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 RAID
126 levels 1/4/5/6, as well as adding or removing a write-intent bitmap.
129 .B "Incremental Assembly"
130 Add a single device to an appropriate array. If the addition of the
131 device makes the array runnable, the array will be started.
132 This provides a convenient interface to a
134 system. As each device is detected,
136 has a chance to include it in some array as appropriate.
142 in this mode, then any arrays within that container will be assembled
147 This is for doing things to specific components of an array such as
148 adding new spares and removing faulty devices.
152 This is an 'everything else' mode that supports operations on active
153 arrays, operations on component devices such as erasing old superblocks, and
154 information gathering operations.
155 .\"This mode allows operations on independent devices such as examine MD
156 .\"superblocks, erasing old superblocks and stopping active arrays.
160 This mode does not act on a specific device or array, but rather it
161 requests the Linux Kernel to activate any auto-detected arrays.
164 .SH Options for selecting a mode are:
167 .BR \-A ", " \-\-assemble
168 Assemble a pre-existing array.
171 .BR \-B ", " \-\-build
172 Build a legacy array without superblocks.
175 .BR \-C ", " \-\-create
179 .BR \-F ", " \-\-follow ", " \-\-monitor
185 .BR \-G ", " \-\-grow
186 Change the size or shape of an active array.
189 .BR \-I ", " \-\-incremental
190 Add a single device into an appropriate array, and possibly start the array.
194 Request that the kernel starts any auto-detected arrays. This can only
197 is compiled into the kernel \(em not if it is a module.
198 Arrays can be auto-detected by the kernel if all the components are in
199 primary MS-DOS partitions with partition type
201 and all use v0.90 metadata.
202 In-kernel autodetect is not recommended for new installations. Using
204 to detect and assemble arrays \(em possibly in an
206 \(em is substantially more flexible and should be preferred.
209 If a device is given before any options, or if the first option is
214 then the MANAGE mode is assumed.
215 Anything other than these will cause the
219 .SH Options that are not mode-specific are:
222 .BR \-h ", " \-\-help
223 Display general help message or, after one of the above options, a
224 mode-specific help message.
228 Display more detailed help about command line parsing and some commonly
232 .BR \-V ", " \-\-version
233 Print version information for mdadm.
236 .BR \-v ", " \-\-verbose
237 Be more verbose about what is happening. This can be used twice to be
239 The extra verbosity currently only affects
240 .B \-\-detail \-\-scan
242 .BR "\-\-examine \-\-scan" .
245 .BR \-q ", " \-\-quiet
246 Avoid printing purely informative messages. With this,
248 will be silent unless there is something really important to report.
251 .BR \-b ", " \-\-brief
252 Be less verbose. This is used with
260 gives an intermediate level of verbosity.
263 .BR \-f ", " \-\-force
264 Be more forceful about certain operations. See the various modes for
265 the exact meaning of this option in different contexts.
268 .BR \-c ", " \-\-config=
269 Specify the config file. Default is to use
270 .BR /etc/mdadm.conf ,
271 or if that is missing then
272 .BR /etc/mdadm/mdadm.conf .
273 If the config file given is
275 then nothing will be read, but
277 will act as though the config file contained exactly
278 .B "DEVICE partitions containers"
281 to find a list of devices to scan, and
283 to find a list of containers to examine.
286 is given for the config file, then
288 will act as though the config file were empty.
291 .BR \-s ", " \-\-scan
294 for missing information.
295 In general, this option gives
297 permission to get any missing information (like component devices,
298 array devices, array identities, and alert destination) from the
299 configuration file (see previous option);
300 one exception is MISC mode when using
306 says to get a list of array devices from
310 .B \-e ", " \-\-metadata=
311 Declare the style of RAID metadata (superblock) to be used. The
314 and to guess for other operations.
315 The default can be overridden by setting the
324 .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.
328 .IP "1, 1.0, 1.1, 1.2"
329 Use the new version-1 format superblock. This has few restrictions.
330 The different sub-versions store the superblock at different locations
331 on the device, either at the end (for 1.0), at the start (for 1.1) or
332 4K from the start (for 1.2).
334 Use the "Industry Standard" DDF (Disk Data Format) format defined by
336 When creating a DDF array a
338 will be created, and normal arrays can be created in that container.
340 Use the Intel(R) Matrix Storage Manager metadata format. This creates a
342 which is managed in a similar manner to DDF, and is supported by an
343 option-rom on some platforms:
345 .B http://www.intel.com/design/chipsets/matrixstorage_sb.htm
351 This will override any
353 setting in the config file and provides the identity of the host which
354 should be considered the home for any arrays.
356 When creating an array, the
358 will be recorded in the metadata. For version-1 superblocks, it will
359 be prefixed to the array name. For version-0.90 superblocks, part of
360 the SHA1 hash of the hostname will be stored in the later half of the
363 When reporting information about an array, any array which is tagged
364 for the given homehost will be reported as such.
366 When using Auto-Assemble, only arrays tagged for the given homehost
367 will be allowed to use 'local' names (i.e. not ending in '_' followed
368 by a digit string). See below under
369 .BR "Auto Assembly" .
371 .SH For create, build, or grow:
374 .BR \-n ", " \-\-raid\-devices=
375 Specify the number of active devices in the array. This, plus the
376 number of spare devices (see below) must equal the number of
378 (including "\fBmissing\fP" devices)
379 that are listed on the command line for
381 Setting a value of 1 is probably
382 a mistake and so requires that
384 be specified first. A value of 1 will then be allowed for linear,
385 multipath, RAID0 and RAID1. It is never allowed for RAID4, RAID5 or RAID6.
387 This number can only be changed using
389 for RAID1, RAID4, RAID5 and RAID6 arrays, and only on kernels which provide
390 the necessary support.
393 .BR \-x ", " \-\-spare\-devices=
394 Specify the number of spare (eXtra) devices in the initial array.
395 Spares can also be added
396 and removed later. The number of component devices listed
397 on the command line must equal the number of RAID devices plus the
398 number of spare devices.
401 .BR \-z ", " \-\-size=
402 Amount (in Kibibytes) of space to use from each drive in RAID levels 1/4/5/6.
403 This must be a multiple of the chunk size, and must leave about 128Kb
404 of space at the end of the drive for the RAID superblock.
405 If this is not specified
406 (as it normally is not) the smallest drive (or partition) sets the
407 size, though if there is a variance among the drives of greater than 1%, a warning is
410 This value can be set with
412 for RAID level 1/4/5/6. If the array was created with a size smaller
413 than the currently active drives, the extra space can be accessed
416 The size can be given as
418 which means to choose the largest size that fits on all current drives.
420 This value can not be used with
422 metadata such as DDF and IMSM.
