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.
141 flag is passed in we will remove the device from any active array
142 instead of adding it.
148 in this mode, then any arrays within that container will be assembled
153 This is for doing things to specific components of an array such as
154 adding new spares and removing faulty devices.
158 This is an 'everything else' mode that supports operations on active
159 arrays, operations on component devices such as erasing old superblocks, and
160 information gathering operations.
161 .\"This mode allows operations on independent devices such as examine MD
162 .\"superblocks, erasing old superblocks and stopping active arrays.
166 This mode does not act on a specific device or array, but rather it
167 requests the Linux Kernel to activate any auto-detected arrays.
170 .SH Options for selecting a mode are:
173 .BR \-A ", " \-\-assemble
174 Assemble a pre-existing array.
177 .BR \-B ", " \-\-build
178 Build a legacy array without superblocks.
181 .BR \-C ", " \-\-create
185 .BR \-F ", " \-\-follow ", " \-\-monitor
191 .BR \-G ", " \-\-grow
192 Change the size or shape of an active array.
195 .BR \-I ", " \-\-incremental
196 Add/remove a single device to/from an appropriate array, and possibly start the array.
200 Request that the kernel starts any auto-detected arrays. This can only
203 is compiled into the kernel \(em not if it is a module.
204 Arrays can be auto-detected by the kernel if all the components are in
205 primary MS-DOS partitions with partition type
207 and all use v0.90 metadata.
208 In-kernel autodetect is not recommended for new installations. Using
210 to detect and assemble arrays \(em possibly in an
212 \(em is substantially more flexible and should be preferred.
215 If a device is given before any options, or if the first option is
220 then the MANAGE mode is assumed.
221 Anything other than these will cause the
225 .SH Options that are not mode-specific are:
228 .BR \-h ", " \-\-help
229 Display general help message or, after one of the above options, a
230 mode-specific help message.
234 Display more detailed help about command line parsing and some commonly
238 .BR \-V ", " \-\-version
239 Print version information for mdadm.
242 .BR \-v ", " \-\-verbose
243 Be more verbose about what is happening. This can be used twice to be
245 The extra verbosity currently only affects
246 .B \-\-detail \-\-scan
248 .BR "\-\-examine \-\-scan" .
251 .BR \-q ", " \-\-quiet
252 Avoid printing purely informative messages. With this,
254 will be silent unless there is something really important to report.
257 .BR \-f ", " \-\-force
258 Be more forceful about certain operations. See the various modes for
259 the exact meaning of this option in different contexts.
262 .BR \-c ", " \-\-config=
263 Specify the config file. Default is to use
264 .BR /etc/mdadm.conf ,
265 or if that is missing then
266 .BR /etc/mdadm/mdadm.conf .
267 If the config file given is
269 then nothing will be read, but
271 will act as though the config file contained exactly
272 .B "DEVICE partitions containers"
275 to find a list of devices to scan, and
277 to find a list of containers to examine.
280 is given for the config file, then
282 will act as though the config file were empty.
285 .BR \-s ", " \-\-scan
288 for missing information.
289 In general, this option gives
291 permission to get any missing information (like component devices,
292 array devices, array identities, and alert destination) from the
293 configuration file (see previous option);
294 one exception is MISC mode when using
300 says to get a list of array devices from
304 .BR \-e ", " \-\-metadata=
305 Declare the style of RAID metadata (superblock) to be used. The
306 default is {DEFAULT_METADATA} for
308 and to guess for other operations.
309 The default can be overridden by setting the
318 .ie '{DEFAULT_METADATA}'0.90'
319 .IP "0, 0.90, default"
323 Use the original 0.90 format superblock. This format limits arrays to
324 28 component devices and limits component devices of levels 1 and
325 greater to 2 terabytes.
326 .ie '{DEFAULT_METADATA}'0.90'
327 .IP "1, 1.0, 1.1, 1.2"
329 .IP "1, 1.0, 1.1, 1.2 default"
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). "1" is equivalent to "1.0".
335 'if '{DEFAULT_METADATA}'1.2' "default" is equivalent to "1.2".
337 Use the "Industry Standard" DDF (Disk Data Format) format defined by
339 When creating a DDF array a
341 will be created, and normal arrays can be created in that container.
343 Use the Intel(R) Matrix Storage Manager metadata format. This creates a
345 which is managed in a similar manner to DDF, and is supported by an
346 option-rom on some platforms:
348 .B http://www.intel.com/design/chipsets/matrixstorage_sb.htm
354 This will override any
356 setting in the config file and provides the identity of the host which
357 should be considered the home for any arrays.
359 When creating an array, the
361 will be recorded in the metadata. For version-1 superblocks, it will
362 be prefixed to the array name. For version-0.90 superblocks, part of
363 the SHA1 hash of the hostname will be stored in the later half of the
366 When reporting information about an array, any array which is tagged
367 for the given homehost will be reported as such.
369 When using Auto-Assemble, only arrays tagged for the given homehost
370 will be allowed to use 'local' names (i.e. not ending in '_' followed
371 by a digit string). See below under
372 .BR "Auto Assembly" .
374 .SH For create, build, or grow:
377 .BR \-n ", " \-\-raid\-devices=
378 Specify the number of active devices in the array. This, plus the
379 number of spare devices (see below) must equal the number of
381 (including "\fBmissing\fP" devices)
382 that are listed on the command line for
384 Setting a value of 1 is probably
385 a mistake and so requires that
387 be specified first. A value of 1 will then be allowed for linear,
388 multipath, RAID0 and RAID1. It is never allowed for RAID4, RAID5 or RAID6.
390 This number can only be changed using
392 for RAID1, RAID4, RAID5 and RAID6 arrays, and only on kernels which provide
393 the necessary support.
396 .BR \-x ", " \-\-spare\-devices=
397 Specify the number of spare (eXtra) devices in the initial array.
398 Spares can also be added
399 and removed later. The number of component devices listed
400 on the command line must equal the number of RAID devices plus the
401 number of spare devices.
404 .BR \-z ", " \-\-size=
405 Amount (in Kibibytes) of space to use from each drive in RAID levels 1/4/5/6.
406 This must be a multiple of the chunk size, and must leave about 128Kb
407 of space at the end of the drive for the RAID superblock.
408 If this is not specified
409 (as it normally is not) the smallest drive (or partition) sets the
410 size, though if there is a variance among the drives of greater than 1%, a warning is
413 A suffix of 'M' or 'G' can be given to indicate Megabytes or
414 Gigabytes respectively.
416 This value can be set with
418 for RAID level 1/4/5/6. If the array was created with a size smaller
419 than the currently active drives, the extra space can be accessed
422 The size can be given as
424 which means to choose the largest size that fits on all current drives.
426 This value can not be used with
428 metadata such as DDF and IMSM.
431 .BR \-Z ", " \-\-array-size=
432 This is only meaningful with
434 and its effect is not persistent: when the array is stopped and
435 restarted the default array size will be restored.
437 Setting the array-size causes the array to appear smaller to programs
438 that access the data. This is particularly needed before reshaping an
439 array so that it will be smaller. As the reshape is not reversible,
440 but setting the size with
442 is, it is required that the array size is reduced as appropriate
443 before the number of devices in the array is reduced.
445 A suffix of 'M' or 'G' can be given to indicate Megabytes or
446 Gigabytes respectively.
449 restores the apparent size of the array to be whatever the real
450 amount of available space is.
453 .BR \-c ", " \-\-chunk=
454 Specify chunk size of kibibytes. The default when creating an
455 array is 512KB. To ensure compatibility with earlier versions, the
456 default when Building and array with no persistent metadata is 64KB.
