2 .\" Copyright Neil Brown and others.
3 .\" This program is free software; you can redistribute it and/or modify
4 .\" it under the terms of the GNU General Public License as published by
5 .\" the Free Software Foundation; either version 2 of the License, or
6 .\" (at your option) any later version.
7 .\" See file COPYING in distribution for details.
10 mdadm \- manage MD devices
16 .BI mdadm " [mode] <raiddevice> [options] <component-devices>"
19 RAID devices are virtual devices created from two or more
20 real block devices. This allows multiple devices (typically disk
21 drives or partitions thereof) to be combined into a single device to
22 hold (for example) a single filesystem.
23 Some RAID levels include redundancy and so can survive some degree of
26 Linux Software RAID devices are implemented through the md (Multiple
27 Devices) device driver.
29 Currently, Linux supports
46 is not a Software RAID mechanism, but does involve
48 each device is a path to one common physical storage device.
49 New installations should not use md/multipath as it is not well
50 supported and has no ongoing development. Use the Device Mapper based
51 multipath-tools instead.
54 is also not true RAID, and it only involves one device. It
55 provides a layer over a true device that can be used to inject faults.
60 is a collection of devices that are
61 managed as a set. This is similar to the set of devices connected to
62 a hardware RAID controller. The set of devices may contain a number
63 of different RAID arrays each utilising some (or all) of the blocks from a
64 number of the devices in the set. For example, two devices in a 5-device set
65 might form a RAID1 using the whole devices. The remaining three might
66 have a RAID5 over the first half of each device, and a RAID0 over the
71 there is one set of metadata that describes all of
72 the arrays in the container. So when
76 device, the device just represents the metadata. Other normal arrays (RAID1
77 etc) can be created inside the container.
80 mdadm has several major modes of operation:
83 Assemble the components of a previously created
84 array into an active array. Components can be explicitly given
85 or can be searched for.
87 checks that the components
88 do form a bona fide array, and can, on request, fiddle superblock
89 information so as to assemble a faulty array.
93 Build an array that doesn't have per-device metadata (superblocks). For these
96 cannot differentiate between initial creation and subsequent assembly
97 of an array. It also cannot perform any checks that appropriate
98 components have been requested. Because of this, the
100 mode should only be used together with a complete understanding of
105 Create a new array with per-device metadata (superblocks).
106 Appropriate metadata is written to each device, and then the array
107 comprising those devices is activated. A 'resync' process is started
108 to make sure that the array is consistent (e.g. both sides of a mirror
109 contain the same data) but the content of the device is left otherwise
111 The array can be used as soon as it has been created. There is no
112 need to wait for the initial resync to finish.
115 .B "Follow or Monitor"
116 Monitor one or more md devices and act on any state changes. This is
117 only meaningful for RAID1, 4, 5, 6, 10 or multipath arrays, as
118 only these have interesting state. RAID0 or Linear never have
119 missing, spare, or failed drives, so there is nothing to monitor.
123 Grow (or shrink) an array, or otherwise reshape it in some way.
124 Currently supported growth options including changing the active size
125 of component devices and changing the number of active devices in
126 Linear and RAID levels 0/1/4/5/6,
127 changing the RAID level between 0, 1, 5, and 6, and between 0 and 10,
128 changing the chunk size and layout for RAID 0,4,5,6, as well as adding or
129 removing a write-intent bitmap.
132 .B "Incremental Assembly"
133 Add a single device to an appropriate array. If the addition of the
134 device makes the array runnable, the array will be started.
135 This provides a convenient interface to a
137 system. As each device is detected,
139 has a chance to include it in some array as appropriate.
142 flag is passed in we will remove the device from any active array
143 instead of adding it.
149 in this mode, then any arrays within that container will be assembled
154 This is for doing things to specific components of an array such as
155 adding new spares and removing faulty devices.
159 This is an 'everything else' mode that supports operations on active
160 arrays, operations on component devices such as erasing old superblocks, and
161 information gathering operations.
162 .\"This mode allows operations on independent devices such as examine MD
163 .\"superblocks, erasing old superblocks and stopping active arrays.
167 This mode does not act on a specific device or array, but rather it
168 requests the Linux Kernel to activate any auto-detected arrays.