425 .BR \-c ", " \-\-chunk=
426 Specify chunk size of kibibytes. The default is 64.
427 This is only meaningful for RAID0, RAID4, RAID5, RAID6, and RAID10.
431 Specify rounding factor for a Linear array. The size of each
432 component will be rounded down to a multiple of this size.
433 This is a synonym for
435 but highlights the different meaning for Linear as compared to other
439 .BR \-l ", " \-\-level=
440 Set RAID level. When used with
442 options are: linear, raid0, 0, stripe, raid1, 1, mirror, raid4, 4,
443 raid5, 5, raid6, 6, raid10, 10, multipath, mp, faulty, container.
444 Obviously some of these are synonymous.
448 metadata type is requested, only the
450 level is permitted, and it does not need to be explicitly given.
454 only linear, stripe, raid0, 0, raid1, multipath, mp, and faulty are valid.
456 Not yet supported with
460 .BR \-p ", " \-\-layout=
461 This option configures the fine details of data layout for RAID5, RAID6,
462 and RAID10 arrays, and controls the failure modes for
465 The layout of the RAID5 parity block can be one of
466 .BR left\-asymmetric ,
467 .BR left\-symmetric ,
468 .BR right\-asymmetric ,
469 .BR right\-symmetric ,
470 .BR la ", " ra ", " ls ", " rs .
472 .BR left\-symmetric .
474 It is also possibly to cause RAID5 to use a RAID4-like layout by
480 Finally for RAID5 there are DDF\-compatible layouts,
481 .BR ddf\-zero\-restart ,
482 .BR ddf\-N\-restart ,
484 .BR ddf\-N\-continue .
486 These same layouts are available for RAID6. There are also 4 layouts
487 that will provide an intermediate stage for converting between RAID5
488 and RAID6. These provide a layout which is identical to the
489 corresponding RAID5 layout on the first N\-1 devices, and has the 'Q'
490 syndrome (the second 'parity' block used by RAID6) on the last device.
492 .BR left\-symmetric\-6 ,
493 .BR right\-symmetric\-6 ,
494 .BR left\-asymmetric\-6 ,
495 .BR right\-asymmetric\-6 ,
497 .BR pairty\-first\-6 .
499 When setting the failure mode for level
502 .BR write\-transient ", " wt ,
503 .BR read\-transient ", " rt ,
504 .BR write\-persistent ", " wp ,
505 .BR read\-persistent ", " rp ,
507 .BR read\-fixable ", " rf ,
508 .BR clear ", " flush ", " none .
510 Each failure mode can be followed by a number, which is used as a period
511 between fault generation. Without a number, the fault is generated
512 once on the first relevant request. With a number, the fault will be
513 generated after that many requests, and will continue to be generated
514 every time the period elapses.
516 Multiple failure modes can be current simultaneously by using the
518 option to set subsequent failure modes.
520 "clear" or "none" will remove any pending or periodic failure modes,
521 and "flush" will clear any persistent faults.
523 To set the parity with
525 the level of the array ("faulty")
526 must be specified before the fault mode is specified.
528 Finally, the layout options for RAID10 are one of 'n', 'o' or 'f' followed
529 by a small number. The default is 'n2'. The supported options are:
532 signals 'near' copies. Multiple copies of one data block are at
533 similar offsets in different devices.
536 signals 'offset' copies. Rather than the chunks being duplicated
537 within a stripe, whole stripes are duplicated but are rotated by one
538 device so duplicate blocks are on different devices. Thus subsequent
539 copies of a block are in the next drive, and are one chunk further
544 (multiple copies have very different offsets).
545 See md(4) for more detail about 'near', 'offset', and 'far'.
547 The number is the number of copies of each datablock. 2 is normal, 3
548 can be useful. This number can be at most equal to the number of
549 devices in the array. It does not need to divide evenly into that
550 number (e.g. it is perfectly legal to have an 'n2' layout for an array
551 with an odd number of devices).
557 (thus explaining the p of
561 .BR \-b ", " \-\-bitmap=
562 Specify a file to store a write-intent bitmap in. The file should not
565 is also given. The same file should be provided
566 when assembling the array. If the word
568 is given, then the bitmap is stored with the metadata on the array,
569 and so is replicated on all devices. If the word
573 mode, then any bitmap that is present is removed.
575 To help catch typing errors, the filename must contain at least one
576 slash ('/') if it is a real file (not 'internal' or 'none').
578 Note: external bitmaps are only known to work on ext2 and ext3.
579 Storing bitmap files on other filesystems may result in serious problems.
582 .BR \-\-bitmap\-chunk=
583 Set the chunksize of the bitmap. Each bit corresponds to that many
584 Kilobytes of storage.
585 When using a file based bitmap, the default is to use the smallest
586 size that is at-least 4 and requires no more than 2^21 chunks.
589 bitmap, the chunksize is automatically determined to make best use of
593 .BR \-W ", " \-\-write\-mostly
594 subsequent devices listed in a
599 command will be flagged as 'write-mostly'. This is valid for RAID1
600 only and means that the 'md' driver will avoid reading from these
601 devices if at all possible. This can be useful if mirroring over a
605 .BR \-\-write\-behind=
606 Specify that write-behind mode should be enabled (valid for RAID1
607 only). If an argument is specified, it will set the maximum number
608 of outstanding writes allowed. The default value is 256.
609 A write-intent bitmap is required in order to use write-behind
610 mode, and write-behind is only attempted on drives marked as
614 .BR \-\-assume\-clean
617 that the array pre-existed and is known to be clean. It can be useful
618 when trying to recover from a major failure as you can be sure that no
619 data will be affected unless you actually write to the array. It can
620 also be used when creating a RAID1 or RAID10 if you want to avoid the
621 initial resync, however this practice \(em while normally safe \(em is not
622 recommended. Use this only if you really know what you are doing.
625 .BR \-\-backup\-file=
628 is used to increase the number of
629 raid-devices in a RAID5 if there are no spare devices available.
630 See the GROW MODE section below on RAID\-DEVICES CHANGES. The file
631 should be stored on a separate device, not on the RAID array being
635 .BR \-N ", " \-\-name=
638 for the array. This is currently only effective when creating an
639 array with a version-1 superblock, or an array in a DDF container.
640 The name is a simple textual string that can be used to identify array
641 components when assembling. If name is needed but not specified, it
642 is taken from the basename of the device that is being created.
654 run the array, even if some of the components
655 appear to be active in another array or filesystem. Normally
657 will ask for confirmation before including such components in an
658 array. This option causes that question to be suppressed.
661 .BR \-f ", " \-\-force
664 accept the geometry and layout specified without question. Normally
666 will not allow creation of an array with only one device, and will try
667 to create a RAID5 array with one missing drive (as this makes the
668 initial resync work faster). With
671 will not try to be so clever.
