppressed with
693 .B "\-\-bitmap=none".
696 .BR \-\-bitmap\-chunk=
697 Set the chunksize of the bitmap. Each bit corresponds to that many
698 Kilobytes of storage.
699 When using a file based bitmap, the default is to use the smallest
700 size that is at-least 4 and requires no more than 2^21 chunks.
703 bitmap, the chunksize defaults to 64Meg, or larger if necessary to
704 fit the bitmap into the available space.
706 A suffix of 'M' or 'G' can be given to indicate Megabytes or
707 Gigabytes respectively.
710 .BR \-W ", " \-\-write\-mostly
711 subsequent devices listed in a
716 command will be flagged as 'write-mostly'. This is valid for RAID1
717 only and means that the 'md' driver will avoid reading from these
718 devices if at all possible. This can be useful if mirroring over a
722 .BR \-\-write\-behind=
723 Specify that write-behind mode should be enabled (valid for RAID1
724 only). If an argument is specified, it will set the maximum number
725 of outstanding writes allowed. The default value is 256.
726 A write-intent bitmap is required in order to use write-behind
727 mode, and write-behind is only attempted on drives marked as
731 .BR \-\-assume\-clean
734 that the array pre-existed and is known to be clean. It can be useful
735 when trying to recover from a major failure as you can be sure that no
736 data will be affected unless you actually write to the array. It can
737 also be used when creating a RAID1 or RAID10 if you want to avoid the
738 initial resync, however this practice \(em while normally safe \(em is not
739 recommended. Use this only if you really know what you are doing.
741 When the devices that will be part of a new array were filled
742 with zeros before creation the operator knows the array is
743 actually clean. If that is the case, such as after running
744 badblocks, this argument can be used to tell mdadm the
745 facts the operator knows.
747 When an array is resized to a larger size with
748 .B "\-\-grow \-\-size="
749 the new space is normally resynced in that same way that the whole
750 array is resynced at creation. From Linux version 3.0,
752 can be used with that command to avoid the automatic resync.
755 .BR \-\-backup\-file=
758 is used to increase the number of raid-devices in a RAID5 or RAID6 if
759 there are no spare devices available, or to shrink, change RAID level
760 or layout. See the GROW MODE section below on RAID\-DEVICES CHANGES.
761 The file must be stored on a separate device, not on the RAID array
766 Arrays with 1.x metadata can leave a gap between the start of the
767 device and the start of array data. This gap can be used for various
768 metadata. The start of data is known as the
770 Normally an appropriate data offset is computed automatically.
771 However it can be useful to set it explicitly such as when re-creating
772 an array which was originally created using a different version of
774 which computed a different offset.
776 Setting the offset explicitly over-rides the default. The value given
777 is in Kilobytes unless an 'M' or 'G' suffix is given.
781 can also be used with
783 for some RAID levels (initially on RAID10). This allows the
784 data\-offset to be changed as part of the reshape process. When the
785 data offset is changed, no backup file is required as the difference
786 in offsets is used to provide the same functionality.
788 When the new offset is earlier than the old offset, the number of
789 devices in the array cannot shrink. When it is after the old offset,
790 the number of devices in the array cannot increase.
792 When creating an array,
796 In the case each member device is expected to have a offset appended
797 to the name, separated by a colon. This makes it possible to recreate
798 exactly an array which has varying data offsets (as can happen when
799 different versions of
801 are used to add different devices).
805 This option is complementary to the
806 .B \-\-freeze-reshape
807 option for assembly. It is needed when
809 operation is interrupted and it is not restarted automatically due to
810 .B \-\-freeze-reshape
811 usage during array assembly. This option is used together with
815 ) command and device for a pending reshape to be continued.
816 All parameters required for reshape continuation will be read from array metadata.
820 .BR \-\-backup\-file=
821 option to be set, continuation option will require to have exactly the same
822 backup file given as well.
824 Any other parameter passed together with
826 option will be ignored.
829 .BR \-N ", " \-\-name=
832 for the array. This is currently only effective when creating an
833 array with a version-1 superblock, or an array in a DDF container.
834 The name is a simple textual string that can be used to identify array
835 components when assembling. If name is needed but not specified, it
836 is taken from the basename of the device that is being created.
848 run the array, even if some of the components
849 appear to be active in another array or filesystem. Normally
851 will ask for confirmation before including such components in an
852 array. This option causes that question to be suppressed.
855 .BR \-f ", " \-\-force
858 accept the geometry and layout specified without question. Normally
860 will not allow creation of an array with only one device, and will try
861 to create a RAID5 array with one missing drive (as this makes the
862 initial resync work faster). With
865 will not try to be so clever.
868 .BR \-o ", " \-\-readonly
871 rather than read-write as normal. No writes will be allowed to the
872 array, and no resync, recovery, or reshape will be started.
875 .BR \-a ", " "\-\-auto{=yes,md,mdp,part,p}{NN}"
876 Instruct mdadm how to create the device file if needed, possibly allocating
877 an unused minor number. "md" causes a non-partitionable array
878 to be used (though since Linux 2.6.28, these array devices are in fact
879 partitionable). "mdp", "part" or "p" causes a partitionable array (2.6 and
880 later) to be used. "yes" requires the named md device to have
881 a 'standard' format, and the type and minor number will be determined
882 from this. With mdadm 3.0, device creation is normally left up to
884 so this option is unlikely to be needed.
885 See DEVICE NAMES below.
887 The argument can also come immediately after
892 is not given on the command line or in the config file, then
898 is also given, then any
900 entries in the config file will override the
902 instruction given on the command line.
904 For partitionable arrays,
906 will create the device file for the whole array and for the first 4
907 partitions. A different number of partitions can be specified at the
908 end of this option (e.g.
910 If the device name ends with a digit, the partition names add a 'p',
912 .IR /dev/md/home1p3 .
913 If there is no trailing digit, then the partition names just have a
915 .IR /dev/md/scratch3 .
917 If the md device name is in a 'standard' format as described in DEVICE
918 NAMES, then it will be created, if necessary, with the appropriate
919 device number based on that name. If the device name is not in one of these
920 formats, then a unused device number will be allocated. The device
921 number will be considered unused if there is no active array for that
922 number, and there is no entry in /dev for that number and with a
923 non-standard name. Names that are not in 'standard' format are only
924 allowed in "/dev/md/".
926 This is meaningful with
932 .BR \-a ", " "\-\-add"
933 This option can be used in Grow mode in two cases.
935 If the target array is a Linear array, then
937 can be used to add one or more devices to the array. They
938 are simply catenated on to the end of the array. Once added, the
939 devices cannot be removed.
943 option is being used to increase the number of devices in an array,
946 can be used to add some extra devices to be included in the array.
947 In most cases this is not needed as the extra devices can be added as
948 spares first, and then the number of raid-disks can be changed.
949 However for RAID0, it is not possible to add spares. So to increase
950 the number of devices in a RAID0, it is necessary to set the new
951 number of devices, and to add the new devices, in the same command.
