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, changing the RAID level between 1, 5, and 6, changing
127 the chunk size and layout for RAID5 and RAID5, as well as adding or
128 removing a write-intent bitmap.
131 .B "Incremental Assembly"
132 Add a single device to an appropriate array. If the addition of the
133 device makes the array runnable, the array will be started.
134 This provides a convenient interface to a
136 system. As each device is detected,
138 has a chance to include it in some array as appropriate.
144 in this mode, then any arrays within that container will be assembled
149 This is for doing things to specific components of an array such as
150 adding new spares and removing faulty devices.
154 This is an 'everything else' mode that supports operations on active
155 arrays, operations on component devices such as erasing old superblocks, and
156 information gathering operations.
157 .\"This mode allows operations on independent devices such as examine MD
158 .\"superblocks, erasing old superblocks and stopping active arrays.
162 This mode does not act on a specific device or array, but rather it
163 requests the Linux Kernel to activate any auto-detected arrays.
166 .SH Options for selecting a mode are:
169 .BR \-A ", " \-\-assemble
170 Assemble a pre-existing array.
173 .BR \-B ", " \-\-build
174 Build a legacy array without superblocks.
177 .BR \-C ", " \-\-create
181 .BR \-F ", " \-\-follow ", " \-\-monitor
187 .BR \-G ", " \-\-grow
188 Change the size or shape of an active array.
191 .BR \-I ", " \-\-incremental
192 Add a single device into an appropriate array, and possibly start the array.
196 Request that the kernel starts any auto-detected arrays. This can only
199 is compiled into the kernel \(em not if it is a module.
200 Arrays can be auto-detected by the kernel if all the components are in
201 primary MS-DOS partitions with partition type
203 and all use v0.90 metadata.
204 In-kernel autodetect is not recommended for new installations. Using
206 to detect and assemble arrays \(em possibly in an
208 \(em is substantially more flexible and should be preferred.
211 If a device is given before any options, or if the first option is
216 then the MANAGE mode is assumed.
217 Anything other than these will cause the
221 .SH Options that are not mode-specific are:
224 .BR \-h ", " \-\-help
225 Display general help message or, after one of the above options, a
226 mode-specific help message.
230 Display more detailed help about command line parsing and some commonly
234 .BR \-V ", " \-\-version
235 Print version information for mdadm.
238 .BR \-v ", " \-\-verbose
239 Be more verbose about what is happening. This can be used twice to be
241 The extra verbosity currently only affects
242 .B \-\-detail \-\-scan
244 .BR "\-\-examine \-\-scan" .
247 .BR \-q ", " \-\-quiet
248 Avoid printing purely informative messages. With this,
250 will be silent unless there is something really important to report.
253 .BR \-b ", " \-\-brief
254 Be less verbose. This is used with
262 gives an intermediate level of verbosity.
265 .BR \-f ", " \-\-force
266 Be more forceful about certain operations. See the various modes for
267 the exact meaning of this option in different contexts.
270 .BR \-c ", " \-\-config=
271 Specify the config file. Default is to use
272 .BR /etc/mdadm.conf ,
273 or if that is missing then
274 .BR /etc/mdadm/mdadm.conf .
275 If the config file given is
277 then nothing will be read, but
279 will act as though the config file contained exactly
280 .B "DEVICE partitions containers"
283 to find a list of devices to scan, and
285 to find a list of containers to examine.
288 is given for the config file, then
290 will act as though the config file were empty.
293 .BR \-s ", " \-\-scan
296 for missing information.
297 In general, this option gives
299 permission to get any missing information (like component devices,
300 array devices, array identities, and alert destination) from the
301 configuration file (see previous option);
302 one exception is MISC mode when using
308 says to get a list of array devices from
312 .BR \-e ", " \-\-metadata=
313 Declare the style of RAID metadata (superblock) to be used. The
316 and to guess for other operations.
317 The default can be overridden by setting the
326 .IP "0, 0.90, default"
327 Use the original 0.90 format superblock. This format limits arrays to
328 28 component devices and limits component devices of levels 1 and
329 greater to 2 terabytes.
330 .IP "1, 1.0, 1.1, 1.2"
331 Use the new version-1 format superblock. This has few restrictions.
332 The different sub-versions store the superblock at different locations
333 on the device, either at the end (for 1.0), at the start (for 1.1) or
334 4K from the start (for 1.2).
336 Use the "Industry Standard" DDF (Disk Data Format) format defined by
338 When creating a DDF array a
340 will be created, and normal arrays can be created in that container.
342 Use the Intel(R) Matrix Storage Manager metadata format. This creates a
344 which is managed in a similar manner to DDF, and is supported by an
345 option-rom on some platforms:
347 .B http://www.intel.com/design/chipsets/matrixstorage_sb.htm
353 This will override any
355 setting in the config file and provides the identity of the host which
356 should be considered the home for any arrays.
358 When creating an array, the
360 will be recorded in the metadata. For version-1 superblocks, it will
361 be prefixed to the array name. For version-0.90 superblocks, part of
362 the SHA1 hash of the hostname will be stored in the later half of the
365 When reporting information about an array, any array which is tagged
366 for the given homehost will be reported as such.
368 When using Auto-Assemble, only arrays tagged for the given homehost
369 will be allowed to use 'local' names (i.e. not ending in '_' followed
370 by a digit string). See below under
371 .BR "Auto Assembly" .
373 .SH For create, build, or grow:
376 .BR \-n ", " \-\-raid\-devices=
377 Specify the number of active devices in the array. This, plus the
378 number of spare devices (see below) must equal the number of
380 (including "\fBmissing\fP" devices)
381 that are listed on the command line for
383 Setting a value of 1 is probably
384 a mistake and so requires that
386 be specified first. A value of 1 will then be allowed for linear,
387 multipath, RAID0 and RAID1. It is never allowed for RAID4, RAID5 or RAID6.
389 This number can only be changed using
391 for RAID1, RAID4, RAID5 and RAID6 arrays, and only on kernels which provide
392 the necessary support.
395 .BR \-x ", " \-\-spare\-devices=
396 Specify the number of spare (eXtra) devices in the initial array.
397 Spares can also be added
398 and removed later. The number of component devices listed
399 on the command line must equal the number of RAID devices plus the
400 number of spare devices.
403 .BR \-z ", " \-\-size=
404 Amount (in Kibibytes) of space to use from each drive in RAID levels 1/4/5/6.
405 This must be a multiple of the chunk size, and must leave about 128Kb
406 of space at the end of the drive for the RAID superblock.
407 If this is not specified
408 (as it normally is not) the smallest drive (or partition) sets the
409 size, though if there is a variance among the drives of greater than 1%, a warning is
412 This value can be set with
414 for RAID level 1/4/5/6. If the array was created with a size smaller
415 than the currently active drives, the extra space can be accessed
418 The size can be given as
420 which means to choose the largest size that fits on all current drives.
422 This value can not be used with
424 metadata such as DDF and IMSM.
427 .BR \-Z ", " \-\-array-size=
428 This is only meaningful with
430 and its effect is not persistent: when the array is stopped an
431 restarted the default array size will be restored.
433 Setting the array-size causes the array to appear smaller to programs
434 that access the data. This is particularly needed before reshaping an
435 array so that it will be smaller. As the reshape is not reversible,
436 but setting the size with
438 is, it is required that the array size is reduced as appropriate
439 before the number of devices in the array is reduced.