674 .BR \-a ", " "\-\-auto{=yes,md,mdp,part,p}{NN}"
675 Instruct mdadm how to create the device file if needed, possibly allocating
676 an unused minor number. "md" causes a non-partitionable array
677 to be used (though since Linux 2.6.28, these array devices are in fact
678 partitionable). "mdp", "part" or "p" causes a partitionable array (2.6 and
679 later) to be used. "yes" requires the named md device to have
680 a 'standard' format, and the type and minor number will be determined
681 from this. With mdadm 3.0, device creation is normally left up to
683 so this option is unlikely to be needed.
684 See DEVICE NAMES below.
686 The argument can also come immediately after
691 is not given on the command line or in the config file, then
697 is also given, then any
699 entries in the config file will override the
701 instruction given on the command line.
703 For partitionable arrays,
705 will create the device file for the whole array and for the first 4
706 partitions. A different number of partitions can be specified at the
707 end of this option (e.g.
709 If the device name ends with a digit, the partition names add a 'p',
711 .IR /dev/md/home1p3 .
712 If there is no trailing digit, then the partition names just have a
714 .IR /dev/md/scratch3 .
716 If the md device name is in a 'standard' format as described in DEVICE
717 NAMES, then it will be created, if necessary, with the appropriate
718 device number based on that name. If the device name is not in one of these
719 formats, then a unused device number will be allocated. The device
720 number will be considered unused if there is no active array for that
721 number, and there is no entry in /dev for that number and with a
722 non-standard name. Names that are not in 'standard' format are only
723 allowed in "/dev/md/".
726 .\".BR \-\-symlink = no
731 .\"to create devices in
733 .\"it will also create symlinks from
735 .\"with names starting with
741 .\"to suppress this, or
742 .\".B \-\-symlink=yes
743 .\"to enforce this even if it is suppressing
750 .BR \-u ", " \-\-uuid=
751 uuid of array to assemble. Devices which don't have this uuid are
755 .BR \-m ", " \-\-super\-minor=
756 Minor number of device that array was created for. Devices which
757 don't have this minor number are excluded. If you create an array as
758 /dev/md1, then all superblocks will contain the minor number 1, even if
759 the array is later assembled as /dev/md2.
761 Giving the literal word "dev" for
765 to use the minor number of the md device that is being assembled.
768 .B \-\-super\-minor=dev
769 will look for super blocks with a minor number of 0.
772 is only relevant for v0.90 metadata, and should not normally be used.
778 .BR \-N ", " \-\-name=
779 Specify the name of the array to assemble. This must be the name
780 that was specified when creating the array. It must either match
781 the name stored in the superblock exactly, or it must match
784 prefixed to the start of the given name.
787 .BR \-f ", " \-\-force
788 Assemble the array even if the metadata on some devices appears to be
791 cannot find enough working devices to start the array, but can find
792 some devices that are recorded as having failed, then it will mark
793 those devices as working so that the array can be started.
794 An array which requires
796 to be started may contain data corruption. Use it carefully.
800 Attempt to start the array even if fewer drives were given than were
801 present last time the array was active. Normally if not all the
802 expected drives are found and
804 is not used, then the array will be assembled but not started.
807 an attempt will be made to start it anyway.
811 This is the reverse of
813 in that it inhibits the startup of array unless all expected drives
814 are present. This is only needed with
816 and can be used if the physical connections to devices are
817 not as reliable as you would like.
820 .BR \-a ", " "\-\-auto{=no,yes,md,mdp,part}"
821 See this option under Create and Build options.
824 .BR \-b ", " \-\-bitmap=
825 Specify the bitmap file that was given when the array was created. If
828 bitmap, there is no need to specify this when assembling the array.
831 .BR \-\-backup\-file=
834 was used to grow the number of raid-devices in a RAID5, and the system
835 crashed during the critical section, then the same
839 to allow possibly corrupted data to be restored.
842 .BR \-U ", " \-\-update=
843 Update the superblock on each device while assembling the array. The
844 argument given to this flag can be one of
858 option will adjust the superblock of an array what was created on a Sparc
859 machine running a patched 2.2 Linux kernel. This kernel got the
860 alignment of part of the superblock wrong. You can use the
861 .B "\-\-examine \-\-sparc2.2"
864 to see what effect this would have.
868 option will update the
870 field on each superblock to match the minor number of the array being
872 This can be useful if
874 reports a different "Preferred Minor" to
876 In some cases this update will be performed automatically
877 by the kernel driver. In particular the update happens automatically
878 at the first write to an array with redundancy (RAID level 1 or
879 greater) on a 2.6 (or later) kernel.
883 option will change the uuid of the array. If a UUID is given with the
885 option that UUID will be used as a new UUID and will
887 be used to help identify the devices in the array.
890 is given, a random UUID is chosen.
894 option will change the
896 of the array as stored in the superblock. This is only supported for
897 version-1 superblocks.
901 option will change the
903 as recorded in the superblock. For version-0 superblocks, this is the
904 same as updating the UUID.
905 For version-1 superblocks, this involves updating the name.
909 option will cause the array to be marked
911 meaning that any redundancy in the array (e.g. parity for RAID5,
912 copies for RAID1) may be incorrect. This will cause the RAID system
913 to perform a "resync" pass to make sure that all redundant information
918 option allows arrays to be moved between machines with different
920 When assembling such an array for the first time after a move, giving
921 .B "\-\-update=byteorder"
924 to expect superblocks to have their byteorder reversed, and will
925 correct that order before assembling the array. This is only valid
926 with original (Version 0.90) superblocks.
930 option will correct the summaries in the superblock. That is the
931 counts of total, working, active, failed, and spare devices.
935 will rarely be of use. It applies to version 1.1 and 1.2 metadata
936 only (where the metadata is at the start of the device) and is only
937 useful when the component device has changed size (typically become
938 larger). The version 1 metadata records the amount of the device that
939 can be used to store data, so if a device in a version 1.1 or 1.2
940 array becomes larger, the metadata will still be visible, but the
941 extra space will not. In this case it might be useful to assemble the
943 .BR \-\-update=devicesize .
946 to determine the maximum usable amount of space on each device and
947 update the relevant field in the metadata.
951 .B \-\-auto\-update\-homehost
952 This flag is only meaningful with auto-assembly (see discussion below).
953 In that situation, if no suitable arrays are found for this homehost,
955 will rescan for any arrays at all and will assemble them and update the
956 homehost to match the current host.
963 hot-add listed devices. For arrays with redundancy, the listed
964 devices become available as spares. If the array is degraded, it will
965 immediately start recovering data on to one of these spares.
969 re-add a device that was recently removed from an array. This is only
970 needed for arrays that have be built (i.e. with
972 For created arrays, devices are always re-added if that is possible.
973 When re-adding a device, if nothing has changed on the array since the
974 device was removed, no recovery is performed. Also, if the array has
975 a write-intent bitmap, then the recovery performed after a re-add will
976 be limited to those blocks which, according to the bitmap, might have
977 changed since the device was removed.