956 .BR \-u ", " \-\-uuid=
957 uuid of array to assemble. Devices which don't have this uuid are
961 .BR \-m ", " \-\-super\-minor=
962 Minor number of device that array was created for. Devices which
963 don't have this minor number are excluded. If you create an array as
964 /dev/md1, then all superblocks will contain the minor number 1, even if
965 the array is later assembled as /dev/md2.
967 Giving the literal word "dev" for
971 to use the minor number of the md device that is being assembled.
974 .B \-\-super\-minor=dev
975 will look for super blocks with a minor number of 0.
978 is only relevant for v0.90 metadata, and should not normally be used.
984 .BR \-N ", " \-\-name=
985 Specify the name of the array to assemble. This must be the name
986 that was specified when creating the array. It must either match
987 the name stored in the superblock exactly, or it must match
990 prefixed to the start of the given name.
993 .BR \-f ", " \-\-force
994 Assemble the array even if the metadata on some devices appears to be
997 cannot find enough working devices to start the array, but can find
998 some devices that are recorded as having failed, then it will mark
999 those devices as working so that the array can be started.
1000 An array which requires
1002 to be started may contain data corruption. Use it carefully.
1005 .BR \-R ", " \-\-run
1006 Attempt to start the array even if fewer drives were given than were
1007 present last time the array was active. Normally if not all the
1008 expected drives are found and
1010 is not used, then the array will be assembled but not started.
1013 an attempt will be made to start it anyway.
1017 This is the reverse of
1019 in that it inhibits the startup of array unless all expected drives
1020 are present. This is only needed with
1022 and can be used if the physical connections to devices are
1023 not as reliable as you would like.
1026 .BR \-a ", " "\-\-auto{=no,yes,md,mdp,part}"
1027 See this option under Create and Build options.
1030 .BR \-b ", " \-\-bitmap=
1031 Specify the bitmap file that was given when the array was created. If
1034 bitmap, there is no need to specify this when assembling the array.
1037 .BR \-\-backup\-file=
1040 was used while reshaping an array (e.g. changing number of devices or
1041 chunk size) and the system crashed during the critical section, then the same
1043 must be presented to
1045 to allow possibly corrupted data to be restored, and the reshape
1049 .BR \-\-invalid\-backup
1050 If the file needed for the above option is not available for any
1051 reason an empty file can be given together with this option to
1052 indicate that the backup file is invalid. In this case the data that
1053 was being rearranged at the time of the crash could be irrecoverably
1054 lost, but the rest of the array may still be recoverable. This option
1055 should only be used as a last resort if there is no way to recover the
1060 .BR \-U ", " \-\-update=
1061 Update the superblock on each device while assembling the array. The
1062 argument given to this flag can be one of
1079 option will adjust the superblock of an array what was created on a Sparc
1080 machine running a patched 2.2 Linux kernel. This kernel got the
1081 alignment of part of the superblock wrong. You can use the
1082 .B "\-\-examine \-\-sparc2.2"
1085 to see what effect this would have.
1089 option will update the
1090 .B "preferred minor"
1091 field on each superblock to match the minor number of the array being
1093 This can be useful if
1095 reports a different "Preferred Minor" to
1097 In some cases this update will be performed automatically
1098 by the kernel driver. In particular the update happens automatically
1099 at the first write to an array with redundancy (RAID level 1 or
1100 greater) on a 2.6 (or later) kernel.
1104 option will change the uuid of the array. If a UUID is given with the
1106 option that UUID will be used as a new UUID and will
1108 be used to help identify the devices in the array.
1111 is given, a random UUID is chosen.
1115 option will change the
1117 of the array as stored in the superblock. This is only supported for
1118 version-1 superblocks.
1122 option will change the
1124 as recorded in the superblock. For version-0 superblocks, this is the
1125 same as updating the UUID.
1126 For version-1 superblocks, this involves updating the name.
1130 option will cause the array to be marked
1132 meaning that any redundancy in the array (e.g. parity for RAID5,
1133 copies for RAID1) may be incorrect. This will cause the RAID system
1134 to perform a "resync" pass to make sure that all redundant information
1139 option allows arrays to be moved between machines with different
1141 When assembling such an array for the first time after a move, giving
1142 .B "\-\-update=byteorder"
1145 to expect superblocks to have their byteorder reversed, and will
1146 correct that order before assembling the array. This is only valid
1147 with original (Version 0.90) superblocks.
1151 option will correct the summaries in the superblock. That is the
1152 counts of total, working, active, failed, and spare devices.
1156 option will rarely be of use. It applies to version 1.1 and 1.2 metadata
1157 only (where the metadata is at the start of the device) and is only
1158 useful when the component device has changed size (typically become
1159 larger). The version 1 metadata records the amount of the device that
1160 can be used to store data, so if a device in a version 1.1 or 1.2
1161 array becomes larger, the metadata will still be visible, but the
1162 extra space will not. In this case it might be useful to assemble the
1164 .BR \-\-update=devicesize .
1167 to determine the maximum usable amount of space on each device and
1168 update the relevant field in the metadata.
1172 option can be used when an array has an internal bitmap which is
1173 corrupt in some way so that assembling the array normally fails. It
1174 will cause any internal bitmap to be ignored.
1178 option will reserve space in each device for a bad block list. This
1179 will be 4K in size and positioned near the end of any free space
1180 between the superblock and the data.
1184 option will cause any reservation of space for a bad block list to be
1185 removed. If the bad block list contains entries, this will fail, as
1186 removing the list could cause data corruption.
1189 .BR \-\-freeze\-reshape
1190 Option is intended to be used in start-up scripts during initrd boot phase.
1191 When array under reshape is assembled during initrd phase, this option
1192 stops reshape after reshape critical section is being restored. This happens
1193 before file system pivot operation and avoids loss of file system context.
1194 Losing file system context would cause reshape to be broken.
1196 Reshape can be continued later using the
1198 option for the grow command.
1200 .SH For Manage mode:
1203 .BR \-t ", " \-\-test
1204 Unless a more serious error occurred,
1206 will exit with a status of 2 if no changes were made to the array and
1207 0 if at least one change was made.
1208 This can be useful when an indirect specifier such as
1213 is used in requesting an operation on the array.
1215 will report failure if these specifiers didn't find any match.
1218 .BR \-a ", " \-\-add
1219 hot-add listed devices.
1220 If a device appears to have recently been part of the array
1221 (possibly it failed or was removed) the device is re\-added as described
1223 If that fails or the device was never part of the array, the device is
1224 added as a hot-spare.
1225 If the array is degraded, it will immediately start to rebuild data
1228 Note that this and the following options are only meaningful on array
1229 with redundancy. They don't apply to RAID0 or Linear.
1233 re\-add a device that was previous removed from an array.
1234 If the metadata on the device reports that it is a member of the
1235 array, and the slot that it used is still vacant, then the device will
1236 be added back to the array in the same position. This will normally
1237 cause the data for that device to be recovered. However based on the
1238 event count on the device, the recovery may only require sections that
1239 are flagged a write-intent bitmap to be recovered or may not require
1240 any recovery at all.
1242 When used on an array that has no metadata (i.e. it was built with
1244 it will be assumed that bitmap-based recovery is enough to make the
1245 device fully consistent with the array.
1247 When used with v1.x metadata,
1249 can be accompanied by
1250 .BR \-\-update=devicesize ,
1251 .BR \-\-update=bbl ", or"
1252 .BR \-\-update=no\-bbl .