442 .BR \-c ", " \-\-chunk=
443 Specify chunk size of kibibytes. The default when creating an
444 array is 512KB. To ensure compatibility with earlier versions, the
445 default when Building and array with no persistent metadata is 64KB.
446 This is only meaningful for RAID0, RAID4, RAID5, RAID6, and RAID10.
450 Specify rounding factor for a Linear array. The size of each
451 component will be rounded down to a multiple of this size.
452 This is a synonym for
454 but highlights the different meaning for Linear as compared to other
455 RAID levels. The default is 64K if a kernel earlier than 2.6.16 is in
456 use, and is 0K (i.e. no rounding) in later kernels.
459 .BR \-l ", " \-\-level=
460 Set RAID level. When used with
462 options are: linear, raid0, 0, stripe, raid1, 1, mirror, raid4, 4,
463 raid5, 5, raid6, 6, raid10, 10, multipath, mp, faulty, container.
464 Obviously some of these are synonymous.
468 metadata type is requested, only the
470 level is permitted, and it does not need to be explicitly given.
474 only linear, stripe, raid0, 0, raid1, multipath, mp, and faulty are valid.
476 Not yet supported with
480 .BR \-p ", " \-\-layout=
481 This option configures the fine details of data layout for RAID5, RAID6,
482 and RAID10 arrays, and controls the failure modes for
485 The layout of the RAID5 parity block can be one of
486 .BR left\-asymmetric ,
487 .BR left\-symmetric ,
488 .BR right\-asymmetric ,
489 .BR right\-symmetric ,
490 .BR la ", " ra ", " ls ", " rs .
492 .BR left\-symmetric .
494 It is also possibly to cause RAID5 to use a RAID4-like layout by
500 Finally for RAID5 there are DDF\-compatible layouts,
501 .BR ddf\-zero\-restart ,
502 .BR ddf\-N\-restart ,
504 .BR ddf\-N\-continue .
506 These same layouts are available for RAID6. There are also 4 layouts
507 that will provide an intermediate stage for converting between RAID5
508 and RAID6. These provide a layout which is identical to the
509 corresponding RAID5 layout on the first N\-1 devices, and has the 'Q'
510 syndrome (the second 'parity' block used by RAID6) on the last device.
512 .BR left\-symmetric\-6 ,
513 .BR right\-symmetric\-6 ,
514 .BR left\-asymmetric\-6 ,
515 .BR right\-asymmetric\-6 ,
517 .BR pairty\-first\-6 .
519 When setting the failure mode for level
522 .BR write\-transient ", " wt ,
523 .BR read\-transient ", " rt ,
524 .BR write\-persistent ", " wp ,
525 .BR read\-persistent ", " rp ,
527 .BR read\-fixable ", " rf ,
528 .BR clear ", " flush ", " none .
530 Each failure mode can be followed by a number, which is used as a period
531 between fault generation. Without a number, the fault is generated
532 once on the first relevant request. With a number, the fault will be
533 generated after that many requests, and will continue to be generated
534 every time the period elapses.
536 Multiple failure modes can be current simultaneously by using the
538 option to set subsequent failure modes.
540 "clear" or "none" will remove any pending or periodic failure modes,
541 and "flush" will clear any persistent faults.
543 Finally, the layout options for RAID10 are one of 'n', 'o' or 'f' followed
544 by a small number. The default is 'n2'. The supported options are:
547 signals 'near' copies. Multiple copies of one data block are at
548 similar offsets in different devices.
551 signals 'offset' copies. Rather than the chunks being duplicated
552 within a stripe, whole stripes are duplicated but are rotated by one
553 device so duplicate blocks are on different devices. Thus subsequent
554 copies of a block are in the next drive, and are one chunk further
559 (multiple copies have very different offsets).
560 See md(4) for more detail about 'near', 'offset', and 'far'.
562 The number is the number of copies of each datablock. 2 is normal, 3
563 can be useful. This number can be at most equal to the number of
564 devices in the array. It does not need to divide evenly into that
565 number (e.g. it is perfectly legal to have an 'n2' layout for an array
566 with an odd number of devices).
568 When an array is converted between RAID5 and RAID6 an intermediate
569 RAID6 layout is used in which the second parity block (Q) is always on
570 the last device. To convert a RAID5 to RAID6 and leave it in this new
571 layout (which does not require re-striping) use
572 .BR \-\-layout=preserve .
573 This will try to avoid any restriping.
575 The converse of this is
576 .B \-\-layout=normalise
577 which will change a non-standard RAID6 layout into a more standard
584 (thus explaining the p of
588 .BR \-b ", " \-\-bitmap=
589 Specify a file to store a write-intent bitmap in. The file should not
592 is also given. The same file should be provided
593 when assembling the array. If the word
595 is given, then the bitmap is stored with the metadata on the array,
596 and so is replicated on all devices. If the word
600 mode, then any bitmap that is present is removed.
602 To help catch typing errors, the filename must contain at least one
603 slash ('/') if it is a real file (not 'internal' or 'none').
605 Note: external bitmaps are only known to work on ext2 and ext3.
606 Storing bitmap files on other filesystems may result in serious problems.
609 .BR \-\-bitmap\-chunk=
610 Set the chunksize of the bitmap. Each bit corresponds to that many
611 Kilobytes of storage.
612 When using a file based bitmap, the default is to use the smallest
613 size that is at-least 4 and requires no more than 2^21 chunks.
616 bitmap, the chunksize is automatically determined to make best use of
620 .BR \-W ", " \-\-write\-mostly
621 subsequent devices listed in a
626 command will be flagged as 'write-mostly'. This is valid for RAID1
627 only and means that the 'md' driver will avoid reading from these
628 devices if at all possible. This can be useful if mirroring over a
632 .BR \-\-write\-behind=
633 Specify that write-behind mode should be enabled (valid for RAID1
634 only). If an argument is specified, it will set the maximum number
635 of outstanding writes allowed. The default value is 256.
636 A write-intent bitmap is required in order to use write-behind
637 mode, and write-behind is only attempted on drives marked as
641 .BR \-\-assume\-clean
644 that the array pre-existed and is known to be clean. It can be useful
645 when trying to recover from a major failure as you can be sure that no
646 data will be affected unless you actually write to the array. It can
647 also be used when creating a RAID1 or RAID10 if you want to avoid the
648 initial resync, however this practice \(em while normally safe \(em is not
649 recommended. Use this only if you really know what you are doing.
652 .BR \-\-backup\-file=
655 is used to increase the number of
656 raid-devices in a RAID5 if there are no spare devices available.
657 See the GROW MODE section below on RAID\-DEVICES CHANGES. The file
658 should be stored on a separate device, not on the RAID array being
662 .BR \-\-array-size= ", " \-Z
663 Set the size of the array which is seen by users of the device such as
664 filesystems. This can be less that the real size, but never greater.
665 The size set this way does not persist across restarts of the array.
667 This is most useful when reducing the number of devices in a RAID5 or
668 RAID6. Such arrays require the array-size to be reduced before a
669 reshape can be performed that reduces the real size.
673 restores the apparent size of the array to be whatever the real
674 amount of available space is.
677 .BR \-N ", " \-\-name=
680 for the array. This is currently only effective when creating an
681 array with a version-1 superblock, or an array in a DDF container.