980 .BR \-r ", " \-\-remove
981 remove listed devices. They must not be active. i.e. they should
982 be failed or spare devices. As well as the name of a device file
991 The first causes all failed device to be removed. The second causes
992 any device which is no longer connected to the system (i.e an 'open'
995 to be removed. This will only succeed for devices that are spares or
996 have already been marked as failed.
999 .BR \-f ", " \-\-fail
1000 mark listed devices as faulty.
1001 As well as the name of a device file, the word
1003 can be given. This will cause any device that has been detached from
1004 the system to be marked as failed. It can then be removed.
1012 .BR \-\-write\-mostly
1013 Subsequent devices that are added or re-added will have the 'write-mostly'
1014 flag set. This is only valid for RAID1 and means that the 'md' driver
1015 will avoid reading from these devices if possible.
1018 Subsequent devices that are added or re-added will have the 'write-mostly'
1022 Each of these options requires that the first device listed is the array
1023 to be acted upon, and the remainder are component devices to be added,
1024 removed, marked as faulty, etc. Several different operations can be
1025 specified for different devices, e.g.
1027 mdadm /dev/md0 \-\-add /dev/sda1 \-\-fail /dev/sdb1 \-\-remove /dev/sdb1
1029 Each operation applies to all devices listed until the next
1032 If an array is using a write-intent bitmap, then devices which have
1033 been removed can be re-added in a way that avoids a full
1034 reconstruction but instead just updates the blocks that have changed
1035 since the device was removed. For arrays with persistent metadata
1036 (superblocks) this is done automatically. For arrays created with
1038 mdadm needs to be told that this device we removed recently with
1041 Devices can only be removed from an array if they are not in active
1042 use, i.e. that must be spares or failed devices. To remove an active
1043 device, it must first be marked as
1049 .BR \-Q ", " \-\-query
1050 Examine a device to see
1051 (1) if it is an md device and (2) if it is a component of an md
1053 Information about what is discovered is presented.
1056 .BR \-D ", " \-\-detail
1057 Print details of one or more md devices.
1060 .BR \-\-detail\-platform
1061 Print details of the platform's RAID capabilities (firmware / hardware
1062 topology) for a given metadata format.
1065 .BR \-Y ", " \-\-export
1070 output will be formatted as
1072 pairs for easy import into the environment.
1075 .BR \-E ", " \-\-examine
1076 Print contents of the metadata stored on the named device(s).
1077 Note the contrast between
1082 applies to devices which are components of an array, while
1084 applies to a whole array which is currently active.
1087 If an array was created on a SPARC machine with a 2.2 Linux kernel
1088 patched with RAID support, the superblock will have been created
1089 incorrectly, or at least incompatibly with 2.4 and later kernels.
1094 will fix the superblock before displaying it. If this appears to do
1095 the right thing, then the array can be successfully assembled using
1096 .BR "\-\-assemble \-\-update=sparc2.2" .
1099 .BR \-X ", " \-\-examine\-bitmap
1100 Report information about a bitmap file.
1101 The argument is either an external bitmap file or an array component
1102 in case of an internal bitmap. Note that running this on an array
1105 does not report the bitmap for that array.
1108 .BR \-R ", " \-\-run
1109 start a partially assembled array. If
1111 did not find enough devices to fully start the array, it might leaving
1112 it partially assembled. If you wish, you can then use
1114 to start the array in degraded mode.
1117 .BR \-S ", " \-\-stop
1118 deactivate array, releasing all resources.
1121 .BR \-o ", " \-\-readonly
1122 mark array as readonly.
1125 .BR \-w ", " \-\-readwrite
1126 mark array as readwrite.
1129 .B \-\-zero\-superblock
1130 If the device contains a valid md superblock, the block is
1131 overwritten with zeros. With
1133 the block where the superblock would be is overwritten even if it
1134 doesn't appear to be valid.
1137 .BR \-t ", " \-\-test
1142 is set to reflect the status of the device. See below in
1147 .BR \-W ", " \-\-wait
1148 For each md device given, wait for any resync, recovery, or reshape
1149 activity to finish before returning.
1151 will return with success if it actually waited for every device
1152 listed, otherwise it will return failure.
1156 For each md device given, or each device in /proc/mdstat if
1158 is given, arrange for the array to be marked clean as soon as possible.
1159 Also, quiesce resync so that the monitor for external metadata arrays
1160 (mdmon) has an opportunity to checkpoint the resync position.
1162 will return with success if the array uses external metadata and we
1163 successfully waited. For native arrays this returns immediately as the
1164 kernel handles both dirty-clean transitions and resync checkpointing in
1165 the kernel at shutdown. No action is taken if safe-mode handling is
1168 .SH For Incremental Assembly mode:
1170 .BR \-\-rebuild\-map ", " \-r
1171 Rebuild the map file
1172 .RB ( /var/run/mdadm/map )
1175 uses to help track which arrays are currently being assembled.
1178 .BR \-\-run ", " \-R
1179 Run any array assembled as soon as a minimal number of devices are
1180 available, rather than waiting until all expected devices are present.
1184 This allows the hot-plug system to prevent arrays from running when it knows
1185 that more disks may arrive later in the discovery process.
1188 .BR \-\-scan ", " \-s
1189 Only meaningful with
1193 file for arrays that are being incrementally assembled and will try to
1194 start any that are not already started. If any such array is listed
1197 as requiring an external bitmap, that bitmap will be attached first.
1199 .SH For Monitor mode:
1201 .BR \-m ", " \-\-mail
1202 Give a mail address to send alerts to.
1205 .BR \-p ", " \-\-program ", " \-\-alert
1206 Give a program to be run whenever an event is detected.
1209 .BR \-y ", " \-\-syslog
1210 Cause all events to be reported through 'syslog'. The messages have
1211 facility of 'daemon' and varying priorities.
1214 .BR \-d ", " \-\-delay
1215 Give a delay in seconds.
1217 polls the md arrays and then waits this many seconds before polling
1218 again. The default is 60 seconds. Since 2.6.16, there is no need to
1219 reduce this as the kernel alerts
1221 immediately when there is any change.
1224 .BR \-f ", " \-\-daemonise
1227 to run as a background daemon if it decides to monitor anything. This
1228 causes it to fork and run in the child, and to disconnect from the
1229 terminal. The process id of the child is written to stdout.
1232 which will only continue monitoring if a mail address or alert program
1233 is found in the config file.
1236 .BR \-i ", " \-\-pid\-file
1239 is running in daemon mode, write the pid of the daemon process to
1240 the specified file, instead of printing it on standard output.
1243 .BR \-1 ", " \-\-oneshot
1244 Check arrays only once. This will generate
1246 events and more significantly
1252 .B " mdadm \-\-monitor \-\-scan \-1"
1254 from a cron script will ensure regular notification of any degraded arrays.