1253 See the description of these option when used in Assemble mode for an
1254 explanation of their use.
1256 If the device name given is
1260 will try to find any device that looks like it should be
1261 part of the array but isn't and will try to re\-add all such devices.
1263 If the device name given is
1267 will find all devices in the array that are marked
1269 remove them and attempt to immediately re\-add them. This can be
1270 useful if you are certain that the reason for failure has been
1274 .BR \-r ", " \-\-remove
1275 remove listed devices. They must not be active. i.e. they should
1276 be failed or spare devices. As well as the name of a device file
1285 The first causes all failed device to be removed. The second causes
1286 any device which is no longer connected to the system (i.e an 'open'
1289 to be removed. This will only succeed for devices that are spares or
1290 have already been marked as failed.
1293 .BR \-f ", " \-\-fail
1294 Mark listed devices as faulty.
1295 As well as the name of a device file, the word
1297 can be given. This will cause any device that has been detached from
1298 the system to be marked as failed. It can then be removed.
1307 Mark listed devices as requiring replacement. As soon as a spare is
1308 available, it will be rebuilt and will replace the marked device.
1309 This is similar to marking a device as faulty, but the device remains
1310 in service during the recovery process to increase resilience against
1311 multiple failures. When the replacement process finishes, the
1312 replaced device will be marked as faulty.
1316 This can follow a list of
1318 devices. The devices listed after
1320 will be preferentially used to replace the devices listed after
1322 These device must already be spare devices in the array.
1325 .BR \-\-write\-mostly
1326 Subsequent devices that are added or re\-added will have the 'write-mostly'
1327 flag set. This is only valid for RAID1 and means that the 'md' driver
1328 will avoid reading from these devices if possible.
1331 Subsequent devices that are added or re\-added will have the 'write-mostly'
1335 Each of these options requires that the first device listed is the array
1336 to be acted upon, and the remainder are component devices to be added,
1337 removed, marked as faulty, etc. Several different operations can be
1338 specified for different devices, e.g.
1340 mdadm /dev/md0 \-\-add /dev/sda1 \-\-fail /dev/sdb1 \-\-remove /dev/sdb1
1342 Each operation applies to all devices listed until the next
1345 If an array is using a write-intent bitmap, then devices which have
1346 been removed can be re\-added in a way that avoids a full
1347 reconstruction but instead just updates the blocks that have changed
1348 since the device was removed. For arrays with persistent metadata
1349 (superblocks) this is done automatically. For arrays created with
1351 mdadm needs to be told that this device we removed recently with
1354 Devices can only be removed from an array if they are not in active
1355 use, i.e. that must be spares or failed devices. To remove an active
1356 device, it must first be marked as
1362 .BR \-Q ", " \-\-query
1363 Examine a device to see
1364 (1) if it is an md device and (2) if it is a component of an md
1366 Information about what is discovered is presented.
1369 .BR \-D ", " \-\-detail
1370 Print details of one or more md devices.
1373 .BR \-\-detail\-platform
1374 Print details of the platform's RAID capabilities (firmware / hardware
1375 topology) for a given metadata format. If used without argument, mdadm
1376 will scan all controllers looking for their capabilities. Otherwise, mdadm
1377 will only look at the controller specified by the argument in form of an
1378 absolute filepath or a link, e.g.
1379 .IR /sys/devices/pci0000:00/0000:00:1f.2 .
1382 .BR \-Y ", " \-\-export
1384 .B \-\-detail , \-\-detail-platform
1387 output will be formatted as
1389 pairs for easy import into the environment.
1392 .BR \-E ", " \-\-examine
1393 Print contents of the metadata stored on the named device(s).
1394 Note the contrast between
1399 applies to devices which are components of an array, while
1401 applies to a whole array which is currently active.
1404 If an array was created on a SPARC machine with a 2.2 Linux kernel
1405 patched with RAID support, the superblock will have been created
1406 incorrectly, or at least incompatibly with 2.4 and later kernels.
1411 will fix the superblock before displaying it. If this appears to do
1412 the right thing, then the array can be successfully assembled using
1413 .BR "\-\-assemble \-\-update=sparc2.2" .
1416 .BR \-X ", " \-\-examine\-bitmap
1417 Report information about a bitmap file.
1418 The argument is either an external bitmap file or an array component
1419 in case of an internal bitmap. Note that running this on an array
1422 does not report the bitmap for that array.
1425 .B \-\-examine\-badblocks
1426 List the bad-blocks recorded for the device, if a bad-blocks list has
1427 been configured. Currently only
1429 metadata supports bad-blocks lists.
1432 .BR \-R ", " \-\-run
1433 start a partially assembled array. If
1435 did not find enough devices to fully start the array, it might leaving
1436 it partially assembled. If you wish, you can then use
1438 to start the array in degraded mode.
1441 .BR \-S ", " \-\-stop
1442 deactivate array, releasing all resources.
1445 .BR \-o ", " \-\-readonly
1446 mark array as readonly.
1449 .BR \-w ", " \-\-readwrite
1450 mark array as readwrite.
1453 .B \-\-zero\-superblock
1454 If the device contains a valid md superblock, the block is
1455 overwritten with zeros. With
1457 the block where the superblock would be is overwritten even if it
1458 doesn't appear to be valid.
1461 .B \-\-kill\-subarray=
1462 If the device is a container and the argument to \-\-kill\-subarray
1463 specifies an inactive subarray in the container, then the subarray is
1464 deleted. Deleting all subarrays will leave an 'empty-container' or
1465 spare superblock on the drives. See \-\-zero\-superblock for completely
1466 removing a superblock. Note that some formats depend on the subarray
1467 index for generating a UUID, this command will fail if it would change
1468 the UUID of an active subarray.
1471 .B \-\-update\-subarray=
1472 If the device is a container and the argument to \-\-update\-subarray
1473 specifies a subarray in the container, then attempt to update the given
1474 superblock field in the subarray. See below in
1479 .BR \-t ", " \-\-test
1484 is set to reflect the status of the device. See below in
1489 .BR \-W ", " \-\-wait
1490 For each md device given, wait for any resync, recovery, or reshape
1491 activity to finish before returning.
1493 will return with success if it actually waited for every device
1494 listed, otherwise it will return failure.
1498 For each md device given, or each device in /proc/mdstat if
1500 is given, arrange for the array to be marked clean as soon as possible.
1502 will return with success if the array uses external metadata and we
1503 successfully waited. For native arrays this returns immediately as the
1504 kernel handles dirty-clean transitions at shutdown. No action is taken
1505 if safe-mode handling is disabled.
1507 .SH For Incremental Assembly mode:
1509 .BR \-\-rebuild\-map ", " \-r
1510 Rebuild the map file
1514 uses to help track which arrays are currently being assembled.
1517 .BR \-\-run ", " \-R
1518 Run any array assembled as soon as a minimal number of devices are
1519 available, rather than waiting until all expected devices are present.
1522 .BR \-\-scan ", " \-s
1523 Only meaningful with
1527 file for arrays that are being incrementally assembled and will try to
1528 start any that are not already started. If any such array is listed
1531 as requiring an external bitmap, that bitmap will be attached first.