457 This is only meaningful for RAID0, RAID4, RAID5, RAID6, and RAID10.
459 A suffix of 'M' or 'G' can be given to indicate Megabytes or
460 Gigabytes respectively.
464 Specify rounding factor for a Linear array. The size of each
465 component will be rounded down to a multiple of this size.
466 This is a synonym for
468 but highlights the different meaning for Linear as compared to other
469 RAID levels. The default is 64K if a kernel earlier than 2.6.16 is in
470 use, and is 0K (i.e. no rounding) in later kernels.
473 .BR \-l ", " \-\-level=
474 Set RAID level. When used with
476 options are: linear, raid0, 0, stripe, raid1, 1, mirror, raid4, 4,
477 raid5, 5, raid6, 6, raid10, 10, multipath, mp, faulty, container.
478 Obviously some of these are synonymous.
482 metadata type is requested, only the
484 level is permitted, and it does not need to be explicitly given.
488 only linear, stripe, raid0, 0, raid1, multipath, mp, and faulty are valid.
492 to change the RAID level in some cases. See LEVEL CHANGES below.
495 .BR \-p ", " \-\-layout=
496 This option configures the fine details of data layout for RAID5, RAID6,
497 and RAID10 arrays, and controls the failure modes for
500 The layout of the RAID5 parity block can be one of
501 .BR left\-asymmetric ,
502 .BR left\-symmetric ,
503 .BR right\-asymmetric ,
504 .BR right\-symmetric ,
505 .BR la ", " ra ", " ls ", " rs .
507 .BR left\-symmetric .
509 It is also possibly to cause RAID5 to use a RAID4-like layout by
515 Finally for RAID5 there are DDF\-compatible layouts,
516 .BR ddf\-zero\-restart ,
517 .BR ddf\-N\-restart ,
519 .BR ddf\-N\-continue .
521 These same layouts are available for RAID6. There are also 4 layouts
522 that will provide an intermediate stage for converting between RAID5
523 and RAID6. These provide a layout which is identical to the
524 corresponding RAID5 layout on the first N\-1 devices, and has the 'Q'
525 syndrome (the second 'parity' block used by RAID6) on the last device.
527 .BR left\-symmetric\-6 ,
528 .BR right\-symmetric\-6 ,
529 .BR left\-asymmetric\-6 ,
530 .BR right\-asymmetric\-6 ,
532 .BR parity\-first\-6 .
534 When setting the failure mode for level
537 .BR write\-transient ", " wt ,
538 .BR read\-transient ", " rt ,
539 .BR write\-persistent ", " wp ,
540 .BR read\-persistent ", " rp ,
542 .BR read\-fixable ", " rf ,
543 .BR clear ", " flush ", " none .
545 Each failure mode can be followed by a number, which is used as a period
546 between fault generation. Without a number, the fault is generated
547 once on the first relevant request. With a number, the fault will be
548 generated after that many requests, and will continue to be generated
549 every time the period elapses.
551 Multiple failure modes can be current simultaneously by using the
553 option to set subsequent failure modes.
555 "clear" or "none" will remove any pending or periodic failure modes,
556 and "flush" will clear any persistent faults.
558 Finally, the layout options for RAID10 are one of 'n', 'o' or 'f' followed
559 by a small number. The default is 'n2'. The supported options are:
562 signals 'near' copies. Multiple copies of one data block are at
563 similar offsets in different devices.
566 signals 'offset' copies. Rather than the chunks being duplicated
567 within a stripe, whole stripes are duplicated but are rotated by one
568 device so duplicate blocks are on different devices. Thus subsequent
569 copies of a block are in the next drive, and are one chunk further
574 (multiple copies have very different offsets).
575 See md(4) for more detail about 'near', 'offset', and 'far'.
577 The number is the number of copies of each datablock. 2 is normal, 3
578 can be useful. This number can be at most equal to the number of
579 devices in the array. It does not need to divide evenly into that
580 number (e.g. it is perfectly legal to have an 'n2' layout for an array
581 with an odd number of devices).
583 When an array is converted between RAID5 and RAID6 an intermediate
584 RAID6 layout is used in which the second parity block (Q) is always on
585 the last device. To convert a RAID5 to RAID6 and leave it in this new
586 layout (which does not require re-striping) use
587 .BR \-\-layout=preserve .
588 This will try to avoid any restriping.
590 The converse of this is
591 .B \-\-layout=normalise
592 which will change a non-standard RAID6 layout into a more standard
599 (thus explaining the p of
603 .BR \-b ", " \-\-bitmap=
604 Specify a file to store a write-intent bitmap in. The file should not
607 is also given. The same file should be provided
608 when assembling the array. If the word
610 is given, then the bitmap is stored with the metadata on the array,
611 and so is replicated on all devices. If the word
615 mode, then any bitmap that is present is removed.
617 To help catch typing errors, the filename must contain at least one
618 slash ('/') if it is a real file (not 'internal' or 'none').
620 Note: external bitmaps are only known to work on ext2 and ext3.
621 Storing bitmap files on other filesystems may result in serious problems.
624 .BR \-\-bitmap\-chunk=
625 Set the chunksize of the bitmap. Each bit corresponds to that many
626 Kilobytes of storage.
627 When using a file based bitmap, the default is to use the smallest
628 size that is at-least 4 and requires no more than 2^21 chunks.
631 bitmap, the chunksize defaults to 64Meg, or larger if necessary to
632 fit the bitmap into the available space.
634 A suffix of 'M' or 'G' can be given to indicate Megabytes or
635 Gigabytes respectively.
638 .BR \-W ", " \-\-write\-mostly
639 subsequent devices listed in a
644 command will be flagged as 'write-mostly'. This is valid for RAID1
645 only and means that the 'md' driver will avoid reading from these
646 devices if at all possible. This can be useful if mirroring over a
650 .BR \-\-write\-behind=
651 Specify that write-behind mode should be enabled (valid for RAID1
652 only). If an argument is specified, it will set the maximum number
653 of outstanding writes allowed. The default value is 256.
654 A write-intent bitmap is required in order to use write-behind
655 mode, and write-behind is only attempted on drives marked as
659 .BR \-\-assume\-clean
662 that the array pre-existed and is known to be clean. It can be useful
663 when trying to recover from a major failure as you can be sure that no
664 data will be affected unless you actually write to the array. It can
665 also be used when creating a RAID1 or RAID10 if you want to avoid the
666 initial resync, however this practice \(em while normally safe \(em is not
667 recommended. Use this only if you really know what you are doing.
669 When the devices that will be part of a new array were filled
670 with zeros before creation the operator knows the array is
671 actually clean. If that is the case, such as after running
672 badblocks, this argument can be used to tell mdadm the
673 facts the operator knows.
676 .BR \-\-backup\-file=
679 is used to increase the number of
680 raid-devices in a RAID5 if there are no spare devices available.
681 See the GROW MODE section below on RAID\-DEVICES CHANGES. The file
682 should be stored on a separate device, not on the RAID array being
686 .BR \-N ", " \-\-name=
689 for the array. This is currently only effective when creating an
690 array with a version-1 superblock, or an array in a DDF container.
691 The name is a simple textual string that can be used to identify array
692 components when assembling. If name is needed but not specified, it
693 is taken from the basename of the device that is being created.
705 run the array, even if some of the components
706 appear to be active in another array or filesystem. Normally
708 will ask for confirmation before including such components in an
709 array. This option causes that question to be suppressed.
712 .BR \-f ", " \-\-force
715 accept the geometry and layout specified without question. Normally
717 will not allow creation of an array with only one device, and will try
718 to create a RAID5 array with one missing drive (as this makes the
719 initial resync work faster). With
722 will not try to be so clever.