1257 .BR \-t ", " \-\-test
1260 alert for every array found at startup. This alert gets mailed and
1261 passed to the alert program. This can be used for testing that alert
1262 message do get through successfully.
1268 .B mdadm \-\-assemble
1269 .I md-device options-and-component-devices...
1272 .B mdadm \-\-assemble \-\-scan
1273 .I md-devices-and-options...
1276 .B mdadm \-\-assemble \-\-scan
1280 This usage assembles one or more RAID arrays from pre-existing components.
1281 For each array, mdadm needs to know the md device, the identity of the
1282 array, and a number of component-devices. These can be found in a number of ways.
1284 In the first usage example (without the
1286 the first device given is the md device.
1287 In the second usage example, all devices listed are treated as md
1288 devices and assembly is attempted.
1289 In the third (where no devices are listed) all md devices that are
1290 listed in the configuration file are assembled. If not arrays are
1291 described by the configuration file, then any arrays that
1292 can be found on unused devices will be assembled.
1294 If precisely one device is listed, but
1300 was given and identity information is extracted from the configuration file.
1302 The identity can be given with the
1308 option, will be taken from the md-device record in the config file, or
1309 will be taken from the super block of the first component-device
1310 listed on the command line.
1312 Devices can be given on the
1314 command line or in the config file. Only devices which have an md
1315 superblock which contains the right identity will be considered for
1318 The config file is only used if explicitly named with
1320 or requested with (a possibly implicit)
1325 .B /etc/mdadm/mdadm.conf
1330 is not given, then the config file will only be used to find the
1331 identity of md arrays.
1333 Normally the array will be started after it is assembled. However if
1335 is not given and not all expected drives were listed, then the array
1336 is not started (to guard against usage errors). To insist that the
1337 array be started in this case (as may work for RAID1, 4, 5, 6, or 10),
1346 does not create any entries in
1350 It does record information in
1351 .B /var/run/mdadm/map
1354 to choose the correct name.
1358 detects that udev is not configured, it will create the devices in
1362 In Linux kernels prior to version 2.6.28 there were two distinctly
1363 different types of md devices that could be created: one that could be
1364 partitioned using standard partitioning tools and one that could not.
1365 Since 2.6.28 that distinction is no longer relevant as both type of
1366 devices can be partitioned.
1368 will normally create the type that originally could not be partitioned
1369 as it has a well defined major number (9).
1371 Prior to 2.6.28, it is important that mdadm chooses the correct type
1372 of array device to use. This can be controlled with the
1374 option. In particular, a value of "mdp" or "part" or "p" tells mdadm
1375 to use a partitionable device rather than the default.
1377 In the no-udev case, the value given to
1379 can be suffixed by a number. This tells
1381 to create that number of partition devices rather than the default of 4.
1385 can also be given in the configuration file as a word starting
1387 on the ARRAY line for the relevant array.
1394 and no devices are listed,
1396 will first attempt to assemble all the arrays listed in the config
1399 In no array at listed in the config (other than those marked
1401 it will look through the available devices for possible arrays and
1402 will try to assemble anything that it finds. Arrays which are tagged
1403 as belonging to the given homehost will be assembled and started
1404 normally. Arrays which do not obviously belong to this host are given
1405 names that are expected not to conflict with anything local, and are
1406 started "read-auto" so that nothing is written to any device until the
1407 array is written to. i.e. automatic resync etc is delayed.
1411 finds a consistent set of devices that look like they should comprise
1412 an array, and if the superblock is tagged as belonging to the given
1413 home host, it will automatically choose a device name and try to
1414 assemble the array. If the array uses version-0.90 metadata, then the
1416 number as recorded in the superblock is used to create a name in
1420 If the array uses version-1 metadata, then the
1422 from the superblock is used to similarly create a name in
1424 (the name will have any 'host' prefix stripped first).
1429 cannot find any array for the given host at all, and if
1430 .B \-\-auto\-update\-homehost
1433 will search again for any array (not just an array created for this
1434 host) and will assemble each assuming
1435 .BR \-\-update=homehost .
1436 This will change the host tag in the superblock so that on the next run,
1437 these arrays will be found without the second pass. The intention of
1438 this feature is to support transitioning a set of md arrays to using
1441 The reason for requiring arrays to be tagged with the homehost for
1442 auto assembly is to guard against problems that can arise when moving
1443 devices from one host to another.
1454 .BI \-\-raid\-devices= Z
1458 This usage is similar to
1460 The difference is that it creates an array without a superblock. With
1461 these arrays there is no difference between initially creating the array and
1462 subsequently assembling the array, except that hopefully there is useful
1463 data there in the second case.
1465 The level may raid0, linear, raid1, raid10, multipath, or faulty, or
1466 one of their synonyms. All devices must be listed and the array will
1467 be started once complete. It will often be appropriate to use
1468 .B \-\-assume\-clean
1469 with levels raid1 or raid10.
1480 .BI \-\-raid\-devices= Z
1484 This usage will initialise a new md array, associate some devices with
1485 it, and activate the array.
1487 The named device will normally not exist when
1488 .I "mdadm \-\-create"
1489 is run, but will be created by
1491 once the array becomes active.
1493 As devices are added, they are checked to see if they contain RAID
1494 superblocks or filesystems. They are also checked to see if the variance in
1495 device size exceeds 1%.
1497 If any discrepancy is found, the array will not automatically be run, though
1500 can override this caution.
1502 To create a "degraded" array in which some devices are missing, simply
1503 give the word "\fBmissing\fP"
1504 in place of a device name. This will cause
1506 to leave the corresponding slot in the array empty.
1507 For a RAID4 or RAID5 array at most one slot can be
1508 "\fBmissing\fP"; for a RAID6 array at most two slots.
1509 For a RAID1 array, only one real device needs to be given. All of the
1513 When creating a RAID5 array,
1515 will automatically create a degraded array with an extra spare drive.
1516 This is because building the spare into a degraded array is in general
1517 faster than resyncing the parity on a non-degraded, but not clean,
1518 array. This feature can be overridden with the
1522 When creating an array with version-1 metadata a name for the array is
1524 If this is not given with the
1528 will choose a name based on the last component of the name of the
1529 device being created. So if
1531 is being created, then the name
1536 is being created, then the name
1540 When creating a partition based array, using
1542 with version-1.x metadata, the partition type should be set to
1544 (non fs-data). This type selection allows for greater precision since
1545 using any other [RAID auto-detect (0xFD) or a GNU/Linux partition (0x83)],
1546 might create problems in the event of array recovery through a live cdrom.
1548 A new array will normally get a randomly assigned 128bit UUID which is
1549 very likely to be unique. If you have a specific need, you can choose
1550 a UUID for the array by giving the
1552 option. Be warned that creating two arrays with the same UUID is a
1553 recipe for disaster. Also, using
1555 when creating a v0.90 array will silently override any
1560 .\"option is given, it is not necessary to list any component-devices in this command.