682 The name is a simple textual string that can be used to identify array
683 components when assembling. If name is needed but not specified, it
684 is taken from the basename of the device that is being created.
696 run the array, even if some of the components
697 appear to be active in another array or filesystem. Normally
699 will ask for confirmation before including such components in an
700 array. This option causes that question to be suppressed.
703 .BR \-f ", " \-\-force
706 accept the geometry and layout specified without question. Normally
708 will not allow creation of an array with only one device, and will try
709 to create a RAID5 array with one missing drive (as this makes the
710 initial resync work faster). With
713 will not try to be so clever.
716 .BR \-a ", " "\-\-auto{=yes,md,mdp,part,p}{NN}"
717 Instruct mdadm how to create the device file if needed, possibly allocating
718 an unused minor number. "md" causes a non-partitionable array
719 to be used (though since Linux 2.6.28, these array devices are in fact
720 partitionable). "mdp", "part" or "p" causes a partitionable array (2.6 and
721 later) to be used. "yes" requires the named md device to have
722 a 'standard' format, and the type and minor number will be determined
723 from this. With mdadm 3.0, device creation is normally left up to
725 so this option is unlikely to be needed.
726 See DEVICE NAMES below.
728 The argument can also come immediately after
733 is not given on the command line or in the config file, then
739 is also given, then any
741 entries in the config file will override the
743 instruction given on the command line.
745 For partitionable arrays,
747 will create the device file for the whole array and for the first 4
748 partitions. A different number of partitions can be specified at the
749 end of this option (e.g.
751 If the device name ends with a digit, the partition names add a 'p',
753 .IR /dev/md/home1p3 .
754 If there is no trailing digit, then the partition names just have a
756 .IR /dev/md/scratch3 .
758 If the md device name is in a 'standard' format as described in DEVICE
759 NAMES, then it will be created, if necessary, with the appropriate
760 device number based on that name. If the device name is not in one of these
761 formats, then a unused device number will be allocated. The device
762 number will be considered unused if there is no active array for that
763 number, and there is no entry in /dev for that number and with a
764 non-standard name. Names that are not in 'standard' format are only
765 allowed in "/dev/md/".
769 .\".BR \-\-symlink = no
774 .\"to create devices in
776 .\"it will also create symlinks from
778 .\"with names starting with
784 .\"to suppress this, or
785 .\".B \-\-symlink=yes
786 .\"to enforce this even if it is suppressing
794 .BR \-u ", " \-\-uuid=
795 uuid of array to assemble. Devices which don't have this uuid are
799 .BR \-m ", " \-\-super\-minor=
800 Minor number of device that array was created for. Devices which
801 don't have this minor number are excluded. If you create an array as
802 /dev/md1, then all superblocks will contain the minor number 1, even if
803 the array is later assembled as /dev/md2.
805 Giving the literal word "dev" for
809 to use the minor number of the md device that is being assembled.
812 .B \-\-super\-minor=dev
813 will look for super blocks with a minor number of 0.
816 is only relevant for v0.90 metadata, and should not normally be used.
822 .BR \-N ", " \-\-name=
823 Specify the name of the array to assemble. This must be the name
824 that was specified when creating the array. It must either match
825 the name stored in the superblock exactly, or it must match
828 prefixed to the start of the given name.
831 .BR \-f ", " \-\-force
832 Assemble the array even if the metadata on some devices appears to be
835 cannot find enough working devices to start the array, but can find
836 some devices that are recorded as having failed, then it will mark
837 those devices as working so that the array can be started.
838 An array which requires
840 to be started may contain data corruption. Use it carefully.
844 Attempt to start the array even if fewer drives were given than were
845 present last time the array was active. Normally if not all the
846 expected drives are found and
848 is not used, then the array will be assembled but not started.
851 an attempt will be made to start it anyway.
855 This is the reverse of
857 in that it inhibits the startup of array unless all expected drives
858 are present. This is only needed with
860 and can be used if the physical connections to devices are
861 not as reliable as you would like.
864 .BR \-a ", " "\-\-auto{=no,yes,md,mdp,part}"
865 See this option under Create and Build options.
868 .BR \-b ", " \-\-bitmap=
869 Specify the bitmap file that was given when the array was created. If
872 bitmap, there is no need to specify this when assembling the array.
875 .BR \-\-backup\-file=
878 was used to grow the number of raid-devices in a RAID5, and the system
879 crashed during the critical section, then the same
883 to allow possibly corrupted data to be restored.
886 .BR \-U ", " \-\-update=
887 Update the superblock on each device while assembling the array. The
888 argument given to this flag can be one of
902 option will adjust the superblock of an array what was created on a Sparc
903 machine running a patched 2.2 Linux kernel. This kernel got the
904 alignment of part of the superblock wrong. You can use the
905 .B "\-\-examine \-\-sparc2.2"
908 to see what effect this would have.
912 option will update the
914 field on each superblock to match the minor number of the array being
916 This can be useful if
918 reports a different "Preferred Minor" to
920 In some cases this update will be performed automatically
921 by the kernel driver. In particular the update happens automatically
922 at the first write to an array with redundancy (RAID level 1 or
923 greater) on a 2.6 (or later) kernel.
927 option will change the uuid of the array. If a UUID is given with the
929 option that UUID will be used as a new UUID and will
931 be used to help identify the devices in the array.
934 is given, a random UUID is chosen.
938 option will change the
940 of the array as stored in the superblock. This is only supported for
941 version-1 superblocks.
945 option will change the
947 as recorded in the superblock. For version-0 superblocks, this is the
948 same as updating the UUID.
949 For version-1 superblocks, this involves updating the name.
953 option will cause the array to be marked
955 meaning that any redundancy in the array (e.g. parity for RAID5,
956 copies for RAID1) may be incorrect. This will cause the RAID system
957 to perform a "resync" pass to make sure that all redundant information
962 option allows arrays to be moved between machines with different
964 When assembling such an array for the first time after a move, giving
965 .B "\-\-update=byteorder"
968 to expect superblocks to have their byteorder reversed, and will
969 correct that order before assembling the array. This is only valid
970 with original (Version 0.90) superblocks.
974 option will correct the summaries in the superblock. That is the
975 counts of total, working, active, failed, and spare devices.
979 will rarely be of use. It applies to version 1.1 and 1.2 metadata
980 only (where the metadata is at the start of the device) and is only
981 useful when the component device has changed size (typically become
982 larger). The version 1 metadata records the amount of the device that
983 can be used to store data, so if a device in a version 1.1 or 1.2
984 array becomes larger, the metadata will still be visible, but the
985 extra space will not. In this case it might be useful to assemble the
987 .BR \-\-update=devicesize .
990 to determine the maximum usable amount of space on each device and
991 update the relevant field in the metadata.
995 .B \-\-auto\-update\-homehost
996 This flag is only meaningful with auto-assembly (see discussion below).
997 In that situation, if no suitable arrays are found for this homehost,
999 will rescan for any arrays at all and will assemble them and update the
1000 homehost to match the current host.
1003 .SH For Manage mode:
1006 .BR \-a ", " \-\-add
1007 hot-add listed devices. For arrays with redundancy, the listed
1008 devices become available as spares. If the array is degraded, it will
1009 immediately start recovering data on to one of these spares.