725 .BR \-a ", " "\-\-auto{=yes,md,mdp,part,p}{NN}"
726 Instruct mdadm how to create the device file if needed, possibly allocating
727 an unused minor number. "md" causes a non-partitionable array
728 to be used (though since Linux 2.6.28, these array devices are in fact
729 partitionable). "mdp", "part" or "p" causes a partitionable array (2.6 and
730 later) to be used. "yes" requires the named md device to have
731 a 'standard' format, and the type and minor number will be determined
732 from this. With mdadm 3.0, device creation is normally left up to
734 so this option is unlikely to be needed.
735 See DEVICE NAMES below.
737 The argument can also come immediately after
742 is not given on the command line or in the config file, then
748 is also given, then any
750 entries in the config file will override the
752 instruction given on the command line.
754 For partitionable arrays,
756 will create the device file for the whole array and for the first 4
757 partitions. A different number of partitions can be specified at the
758 end of this option (e.g.
760 If the device name ends with a digit, the partition names add a 'p',
762 .IR /dev/md/home1p3 .
763 If there is no trailing digit, then the partition names just have a
765 .IR /dev/md/scratch3 .
767 If the md device name is in a 'standard' format as described in DEVICE
768 NAMES, then it will be created, if necessary, with the appropriate
769 device number based on that name. If the device name is not in one of these
770 formats, then a unused device number will be allocated. The device
771 number will be considered unused if there is no active array for that
772 number, and there is no entry in /dev for that number and with a
773 non-standard name. Names that are not in 'standard' format are only
774 allowed in "/dev/md/".
778 .\".BR \-\-symlink = no
783 .\"to create devices in
785 .\"it will also create symlinks from
787 .\"with names starting with
793 .\"to suppress this, or
794 .\".B \-\-symlink=yes
795 .\"to enforce this even if it is suppressing
803 .BR \-u ", " \-\-uuid=
804 uuid of array to assemble. Devices which don't have this uuid are
808 .BR \-m ", " \-\-super\-minor=
809 Minor number of device that array was created for. Devices which
810 don't have this minor number are excluded. If you create an array as
811 /dev/md1, then all superblocks will contain the minor number 1, even if
812 the array is later assembled as /dev/md2.
814 Giving the literal word "dev" for
818 to use the minor number of the md device that is being assembled.
821 .B \-\-super\-minor=dev
822 will look for super blocks with a minor number of 0.
825 is only relevant for v0.90 metadata, and should not normally be used.
831 .BR \-N ", " \-\-name=
832 Specify the name of the array to assemble. This must be the name
833 that was specified when creating the array. It must either match
834 the name stored in the superblock exactly, or it must match
837 prefixed to the start of the given name.
840 .BR \-f ", " \-\-force
841 Assemble the array even if the metadata on some devices appears to be
844 cannot find enough working devices to start the array, but can find
845 some devices that are recorded as having failed, then it will mark
846 those devices as working so that the array can be started.
847 An array which requires
849 to be started may contain data corruption. Use it carefully.
853 Attempt to start the array even if fewer drives were given than were
854 present last time the array was active. Normally if not all the
855 expected drives are found and
857 is not used, then the array will be assembled but not started.
860 an attempt will be made to start it anyway.
864 This is the reverse of
866 in that it inhibits the startup of array unless all expected drives
867 are present. This is only needed with
869 and can be used if the physical connections to devices are
870 not as reliable as you would like.
873 .BR \-a ", " "\-\-auto{=no,yes,md,mdp,part}"
874 See this option under Create and Build options.
877 .BR \-b ", " \-\-bitmap=
878 Specify the bitmap file that was given when the array was created. If
881 bitmap, there is no need to specify this when assembling the array.
884 .BR \-\-backup\-file=
887 was used to grow the number of raid-devices in a RAID5, and the system
888 crashed during the critical section, then the same
892 to allow possibly corrupted data to be restored.
895 .BR \-U ", " \-\-update=
896 Update the superblock on each device while assembling the array. The
897 argument given to this flag can be one of
911 option will adjust the superblock of an array what was created on a Sparc
912 machine running a patched 2.2 Linux kernel. This kernel got the
913 alignment of part of the superblock wrong. You can use the
914 .B "\-\-examine \-\-sparc2.2"
917 to see what effect this would have.
921 option will update the
923 field on each superblock to match the minor number of the array being
925 This can be useful if
927 reports a different "Preferred Minor" to
929 In some cases this update will be performed automatically
930 by the kernel driver. In particular the update happens automatically
931 at the first write to an array with redundancy (RAID level 1 or
932 greater) on a 2.6 (or later) kernel.
936 option will change the uuid of the array. If a UUID is given with the
938 option that UUID will be used as a new UUID and will
940 be used to help identify the devices in the array.
943 is given, a random UUID is chosen.
947 option will change the
949 of the array as stored in the superblock. This is only supported for
950 version-1 superblocks.
954 option will change the
956 as recorded in the superblock. For version-0 superblocks, this is the
957 same as updating the UUID.
958 For version-1 superblocks, this involves updating the name.
962 option will cause the array to be marked
964 meaning that any redundancy in the array (e.g. parity for RAID5,
965 copies for RAID1) may be incorrect. This will cause the RAID system
966 to perform a "resync" pass to make sure that all redundant information
971 option allows arrays to be moved between machines with different
973 When assembling such an array for the first time after a move, giving
974 .B "\-\-update=byteorder"
977 to expect superblocks to have their byteorder reversed, and will
978 correct that order before assembling the array. This is only valid
979 with original (Version 0.90) superblocks.
983 option will correct the summaries in the superblock. That is the
984 counts of total, working, active, failed, and spare devices.
988 will rarely be of use. It applies to version 1.1 and 1.2 metadata
989 only (where the metadata is at the start of the device) and is only
990 useful when the component device has changed size (typically become
991 larger). The version 1 metadata records the amount of the device that
992 can be used to store data, so if a device in a version 1.1 or 1.2
993 array becomes larger, the metadata will still be visible, but the
994 extra space will not. In this case it might be useful to assemble the
996 .BR \-\-update=devicesize .
999 to determine the maximum usable amount of space on each device and
1000 update the relevant field in the metadata.
1004 .B \-\-auto\-update\-homehost
1005 This flag is only meaningful with auto-assembly (see discussion below).
1006 In that situation, if no suitable arrays are found for this homehost,
1008 will rescan for any arrays at all and will assemble them and update the
1009 homehost to match the current host.
1012 .SH For Manage mode:
1015 .BR \-t ", " \-\-test
1016 Unless a more serious error occurred,
1018 will exit with a status of 2 if no changes were made to the array and
1019 0 if at least one change was made.
1020 This can be useful when an indirect specifier such as
1025 is used in requesting an operation on the array.
1027 will report failure if these specifiers didn't find any match.
1030 .BR \-a ", " \-\-add
1031 hot-add listed devices.
1032 If a device appears to have recently been part of the array
1033 (possibly it failed or was removed) the device is re-added as describe
1035 If that fails or the device was never part of the array, the device is
1036 added as a hot-spare.
1037 If the array is degraded, it will immediately start to rebuild data
1040 Note that this and the following options are only meaningful on array
1041 with redundancy. They don't apply to RAID0 or Linear.
1045 re\-add a device that was previous removed from an array.
1046 If the metadata on the device reports that it is a member of the
1047 array, and the slot that it used is still vacant, then the device will
1048 be added back to the array in the same position. This will normally
1049 cause the data for that device to be recovered. However based on the
1050 event count on the device, the recovery may only require sections that
1051 are flagged a write-intent bitmap to be recovered or may not require
1052 any recovery at all.
1054 When used on an array that has no metadata (i.e. it was built with
1056 it will be assumed that bitmap-based recovery is enough to make the
1057 device fully consistent with the array.