1534 .BR \-\-fail ", " \-f
1535 This allows the hot-plug system to remove devices that have fully disappeared
1536 from the kernel. It will first fail and then remove the device from any
1537 array it belongs to.
1538 The device name given should be a kernel device name such as "sda",
1544 Only used with \-\-fail. The 'path' given will be recorded so that if
1545 a new device appears at the same location it can be automatically
1546 added to the same array. This allows the failed device to be
1547 automatically replaced by a new device without metadata if it appears
1548 at specified path. This option is normally only set by a
1552 .SH For Monitor mode:
1554 .BR \-m ", " \-\-mail
1555 Give a mail address to send alerts to.
1558 .BR \-p ", " \-\-program ", " \-\-alert
1559 Give a program to be run whenever an event is detected.
1562 .BR \-y ", " \-\-syslog
1563 Cause all events to be reported through 'syslog'. The messages have
1564 facility of 'daemon' and varying priorities.
1567 .BR \-d ", " \-\-delay
1568 Give a delay in seconds.
1570 polls the md arrays and then waits this many seconds before polling
1571 again. The default is 60 seconds. Since 2.6.16, there is no need to
1572 reduce this as the kernel alerts
1574 immediately when there is any change.
1577 .BR \-r ", " \-\-increment
1578 Give a percentage increment.
1580 will generate RebuildNN events with the given percentage increment.
1583 .BR \-f ", " \-\-daemonise
1586 to run as a background daemon if it decides to monitor anything. This
1587 causes it to fork and run in the child, and to disconnect from the
1588 terminal. The process id of the child is written to stdout.
1591 which will only continue monitoring if a mail address or alert program
1592 is found in the config file.
1595 .BR \-i ", " \-\-pid\-file
1598 is running in daemon mode, write the pid of the daemon process to
1599 the specified file, instead of printing it on standard output.
1602 .BR \-1 ", " \-\-oneshot
1603 Check arrays only once. This will generate
1605 events and more significantly
1611 .B " mdadm \-\-monitor \-\-scan \-1"
1613 from a cron script will ensure regular notification of any degraded arrays.
1616 .BR \-t ", " \-\-test
1619 alert for every array found at startup. This alert gets mailed and
1620 passed to the alert program. This can be used for testing that alert
1621 message do get through successfully.
1625 This inhibits the functionality for moving spares between arrays.
1626 Only one monitoring process started with
1628 but without this flag is allowed, otherwise the two could interfere
1635 .B mdadm \-\-assemble
1636 .I md-device options-and-component-devices...
1639 .B mdadm \-\-assemble \-\-scan
1640 .I md-devices-and-options...
1643 .B mdadm \-\-assemble \-\-scan
1647 This usage assembles one or more RAID arrays from pre-existing components.
1648 For each array, mdadm needs to know the md device, the identity of the
1649 array, and a number of component-devices. These can be found in a number of ways.
1651 In the first usage example (without the
1653 the first device given is the md device.
1654 In the second usage example, all devices listed are treated as md
1655 devices and assembly is attempted.
1656 In the third (where no devices are listed) all md devices that are
1657 listed in the configuration file are assembled. If no arrays are
1658 described by the configuration file, then any arrays that
1659 can be found on unused devices will be assembled.
1661 If precisely one device is listed, but
1667 was given and identity information is extracted from the configuration file.
1669 The identity can be given with the
1675 option, will be taken from the md-device record in the config file, or
1676 will be taken from the super block of the first component-device
1677 listed on the command line.
1679 Devices can be given on the
1681 command line or in the config file. Only devices which have an md
1682 superblock which contains the right identity will be considered for
1685 The config file is only used if explicitly named with
1687 or requested with (a possibly implicit)
1692 .B /etc/mdadm/mdadm.conf
1697 is not given, then the config file will only be used to find the
1698 identity of md arrays.
1700 Normally the array will be started after it is assembled. However if
1702 is not given and not all expected drives were listed, then the array
1703 is not started (to guard against usage errors). To insist that the
1704 array be started in this case (as may work for RAID1, 4, 5, 6, or 10),
1713 does not create any entries in
1717 It does record information in
1721 to choose the correct name.
1725 detects that udev is not configured, it will create the devices in
1729 In Linux kernels prior to version 2.6.28 there were two distinctly
1730 different types of md devices that could be created: one that could be
1731 partitioned using standard partitioning tools and one that could not.
1732 Since 2.6.28 that distinction is no longer relevant as both type of
1733 devices can be partitioned.
1735 will normally create the type that originally could not be partitioned
1736 as it has a well defined major number (9).
1738 Prior to 2.6.28, it is important that mdadm chooses the correct type
1739 of array device to use. This can be controlled with the
1741 option. In particular, a value of "mdp" or "part" or "p" tells mdadm
1742 to use a partitionable device rather than the default.
1744 In the no-udev case, the value given to
1746 can be suffixed by a number. This tells
1748 to create that number of partition devices rather than the default of 4.
1752 can also be given in the configuration file as a word starting
1754 on the ARRAY line for the relevant array.
1761 and no devices are listed,
1763 will first attempt to assemble all the arrays listed in the config
1766 If no arrays are listed in the config (other than those marked
1768 it will look through the available devices for possible arrays and
1769 will try to assemble anything that it finds. Arrays which are tagged
1770 as belonging to the given homehost will be assembled and started
1771 normally. Arrays which do not obviously belong to this host are given
1772 names that are expected not to conflict with anything local, and are
1773 started "read-auto" so that nothing is written to any device until the
1774 array is written to. i.e. automatic resync etc is delayed.
1778 finds a consistent set of devices that look like they should comprise
1779 an array, and if the superblock is tagged as belonging to the given
1780 home host, it will automatically choose a device name and try to
1781 assemble the array. If the array uses version-0.90 metadata, then the
1783 number as recorded in the superblock is used to create a name in
1787 If the array uses version-1 metadata, then the
1789 from the superblock is used to similarly create a name in
1791 (the name will have any 'host' prefix stripped first).
1793 This behaviour can be modified by the
1797 configuration file. This line can indicate that specific metadata
1798 type should, or should not, be automatically assembled. If an array
1799 is found which is not listed in
1801 and has a metadata format that is denied by the
1803 line, then it will not be assembled.
1806 line can also request that all arrays identified as being for this
1807 homehost should be assembled regardless of their metadata type.
1810 for further details.
1812 Note: Auto assembly cannot be used for assembling and activating some
1813 arrays which are undergoing reshape. In particular as the
1815 cannot be given, any reshape which requires a backup-file to continue
1816 cannot be started by auto assembly. An array which is growing to more
1817 devices and has passed the critical section can be assembled using
1828 .BI \-\-raid\-devices= Z
1832 This usage is similar to
1834 The difference is that it creates an array without a superblock. With
1835 these arrays there is no difference between initially creating the array and
1836 subsequently assembling the array, except that hopefully there is useful
1837 data there in the second case.
1839 The level may raid0, linear, raid1, raid10, multipath, or faulty, or
1840 one of their synonyms. All devices must be listed and the array will
1841 be started once complete. It will often be appropriate to use
1842 .B \-\-assume\-clean
1843 with levels raid1 or raid10.