1013 re-add a device that was recently removed from an array. This is only
1014 needed for arrays that have be built (i.e. with
1016 For created arrays, devices are always re-added if that is possible.
1017 When re-adding a device, if nothing has changed on the array since the
1018 device was removed, no recovery is performed. Also, if the array has
1019 a write-intent bitmap, then the recovery performed after a re-add will
1020 be limited to those blocks which, according to the bitmap, might have
1021 changed since the device was removed.
1024 .BR \-r ", " \-\-remove
1025 remove listed devices. They must not be active. i.e. they should
1026 be failed or spare devices. As well as the name of a device file
1035 The first causes all failed device to be removed. The second causes
1036 any device which is no longer connected to the system (i.e an 'open'
1039 to be removed. This will only succeed for devices that are spares or
1040 have already been marked as failed.
1043 .BR \-f ", " \-\-fail
1044 mark listed devices as faulty.
1045 As well as the name of a device file, the word
1047 can be given. This will cause any device that has been detached from
1048 the system to be marked as failed. It can then be removed.
1056 .BR \-\-write\-mostly
1057 Subsequent devices that are added or re-added will have the 'write-mostly'
1058 flag set. This is only valid for RAID1 and means that the 'md' driver
1059 will avoid reading from these devices if possible.
1062 Subsequent devices that are added or re-added will have the 'write-mostly'
1066 Each of these options requires that the first device listed is the array
1067 to be acted upon, and the remainder are component devices to be added,
1068 removed, marked as faulty, etc. Several different operations can be
1069 specified for different devices, e.g.
1071 mdadm /dev/md0 \-\-add /dev/sda1 \-\-fail /dev/sdb1 \-\-remove /dev/sdb1
1073 Each operation applies to all devices listed until the next
1076 If an array is using a write-intent bitmap, then devices which have
1077 been removed can be re-added in a way that avoids a full
1078 reconstruction but instead just updates the blocks that have changed
1079 since the device was removed. For arrays with persistent metadata
1080 (superblocks) this is done automatically. For arrays created with
1082 mdadm needs to be told that this device we removed recently with
1085 Devices can only be removed from an array if they are not in active
1086 use, i.e. that must be spares or failed devices. To remove an active
1087 device, it must first be marked as
1093 .BR \-Q ", " \-\-query
1094 Examine a device to see
1095 (1) if it is an md device and (2) if it is a component of an md
1097 Information about what is discovered is presented.
1100 .BR \-D ", " \-\-detail
1101 Print details of one or more md devices.
1104 .BR \-\-detail\-platform
1105 Print details of the platform's RAID capabilities (firmware / hardware
1106 topology) for a given metadata format.
1109 .BR \-Y ", " \-\-export
1114 output will be formatted as
1116 pairs for easy import into the environment.
1119 .BR \-E ", " \-\-examine
1120 Print contents of the metadata stored on the named device(s).
1121 Note the contrast between
1126 applies to devices which are components of an array, while
1128 applies to a whole array which is currently active.
1131 If an array was created on a SPARC machine with a 2.2 Linux kernel
1132 patched with RAID support, the superblock will have been created
1133 incorrectly, or at least incompatibly with 2.4 and later kernels.
1138 will fix the superblock before displaying it. If this appears to do
1139 the right thing, then the array can be successfully assembled using
1140 .BR "\-\-assemble \-\-update=sparc2.2" .
1143 .BR \-X ", " \-\-examine\-bitmap
1144 Report information about a bitmap file.
1145 The argument is either an external bitmap file or an array component
1146 in case of an internal bitmap. Note that running this on an array
1149 does not report the bitmap for that array.
1152 .BR \-R ", " \-\-run
1153 start a partially assembled array. If
1155 did not find enough devices to fully start the array, it might leaving
1156 it partially assembled. If you wish, you can then use
1158 to start the array in degraded mode.
1161 .BR \-S ", " \-\-stop
1162 deactivate array, releasing all resources.
1165 .BR \-o ", " \-\-readonly
1166 mark array as readonly.
1169 .BR \-w ", " \-\-readwrite
1170 mark array as readwrite.
1173 .B \-\-zero\-superblock
1174 If the device contains a valid md superblock, the block is
1175 overwritten with zeros. With
1177 the block where the superblock would be is overwritten even if it
1178 doesn't appear to be valid.
1181 .BR \-t ", " \-\-test
1186 is set to reflect the status of the device. See below in
1191 .BR \-W ", " \-\-wait
1192 For each md device given, wait for any resync, recovery, or reshape
1193 activity to finish before returning.
1195 will return with success if it actually waited for every device
1196 listed, otherwise it will return failure.
1200 For each md device given, or each device in /proc/mdstat if
1202 is given, arrange for the array to be marked clean as soon as possible.
1203 Also, quiesce resync so that the monitor for external metadata arrays
1204 (mdmon) has an opportunity to checkpoint the resync position.
1206 will return with success if the array uses external metadata and we
1207 successfully waited. For native arrays this returns immediately as the
1208 kernel handles both dirty-clean transitions and resync checkpointing in
1209 the kernel at shutdown. No action is taken if safe-mode handling is
1212 .SH For Incremental Assembly mode:
1214 .BR \-\-rebuild\-map ", " \-r
1215 Rebuild the map file
1216 .RB ( /var/run/mdadm/map )
1219 uses to help track which arrays are currently being assembled.
1222 .BR \-\-run ", " \-R
1223 Run any array assembled as soon as a minimal number of devices are
1224 available, rather than waiting until all expected devices are present.
1228 This allows the hot-plug system to prevent arrays from running when it knows
1229 that more disks may arrive later in the discovery process.
1232 .BR \-\-scan ", " \-s
1233 Only meaningful with
1237 file for arrays that are being incrementally assembled and will try to
1238 start any that are not already started. If any such array is listed
1241 as requiring an external bitmap, that bitmap will be attached first.
1243 .SH For Monitor mode:
1245 .BR \-m ", " \-\-mail
1246 Give a mail address to send alerts to.
1249 .BR \-p ", " \-\-program ", " \-\-alert
1250 Give a program to be run whenever an event is detected.
1253 .BR \-y ", " \-\-syslog
1254 Cause all events to be reported through 'syslog'. The messages have
1255 facility of 'daemon' and varying priorities.
1258 .BR \-d ", " \-\-delay
1259 Give a delay in seconds.
1261 polls the md arrays and then waits this many seconds before polling
1262 again. The default is 60 seconds. Since 2.6.16, there is no need to
1263 reduce this as the kernel alerts
1265 immediately when there is any change.
1268 .BR \-r ", " \-\-increment
1269 Give a percentage increment.
1271 will generate RebuildNN events with the given percentage increment.
1274 .BR \-f ", " \-\-daemonise
1277 to run as a background daemon if it decides to monitor anything. This
1278 causes it to fork and run in the child, and to disconnect from the
1279 terminal. The process id of the child is written to stdout.
1282 which will only continue monitoring if a mail address or alert program
1283 is found in the config file.
1286 .BR \-i ", " \-\-pid\-file
1289 is running in daemon mode, write the pid of the daemon process to
1290 the specified file, instead of printing it on standard output.
1293 .BR \-1 ", " \-\-oneshot
1294 Check arrays only once. This will generate
1296 events and more significantly
1302 .B " mdadm \-\-monitor \-\-scan \-1"
1304 from a cron script will ensure regular notification of any degraded arrays.