1059 If the device name given is
1061 then mdadm will try to find any device that looks like it should be
1062 part of the array but isn't and will try to re\-add all such devices.
1065 .BR \-r ", " \-\-remove
1066 remove listed devices. They must not be active. i.e. they should
1067 be failed or spare devices. As well as the name of a device file
1076 The first causes all failed device to be removed. The second causes
1077 any device which is no longer connected to the system (i.e an 'open'
1080 to be removed. This will only succeed for devices that are spares or
1081 have already been marked as failed.
1084 .BR \-f ", " \-\-fail
1085 mark listed devices as faulty.
1086 As well as the name of a device file, the word
1088 can be given. This will cause any device that has been detached from
1089 the system to be marked as failed. It can then be removed.
1097 .BR \-\-write\-mostly
1098 Subsequent devices that are added or re\-added will have the 'write-mostly'
1099 flag set. This is only valid for RAID1 and means that the 'md' driver
1100 will avoid reading from these devices if possible.
1103 Subsequent devices that are added or re\-added will have the 'write-mostly'
1107 Each of these options requires that the first device listed is the array
1108 to be acted upon, and the remainder are component devices to be added,
1109 removed, marked as faulty, etc. Several different operations can be
1110 specified for different devices, e.g.
1112 mdadm /dev/md0 \-\-add /dev/sda1 \-\-fail /dev/sdb1 \-\-remove /dev/sdb1
1114 Each operation applies to all devices listed until the next
1117 If an array is using a write-intent bitmap, then devices which have
1118 been removed can be re\-added in a way that avoids a full
1119 reconstruction but instead just updates the blocks that have changed
1120 since the device was removed. For arrays with persistent metadata
1121 (superblocks) this is done automatically. For arrays created with
1123 mdadm needs to be told that this device we removed recently with
1126 Devices can only be removed from an array if they are not in active
1127 use, i.e. that must be spares or failed devices. To remove an active
1128 device, it must first be marked as
1134 .BR \-Q ", " \-\-query
1135 Examine a device to see
1136 (1) if it is an md device and (2) if it is a component of an md
1138 Information about what is discovered is presented.
1141 .BR \-D ", " \-\-detail
1142 Print details of one or more md devices.
1145 .BR \-\-detail\-platform
1146 Print details of the platform's RAID capabilities (firmware / hardware
1147 topology) for a given metadata format.
1150 .BR \-Y ", " \-\-export
1155 output will be formatted as
1157 pairs for easy import into the environment.
1160 .BR \-E ", " \-\-examine
1161 Print contents of the metadata stored on the named device(s).
1162 Note the contrast between
1167 applies to devices which are components of an array, while
1169 applies to a whole array which is currently active.
1172 If an array was created on a SPARC machine with a 2.2 Linux kernel
1173 patched with RAID support, the superblock will have been created
1174 incorrectly, or at least incompatibly with 2.4 and later kernels.
1179 will fix the superblock before displaying it. If this appears to do
1180 the right thing, then the array can be successfully assembled using
1181 .BR "\-\-assemble \-\-update=sparc2.2" .
1184 .BR \-X ", " \-\-examine\-bitmap
1185 Report information about a bitmap file.
1186 The argument is either an external bitmap file or an array component
1187 in case of an internal bitmap. Note that running this on an array
1190 does not report the bitmap for that array.
1193 .BR \-R ", " \-\-run
1194 start a partially assembled array. If
1196 did not find enough devices to fully start the array, it might leaving
1197 it partially assembled. If you wish, you can then use
1199 to start the array in degraded mode.
1202 .BR \-S ", " \-\-stop
1203 deactivate array, releasing all resources.
1206 .BR \-o ", " \-\-readonly
1207 mark array as readonly.
1210 .BR \-w ", " \-\-readwrite
1211 mark array as readwrite.
1214 .B \-\-zero\-superblock
1215 If the device contains a valid md superblock, the block is
1216 overwritten with zeros. With
1218 the block where the superblock would be is overwritten even if it
1219 doesn't appear to be valid.
1222 .B \-\-kill\-subarray=
1223 If the device is a container and the argument to \-\-kill\-subarray
1224 specifies an inactive subarray in the container, then the subarray is
1225 deleted. Deleting all subarrays will leave an 'empty-container' or
1226 spare superblock on the drives. See \-\-zero\-superblock for completely
1227 removing a superblock. Note that some formats depend on the subarray
1228 index for generating a UUID, this command will fail if it would change
1229 the UUID of an active subarray.
1232 .B \-\-update\-subarray=
1233 If the device is a container and the argument to \-\-update\-subarray
1234 specifies a subarray in the container, then attempt to update the given
1235 superblock field in the subarray. See below in
1240 .BR \-t ", " \-\-test
1245 is set to reflect the status of the device. See below in
1250 .BR \-W ", " \-\-wait
1251 For each md device given, wait for any resync, recovery, or reshape
1252 activity to finish before returning.
1254 will return with success if it actually waited for every device
1255 listed, otherwise it will return failure.
1259 For each md device given, or each device in /proc/mdstat if
1261 is given, arrange for the array to be marked clean as soon as possible.
1263 will return with success if the array uses external metadata and we
1264 successfully waited. For native arrays this returns immediately as the
1265 kernel handles dirty-clean transitions at shutdown. No action is taken
1266 if safe-mode handling is disabled.
1268 .SH For Incremental Assembly mode:
1270 .BR \-\-rebuild\-map ", " \-r
1271 Rebuild the map file
1272 .RB ( /var/run/mdadm/map )
1275 uses to help track which arrays are currently being assembled.
1278 .BR \-\-run ", " \-R
1279 Run any array assembled as soon as a minimal number of devices are
1280 available, rather than waiting until all expected devices are present.
1283 .BR \-\-scan ", " \-s
1284 Only meaningful with
1288 file for arrays that are being incrementally assembled and will try to
1289 start any that are not already started. If any such array is listed
1292 as requiring an external bitmap, that bitmap will be attached first.
1295 .BR \-\-fail ", " \-f
1296 This allows the hot-plug system to remove devices that have fully disappeared
1297 from the kernel. It will first fail and then remove the device from any
1298 array it belongs to.
1299 The device name given should be a kernel device name such as "sda",
1303 .SH For Monitor mode:
1305 .BR \-m ", " \-\-mail
1306 Give a mail address to send alerts to.
1309 .BR \-p ", " \-\-program ", " \-\-alert
1310 Give a program to be run whenever an event is detected.
1313 .BR \-y ", " \-\-syslog
1314 Cause all events to be reported through 'syslog'. The messages have
1315 facility of 'daemon' and varying priorities.
1318 .BR \-d ", " \-\-delay
1319 Give a delay in seconds.
1321 polls the md arrays and then waits this many seconds before polling
1322 again. The default is 60 seconds. Since 2.6.16, there is no need to
1323 reduce this as the kernel alerts
1325 immediately when there is any change.
1328 .BR \-r ", " \-\-increment
1329 Give a percentage increment.
1331 will generate RebuildNN events with the given percentage increment.
1334 .BR \-f ", " \-\-daemonise
1337 to run as a background daemon if it decides to monitor anything. This
1338 causes it to fork and run in the child, and to disconnect from the
1339 terminal. The process id of the child is written to stdout.
1342 which will only continue monitoring if a mail address or alert program
1343 is found in the config file.
1346 .BR \-i ", " \-\-pid\-file
1349 is running in daemon mode, write the pid of the daemon process to
1350 the specified file, instead of printing it on standard output.