1854 .BI \-\-raid\-devices= Z
1858 This usage will initialise a new md array, associate some devices with
1859 it, and activate the array.
1861 The named device will normally not exist when
1862 .I "mdadm \-\-create"
1863 is run, but will be created by
1865 once the array becomes active.
1867 As devices are added, they are checked to see if they contain RAID
1868 superblocks or filesystems. They are also checked to see if the variance in
1869 device size exceeds 1%.
1871 If any discrepancy is found, the array will not automatically be run, though
1874 can override this caution.
1876 To create a "degraded" array in which some devices are missing, simply
1877 give the word "\fBmissing\fP"
1878 in place of a device name. This will cause
1880 to leave the corresponding slot in the array empty.
1881 For a RAID4 or RAID5 array at most one slot can be
1882 "\fBmissing\fP"; for a RAID6 array at most two slots.
1883 For a RAID1 array, only one real device needs to be given. All of the
1887 When creating a RAID5 array,
1889 will automatically create a degraded array with an extra spare drive.
1890 This is because building the spare into a degraded array is in general
1891 faster than resyncing the parity on a non-degraded, but not clean,
1892 array. This feature can be overridden with the
1896 When creating an array with version-1 metadata a name for the array is
1898 If this is not given with the
1902 will choose a name based on the last component of the name of the
1903 device being created. So if
1905 is being created, then the name
1910 is being created, then the name
1914 When creating a partition based array, using
1916 with version-1.x metadata, the partition type should be set to
1918 (non fs-data). This type selection allows for greater precision since
1919 using any other [RAID auto-detect (0xFD) or a GNU/Linux partition (0x83)],
1920 might create problems in the event of array recovery through a live cdrom.
1922 A new array will normally get a randomly assigned 128bit UUID which is
1923 very likely to be unique. If you have a specific need, you can choose
1924 a UUID for the array by giving the
1926 option. Be warned that creating two arrays with the same UUID is a
1927 recipe for disaster. Also, using
1929 when creating a v0.90 array will silently override any
1934 .\"option is given, it is not necessary to list any component-devices in this command.
1935 .\"They can be added later, before a
1939 .\"is given, the apparent size of the smallest drive given is used.
1941 If the array type supports a write-intent bitmap, and if the devices
1942 in the array exceed 100G is size, an internal write-intent bitmap
1943 will automatically be added unless some other option is explicitly
1946 option. In any case space for a bitmap will be reserved so that one
1947 can be added layer with
1948 .BR "\-\-grow \-\-bitmap=internal" .
1950 If the metadata type supports it (currently only 1.x metadata), space
1951 will be allocated to store a bad block list. This allows a modest
1952 number of bad blocks to be recorded, allowing the drive to remain in
1953 service while only partially functional.
1955 When creating an array within a
1958 can be given either the list of devices to use, or simply the name of
1959 the container. The former case gives control over which devices in
1960 the container will be used for the array. The latter case allows
1962 to automatically choose which devices to use based on how much spare
1965 The General Management options that are valid with
1970 insist on running the array even if some devices look like they might
1975 start the array readonly \(em not supported yet.
1982 .I options... devices...
1985 This usage will allow individual devices in an array to be failed,
1986 removed or added. It is possible to perform multiple operations with
1987 on command. For example:
1989 .B " mdadm /dev/md0 \-f /dev/hda1 \-r /dev/hda1 \-a /dev/hda1"
1995 and will then remove it from the array and finally add it back
1996 in as a spare. However only one md array can be affected by a single
1999 When a device is added to an active array, mdadm checks to see if it
2000 has metadata on it which suggests that it was recently a member of the
2001 array. If it does, it tries to "re\-add" the device. If there have
2002 been no changes since the device was removed, or if the array has a
2003 write-intent bitmap which has recorded whatever changes there were,
2004 then the device will immediately become a full member of the array and
2005 those differences recorded in the bitmap will be resolved.
2015 MISC mode includes a number of distinct operations that
2016 operate on distinct devices. The operations are:
2019 The device is examined to see if it is
2020 (1) an active md array, or
2021 (2) a component of an md array.
2022 The information discovered is reported.
2026 The device should be an active md device.
2028 will display a detailed description of the array.
2032 will cause the output to be less detailed and the format to be
2033 suitable for inclusion in
2037 will normally be 0 unless
2039 failed to get useful information about the device(s); however, if the
2041 option is given, then the exit status will be:
2045 The array is functioning normally.
2048 The array has at least one failed device.
2051 The array has multiple failed devices such that it is unusable.
2054 There was an error while trying to get information about the device.
2058 .B \-\-detail\-platform
2059 Print detail of the platform's RAID capabilities (firmware / hardware
2060 topology). If the metadata is specified with
2064 then the return status will be:
2068 metadata successfully enumerated its platform components on this system
2071 metadata is platform independent
2074 metadata failed to find its platform components on this system
2078 .B \-\-update\-subarray=
2079 If the device is a container and the argument to \-\-update\-subarray
2080 specifies a subarray in the container, then attempt to update the given
2081 superblock field in the subarray. Similar to updating an array in
2082 "assemble" mode, the field to update is selected by
2086 option. Currently only
2092 option updates the subarray name in the metadata, it may not affect the
2093 device node name or the device node symlink until the subarray is
2094 re\-assembled. If updating
2096 would change the UUID of an active subarray this operation is blocked,
2097 and the command will end in an error.
2101 The device should be a component of an md array.
2103 will read the md superblock of the device and display the contents.
2108 is given, then multiple devices that are components of the one array
2109 are grouped together and reported in a single entry suitable
2115 without listing any devices will cause all devices listed in the
2116 config file to be examined.
2120 The devices should be active md arrays which will be deactivated, as
2121 long as they are not currently in use.
2125 This will fully activate a partially assembled md array.
2129 This will mark an active array as read-only, providing that it is
2130 not currently being used.
2136 array back to being read/write.
2140 For all operations except
2143 will cause the operation to be applied to all arrays listed in
2148 causes all devices listed in the config file to be examined.
2151 .BR \-b ", " \-\-brief
2152 Be less verbose. This is used with
2160 gives an intermediate level of verbosity.
2166 .B mdadm \-\-monitor
2167 .I options... devices...
2172 to periodically poll a number of md arrays and to report on any events
2175 will never exit once it decides that there are arrays to be checked,
2176 so it should normally be run in the background.
2178 As well as reporting events,
2180 may move a spare drive from one array to another if they are in the
2185 and if the destination array has a failed drive but no spares.
2187 If any devices are listed on the command line,
2189 will only monitor those devices. Otherwise all arrays listed in the
2190 configuration file will be monitored. Further, if
2192 is given, then any other md devices that appear in
2194 will also be monitored.
2196 The result of monitoring the arrays is the generation of events.
2197 These events are passed to a separate program (if specified) and may
2198 be mailed to a given E-mail address.
2200 When passing events to a program, the program is run once for each event,
2201 and is given 2 or 3 command-line arguments: the first is the
2202 name of the event (see below), the second is the name of the
2203 md device which is affected, and the third is the name of a related
2204 device if relevant (such as a component device that has failed).