1307 .BR \-t ", " \-\-test
1310 alert for every array found at startup. This alert gets mailed and
1311 passed to the alert program. This can be used for testing that alert
1312 message do get through successfully.
1318 .B mdadm \-\-assemble
1319 .I md-device options-and-component-devices...
1322 .B mdadm \-\-assemble \-\-scan
1323 .I md-devices-and-options...
1326 .B mdadm \-\-assemble \-\-scan
1330 This usage assembles one or more RAID arrays from pre-existing components.
1331 For each array, mdadm needs to know the md device, the identity of the
1332 array, and a number of component-devices. These can be found in a number of ways.
1334 In the first usage example (without the
1336 the first device given is the md device.
1337 In the second usage example, all devices listed are treated as md
1338 devices and assembly is attempted.
1339 In the third (where no devices are listed) all md devices that are
1340 listed in the configuration file are assembled. If not arrays are
1341 described by the configuration file, then any arrays that
1342 can be found on unused devices will be assembled.
1344 If precisely one device is listed, but
1350 was given and identity information is extracted from the configuration file.
1352 The identity can be given with the
1358 option, will be taken from the md-device record in the config file, or
1359 will be taken from the super block of the first component-device
1360 listed on the command line.
1362 Devices can be given on the
1364 command line or in the config file. Only devices which have an md
1365 superblock which contains the right identity will be considered for
1368 The config file is only used if explicitly named with
1370 or requested with (a possibly implicit)
1375 .B /etc/mdadm/mdadm.conf
1380 is not given, then the config file will only be used to find the
1381 identity of md arrays.
1383 Normally the array will be started after it is assembled. However if
1385 is not given and not all expected drives were listed, then the array
1386 is not started (to guard against usage errors). To insist that the
1387 array be started in this case (as may work for RAID1, 4, 5, 6, or 10),
1396 does not create any entries in
1400 It does record information in
1401 .B /var/run/mdadm/map
1404 to choose the correct name.
1408 detects that udev is not configured, it will create the devices in
1412 In Linux kernels prior to version 2.6.28 there were two distinctly
1413 different types of md devices that could be created: one that could be
1414 partitioned using standard partitioning tools and one that could not.
1415 Since 2.6.28 that distinction is no longer relevant as both type of
1416 devices can be partitioned.
1418 will normally create the type that originally could not be partitioned
1419 as it has a well defined major number (9).
1421 Prior to 2.6.28, it is important that mdadm chooses the correct type
1422 of array device to use. This can be controlled with the
1424 option. In particular, a value of "mdp" or "part" or "p" tells mdadm
1425 to use a partitionable device rather than the default.
1427 In the no-udev case, the value given to
1429 can be suffixed by a number. This tells
1431 to create that number of partition devices rather than the default of 4.
1435 can also be given in the configuration file as a word starting
1437 on the ARRAY line for the relevant array.
1444 and no devices are listed,
1446 will first attempt to assemble all the arrays listed in the config
1449 In no array at listed in the config (other than those marked
1451 it will look through the available devices for possible arrays and
1452 will try to assemble anything that it finds. Arrays which are tagged
1453 as belonging to the given homehost will be assembled and started
1454 normally. Arrays which do not obviously belong to this host are given
1455 names that are expected not to conflict with anything local, and are
1456 started "read-auto" so that nothing is written to any device until the
1457 array is written to. i.e. automatic resync etc is delayed.
1461 finds a consistent set of devices that look like they should comprise
1462 an array, and if the superblock is tagged as belonging to the given
1463 home host, it will automatically choose a device name and try to
1464 assemble the array. If the array uses version-0.90 metadata, then the
1466 number as recorded in the superblock is used to create a name in
1470 If the array uses version-1 metadata, then the
1472 from the superblock is used to similarly create a name in
1474 (the name will have any 'host' prefix stripped first).
1479 cannot find any array for the given host at all, and if
1480 .B \-\-auto\-update\-homehost
1483 will search again for any array (not just an array created for this
1484 host) and will assemble each assuming
1485 .BR \-\-update=homehost .
1486 This will change the host tag in the superblock so that on the next run,
1487 these arrays will be found without the second pass. The intention of
1488 this feature is to support transitioning a set of md arrays to using
1491 The reason for requiring arrays to be tagged with the homehost for
1492 auto assembly is to guard against problems that can arise when moving
1493 devices from one host to another.
1504 .BI \-\-raid\-devices= Z
1508 This usage is similar to
1510 The difference is that it creates an array without a superblock. With
1511 these arrays there is no difference between initially creating the array and
1512 subsequently assembling the array, except that hopefully there is useful
1513 data there in the second case.
1515 The level may raid0, linear, raid1, raid10, multipath, or faulty, or
1516 one of their synonyms. All devices must be listed and the array will
1517 be started once complete. It will often be appropriate to use
1518 .B \-\-assume\-clean
1519 with levels raid1 or raid10.
1530 .BI \-\-raid\-devices= Z
1534 This usage will initialise a new md array, associate some devices with
1535 it, and activate the array.
1537 The named device will normally not exist when
1538 .I "mdadm \-\-create"
1539 is run, but will be created by
1541 once the array becomes active.
1543 As devices are added, they are checked to see if they contain RAID
1544 superblocks or filesystems. They are also checked to see if the variance in
1545 device size exceeds 1%.
1547 If any discrepancy is found, the array will not automatically be run, though
1550 can override this caution.
1552 To create a "degraded" array in which some devices are missing, simply
1553 give the word "\fBmissing\fP"
1554 in place of a device name. This will cause
1556 to leave the corresponding slot in the array empty.
1557 For a RAID4 or RAID5 array at most one slot can be
1558 "\fBmissing\fP"; for a RAID6 array at most two slots.
1559 For a RAID1 array, only one real device needs to be given. All of the
1563 When creating a RAID5 array,
1565 will automatically create a degraded array with an extra spare drive.
1566 This is because building the spare into a degraded array is in general
1567 faster than resyncing the parity on a non-degraded, but not clean,
1568 array. This feature can be overridden with the
1572 When creating an array with version-1 metadata a name for the array is
1574 If this is not given with the
1578 will choose a name based on the last component of the name of the
1579 device being created. So if
1581 is being created, then the name
1586 is being created, then the name
1590 When creating a partition based array, using
1592 with version-1.x metadata, the partition type should be set to
1594 (non fs-data). This type selection allows for greater precision since
1595 using any other [RAID auto-detect (0xFD) or a GNU/Linux partition (0x83)],
1596 might create problems in the event of array recovery through a live cdrom.
1598 A new array will normally get a randomly assigned 128bit UUID which is
1599 very likely to be unique. If you have a specific need, you can choose
1600 a UUID for the array by giving the
1602 option. Be warned that creating two arrays with the same UUID is a
1603 recipe for disaster. Also, using
1605 when creating a v0.90 array will silently override any
1610 .\"option is given, it is not necessary to list any component-devices in this command.
1611 .\"They can be added later, before a
1615 .\"is given, the apparent size of the smallest drive given is used.
1617 When creating an array within a
1620 can be given either the list of devices to use, or simply the name of
1621 the container. The former case gives control over which devices in
1622 the container will be used for the array. The latter case allows
1624 to automatically choose which devices to use based on how much spare
1627 The General Management options that are valid with
1632 insist on running the array even if some devices look like they might
1637 start the array readonly \(em not supported yet.