1353 .BR \-1 ", " \-\-oneshot
1354 Check arrays only once. This will generate
1356 events and more significantly
1362 .B " mdadm \-\-monitor \-\-scan \-1"
1364 from a cron script will ensure regular notification of any degraded arrays.
1367 .BR \-t ", " \-\-test
1370 alert for every array found at startup. This alert gets mailed and
1371 passed to the alert program. This can be used for testing that alert
1372 message do get through successfully.
1378 .B mdadm \-\-assemble
1379 .I md-device options-and-component-devices...
1382 .B mdadm \-\-assemble \-\-scan
1383 .I md-devices-and-options...
1386 .B mdadm \-\-assemble \-\-scan
1390 This usage assembles one or more RAID arrays from pre-existing components.
1391 For each array, mdadm needs to know the md device, the identity of the
1392 array, and a number of component-devices. These can be found in a number of ways.
1394 In the first usage example (without the
1396 the first device given is the md device.
1397 In the second usage example, all devices listed are treated as md
1398 devices and assembly is attempted.
1399 In the third (where no devices are listed) all md devices that are
1400 listed in the configuration file are assembled. If not arrays are
1401 described by the configuration file, then any arrays that
1402 can be found on unused devices will be assembled.
1404 If precisely one device is listed, but
1410 was given and identity information is extracted from the configuration file.
1412 The identity can be given with the
1418 option, will be taken from the md-device record in the config file, or
1419 will be taken from the super block of the first component-device
1420 listed on the command line.
1422 Devices can be given on the
1424 command line or in the config file. Only devices which have an md
1425 superblock which contains the right identity will be considered for
1428 The config file is only used if explicitly named with
1430 or requested with (a possibly implicit)
1435 .B /etc/mdadm/mdadm.conf
1440 is not given, then the config file will only be used to find the
1441 identity of md arrays.
1443 Normally the array will be started after it is assembled. However if
1445 is not given and not all expected drives were listed, then the array
1446 is not started (to guard against usage errors). To insist that the
1447 array be started in this case (as may work for RAID1, 4, 5, 6, or 10),
1456 does not create any entries in
1460 It does record information in
1461 .B /var/run/mdadm/map
1464 to choose the correct name.
1468 detects that udev is not configured, it will create the devices in
1472 In Linux kernels prior to version 2.6.28 there were two distinctly
1473 different types of md devices that could be created: one that could be
1474 partitioned using standard partitioning tools and one that could not.
1475 Since 2.6.28 that distinction is no longer relevant as both type of
1476 devices can be partitioned.
1478 will normally create the type that originally could not be partitioned
1479 as it has a well defined major number (9).
1481 Prior to 2.6.28, it is important that mdadm chooses the correct type
1482 of array device to use. This can be controlled with the
1484 option. In particular, a value of "mdp" or "part" or "p" tells mdadm
1485 to use a partitionable device rather than the default.
1487 In the no-udev case, the value given to
1489 can be suffixed by a number. This tells
1491 to create that number of partition devices rather than the default of 4.
1495 can also be given in the configuration file as a word starting
1497 on the ARRAY line for the relevant array.
1504 and no devices are listed,
1506 will first attempt to assemble all the arrays listed in the config
1509 In no array at listed in the config (other than those marked
1511 it will look through the available devices for possible arrays and
1512 will try to assemble anything that it finds. Arrays which are tagged
1513 as belonging to the given homehost will be assembled and started
1514 normally. Arrays which do not obviously belong to this host are given
1515 names that are expected not to conflict with anything local, and are
1516 started "read-auto" so that nothing is written to any device until the
1517 array is written to. i.e. automatic resync etc is delayed.
1521 finds a consistent set of devices that look like they should comprise
1522 an array, and if the superblock is tagged as belonging to the given
1523 home host, it will automatically choose a device name and try to
1524 assemble the array. If the array uses version-0.90 metadata, then the
1526 number as recorded in the superblock is used to create a name in
1530 If the array uses version-1 metadata, then the
1532 from the superblock is used to similarly create a name in
1534 (the name will have any 'host' prefix stripped first).
1536 This behaviour can be modified by the
1540 configuration file. This line can indicate that specific metadata
1541 type should, or should not, be automatically assembled. If an array
1542 is found which is not listed in
1544 and has a metadata format that is denied by the
1546 line, then it will not be assembled.
1549 line can also request that all arrays identified as being for this
1550 homehost should be assembled regardless of their metadata type.
1553 for further details.
1558 cannot find any array for the given host at all, and if
1559 .B \-\-auto\-update\-homehost
1562 will search again for any array (not just an array created for this
1563 host) and will assemble each assuming
1564 .BR \-\-update=homehost .
1565 This will change the host tag in the superblock so that on the next run,
1566 these arrays will be found without the second pass. The intention of
1567 this feature is to support transitioning a set of md arrays to using
1570 The reason for requiring arrays to be tagged with the homehost for
1571 auto assembly is to guard against problems that can arise when moving
1572 devices from one host to another.
1583 .BI \-\-raid\-devices= Z
1587 This usage is similar to
1589 The difference is that it creates an array without a superblock. With
1590 these arrays there is no difference between initially creating the array and
1591 subsequently assembling the array, except that hopefully there is useful
1592 data there in the second case.
1594 The level may raid0, linear, raid1, raid10, multipath, or faulty, or
1595 one of their synonyms. All devices must be listed and the array will
1596 be started once complete. It will often be appropriate to use
1597 .B \-\-assume\-clean
1598 with levels raid1 or raid10.
1609 .BI \-\-raid\-devices= Z
1613 This usage will initialise a new md array, associate some devices with
1614 it, and activate the array.
1616 The named device will normally not exist when
1617 .I "mdadm \-\-create"
1618 is run, but will be created by
1620 once the array becomes active.
1622 As devices are added, they are checked to see if they contain RAID
1623 superblocks or filesystems. They are also checked to see if the variance in
1624 device size exceeds 1%.
1626 If any discrepancy is found, the array will not automatically be run, though
1629 can override this caution.
1631 To create a "degraded" array in which some devices are missing, simply
1632 give the word "\fBmissing\fP"
1633 in place of a device name. This will cause
1635 to leave the corresponding slot in the array empty.
1636 For a RAID4 or RAID5 array at most one slot can be
1637 "\fBmissing\fP"; for a RAID6 array at most two slots.
1638 For a RAID1 array, only one real device needs to be given. All of the
1642 When creating a RAID5 array,
1644 will automatically create a degraded array with an extra spare drive.
1645 This is because building the spare into a degraded array is in general
1646 faster than resyncing the parity on a non-degraded, but not clean,
1647 array. This feature can be overridden with the
1651 When creating an array with version-1 metadata a name for the array is
1653 If this is not given with the
1657 will choose a name based on the last component of the name of the
1658 device being created. So if
1660 is being created, then the name
1665 is being created, then the name
1669 When creating a partition based array, using
1671 with version-1.x metadata, the partition type should be set to
1673 (non fs-data). This type selection allows for greater precision since
1674 using any other [RAID auto-detect (0xFD) or a GNU/Linux partition (0x83)],
1675 might create problems in the event of array recovery through a live cdrom.
1677 A new array will normally get a randomly assigned 128bit UUID which is
1678 very likely to be unique. If you have a specific need, you can choose
1679 a UUID for the array by giving the
1681 option. Be warned that creating two arrays with the same UUID is a
1682 recipe for disaster. Also, using
1684 when creating a v0.90 array will silently override any
1689 .\"option is given, it is not necessary to list any component-devices in this command.
1690 .\"They can be added later, before a
1694 .\"is given, the apparent size of the smallest drive given is used.