2208 is given, then a program or an E-mail address must be specified on the
2209 command line or in the config file. If neither are available, then
2211 will not monitor anything.
2215 will continue monitoring as long as something was found to monitor. If
2216 no program or email is given, then each event is reported to
2219 The different events are:
2223 .B DeviceDisappeared
2224 An md array which previously was configured appears to no longer be
2225 configured. (syslog priority: Critical)
2229 was told to monitor an array which is RAID0 or Linear, then it will
2231 .B DeviceDisappeared
2232 with the extra information
2234 This is because RAID0 and Linear do not support the device-failed,
2235 hot-spare and resync operations which are monitored.
2239 An md array started reconstruction. (syslog priority: Warning)
2245 is a two-digit number (ie. 05, 48). This indicates that rebuild
2246 has passed that many percent of the total. The events are generated
2247 with fixed increment since 0. Increment size may be specified with
2248 a commandline option (default is 20). (syslog priority: Warning)
2252 An md array that was rebuilding, isn't any more, either because it
2253 finished normally or was aborted. (syslog priority: Warning)
2257 An active component device of an array has been marked as
2258 faulty. (syslog priority: Critical)
2262 A spare component device which was being rebuilt to replace a faulty
2263 device has failed. (syslog priority: Critical)
2267 A spare component device which was being rebuilt to replace a faulty
2268 device has been successfully rebuilt and has been made active.
2269 (syslog priority: Info)
2273 A new md array has been detected in the
2275 file. (syslog priority: Info)
2279 A newly noticed array appears to be degraded. This message is not
2282 notices a drive failure which causes degradation, but only when
2284 notices that an array is degraded when it first sees the array.
2285 (syslog priority: Critical)
2289 A spare drive has been moved from one array in a
2293 to another to allow a failed drive to be replaced.
2294 (syslog priority: Info)
2300 has been told, via the config file, that an array should have a certain
2301 number of spare devices, and
2303 detects that it has fewer than this number when it first sees the
2304 array, it will report a
2307 (syslog priority: Warning)
2311 An array was found at startup, and the
2314 (syslog priority: Info)
2324 cause Email to be sent. All events cause the program to be run.
2325 The program is run with two or three arguments: the event
2326 name, the array device and possibly a second device.
2328 Each event has an associated array device (e.g.
2330 and possibly a second device. For
2335 the second device is the relevant component device.
2338 the second device is the array that the spare was moved from.
2342 to move spares from one array to another, the different arrays need to
2343 be labeled with the same
2345 or the spares must be allowed to migrate through matching POLICY domains
2346 in the configuration file. The
2348 name can be any string; it is only necessary that different spare
2349 groups use different names.
2353 detects that an array in a spare group has fewer active
2354 devices than necessary for the complete array, and has no spare
2355 devices, it will look for another array in the same spare group that
2356 has a full complement of working drive and a spare. It will then
2357 attempt to remove the spare from the second drive and add it to the
2359 If the removal succeeds but the adding fails, then it is added back to
2362 If the spare group for a degraded array is not defined,
2364 will look at the rules of spare migration specified by POLICY lines in
2366 and then follow similar steps as above if a matching spare is found.
2369 The GROW mode is used for changing the size or shape of an active
2371 For this to work, the kernel must support the necessary change.
2372 Various types of growth are being added during 2.6 development.
2374 Currently the supported changes include
2376 change the "size" attribute for RAID1, RAID4, RAID5 and RAID6.
2378 increase or decrease the "raid\-devices" attribute of RAID0, RAID1, RAID4,
2381 change the chunk-size and layout of RAID0, RAID4, RAID5 and RAID6.
2383 convert between RAID1 and RAID5, between RAID5 and RAID6, between
2384 RAID0, RAID4, and RAID5, and between RAID0 and RAID10 (in the near-2 mode).
2386 add a write-intent bitmap to any array which supports these bitmaps, or
2387 remove a write-intent bitmap from such an array.
2390 Using GROW on containers is currently supported only for Intel's IMSM
2391 container format. The number of devices in a container can be
2392 increased - which affects all arrays in the container - or an array
2393 in a container can be converted between levels where those levels are
2394 supported by the container, and the conversion is on of those listed
2395 above. Resizing arrays in an IMSM container with
2397 is not yet supported.
2399 Grow functionality (e.g. expand a number of raid devices) for Intel's
2400 IMSM container format has an experimental status. It is guarded by the
2401 .B MDADM_EXPERIMENTAL
2402 environment variable which must be set to '1' for a GROW command to
2404 This is for the following reasons:
2407 Intel's native IMSM check-pointing is not fully tested yet.
2408 This can causes IMSM incompatibility during the grow process: an array
2409 which is growing cannot roam between Microsoft Windows(R) and Linux
2413 Interrupting a grow operation is not recommended, because it
2414 has not been fully tested for Intel's IMSM container format yet.
2417 Note: Intel's native checkpointing doesn't use
2419 option and it is transparent for assembly feature.
2422 Normally when an array is built the "size" is taken from the smallest
2423 of the drives. If all the small drives in an arrays are, one at a
2424 time, removed and replaced with larger drives, then you could have an
2425 array of large drives with only a small amount used. In this
2426 situation, changing the "size" with "GROW" mode will allow the extra
2427 space to start being used. If the size is increased in this way, a
2428 "resync" process will start to make sure the new parts of the array
2431 Note that when an array changes size, any filesystem that may be
2432 stored in the array will not automatically grow or shrink to use or
2433 vacate the space. The
2434 filesystem will need to be explicitly told to use the extra space
2435 after growing, or to reduce its size
2437 to shrinking the array.
2439 Also the size of an array cannot be changed while it has an active
2440 bitmap. If an array has a bitmap, it must be removed before the size
2441 can be changed. Once the change is complete a new bitmap can be created.
2443 .SS RAID\-DEVICES CHANGES
2445 A RAID1 array can work with any number of devices from 1 upwards
2446 (though 1 is not very useful). There may be times which you want to
2447 increase or decrease the number of active devices. Note that this is
2448 different to hot-add or hot-remove which changes the number of
2451 When reducing the number of devices in a RAID1 array, the slots which
2452 are to be removed from the array must already be vacant. That is, the
2453 devices which were in those slots must be failed and removed.
2455 When the number of devices is increased, any hot spares that are
2456 present will be activated immediately.
2458 Changing the number of active devices in a RAID5 or RAID6 is much more
2459 effort. Every block in the array will need to be read and written
2460 back to a new location. From 2.6.17, the Linux Kernel is able to
2461 increase the number of devices in a RAID5 safely, including restarting
2462 an interrupted "reshape". From 2.6.31, the Linux Kernel is able to
2463 increase or decrease the number of devices in a RAID5 or RAID6.
2465 From 2.6.35, the Linux Kernel is able to convert a RAID0 in to a RAID4
2468 uses this functionality and the ability to add
2469 devices to a RAID4 to allow devices to be added to a RAID0. When
2470 requested to do this,
2472 will convert the RAID0 to a RAID4, add the necessary disks and make
2473 the reshape happen, and then convert the RAID4 back to RAID0.