1561 .\"They can be added later, before a
1565 .\"is given, the apparent size of the smallest drive given is used.
1567 When creating an array within a
1570 can be given either the list of devices to use, or simply the name of
1571 the container. The former case gives control over which devices in
1572 the container will be used for the array. The latter case allows
1574 to automatically choose which devices to use based on how much spare
1577 The General Management options that are valid with
1582 insist on running the array even if some devices look like they might
1587 start the array readonly \(em not supported yet.
1594 .I options... devices...
1597 This usage will allow individual devices in an array to be failed,
1598 removed or added. It is possible to perform multiple operations with
1599 on command. For example:
1601 .B " mdadm /dev/md0 \-f /dev/hda1 \-r /dev/hda1 \-a /dev/hda1"
1607 and will then remove it from the array and finally add it back
1608 in as a spare. However only one md array can be affected by a single
1611 When a device is added to an active array, mdadm checks to see if it
1612 has metadata on it which suggests that it was recently a member of the
1613 array. If it does, it tried to "re-add" the device. If there have
1614 been no changes since the device was removed, or if the array has a
1615 write-intent bitmap which has recorded whatever changes there were,
1616 then the device will immediately become a full member of the array and
1617 those differences recorded in the bitmap will be resolved.
1627 MISC mode includes a number of distinct operations that
1628 operate on distinct devices. The operations are:
1631 The device is examined to see if it is
1632 (1) an active md array, or
1633 (2) a component of an md array.
1634 The information discovered is reported.
1638 The device should be an active md device.
1640 will display a detailed description of the array.
1644 will cause the output to be less detailed and the format to be
1645 suitable for inclusion in
1646 .BR /etc/mdadm.conf .
1649 will normally be 0 unless
1651 failed to get useful information about the device(s); however, if the
1653 option is given, then the exit status will be:
1657 The array is functioning normally.
1660 The array has at least one failed device.
1663 The array has multiple failed devices such that it is unusable.
1666 There was an error while trying to get information about the device.
1670 .B \-\-detail\-platform
1671 Print detail of the platform's RAID capabilities (firmware / hardware
1672 topology). If the metadata is specified with
1676 then the return status will be:
1680 metadata successfully enumerated its platform components on this system
1683 metadata is platform independent
1686 metadata failed to find its platform components on this system
1691 The device should be a component of an md array.
1693 will read the md superblock of the device and display the contents.
1698 is given, then multiple devices that are components of the one array
1699 are grouped together and reported in a single entry suitable
1701 .BR /etc/mdadm.conf .
1705 without listing any devices will cause all devices listed in the
1706 config file to be examined.
1710 The devices should be active md arrays which will be deactivated, as
1711 long as they are not currently in use.
1715 This will fully activate a partially assembled md array.
1719 This will mark an active array as read-only, providing that it is
1720 not currently being used.
1726 array back to being read/write.
1730 For all operations except
1733 will cause the operation to be applied to all arrays listed in
1738 causes all devices listed in the config file to be examined.
1744 .B mdadm \-\-monitor
1745 .I options... devices...
1750 to periodically poll a number of md arrays and to report on any events
1753 will never exit once it decides that there are arrays to be checked,
1754 so it should normally be run in the background.
1756 As well as reporting events,
1758 may move a spare drive from one array to another if they are in the
1761 and if the destination array has a failed drive but no spares.
1763 If any devices are listed on the command line,
1765 will only monitor those devices. Otherwise all arrays listed in the
1766 configuration file will be monitored. Further, if
1768 is given, then any other md devices that appear in
1770 will also be monitored.
1772 The result of monitoring the arrays is the generation of events.
1773 These events are passed to a separate program (if specified) and may
1774 be mailed to a given E-mail address.
1776 When passing events to a program, the program is run once for each event,
1777 and is given 2 or 3 command-line arguments: the first is the
1778 name of the event (see below), the second is the name of the
1779 md device which is affected, and the third is the name of a related
1780 device if relevant (such as a component device that has failed).
1784 is given, then a program or an E-mail address must be specified on the
1785 command line or in the config file. If neither are available, then
1787 will not monitor anything.
1791 will continue monitoring as long as something was found to monitor. If
1792 no program or email is given, then each event is reported to
1795 The different events are:
1799 .B DeviceDisappeared
1800 An md array which previously was configured appears to no longer be
1801 configured. (syslog priority: Critical)
1805 was told to monitor an array which is RAID0 or Linear, then it will
1807 .B DeviceDisappeared
1808 with the extra information
1810 This is because RAID0 and Linear do not support the device-failed,
1811 hot-spare and resync operations which are monitored.
1815 An md array started reconstruction. (syslog priority: Warning)
1821 is 20, 40, 60, or 80, this indicates that rebuild has passed that many
1822 percentage of the total. (syslog priority: Warning)
1826 An md array that was rebuilding, isn't any more, either because it
1827 finished normally or was aborted. (syslog priority: Warning)
1831 An active component device of an array has been marked as
1832 faulty. (syslog priority: Critical)
1836 A spare component device which was being rebuilt to replace a faulty
1837 device has failed. (syslog priority: Critical)
1841 A spare component device which was being rebuilt to replace a faulty
1842 device has been successfully rebuilt and has been made active.
1843 (syslog priority: Info)
1847 A new md array has been detected in the
1849 file. (syslog priority: Info)
1853 A newly noticed array appears to be degraded. This message is not
1856 notices a drive failure which causes degradation, but only when
1858 notices that an array is degraded when it first sees the array.
1859 (syslog priority: Critical)
1863 A spare drive has been moved from one array in a
1865 to another to allow a failed drive to be replaced.
1866 (syslog priority: Info)
1872 has been told, via the config file, that an array should have a certain
1873 number of spare devices, and
1875 detects that it has fewer than this number when it first sees the
1876 array, it will report a
1879 (syslog priority: Warning)
1883 An array was found at startup, and the
1886 (syslog priority: Info)
1896 cause Email to be sent. All events cause the program to be run.
1897 The program is run with two or three arguments: the event
1898 name, the array device and possibly a second device.
1900 Each event has an associated array device (e.g.
1902 and possibly a second device. For
1907 the second device is the relevant component device.
1910 the second device is the array that the spare was moved from.
1914 to move spares from one array to another, the different arrays need to
1915 be labeled with the same
1917 in the configuration file. The
1919 name can be any string; it is only necessary that different spare
1920 groups use different names.
1924 detects that an array in a spare group has fewer active
1925 devices than necessary for the complete array, and has no spare
1926 devices, it will look for another array in the same spare group that
1927 has a full complement of working drive and a spare. It will then
1928 attempt to remove the spare from the second drive and add it to the
1930 If the removal succeeds but the adding fails, then it is added back to
1934 The GROW mode is used for changing the size or shape of an active
1936 For this to work, the kernel must support the necessary change.
1937 Various types of growth are being added during 2.6 development,
1938 including restructuring a RAID5 array to have more active devices.