1696 When creating an array within a
1699 can be given either the list of devices to use, or simply the name of
1700 the container. The former case gives control over which devices in
1701 the container will be used for the array. The latter case allows
1703 to automatically choose which devices to use based on how much spare
1706 The General Management options that are valid with
1711 insist on running the array even if some devices look like they might
1716 start the array readonly \(em not supported yet.
1723 .I options... devices...
1726 This usage will allow individual devices in an array to be failed,
1727 removed or added. It is possible to perform multiple operations with
1728 on command. For example:
1730 .B " mdadm /dev/md0 \-f /dev/hda1 \-r /dev/hda1 \-a /dev/hda1"
1736 and will then remove it from the array and finally add it back
1737 in as a spare. However only one md array can be affected by a single
1740 When a device is added to an active array, mdadm checks to see if it
1741 has metadata on it which suggests that it was recently a member of the
1742 array. If it does, it tries to "re\-add" the device. If there have
1743 been no changes since the device was removed, or if the array has a
1744 write-intent bitmap which has recorded whatever changes there were,
1745 then the device will immediately become a full member of the array and
1746 those differences recorded in the bitmap will be resolved.
1756 MISC mode includes a number of distinct operations that
1757 operate on distinct devices. The operations are:
1760 The device is examined to see if it is
1761 (1) an active md array, or
1762 (2) a component of an md array.
1763 The information discovered is reported.
1767 The device should be an active md device.
1769 will display a detailed description of the array.
1773 will cause the output to be less detailed and the format to be
1774 suitable for inclusion in
1775 .BR /etc/mdadm.conf .
1778 will normally be 0 unless
1780 failed to get useful information about the device(s); however, if the
1782 option is given, then the exit status will be:
1786 The array is functioning normally.
1789 The array has at least one failed device.
1792 The array has multiple failed devices such that it is unusable.
1795 There was an error while trying to get information about the device.
1799 .B \-\-detail\-platform
1800 Print detail of the platform's RAID capabilities (firmware / hardware
1801 topology). If the metadata is specified with
1805 then the return status will be:
1809 metadata successfully enumerated its platform components on this system
1812 metadata is platform independent
1815 metadata failed to find its platform components on this system
1819 .B \-\-update\-subarray=
1820 If the device is a container and the argument to \-\-update\-subarray
1821 specifies a subarray in the container, then attempt to update the given
1822 superblock field in the subarray. Similar to updating an array in
1823 "assemble" mode, the field to update is selected by
1827 option. Currently only
1833 option updates the subarray name in the metadata, it may not affect the
1834 device node name or the device node symlink until the subarray is
1835 re\-assembled. If updating
1837 would change the UUID of an active subarray this operation is blocked,
1838 and the command will end in an error.
1842 The device should be a component of an md array.
1844 will read the md superblock of the device and display the contents.
1849 is given, then multiple devices that are components of the one array
1850 are grouped together and reported in a single entry suitable
1852 .BR /etc/mdadm.conf .
1856 without listing any devices will cause all devices listed in the
1857 config file to be examined.
1861 The devices should be active md arrays which will be deactivated, as
1862 long as they are not currently in use.
1866 This will fully activate a partially assembled md array.
1870 This will mark an active array as read-only, providing that it is
1871 not currently being used.
1877 array back to being read/write.
1881 For all operations except
1884 will cause the operation to be applied to all arrays listed in
1889 causes all devices listed in the config file to be examined.
1892 .BR \-b ", " \-\-brief
1893 Be less verbose. This is used with
1901 gives an intermediate level of verbosity.
1907 .B mdadm \-\-monitor
1908 .I options... devices...
1913 to periodically poll a number of md arrays and to report on any events
1916 will never exit once it decides that there are arrays to be checked,
1917 so it should normally be run in the background.
1919 As well as reporting events,
1921 may move a spare drive from one array to another if they are in the
1924 and if the destination array has a failed drive but no spares.
1926 If any devices are listed on the command line,
1928 will only monitor those devices. Otherwise all arrays listed in the
1929 configuration file will be monitored. Further, if
1931 is given, then any other md devices that appear in
1933 will also be monitored.
1935 The result of monitoring the arrays is the generation of events.
1936 These events are passed to a separate program (if specified) and may
1937 be mailed to a given E-mail address.
1939 When passing events to a program, the program is run once for each event,
1940 and is given 2 or 3 command-line arguments: the first is the
1941 name of the event (see below), the second is the name of the
1942 md device which is affected, and the third is the name of a related
1943 device if relevant (such as a component device that has failed).
1947 is given, then a program or an E-mail address must be specified on the
1948 command line or in the config file. If neither are available, then
1950 will not monitor anything.
1954 will continue monitoring as long as something was found to monitor. If
1955 no program or email is given, then each event is reported to
1958 The different events are:
1962 .B DeviceDisappeared
1963 An md array which previously was configured appears to no longer be
1964 configured. (syslog priority: Critical)
1968 was told to monitor an array which is RAID0 or Linear, then it will
1970 .B DeviceDisappeared
1971 with the extra information
1973 This is because RAID0 and Linear do not support the device-failed,
1974 hot-spare and resync operations which are monitored.
1978 An md array started reconstruction. (syslog priority: Warning)
1984 is a two-digit number (ie. 05, 48). This indicates that rebuild
1985 has passed that many percent of the total. The events are generated
1986 with fixed increment since 0. Increment size may be specified with
1987 a commandline option (default is 20). (syslog priority: Warning)
1991 An md array that was rebuilding, isn't any more, either because it
1992 finished normally or was aborted. (syslog priority: Warning)
1996 An active component device of an array has been marked as
1997 faulty. (syslog priority: Critical)
2001 A spare component device which was being rebuilt to replace a faulty
2002 device has failed. (syslog priority: Critical)
2006 A spare component device which was being rebuilt to replace a faulty
2007 device has been successfully rebuilt and has been made active.
2008 (syslog priority: Info)
2012 A new md array has been detected in the
2014 file. (syslog priority: Info)
2018 A newly noticed array appears to be degraded. This message is not
2021 notices a drive failure which causes degradation, but only when
2023 notices that an array is degraded when it first sees the array.
2024 (syslog priority: Critical)
2028 A spare drive has been moved from one array in a
2030 to another to allow a failed drive to be replaced.
2031 (syslog priority: Info)
2037 has been told, via the config file, that an array should have a certain
2038 number of spare devices, and
2040 detects that it has fewer than this number when it first sees the
2041 array, it will report a
2044 (syslog priority: Warning)
2048 An array was found at startup, and the
2051 (syslog priority: Info)
2061 cause Email to be sent. All events cause the program to be run.
2062 The program is run with two or three arguments: the event
2063 name, the array device and possibly a second device.
2065 Each event has an associated array device (e.g.
2067 and possibly a second device. For
2072 the second device is the relevant component device.
2075 the second device is the array that the spare was moved from.
2079 to move spares from one array to another, the different arrays need to
2080 be labeled with the same
2082 in the configuration file. The
2084 name can be any string; it is only necessary that different spare
2085 groups use different names.
2089 detects that an array in a spare group has fewer active
2090 devices than necessary for the complete array, and has no spare
2091 devices, it will look for another array in the same spare group that
2092 has a full complement of working drive and a spare. It will then
2093 attempt to remove the spare from the second drive and add it to the
2095 If the removal succeeds but the adding fails, then it is added back to
2099 The GROW mode is used for changing the size or shape of an active
2101 For this to work, the kernel must support the necessary change.
2102 Various types of growth are being added during 2.6 development,
2103 including restructuring a RAID5 array to have more active devices.
2105 Currently the only support available is to
2107 change the "size" attribute
2108 for RAID1, RAID5 and RAID6.
2110 increase or decrease the "raid\-devices" attribute of RAID1, RAID5,
2113 change the chunk-size and layout of RAID5 and RAID6.