171 .SH Options for selecting a mode are:
174 .BR \-A ", " \-\-assemble
175 Assemble a pre-existing array.
178 .BR \-B ", " \-\-build
179 Build a legacy array without superblocks.
182 .BR \-C ", " \-\-create
186 .BR \-F ", " \-\-follow ", " \-\-monitor
192 .BR \-G ", " \-\-grow
193 Change the size or shape of an active array.
196 .BR \-I ", " \-\-incremental
197 Add/remove a single device to/from an appropriate array, and possibly start the array.
201 Request that the kernel starts any auto-detected arrays. This can only
204 is compiled into the kernel \(em not if it is a module.
205 Arrays can be auto-detected by the kernel if all the components are in
206 primary MS-DOS partitions with partition type
208 and all use v0.90 metadata.
209 In-kernel autodetect is not recommended for new installations. Using
211 to detect and assemble arrays \(em possibly in an
213 \(em is substantially more flexible and should be preferred.
216 If a device is given before any options, or if the first option is
222 then the MANAGE mode is assumed.
223 Anything other than these will cause the
227 .SH Options that are not mode-specific are:
230 .BR \-h ", " \-\-help
231 Display general help message or, after one of the above options, a
232 mode-specific help message.
236 Display more detailed help about command line parsing and some commonly
240 .BR \-V ", " \-\-version
241 Print version information for mdadm.
244 .BR \-v ", " \-\-verbose
245 Be more verbose about what is happening. This can be used twice to be
247 The extra verbosity currently only affects
248 .B \-\-detail \-\-scan
250 .BR "\-\-examine \-\-scan" .
253 .BR \-q ", " \-\-quiet
254 Avoid printing purely informative messages. With this,
256 will be silent unless there is something really important to report.
260 Set first character of argv[0] to @ to indicate mdadm was launched
261 from initrd/initramfs and should not be shutdown by systemd as part of
262 the regular shutdown process. This option is normally only used by
263 the system's initscripts. Please see here for more details on how
264 systemd handled argv[0]:
266 .B http://www.freedesktop.org/wiki/Software/systemd/RootStorageDaemons
271 .BR \-f ", " \-\-force
272 Be more forceful about certain operations. See the various modes for
273 the exact meaning of this option in different contexts.
276 .BR \-c ", " \-\-config=
277 Specify the config file. Default is to use
278 .BR /etc/mdadm.conf ,
279 or if that is missing then
280 .BR /etc/mdadm/mdadm.conf .
281 If the config file given is
283 then nothing will be read, but
285 will act as though the config file contained exactly
286 .B "DEVICE partitions containers"
289 to find a list of devices to scan, and
291 to find a list of containers to examine.
294 is given for the config file, then
296 will act as though the config file were empty.
299 .BR \-s ", " \-\-scan
302 for missing information.
303 In general, this option gives
305 permission to get any missing information (like component devices,
306 array devices, array identities, and alert destination) from the
307 configuration file (see previous option);
308 one exception is MISC mode when using
314 says to get a list of array devices from
318 .BR \-e ", " \-\-metadata=
319 Declare the style of RAID metadata (superblock) to be used. The
320 default is {DEFAULT_METADATA} for
322 and to guess for other operations.
323 The default can be overridden by setting the
332 .ie '{DEFAULT_METADATA}'0.90'
333 .IP "0, 0.90, default"
336 Use the original 0.90 format superblock. This format limits arrays to
337 28 component devices and limits component devices of levels 1 and
338 greater to 2 terabytes. It is also possible for there to be confusion
339 about whether the superblock applies to a whole device or just the
340 last partition, if that partition starts on a 64K boundary.
341 .ie '{DEFAULT_METADATA}'0.90'
342 .IP "1, 1.0, 1.1, 1.2"
344 .IP "1, 1.0, 1.1, 1.2 default"
345 Use the new version-1 format superblock. This has fewer restrictions.
346 It can easily be moved between hosts with different endian-ness, and a
347 recovery operation can be checkpointed and restarted. The different
348 sub-versions store the superblock at different locations on the
349 device, either at the end (for 1.0), at the start (for 1.1) or 4K from
350 the start (for 1.2). "1" is equivalent to "1.2" (the commonly
351 preferred 1.x format).