1940 Currently the only support available is to
1942 change the "size" attribute
1943 for RAID1, RAID5 and RAID6.
1945 increase the "raid\-devices" attribute of RAID1, RAID5, and RAID6.
1947 add a write-intent bitmap to any array which supports these bitmaps, or
1948 remove a write-intent bitmap from such an array.
1951 GROW mode is not currently supported for
1953 or arrays inside containers.
1956 Normally when an array is built the "size" it taken from the smallest
1957 of the drives. If all the small drives in an arrays are, one at a
1958 time, removed and replaced with larger drives, then you could have an
1959 array of large drives with only a small amount used. In this
1960 situation, changing the "size" with "GROW" mode will allow the extra
1961 space to start being used. If the size is increased in this way, a
1962 "resync" process will start to make sure the new parts of the array
1965 Note that when an array changes size, any filesystem that may be
1966 stored in the array will not automatically grow to use the space. The
1967 filesystem will need to be explicitly told to use the extra space.
1969 Also the size of an array cannot be changed while it has an active
1970 bitmap. If an array has a bitmap, it must be removed before the size
1971 can be changed. Once the change it complete a new bitmap can be created.
1973 .SS RAID\-DEVICES CHANGES
1975 A RAID1 array can work with any number of devices from 1 upwards
1976 (though 1 is not very useful). There may be times which you want to
1977 increase or decrease the number of active devices. Note that this is
1978 different to hot-add or hot-remove which changes the number of
1981 When reducing the number of devices in a RAID1 array, the slots which
1982 are to be removed from the array must already be vacant. That is, the
1983 devices which were in those slots must be failed and removed.
1985 When the number of devices is increased, any hot spares that are
1986 present will be activated immediately.
1988 Increasing the number of active devices in a RAID5 is much more
1989 effort. Every block in the array will need to be read and written
1990 back to a new location. From 2.6.17, the Linux Kernel is able to do
1991 this safely, including restarting an interrupted "reshape".
1993 When relocating the first few stripes on a RAID5, it is not possible
1994 to keep the data on disk completely consistent and crash-proof. To
1995 provide the required safety, mdadm disables writes to the array while
1996 this "critical section" is reshaped, and takes a backup of the data
1997 that is in that section. This backup is normally stored in any spare
1998 devices that the array has, however it can also be stored in a
1999 separate file specified with the
2001 option. If this option is used, and the system does crash during the
2002 critical period, the same file must be passed to
2004 to restore the backup and reassemble the array.
2008 A write-intent bitmap can be added to, or removed from, an active
2009 array. Either internal bitmaps, or bitmaps stored in a separate file,
2010 can be added. Note that if you add a bitmap stored in a file which is
2011 in a filesystem that is on the RAID array being affected, the system
2012 will deadlock. The bitmap must be on a separate filesystem.
2014 .SH INCREMENTAL MODE
2018 .B mdadm \-\-incremental
2024 .B mdadm \-\-incremental \-\-rebuild
2027 .B mdadm \-\-incremental \-\-run \-\-scan
2030 This mode is designed to be used in conjunction with a device
2031 discovery system. As devices are found in a system, they can be
2033 .B "mdadm \-\-incremental"
2034 to be conditionally added to an appropriate array.
2036 If the device passed is a
2038 device created by a previous call to
2040 then rather than trying to add that device to an array, all the arrays
2041 described by the metadata of the container will be started.
2044 performs a number of tests to determine if the device is part of an
2045 array, and which array it should be part of. If an appropriate array
2046 is found, or can be created,
2048 adds the device to the array and conditionally starts the array.
2052 will only add devices to an array which were previously working
2053 (active or spare) parts of that array. It does not currently support
2054 automatic inclusion of a new drive as a spare in some array.
2058 makes are as follow:
2060 Is the device permitted by
2062 That is, is it listed in a
2064 line in that file. If
2066 is absent then the default it to allow any device. Similar if
2068 contains the special word
2070 then any device is allowed. Otherwise the device name given to
2072 must match one of the names or patterns in a
2077 Does the device have a valid md superblock. If a specific metadata
2078 version is request with
2082 then only that style of metadata is accepted, otherwise
2084 finds any known version of metadata. If no
2086 metadata is found, the device is rejected.
2090 Does the metadata match an expected array?
2091 The metadata can match in two ways. Either there is an array listed
2094 which identifies the array (either by UUID, by name, by device list,
2095 or by minor-number), or the array was created with a
2101 or on the command line.
2104 is not able to positively identify the array as belonging to the
2105 current host, the device will be rejected.
2109 keeps a list of arrays that it has partially assembled in
2110 .B /var/run/mdadm/map
2112 .B /var/run/mdadm.map
2113 if the directory doesn't exist. Or maybe even
2114 .BR /dev/.mdadm.map ).
2115 If no array exists which matches
2116 the metadata on the new device,
2118 must choose a device name and unit number. It does this based on any
2121 or any name information stored in the metadata. If this name
2122 suggests a unit number, that number will be used, otherwise a free
2123 unit number will be chosen. Normally
2125 will prefer to create a partitionable array, however if the
2129 suggests that a non-partitionable array is preferred, that will be
2132 If the array is not found in the config file and its metadata does not
2133 identify it as belonging to the "homehost", then
2135 will choose a name for the array which is certain not to conflict with
2136 any array which does belong to this host. It does this be adding an
2137 underscore and a small number to the name preferred by the metadata.
2139 Once an appropriate array is found or created and the device is added,
2141 must decide if the array is ready to be started. It will
2142 normally compare the number of available (non-spare) devices to the
2143 number of devices that the metadata suggests need to be active. If
2144 there are at least that many, the array will be started. This means
2145 that if any devices are missing the array will not be restarted.
2151 in which case the array will be run as soon as there are enough
2152 devices present for the data to be accessible. For a RAID1, that
2153 means one device will start the array. For a clean RAID5, the array
2154 will be started as soon as all but one drive is present.
2156 Note that neither of these approaches is really ideal. If it can
2157 be known that all device discovery has completed, then
2161 can be run which will try to start all arrays that are being
2162 incrementally assembled. They are started in "read-auto" mode in
2163 which they are read-only until the first write request. This means
2164 that no metadata updates are made and no attempt at resync or recovery
2165 happens. Further devices that are found before the first write can
2166 still be added safely.
2169 This section describes environment variables that affect how mdadm
2174 Setting this value to 1 will prevent mdadm from automatically launching
2175 mdmon. This variable is intended primarily for debugging mdadm/mdmon.
2181 does not create any device nodes in /dev, but leaves that task to
2185 appears not to be configured, or if this environment variable is set
2188 will create and devices that are needed.
2192 .B " mdadm \-\-query /dev/name-of-device"
2194 This will find out if a given device is a RAID array, or is part of
2195 one, and will provide brief information about the device.