1644 .I options... devices...
1647 This usage will allow individual devices in an array to be failed,
1648 removed or added. It is possible to perform multiple operations with
1649 on command. For example:
1651 .B " mdadm /dev/md0 \-f /dev/hda1 \-r /dev/hda1 \-a /dev/hda1"
1657 and will then remove it from the array and finally add it back
1658 in as a spare. However only one md array can be affected by a single
1661 When a device is added to an active array, mdadm checks to see if it
1662 has metadata on it which suggests that it was recently a member of the
1663 array. If it does, it tried to "re-add" the device. If there have
1664 been no changes since the device was removed, or if the array has a
1665 write-intent bitmap which has recorded whatever changes there were,
1666 then the device will immediately become a full member of the array and
1667 those differences recorded in the bitmap will be resolved.
1677 MISC mode includes a number of distinct operations that
1678 operate on distinct devices. The operations are:
1681 The device is examined to see if it is
1682 (1) an active md array, or
1683 (2) a component of an md array.
1684 The information discovered is reported.
1688 The device should be an active md device.
1690 will display a detailed description of the array.
1694 will cause the output to be less detailed and the format to be
1695 suitable for inclusion in
1696 .BR /etc/mdadm.conf .
1699 will normally be 0 unless
1701 failed to get useful information about the device(s); however, if the
1703 option is given, then the exit status will be:
1707 The array is functioning normally.
1710 The array has at least one failed device.
1713 The array has multiple failed devices such that it is unusable.
1716 There was an error while trying to get information about the device.
1720 .B \-\-detail\-platform
1721 Print detail of the platform's RAID capabilities (firmware / hardware
1722 topology). If the metadata is specified with
1726 then the return status will be:
1730 metadata successfully enumerated its platform components on this system
1733 metadata is platform independent
1736 metadata failed to find its platform components on this system
1741 The device should be a component of an md array.
1743 will read the md superblock of the device and display the contents.
1748 is given, then multiple devices that are components of the one array
1749 are grouped together and reported in a single entry suitable
1751 .BR /etc/mdadm.conf .
1755 without listing any devices will cause all devices listed in the
1756 config file to be examined.
1760 The devices should be active md arrays which will be deactivated, as
1761 long as they are not currently in use.
1765 This will fully activate a partially assembled md array.
1769 This will mark an active array as read-only, providing that it is
1770 not currently being used.
1776 array back to being read/write.
1780 For all operations except
1783 will cause the operation to be applied to all arrays listed in
1788 causes all devices listed in the config file to be examined.
1794 .B mdadm \-\-monitor
1795 .I options... devices...
1800 to periodically poll a number of md arrays and to report on any events
1803 will never exit once it decides that there are arrays to be checked,
1804 so it should normally be run in the background.
1806 As well as reporting events,
1808 may move a spare drive from one array to another if they are in the
1811 and if the destination array has a failed drive but no spares.
1813 If any devices are listed on the command line,
1815 will only monitor those devices. Otherwise all arrays listed in the
1816 configuration file will be monitored. Further, if
1818 is given, then any other md devices that appear in
1820 will also be monitored.
1822 The result of monitoring the arrays is the generation of events.
1823 These events are passed to a separate program (if specified) and may
1824 be mailed to a given E-mail address.
1826 When passing events to a program, the program is run once for each event,
1827 and is given 2 or 3 command-line arguments: the first is the
1828 name of the event (see below), the second is the name of the
1829 md device which is affected, and the third is the name of a related
1830 device if relevant (such as a component device that has failed).
1834 is given, then a program or an E-mail address must be specified on the
1835 command line or in the config file. If neither are available, then
1837 will not monitor anything.
1841 will continue monitoring as long as something was found to monitor. If
1842 no program or email is given, then each event is reported to
1845 The different events are:
1849 .B DeviceDisappeared
1850 An md array which previously was configured appears to no longer be
1851 configured. (syslog priority: Critical)
1855 was told to monitor an array which is RAID0 or Linear, then it will
1857 .B DeviceDisappeared
1858 with the extra information
1860 This is because RAID0 and Linear do not support the device-failed,
1861 hot-spare and resync operations which are monitored.
1865 An md array started reconstruction. (syslog priority: Warning)
1871 is a two-digit number (ie. 05, 48). This indicates that rebuild
1872 has passed that many percent of the total. The events are generated
1873 with fixed increment since 0. Increment size may be specified with
1874 a commandline option (default is 20). (syslog priority: Warning)
1878 An md array that was rebuilding, isn't any more, either because it
1879 finished normally or was aborted. (syslog priority: Warning)
1883 An active component device of an array has been marked as
1884 faulty. (syslog priority: Critical)
1888 A spare component device which was being rebuilt to replace a faulty
1889 device has failed. (syslog priority: Critical)
1893 A spare component device which was being rebuilt to replace a faulty
1894 device has been successfully rebuilt and has been made active.
1895 (syslog priority: Info)
1899 A new md array has been detected in the
1901 file. (syslog priority: Info)
1905 A newly noticed array appears to be degraded. This message is not
1908 notices a drive failure which causes degradation, but only when
1910 notices that an array is degraded when it first sees the array.
1911 (syslog priority: Critical)
1915 A spare drive has been moved from one array in a
1917 to another to allow a failed drive to be replaced.
1918 (syslog priority: Info)
1924 has been told, via the config file, that an array should have a certain
1925 number of spare devices, and
1927 detects that it has fewer than this number when it first sees the
1928 array, it will report a
1931 (syslog priority: Warning)
1935 An array was found at startup, and the
1938 (syslog priority: Info)
1948 cause Email to be sent. All events cause the program to be run.
1949 The program is run with two or three arguments: the event
1950 name, the array device and possibly a second device.
1952 Each event has an associated array device (e.g.
1954 and possibly a second device. For
1959 the second device is the relevant component device.
1962 the second device is the array that the spare was moved from.
1966 to move spares from one array to another, the different arrays need to
1967 be labeled with the same
1969 in the configuration file. The
1971 name can be any string; it is only necessary that different spare
1972 groups use different names.
1976 detects that an array in a spare group has fewer active
1977 devices than necessary for the complete array, and has no spare
1978 devices, it will look for another array in the same spare group that
1979 has a full complement of working drive and a spare. It will then
1980 attempt to remove the spare from the second drive and add it to the
1982 If the removal succeeds but the adding fails, then it is added back to
1986 The GROW mode is used for changing the size or shape of an active
1988 For this to work, the kernel must support the necessary change.
1989 Various types of growth are being added during 2.6 development,
1990 including restructuring a RAID5 array to have more active devices.
1992 Currently the only support available is to
1994 change the "size" attribute
1995 for RAID1, RAID5 and RAID6.
1997 increase or decrease the "raid\-devices" attribute of RAID1, RAID5,
2000 change the chunk-size and layout of RAID5 and RAID6.
2002 convert between RAID1 and RAID5, and between RAID5 and RAID6.
2004 add a write-intent bitmap to any array which supports these bitmaps, or
2005 remove a write-intent bitmap from such an array.
2008 GROW mode is not currently supported for
2010 or arrays inside containers.