2115 convert between RAID1 and RAID5, and between RAID5 and RAID6.
2117 add a write-intent bitmap to any array which supports these bitmaps, or
2118 remove a write-intent bitmap from such an array.
2121 GROW mode is not currently supported for
2123 or arrays inside containers.
2126 Normally when an array is built the "size" it taken from the smallest
2127 of the drives. If all the small drives in an arrays are, one at a
2128 time, removed and replaced with larger drives, then you could have an
2129 array of large drives with only a small amount used. In this
2130 situation, changing the "size" with "GROW" mode will allow the extra
2131 space to start being used. If the size is increased in this way, a
2132 "resync" process will start to make sure the new parts of the array
2135 Note that when an array changes size, any filesystem that may be
2136 stored in the array will not automatically grow to use the space. The
2137 filesystem will need to be explicitly told to use the extra space.
2139 Also the size of an array cannot be changed while it has an active
2140 bitmap. If an array has a bitmap, it must be removed before the size
2141 can be changed. Once the change it complete a new bitmap can be created.
2143 .SS RAID\-DEVICES CHANGES
2145 A RAID1 array can work with any number of devices from 1 upwards
2146 (though 1 is not very useful). There may be times which you want to
2147 increase or decrease the number of active devices. Note that this is
2148 different to hot-add or hot-remove which changes the number of
2151 When reducing the number of devices in a RAID1 array, the slots which
2152 are to be removed from the array must already be vacant. That is, the
2153 devices which were in those slots must be failed and removed.
2155 When the number of devices is increased, any hot spares that are
2156 present will be activated immediately.
2158 Changing the number of active devices in a RAID5 or RAID6 is much more
2159 effort. Every block in the array will need to be read and written
2160 back to a new location. From 2.6.17, the Linux Kernel is able to
2161 increase the number of devices in a RAID5 safely, including restarting
2162 an interrupted "reshape". From 2.6.31, the Linux Kernel is able to
2163 increase or decrease the number of devices in a RAID5 or RAID6.
2165 When decreasing the number of devices, the size of the array will also
2166 decrease. If there was data in the array, it could get destroyed and
2167 this is not reversible. To help prevent accidents,
2169 requires that the size of the array be decreased first with
2170 .BR "mdadm --grow --array-size" .
2171 This is a reversible change which simply makes the end of the array
2172 inaccessible. The integrity of any data can then be checked before
2173 the non-reversible reduction in the number of devices is request.
2175 When relocating the first few stripes on a RAID5, it is not possible
2176 to keep the data on disk completely consistent and crash-proof. To
2177 provide the required safety, mdadm disables writes to the array while
2178 this "critical section" is reshaped, and takes a backup of the data
2179 that is in that section. This backup is normally stored in any spare
2180 devices that the array has, however it can also be stored in a
2181 separate file specified with the
2183 option. If this option is used, and the system does crash during the
2184 critical period, the same file must be passed to
2186 to restore the backup and reassemble the array.
2190 Changing the RAID level of any array happens instantaneously. However
2191 in the RAID to RAID6 case this requires a non-standard layout of the
2192 RAID6 data, and in the RAID6 to RAID5 case that non-standard layout is
2193 required before the change can be accomplish. So while the level
2194 change is instant, the accompanying layout change can take quite a
2197 .SS CHUNK-SIZE AND LAYOUT CHANGES
2199 Changing the chunk-size of layout without also changing the number of
2200 devices as the same time will involve re-writing all blocks in-place.
2201 To ensure against data loss in the case of a crash, a
2203 must be provided for these changes. Small sections of the array will
2204 be copied to the backup file while they are being rearranged.
2206 If the reshape is interrupted for any reason, this backup file must be
2208 .B "mdadm --assemble"
2209 so the array can be reassembled. Consequently the file cannot be
2210 stored on the device being reshaped.
2215 A write-intent bitmap can be added to, or removed from, an active
2216 array. Either internal bitmaps, or bitmaps stored in a separate file,
2217 can be added. Note that if you add a bitmap stored in a file which is
2218 in a filesystem that is on the RAID array being affected, the system
2219 will deadlock. The bitmap must be on a separate filesystem.
2221 .SH INCREMENTAL MODE
2225 .B mdadm \-\-incremental
2231 .B mdadm \-\-incremental \-\-fail
2235 .B mdadm \-\-incremental \-\-rebuild\-map
2238 .B mdadm \-\-incremental \-\-run \-\-scan
2241 This mode is designed to be used in conjunction with a device
2242 discovery system. As devices are found in a system, they can be
2244 .B "mdadm \-\-incremental"
2245 to be conditionally added to an appropriate array.
2247 Conversely, it can also be used with the
2249 flag to do just the opposite and find whatever array a particular device
2250 is part of and remove the device from that array.
2252 If the device passed is a
2254 device created by a previous call to
2256 then rather than trying to add that device to an array, all the arrays
2257 described by the metadata of the container will be started.
2260 performs a number of tests to determine if the device is part of an
2261 array, and which array it should be part of. If an appropriate array
2262 is found, or can be created,
2264 adds the device to the array and conditionally starts the array.
2268 will only add devices to an array which were previously working
2269 (active or spare) parts of that array. It does not currently support
2270 automatic inclusion of a new drive as a spare in some array.
2274 makes are as follow:
2276 Is the device permitted by
2278 That is, is it listed in a
2280 line in that file. If
2282 is absent then the default it to allow any device. Similar if
2284 contains the special word
2286 then any device is allowed. Otherwise the device name given to
2288 must match one of the names or patterns in a
2293 Does the device have a valid md superblock. If a specific metadata
2294 version is request with
2298 then only that style of metadata is accepted, otherwise
2300 finds any known version of metadata. If no
2302 metadata is found, the device is rejected.
2306 Does the metadata match an expected array?
2307 The metadata can match in two ways. Either there is an array listed
2310 which identifies the array (either by UUID, by name, by device list,
2311 or by minor-number), or the array was created with a
2317 or on the command line.
2320 is not able to positively identify the array as belonging to the
2321 current host, the device will be rejected.
2325 keeps a list of arrays that it has partially assembled in
2326 .B /var/run/mdadm/map
2328 .B /var/run/mdadm.map
2329 if the directory doesn't exist. Or maybe even
2330 .BR /dev/.mdadm.map ).
2331 If no array exists which matches
2332 the metadata on the new device,
2334 must choose a device name and unit number. It does this based on any
2337 or any name information stored in the metadata. If this name
2338 suggests a unit number, that number will be used, otherwise a free
2339 unit number will be chosen. Normally
2341 will prefer to create a partitionable array, however if the
2345 suggests that a non-partitionable array is preferred, that will be
2348 If the array is not found in the config file and its metadata does not
2349 identify it as belonging to the "homehost", then
2351 will choose a name for the array which is certain not to conflict with
2352 any array which does belong to this host. It does this be adding an
2353 underscore and a small number to the name preferred by the metadata.
2355 Once an appropriate array is found or created and the device is added,
2357 must decide if the array is ready to be started. It will
2358 normally compare the number of available (non-spare) devices to the
2359 number of devices that the metadata suggests need to be active. If
2360 there are at least that many, the array will be started. This means
2361 that if any devices are missing the array will not be restarted.
2367 in which case the array will be run as soon as there are enough
2368 devices present for the data to be accessible. For a RAID1, that
2369 means one device will start the array. For a clean RAID5, the array
2370 will be started as soon as all but one drive is present.
2372 Note that neither of these approaches is really ideal. If it can
2373 be known that all device discovery has completed, then
2377 can be run which will try to start all arrays that are being
2378 incrementally assembled. They are started in "read-auto" mode in
2379 which they are read-only until the first write request. This means
2380 that no metadata updates are made and no attempt at resync or recovery
2381 happens. Further devices that are found before the first write can
2382 still be added safely.