2197 .B " mdadm \-\-assemble \-\-scan"
2199 This will assemble and start all arrays listed in the standard config
2200 file. This command will typically go in a system startup file.
2202 .B " mdadm \-\-stop \-\-scan"
2204 This will shut down all arrays that can be shut down (i.e. are not
2205 currently in use). This will typically go in a system shutdown script.
2207 .B " mdadm \-\-follow \-\-scan \-\-delay=120"
2209 If (and only if) there is an Email address or program given in the
2210 standard config file, then
2211 monitor the status of all arrays listed in that file by
2212 polling them ever 2 minutes.
2214 .B " mdadm \-\-create /dev/md0 \-\-level=1 \-\-raid\-devices=2 /dev/hd[ac]1"
2216 Create /dev/md0 as a RAID1 array consisting of /dev/hda1 and /dev/hdc1.
2219 .B " echo 'DEVICE /dev/hd*[0\-9] /dev/sd*[0\-9]' > mdadm.conf"
2221 .B " mdadm \-\-detail \-\-scan >> mdadm.conf"
2223 This will create a prototype config file that describes currently
2224 active arrays that are known to be made from partitions of IDE or SCSI drives.
2225 This file should be reviewed before being used as it may
2226 contain unwanted detail.
2228 .B " echo 'DEVICE /dev/hd[a\-z] /dev/sd*[a\-z]' > mdadm.conf"
2230 .B " mdadm \-\-examine \-\-scan \-\-config=mdadm.conf >> mdadm.conf"
2232 This will find arrays which could be assembled from existing IDE and
2233 SCSI whole drives (not partitions), and store the information in the
2234 format of a config file.
2235 This file is very likely to contain unwanted detail, particularly
2238 entries. It should be reviewed and edited before being used as an
2241 .B " mdadm \-\-examine \-\-brief \-\-scan \-\-config=partitions"
2243 .B " mdadm \-Ebsc partitions"
2245 Create a list of devices by reading
2246 .BR /proc/partitions ,
2247 scan these for RAID superblocks, and printout a brief listing of all
2250 .B " mdadm \-Ac partitions \-m 0 /dev/md0"
2252 Scan all partitions and devices listed in
2253 .BR /proc/partitions
2256 out of all such devices with a RAID superblock with a minor number of 0.
2258 .B " mdadm \-\-monitor \-\-scan \-\-daemonise > /var/run/mdadm"
2260 If config file contains a mail address or alert program, run mdadm in
2261 the background in monitor mode monitoring all md devices. Also write
2262 pid of mdadm daemon to
2263 .BR /var/run/mdadm .
2265 .B " mdadm \-Iq /dev/somedevice"
2267 Try to incorporate newly discovered device into some array as
2270 .B " mdadm \-\-incremental \-\-rebuild \-\-run \-\-scan"
2272 Rebuild the array map from any current arrays, and then start any that
2275 .B " mdadm /dev/md4 --fail detached --remove detached"
2277 Any devices which are components of /dev/md4 will be marked as faulty
2278 and then remove from the array.
2280 .B " mdadm --create /dev/md/ddf --metadata=ddf --raid-disks 6 /dev/sd[a-f]"
2282 Create a DDF array over 6 devices.
2284 .B " mdadm --create /dev/md/home -n3 -l5 -z 30000000 /dev/md/ddf"
2286 Create a RAID5 array over any 3 devices in the given DDF set. Use
2287 only 30 gigabytes of each device.
2289 .B " mdadm -A /dev/md/ddf1 /dev/sd[a-f]"
2291 Assemble a pre-exist ddf array.
2293 .B " mdadm -I /dev/md/ddf1"
2295 Assemble all arrays contained in the ddf array, assigning names as
2298 .B " mdadm \-\-create \-\-help"
2300 Provide help about the Create mode.
2302 .B " mdadm \-\-config \-\-help"
2304 Provide help about the format of the config file.
2306 .B " mdadm \-\-help"
2308 Provide general help.
2318 lists all active md devices with information about them.
2320 uses this to find arrays when
2322 is given in Misc mode, and to monitor array reconstruction
2327 The config file lists which devices may be scanned to see if
2328 they contain MD super block, and gives identifying information
2329 (e.g. UUID) about known MD arrays. See
2333 .SS /var/run/mdadm/map
2336 mode is used, this file gets a list of arrays currently being created.
2339 does not exist as a directory, then
2340 .B /var/run/mdadm.map
2343 is not available (as may be the case during early boot),
2345 is used on the basis that
2347 is usually available very early in boot.
2352 understand two sorts of names for array devices.
2354 The first is the so-called 'standard' format name, which matches the
2355 names used by the kernel and which appear in
2358 The second sort can be freely chosen, but must reside in
2360 When giving a device name to
2362 to create or assemble an array, either full path name such as
2366 can be given, or just the suffix of the second sort of name, such as
2372 chooses device names during auto-assembly or incremental assembly, it
2373 will sometimes add a small sequence number to the end of the name to
2374 avoid conflicted between multiple arrays that have the same name. If
2376 can reasonably determine that the array really is meant for this host,
2377 either by a hostname in the metadata, or by the presence of the array
2378 in /etc/mdadm.conf, then it will leave off the suffix if possible.
2379 Also if the homehost is specified as
2382 will only use a suffix if a different array of the same name already
2383 exists or is listed in the config file.
2385 The standard names for non-partitioned arrays (the only sort of md
2386 array available in 2.4 and earlier) are of the form
2390 where NN is a number.
2391 The standard names for partitionable arrays (as available from 2.6
2392 onwards) are of the form
2396 Partition numbers should be indicated by added "pMM" to these, thus "/dev/md/d1p2".
2398 From kernel version, 2.6.28 the "non-partitioned array" can actually
2399 be partitioned. So the "md_dNN" names are no longer needed, and
2400 partitions such as "/dev/mdNNpXX" are possible.
2404 was previously known as
2408 is completely separate from the
2410 package, and does not use the
2412 configuration file at all.
2415 For further information on mdadm usage, MD and the various levels of
2418 .B http://linux\-raid.osdl.org/
2420 (based upon Jakob \(/Ostergaard's Software\-RAID.HOWTO)
2422 .\"for new releases of the RAID driver check out:
2425 .\".UR ftp://ftp.kernel.org/pub/linux/kernel/people/mingo/raid-patches
2426 .\"ftp://ftp.kernel.org/pub/linux/kernel/people/mingo/raid-patches
2431 .\".UR http://www.cse.unsw.edu.au/~neilb/patches/linux-stable/
2432 .\"http://www.cse.unsw.edu.au/~neilb/patches/linux-stable/
2435 The latest version of
2437 should always be available from
2439 .B http://www.kernel.org/pub/linux/utils/raid/mdadm/
projects / thirdparty / mdadm.git / blob