2013 Normally when an array is built the "size" it taken from the smallest
2014 of the drives. If all the small drives in an arrays are, one at a
2015 time, removed and replaced with larger drives, then you could have an
2016 array of large drives with only a small amount used. In this
2017 situation, changing the "size" with "GROW" mode will allow the extra
2018 space to start being used. If the size is increased in this way, a
2019 "resync" process will start to make sure the new parts of the array
2022 Note that when an array changes size, any filesystem that may be
2023 stored in the array will not automatically grow to use the space. The
2024 filesystem will need to be explicitly told to use the extra space.
2026 Also the size of an array cannot be changed while it has an active
2027 bitmap. If an array has a bitmap, it must be removed before the size
2028 can be changed. Once the change it complete a new bitmap can be created.
2030 .SS RAID\-DEVICES CHANGES
2032 A RAID1 array can work with any number of devices from 1 upwards
2033 (though 1 is not very useful). There may be times which you want to
2034 increase or decrease the number of active devices. Note that this is
2035 different to hot-add or hot-remove which changes the number of
2038 When reducing the number of devices in a RAID1 array, the slots which
2039 are to be removed from the array must already be vacant. That is, the
2040 devices which were in those slots must be failed and removed.
2042 When the number of devices is increased, any hot spares that are
2043 present will be activated immediately.
2045 Changing the number of active devices in a RAID5 or RAID6 is much more
2046 effort. Every block in the array will need to be read and written
2047 back to a new location. From 2.6.17, the Linux Kernel is able to
2048 increase the number of devices in a RAID5 safely, including restarting
2049 an interrupted "reshape". From 2.6.31, the Linux Kernel is able to
2050 increase or decrease the number of devices in a RAID5 or RAID6.
2052 When decreasing the number of devices, the size of the array will also
2053 decrease. If there was data in the array, it could get destroyed and
2054 this is not reversible. To help prevent accidents,
2056 requires that the size of the array be decreased first with
2057 .BR "mdadm --grow --array-size" .
2058 This is a reversible change which simply makes the end of the array
2059 inaccessible. The integrity of any data can then be checked before
2060 the non-reversible reduction in the number of devices is request.
2062 When relocating the first few stripes on a RAID5, it is not possible
2063 to keep the data on disk completely consistent and crash-proof. To
2064 provide the required safety, mdadm disables writes to the array while
2065 this "critical section" is reshaped, and takes a backup of the data
2066 that is in that section. This backup is normally stored in any spare
2067 devices that the array has, however it can also be stored in a
2068 separate file specified with the
2070 option. If this option is used, and the system does crash during the
2071 critical period, the same file must be passed to
2073 to restore the backup and reassemble the array.
2077 Changing the RAID level of any array happens instantaneously. However
2078 in the RAID to RAID6 case this requires a non-standard layout of the
2079 RAID6 data, and in the RAID6 to RAID5 case that non-standard layout is
2080 required before the change can be accomplish. So while the level
2081 change is instant, the accompanying layout change can take quite a
2084 .SS CHUNK-SIZE AND LAYOUT CHANGES
2086 Changing the chunk-size of layout without also changing the number of
2087 devices as the same time will involve re-writing all blocks in-place.
2088 To ensure against data loss in the case of a crash, a
2090 must be provided for these changes. Small sections of the array will
2091 be copied to the backup file while they are being rearranged.
2093 If the reshape is interrupted for any reason, this backup file must be
2095 .B "mdadm --assemble"
2096 so the array can be reassembled. Consequently the file cannot be
2097 stored on the device being reshaped.
2102 A write-intent bitmap can be added to, or removed from, an active
2103 array. Either internal bitmaps, or bitmaps stored in a separate file,
2104 can be added. Note that if you add a bitmap stored in a file which is
2105 in a filesystem that is on the RAID array being affected, the system
2106 will deadlock. The bitmap must be on a separate filesystem.
2108 .SH INCREMENTAL MODE
2112 .B mdadm \-\-incremental
2118 .B mdadm \-\-incremental \-\-rebuild
2121 .B mdadm \-\-incremental \-\-run \-\-scan
2124 This mode is designed to be used in conjunction with a device
2125 discovery system. As devices are found in a system, they can be
2127 .B "mdadm \-\-incremental"
2128 to be conditionally added to an appropriate array.
2130 If the device passed is a
2132 device created by a previous call to
2134 then rather than trying to add that device to an array, all the arrays
2135 described by the metadata of the container will be started.
2138 performs a number of tests to determine if the device is part of an
2139 array, and which array it should be part of. If an appropriate array
2140 is found, or can be created,
2142 adds the device to the array and conditionally starts the array.
2146 will only add devices to an array which were previously working
2147 (active or spare) parts of that array. It does not currently support
2148 automatic inclusion of a new drive as a spare in some array.
2152 makes are as follow:
2154 Is the device permitted by
2156 That is, is it listed in a
2158 line in that file. If
2160 is absent then the default it to allow any device. Similar if
2162 contains the special word
2164 then any device is allowed. Otherwise the device name given to
2166 must match one of the names or patterns in a
2171 Does the device have a valid md superblock. If a specific metadata
2172 version is request with
2176 then only that style of metadata is accepted, otherwise
2178 finds any known version of metadata. If no
2180 metadata is found, the device is rejected.
2184 Does the metadata match an expected array?
2185 The metadata can match in two ways. Either there is an array listed
2188 which identifies the array (either by UUID, by name, by device list,
2189 or by minor-number), or the array was created with a
2195 or on the command line.
2198 is not able to positively identify the array as belonging to the
2199 current host, the device will be rejected.
2203 keeps a list of arrays that it has partially assembled in
2204 .B /var/run/mdadm/map
2206 .B /var/run/mdadm.map
2207 if the directory doesn't exist. Or maybe even
2208 .BR /dev/.mdadm.map ).
2209 If no array exists which matches
2210 the metadata on the new device,
2212 must choose a device name and unit number. It does this based on any
2215 or any name information stored in the metadata. If this name
2216 suggests a unit number, that number will be used, otherwise a free
2217 unit number will be chosen. Normally
2219 will prefer to create a partitionable array, however if the
2223 suggests that a non-partitionable array is preferred, that will be
2226 If the array is not found in the config file and its metadata does not
2227 identify it as belonging to the "homehost", then
2229 will choose a name for the array which is certain not to conflict with
2230 any array which does belong to this host. It does this be adding an
2231 underscore and a small number to the name preferred by the metadata.
2233 Once an appropriate array is found or created and the device is added,
2235 must decide if the array is ready to be started. It will
2236 normally compare the number of available (non-spare) devices to the
2237 number of devices that the metadata suggests need to be active. If
2238 there are at least that many, the array will be started. This means
2239 that if any devices are missing the array will not be restarted.
2245 in which case the array will be run as soon as there are enough
2246 devices present for the data to be accessible. For a RAID1, that
2247 means one device will start the array. For a clean RAID5, the array
2248 will be started as soon as all but one drive is present.
2250 Note that neither of these approaches is really ideal. If it can
2251 be known that all device discovery has completed, then
2255 can be run which will try to start all arrays that are being
2256 incrementally assembled. They are started in "read-auto" mode in
2257 which they are read-only until the first write request. This means
2258 that no metadata updates are made and no attempt at resync or recovery
2259 happens. Further devices that are found before the first write can
2260 still be added safely.
2263 This section describes environment variables that affect how mdadm
2268 Setting this value to 1 will prevent mdadm from automatically launching
2269 mdmon. This variable is intended primarily for debugging mdadm/mdmon.