2475 When decreasing the number of devices, the size of the array will also
2476 decrease. If there was data in the array, it could get destroyed and
2477 this is not reversible, so you should firstly shrink the filesystem on
2478 the array to fit within the new size. To help prevent accidents,
2480 requires that the size of the array be decreased first with
2481 .BR "mdadm --grow --array-size" .
2482 This is a reversible change which simply makes the end of the array
2483 inaccessible. The integrity of any data can then be checked before
2484 the non-reversible reduction in the number of devices is request.
2486 When relocating the first few stripes on a RAID5 or RAID6, it is not
2487 possible to keep the data on disk completely consistent and
2488 crash-proof. To provide the required safety, mdadm disables writes to
2489 the array while this "critical section" is reshaped, and takes a
2490 backup of the data that is in that section. For grows, this backup may be
2491 stored in any spare devices that the array has, however it can also be
2492 stored in a separate file specified with the
2494 option, and is required to be specified for shrinks, RAID level
2495 changes and layout changes. If this option is used, and the system
2496 does crash during the critical period, the same file must be passed to
2498 to restore the backup and reassemble the array. When shrinking rather
2499 than growing the array, the reshape is done from the end towards the
2500 beginning, so the "critical section" is at the end of the reshape.
2504 Changing the RAID level of any array happens instantaneously. However
2505 in the RAID5 to RAID6 case this requires a non-standard layout of the
2506 RAID6 data, and in the RAID6 to RAID5 case that non-standard layout is
2507 required before the change can be accomplished. So while the level
2508 change is instant, the accompanying layout change can take quite a
2511 is required. If the array is not simultaneously being grown or
2512 shrunk, so that the array size will remain the same - for example,
2513 reshaping a 3-drive RAID5 into a 4-drive RAID6 - the backup file will
2514 be used not just for a "cricital section" but throughout the reshape
2515 operation, as described below under LAYOUT CHANGES.
2517 .SS CHUNK-SIZE AND LAYOUT CHANGES
2519 Changing the chunk-size of layout without also changing the number of
2520 devices as the same time will involve re-writing all blocks in-place.
2521 To ensure against data loss in the case of a crash, a
2523 must be provided for these changes. Small sections of the array will
2524 be copied to the backup file while they are being rearranged. This
2525 means that all the data is copied twice, once to the backup and once
2526 to the new layout on the array, so this type of reshape will go very
2529 If the reshape is interrupted for any reason, this backup file must be
2531 .B "mdadm --assemble"
2532 so the array can be reassembled. Consequently the file cannot be
2533 stored on the device being reshaped.
2538 A write-intent bitmap can be added to, or removed from, an active
2539 array. Either internal bitmaps, or bitmaps stored in a separate file,
2540 can be added. Note that if you add a bitmap stored in a file which is
2541 in a filesystem that is on the RAID array being affected, the system
2542 will deadlock. The bitmap must be on a separate filesystem.
2544 .SH INCREMENTAL MODE
2548 .B mdadm \-\-incremental
2554 .B mdadm \-\-incremental \-\-fail
2558 .B mdadm \-\-incremental \-\-rebuild\-map
2561 .B mdadm \-\-incremental \-\-run \-\-scan
2564 This mode is designed to be used in conjunction with a device
2565 discovery system. As devices are found in a system, they can be
2567 .B "mdadm \-\-incremental"
2568 to be conditionally added to an appropriate array.
2570 Conversely, it can also be used with the
2572 flag to do just the opposite and find whatever array a particular device
2573 is part of and remove the device from that array.
2575 If the device passed is a
2577 device created by a previous call to
2579 then rather than trying to add that device to an array, all the arrays
2580 described by the metadata of the container will be started.
2583 performs a number of tests to determine if the device is part of an
2584 array, and which array it should be part of. If an appropriate array
2585 is found, or can be created,
2587 adds the device to the array and conditionally starts the array.
2591 will normally only add devices to an array which were previously working
2592 (active or spare) parts of that array. The support for automatic
2593 inclusion of a new drive as a spare in some array requires
2594 a configuration through POLICY in config file.
2598 makes are as follow:
2600 Is the device permitted by
2602 That is, is it listed in a
2604 line in that file. If
2606 is absent then the default it to allow any device. Similar if
2608 contains the special word
2610 then any device is allowed. Otherwise the device name given to
2612 must match one of the names or patterns in a
2617 Does the device have a valid md superblock? If a specific metadata
2618 version is requested with
2622 then only that style of metadata is accepted, otherwise
2624 finds any known version of metadata. If no
2626 metadata is found, the device may be still added to an array
2627 as a spare if POLICY allows.
2631 Does the metadata match an expected array?
2632 The metadata can match in two ways. Either there is an array listed
2635 which identifies the array (either by UUID, by name, by device list,
2636 or by minor-number), or the array was created with a
2642 or on the command line.
2645 is not able to positively identify the array as belonging to the
2646 current host, the device will be rejected.
2651 keeps a list of arrays that it has partially assembled in
2653 If no array exists which matches
2654 the metadata on the new device,
2656 must choose a device name and unit number. It does this based on any
2659 or any name information stored in the metadata. If this name
2660 suggests a unit number, that number will be used, otherwise a free
2661 unit number will be chosen. Normally
2663 will prefer to create a partitionable array, however if the
2667 suggests that a non-partitionable array is preferred, that will be
2670 If the array is not found in the config file and its metadata does not
2671 identify it as belonging to the "homehost", then
2673 will choose a name for the array which is certain not to conflict with
2674 any array which does belong to this host. It does this be adding an
2675 underscore and a small number to the name preferred by the metadata.
2677 Once an appropriate array is found or created and the device is added,
2679 must decide if the array is ready to be started. It will
2680 normally compare the number of available (non-spare) devices to the
2681 number of devices that the metadata suggests need to be active. If
2682 there are at least that many, the array will be started. This means
2683 that if any devices are missing the array will not be restarted.
2689 in which case the array will be run as soon as there are enough
2690 devices present for the data to be accessible. For a RAID1, that
2691 means one device will start the array. For a clean RAID5, the array
2692 will be started as soon as all but one drive is present.
2694 Note that neither of these approaches is really ideal. If it can
2695 be known that all device discovery has completed, then
2699 can be run which will try to start all arrays that are being
2700 incrementally assembled. They are started in "read-auto" mode in
2701 which they are read-only until the first write request. This means
2702 that no metadata updates are made and no attempt at resync or recovery
2703 happens. Further devices that are found before the first write can
2704 still be added safely.
2707 This section describes environment variables that affect how mdadm
2712 Setting this value to 1 will prevent mdadm from automatically launching
2713 mdmon. This variable is intended primarily for debugging mdadm/mdmon.
2719 does not create any device nodes in /dev, but leaves that task to
2723 appears not to be configured, or if this environment variable is set
2726 will create and devices that are needed.
2730 A key value of IMSM metadata is that it allows interoperability with
2731 boot ROMs on Intel platforms, and with other major operating systems.
2734 will only allow an IMSM array to be created or modified if detects
2735 that it is running on an Intel platform which supports IMSM, and
2736 supports the particular configuration of IMSM that is being requested
2737 (some functionality requires newer OROM support).