2385 This section describes environment variables that affect how mdadm
2390 Setting this value to 1 will prevent mdadm from automatically launching
2391 mdmon. This variable is intended primarily for debugging mdadm/mdmon.
2397 does not create any device nodes in /dev, but leaves that task to
2401 appears not to be configured, or if this environment variable is set
2404 will create and devices that are needed.
2408 .B " mdadm \-\-query /dev/name-of-device"
2410 This will find out if a given device is a RAID array, or is part of
2411 one, and will provide brief information about the device.
2413 .B " mdadm \-\-assemble \-\-scan"
2415 This will assemble and start all arrays listed in the standard config
2416 file. This command will typically go in a system startup file.
2418 .B " mdadm \-\-stop \-\-scan"
2420 This will shut down all arrays that can be shut down (i.e. are not
2421 currently in use). This will typically go in a system shutdown script.
2423 .B " mdadm \-\-follow \-\-scan \-\-delay=120"
2425 If (and only if) there is an Email address or program given in the
2426 standard config file, then
2427 monitor the status of all arrays listed in that file by
2428 polling them ever 2 minutes.
2430 .B " mdadm \-\-create /dev/md0 \-\-level=1 \-\-raid\-devices=2 /dev/hd[ac]1"
2432 Create /dev/md0 as a RAID1 array consisting of /dev/hda1 and /dev/hdc1.
2435 .B " echo 'DEVICE /dev/hd*[0\-9] /dev/sd*[0\-9]' > mdadm.conf"
2437 .B " mdadm \-\-detail \-\-scan >> mdadm.conf"
2439 This will create a prototype config file that describes currently
2440 active arrays that are known to be made from partitions of IDE or SCSI drives.
2441 This file should be reviewed before being used as it may
2442 contain unwanted detail.
2444 .B " echo 'DEVICE /dev/hd[a\-z] /dev/sd*[a\-z]' > mdadm.conf"
2446 .B " mdadm \-\-examine \-\-scan \-\-config=mdadm.conf >> mdadm.conf"
2448 This will find arrays which could be assembled from existing IDE and
2449 SCSI whole drives (not partitions), and store the information in the
2450 format of a config file.
2451 This file is very likely to contain unwanted detail, particularly
2454 entries. It should be reviewed and edited before being used as an
2457 .B " mdadm \-\-examine \-\-brief \-\-scan \-\-config=partitions"
2459 .B " mdadm \-Ebsc partitions"
2461 Create a list of devices by reading
2462 .BR /proc/partitions ,
2463 scan these for RAID superblocks, and printout a brief listing of all
2466 .B " mdadm \-Ac partitions \-m 0 /dev/md0"
2468 Scan all partitions and devices listed in
2469 .BR /proc/partitions
2472 out of all such devices with a RAID superblock with a minor number of 0.
2474 .B " mdadm \-\-monitor \-\-scan \-\-daemonise > /var/run/mdadm"
2476 If config file contains a mail address or alert program, run mdadm in
2477 the background in monitor mode monitoring all md devices. Also write
2478 pid of mdadm daemon to
2479 .BR /var/run/mdadm .
2481 .B " mdadm \-Iq /dev/somedevice"
2483 Try to incorporate newly discovered device into some array as
2486 .B " mdadm \-\-incremental \-\-rebuild\-map \-\-run \-\-scan"
2488 Rebuild the array map from any current arrays, and then start any that
2491 .B " mdadm /dev/md4 --fail detached --remove detached"
2493 Any devices which are components of /dev/md4 will be marked as faulty
2494 and then remove from the array.
2496 .B " mdadm --grow /dev/md4 --level=6 --backup-file=/root/backup-md4
2500 which is currently a RAID5 array will be converted to RAID6. There
2501 should normally already be a spare drive attached to the array as a
2502 RAID6 needs one more drive than a matching RAID5.
2504 .B " mdadm --create /dev/md/ddf --metadata=ddf --raid-disks 6 /dev/sd[a-f]"
2506 Create a DDF array over 6 devices.
2508 .B " mdadm --create /dev/md/home -n3 -l5 -z 30000000 /dev/md/ddf"
2510 Create a RAID5 array over any 3 devices in the given DDF set. Use
2511 only 30 gigabytes of each device.
2513 .B " mdadm -A /dev/md/ddf1 /dev/sd[a-f]"
2515 Assemble a pre-exist ddf array.
2517 .B " mdadm -I /dev/md/ddf1"
2519 Assemble all arrays contained in the ddf array, assigning names as
2522 .B " mdadm \-\-create \-\-help"
2524 Provide help about the Create mode.
2526 .B " mdadm \-\-config \-\-help"
2528 Provide help about the format of the config file.
2530 .B " mdadm \-\-help"
2532 Provide general help.
2542 lists all active md devices with information about them.
2544 uses this to find arrays when
2546 is given in Misc mode, and to monitor array reconstruction
2551 The config file lists which devices may be scanned to see if
2552 they contain MD super block, and gives identifying information
2553 (e.g. UUID) about known MD arrays. See
2557 .SS /var/run/mdadm/map
2560 mode is used, this file gets a list of arrays currently being created.
2563 does not exist as a directory, then
2564 .B /var/run/mdadm.map
2567 is not available (as may be the case during early boot),
2569 is used on the basis that
2571 is usually available very early in boot.
2576 understand two sorts of names for array devices.
2578 The first is the so-called 'standard' format name, which matches the
2579 names used by the kernel and which appear in
2582 The second sort can be freely chosen, but must reside in
2584 When giving a device name to
2586 to create or assemble an array, either full path name such as
2590 can be given, or just the suffix of the second sort of name, such as
2596 chooses device names during auto-assembly or incremental assembly, it
2597 will sometimes add a small sequence number to the end of the name to
2598 avoid conflicted between multiple arrays that have the same name. If
2600 can reasonably determine that the array really is meant for this host,
2601 either by a hostname in the metadata, or by the presence of the array
2602 in /etc/mdadm.conf, then it will leave off the suffix if possible.
2603 Also if the homehost is specified as
2606 will only use a suffix if a different array of the same name already
2607 exists or is listed in the config file.
2609 The standard names for non-partitioned arrays (the only sort of md
2610 array available in 2.4 and earlier) are of the form
2614 where NN is a number.
2615 The standard names for partitionable arrays (as available from 2.6
2616 onwards) are of the form
2620 Partition numbers should be indicated by added "pMM" to these, thus "/dev/md/d1p2".
2622 From kernel version, 2.6.28 the "non-partitioned array" can actually
2623 be partitioned. So the "md_dNN" names are no longer needed, and
2624 partitions such as "/dev/mdNNpXX" are possible.
2628 was previously known as
2632 is completely separate from the
2634 package, and does not use the
2636 configuration file at all.
2639 For further information on mdadm usage, MD and the various levels of
2642 .B http://linux\-raid.osdl.org/
2644 (based upon Jakob \(/Ostergaard's Software\-RAID.HOWTO)
2646 .\"for new releases of the RAID driver check out:
2649 .\".UR ftp://ftp.kernel.org/pub/linux/kernel/people/mingo/raid-patches
2650 .\"ftp://ftp.kernel.org/pub/linux/kernel/people/mingo/raid-patches
2655 .\".UR http://www.cse.unsw.edu.au/~neilb/patches/linux-stable/
2656 .\"http://www.cse.unsw.edu.au/~neilb/patches/linux-stable/
2659 The latest version of
2661 should always be available from
2663 .B http://www.kernel.org/pub/linux/utils/raid/mdadm/