2275 does not create any device nodes in /dev, but leaves that task to
2279 appears not to be configured, or if this environment variable is set
2282 will create and devices that are needed.
2286 .B " mdadm \-\-query /dev/name-of-device"
2288 This will find out if a given device is a RAID array, or is part of
2289 one, and will provide brief information about the device.
2291 .B " mdadm \-\-assemble \-\-scan"
2293 This will assemble and start all arrays listed in the standard config
2294 file. This command will typically go in a system startup file.
2296 .B " mdadm \-\-stop \-\-scan"
2298 This will shut down all arrays that can be shut down (i.e. are not
2299 currently in use). This will typically go in a system shutdown script.
2301 .B " mdadm \-\-follow \-\-scan \-\-delay=120"
2303 If (and only if) there is an Email address or program given in the
2304 standard config file, then
2305 monitor the status of all arrays listed in that file by
2306 polling them ever 2 minutes.
2308 .B " mdadm \-\-create /dev/md0 \-\-level=1 \-\-raid\-devices=2 /dev/hd[ac]1"
2310 Create /dev/md0 as a RAID1 array consisting of /dev/hda1 and /dev/hdc1.
2313 .B " echo 'DEVICE /dev/hd*[0\-9] /dev/sd*[0\-9]' > mdadm.conf"
2315 .B " mdadm \-\-detail \-\-scan >> mdadm.conf"
2317 This will create a prototype config file that describes currently
2318 active arrays that are known to be made from partitions of IDE or SCSI drives.
2319 This file should be reviewed before being used as it may
2320 contain unwanted detail.
2322 .B " echo 'DEVICE /dev/hd[a\-z] /dev/sd*[a\-z]' > mdadm.conf"
2324 .B " mdadm \-\-examine \-\-scan \-\-config=mdadm.conf >> mdadm.conf"
2326 This will find arrays which could be assembled from existing IDE and
2327 SCSI whole drives (not partitions), and store the information in the
2328 format of a config file.
2329 This file is very likely to contain unwanted detail, particularly
2332 entries. It should be reviewed and edited before being used as an
2335 .B " mdadm \-\-examine \-\-brief \-\-scan \-\-config=partitions"
2337 .B " mdadm \-Ebsc partitions"
2339 Create a list of devices by reading
2340 .BR /proc/partitions ,
2341 scan these for RAID superblocks, and printout a brief listing of all
2344 .B " mdadm \-Ac partitions \-m 0 /dev/md0"
2346 Scan all partitions and devices listed in
2347 .BR /proc/partitions
2350 out of all such devices with a RAID superblock with a minor number of 0.
2352 .B " mdadm \-\-monitor \-\-scan \-\-daemonise > /var/run/mdadm"
2354 If config file contains a mail address or alert program, run mdadm in
2355 the background in monitor mode monitoring all md devices. Also write
2356 pid of mdadm daemon to
2357 .BR /var/run/mdadm .
2359 .B " mdadm \-Iq /dev/somedevice"
2361 Try to incorporate newly discovered device into some array as
2364 .B " mdadm \-\-incremental \-\-rebuild \-\-run \-\-scan"
2366 Rebuild the array map from any current arrays, and then start any that
2369 .B " mdadm /dev/md4 --fail detached --remove detached"
2371 Any devices which are components of /dev/md4 will be marked as faulty
2372 and then remove from the array.
2374 .B " mdadm --grow /dev/md4 --level=6 --backup-file=/root/backup-md4
2378 which is currently a RAID5 array will be converted to RAID6. There
2379 should normally already be a spare drive attached to the array as a
2380 RAID6 needs one more drive than a matching RAID5.
2382 .B " mdadm --create /dev/md/ddf --metadata=ddf --raid-disks 6 /dev/sd[a-f]"
2384 Create a DDF array over 6 devices.
2386 .B " mdadm --create /dev/md/home -n3 -l5 -z 30000000 /dev/md/ddf"
2388 Create a RAID5 array over any 3 devices in the given DDF set. Use
2389 only 30 gigabytes of each device.
2391 .B " mdadm -A /dev/md/ddf1 /dev/sd[a-f]"
2393 Assemble a pre-exist ddf array.
2395 .B " mdadm -I /dev/md/ddf1"
2397 Assemble all arrays contained in the ddf array, assigning names as
2400 .B " mdadm \-\-create \-\-help"
2402 Provide help about the Create mode.
2404 .B " mdadm \-\-config \-\-help"
2406 Provide help about the format of the config file.
2408 .B " mdadm \-\-help"
2410 Provide general help.
2420 lists all active md devices with information about them.
2422 uses this to find arrays when
2424 is given in Misc mode, and to monitor array reconstruction
2429 The config file lists which devices may be scanned to see if
2430 they contain MD super block, and gives identifying information
2431 (e.g. UUID) about known MD arrays. See
2435 .SS /var/run/mdadm/map
2438 mode is used, this file gets a list of arrays currently being created.
2441 does not exist as a directory, then
2442 .B /var/run/mdadm.map
2445 is not available (as may be the case during early boot),
2447 is used on the basis that
2449 is usually available very early in boot.
2454 understand two sorts of names for array devices.
2456 The first is the so-called 'standard' format name, which matches the
2457 names used by the kernel and which appear in
2460 The second sort can be freely chosen, but must reside in
2462 When giving a device name to
2464 to create or assemble an array, either full path name such as
2468 can be given, or just the suffix of the second sort of name, such as
2474 chooses device names during auto-assembly or incremental assembly, it
2475 will sometimes add a small sequence number to the end of the name to
2476 avoid conflicted between multiple arrays that have the same name. If
2478 can reasonably determine that the array really is meant for this host,
2479 either by a hostname in the metadata, or by the presence of the array
2480 in /etc/mdadm.conf, then it will leave off the suffix if possible.
2481 Also if the homehost is specified as
2484 will only use a suffix if a different array of the same name already
2485 exists or is listed in the config file.
2487 The standard names for non-partitioned arrays (the only sort of md
2488 array available in 2.4 and earlier) are of the form
2492 where NN is a number.
2493 The standard names for partitionable arrays (as available from 2.6
2494 onwards) are of the form
2498 Partition numbers should be indicated by added "pMM" to these, thus "/dev/md/d1p2".
2500 From kernel version, 2.6.28 the "non-partitioned array" can actually
2501 be partitioned. So the "md_dNN" names are no longer needed, and
2502 partitions such as "/dev/mdNNpXX" are possible.
2506 was previously known as
2510 is completely separate from the
2512 package, and does not use the
2514 configuration file at all.
2517 For further information on mdadm usage, MD and the various levels of
2520 .B http://linux\-raid.osdl.org/
2522 (based upon Jakob \(/Ostergaard's Software\-RAID.HOWTO)
2524 .\"for new releases of the RAID driver check out:
2527 .\".UR ftp://ftp.kernel.org/pub/linux/kernel/people/mingo/raid-patches
2528 .\"ftp://ftp.kernel.org/pub/linux/kernel/people/mingo/raid-patches
2533 .\".UR http://www.cse.unsw.edu.au/~neilb/patches/linux-stable/
2534 .\"http://www.cse.unsw.edu.au/~neilb/patches/linux-stable/
2537 The latest version of
2539 should always be available from
2541 .B http://www.kernel.org/pub/linux/utils/raid/mdadm/