2739 These checks can be suppressed by setting IMSM_NO_PLATFORM=1 in the
2740 environment. This can be useful for testing or for disaster
2741 recovery. You should be aware that interoperability may be
2742 compromised by setting this value.
2745 .B " mdadm \-\-query /dev/name-of-device"
2747 This will find out if a given device is a RAID array, or is part of
2748 one, and will provide brief information about the device.
2750 .B " mdadm \-\-assemble \-\-scan"
2752 This will assemble and start all arrays listed in the standard config
2753 file. This command will typically go in a system startup file.
2755 .B " mdadm \-\-stop \-\-scan"
2757 This will shut down all arrays that can be shut down (i.e. are not
2758 currently in use). This will typically go in a system shutdown script.
2760 .B " mdadm \-\-follow \-\-scan \-\-delay=120"
2762 If (and only if) there is an Email address or program given in the
2763 standard config file, then
2764 monitor the status of all arrays listed in that file by
2765 polling them ever 2 minutes.
2767 .B " mdadm \-\-create /dev/md0 \-\-level=1 \-\-raid\-devices=2 /dev/hd[ac]1"
2769 Create /dev/md0 as a RAID1 array consisting of /dev/hda1 and /dev/hdc1.
2772 .B " echo 'DEVICE /dev/hd*[0\-9] /dev/sd*[0\-9]' > mdadm.conf"
2774 .B " mdadm \-\-detail \-\-scan >> mdadm.conf"
2776 This will create a prototype config file that describes currently
2777 active arrays that are known to be made from partitions of IDE or SCSI drives.
2778 This file should be reviewed before being used as it may
2779 contain unwanted detail.
2781 .B " echo 'DEVICE /dev/hd[a\-z] /dev/sd*[a\-z]' > mdadm.conf"
2783 .B " mdadm \-\-examine \-\-scan \-\-config=mdadm.conf >> mdadm.conf"
2785 This will find arrays which could be assembled from existing IDE and
2786 SCSI whole drives (not partitions), and store the information in the
2787 format of a config file.
2788 This file is very likely to contain unwanted detail, particularly
2791 entries. It should be reviewed and edited before being used as an
2794 .B " mdadm \-\-examine \-\-brief \-\-scan \-\-config=partitions"
2796 .B " mdadm \-Ebsc partitions"
2798 Create a list of devices by reading
2799 .BR /proc/partitions ,
2800 scan these for RAID superblocks, and printout a brief listing of all
2803 .B " mdadm \-Ac partitions \-m 0 /dev/md0"
2805 Scan all partitions and devices listed in
2806 .BR /proc/partitions
2809 out of all such devices with a RAID superblock with a minor number of 0.
2811 .B " mdadm \-\-monitor \-\-scan \-\-daemonise > /run/mdadm/mon.pid"
2813 If config file contains a mail address or alert program, run mdadm in
2814 the background in monitor mode monitoring all md devices. Also write
2815 pid of mdadm daemon to
2816 .BR /run/mdadm/mon.pid .
2818 .B " mdadm \-Iq /dev/somedevice"
2820 Try to incorporate newly discovered device into some array as
2823 .B " mdadm \-\-incremental \-\-rebuild\-map \-\-run \-\-scan"
2825 Rebuild the array map from any current arrays, and then start any that
2828 .B " mdadm /dev/md4 --fail detached --remove detached"
2830 Any devices which are components of /dev/md4 will be marked as faulty
2831 and then remove from the array.
2833 .B " mdadm --grow /dev/md4 --level=6 --backup-file=/root/backup-md4"
2837 which is currently a RAID5 array will be converted to RAID6. There
2838 should normally already be a spare drive attached to the array as a
2839 RAID6 needs one more drive than a matching RAID5.
2841 .B " mdadm --create /dev/md/ddf --metadata=ddf --raid-disks 6 /dev/sd[a-f]"
2843 Create a DDF array over 6 devices.
2845 .B " mdadm --create /dev/md/home -n3 -l5 -z 30000000 /dev/md/ddf"
2847 Create a RAID5 array over any 3 devices in the given DDF set. Use
2848 only 30 gigabytes of each device.
2850 .B " mdadm -A /dev/md/ddf1 /dev/sd[a-f]"
2852 Assemble a pre-exist ddf array.
2854 .B " mdadm -I /dev/md/ddf1"
2856 Assemble all arrays contained in the ddf array, assigning names as
2859 .B " mdadm \-\-create \-\-help"
2861 Provide help about the Create mode.
2863 .B " mdadm \-\-config \-\-help"
2865 Provide help about the format of the config file.
2867 .B " mdadm \-\-help"
2869 Provide general help.
2879 lists all active md devices with information about them.
2881 uses this to find arrays when
2883 is given in Misc mode, and to monitor array reconstruction
2888 The config file lists which devices may be scanned to see if
2889 they contain MD super block, and gives identifying information
2890 (e.g. UUID) about known MD arrays. See
2897 mode is used, this file gets a list of arrays currently being created.
2902 understand two sorts of names for array devices.
2904 The first is the so-called 'standard' format name, which matches the
2905 names used by the kernel and which appear in
2908 The second sort can be freely chosen, but must reside in
2910 When giving a device name to
2912 to create or assemble an array, either full path name such as
2916 can be given, or just the suffix of the second sort of name, such as
2922 chooses device names during auto-assembly or incremental assembly, it
2923 will sometimes add a small sequence number to the end of the name to
2924 avoid conflicted between multiple arrays that have the same name. If
2926 can reasonably determine that the array really is meant for this host,
2927 either by a hostname in the metadata, or by the presence of the array
2930 then it will leave off the suffix if possible.
2931 Also if the homehost is specified as
2934 will only use a suffix if a different array of the same name already
2935 exists or is listed in the config file.
2937 The standard names for non-partitioned arrays (the only sort of md
2938 array available in 2.4 and earlier) are of the form
2942 where NN is a number.
2943 The standard names for partitionable arrays (as available from 2.6
2944 onwards) are of the form
2948 Partition numbers should be indicated by added "pMM" to these, thus "/dev/md/d1p2".
2950 From kernel version, 2.6.28 the "non-partitioned array" can actually
2951 be partitioned. So the "md_dNN" names are no longer needed, and
2952 partitions such as "/dev/mdNNpXX" are possible.
2956 was previously known as
2960 is completely separate from the
2962 package, and does not use the
2964 configuration file at all.
2967 For further information on mdadm usage, MD and the various levels of
2970 .B http://raid.wiki.kernel.org/
2972 (based upon Jakob \(/Ostergaard's Software\-RAID.HOWTO)
2974 .\"for new releases of the RAID driver check out:
2977 .\".UR ftp://ftp.kernel.org/pub/linux/kernel/people/mingo/raid-patches
2978 .\"ftp://ftp.kernel.org/pub/linux/kernel/people/mingo/raid-patches
2983 .\".UR http://www.cse.unsw.edu.au/~neilb/patches/linux-stable/
2984 .\"http://www.cse.unsw.edu.au/~neilb/patches/linux-stable/
2987 The latest version of
2989 should always be available from
2991 .B http://www.kernel.org/pub/linux/utils/raid/mdadm/
projects / thirdparty / mdadm.git / blob