352 'if '{DEFAULT_METADATA}'1.2' "default" is equivalent to "1.2".
354 Use the "Industry Standard" DDF (Disk Data Format) format defined by
356 When creating a DDF array a
358 will be created, and normal arrays can be created in that container.
360 Use the Intel(R) Matrix Storage Manager metadata format. This creates a
362 which is managed in a similar manner to DDF, and is supported by an
363 option-rom on some platforms:
365 .B http://www.intel.com/design/chipsets/matrixstorage_sb.htm
371 This will override any
373 setting in the config file and provides the identity of the host which
374 should be considered the home for any arrays.
376 When creating an array, the
378 will be recorded in the metadata. For version-1 superblocks, it will
379 be prefixed to the array name. For version-0.90 superblocks, part of
380 the SHA1 hash of the hostname will be stored in the later half of the
383 When reporting information about an array, any array which is tagged
384 for the given homehost will be reported as such.
386 When using Auto-Assemble, only arrays tagged for the given homehost
387 will be allowed to use 'local' names (i.e. not ending in '_' followed
388 by a digit string). See below under
389 .BR "Auto Assembly" .
395 needs to print the name for a device it normally finds the name in
397 which refers to the device and is shortest. When a path component is
401 will prefer a longer name if it contains that component. For example
402 .B \-\-prefer=by-uuid
403 will prefer a name in a subdirectory of
408 This functionality is currently only provided by
413 .SH For create, build, or grow:
416 .BR \-n ", " \-\-raid\-devices=
417 Specify the number of active devices in the array. This, plus the
418 number of spare devices (see below) must equal the number of
420 (including "\fBmissing\fP" devices)
421 that are listed on the command line for
423 Setting a value of 1 is probably
424 a mistake and so requires that
426 be specified first. A value of 1 will then be allowed for linear,
427 multipath, RAID0 and RAID1. It is never allowed for RAID4, RAID5 or RAID6.
429 This number can only be changed using
431 for RAID1, RAID4, RAID5 and RAID6 arrays, and only on kernels which provide
432 the necessary support.
435 .BR \-x ", " \-\-spare\-devices=
436 Specify the number of spare (eXtra) devices in the initial array.
437 Spares can also be added
438 and removed later. The number of component devices listed
439 on the command line must equal the number of RAID devices plus the
440 number of spare devices.
443 .BR \-z ", " \-\-size=
444 Amount (in Kibibytes) of space to use from each drive in RAID levels 1/4/5/6.
445 This must be a multiple of the chunk size, and must leave about 128Kb
446 of space at the end of the drive for the RAID superblock.
447 If this is not specified
448 (as it normally is not) the smallest drive (or partition) sets the
449 size, though if there is a variance among the drives of greater than 1%, a warning is
452 A suffix of 'M' or 'G' can be given to indicate Megabytes or
453 Gigabytes respectively.
455 Sometimes a replacement drive can be a little smaller than the
456 original drives though this should be minimised by IDEMA standards.
457 Such a replacement drive will be rejected by
459 To guard against this it can be useful to set the initial size
460 slightly smaller than the smaller device with the aim that it will
461 still be larger than any replacement.
463 This value can be set with
465 for RAID level 1/4/5/6 though
467 based arrays such as those with IMSM metadata may not be able to
469 If the array was created with a size smaller than the currently
470 active drives, the extra space can be accessed using
472 The size can be given as
474 which means to choose the largest size that fits on all current drives.
476 Before reducing the size of the array (with
477 .BR "\-\-grow \-\-size=" )
478 you should make sure that space isn't needed. If the device holds a
479 filesystem, you would need to resize the filesystem to use less space.
481 After reducing the array size you should check that the data stored in
482 the device is still available. If the device holds a filesystem, then
483 an 'fsck' of the filesystem is a minimum requirement. If there are
484 problems the array can be made bigger again with no loss with another
485 .B "\-\-grow \-\-size="
488 This value cannot be used when creating a
490 such as with DDF and IMSM metadata, though it perfectly valid when
491 creating an array inside a container.
494 .BR \-Z ", " \-\-array\-size=
495 This is only meaningful with
497 and its effect is not persistent: when the array is stopped and
498 restarted the default array size will be restored.
500 Setting the array-size causes the array to appear smaller to programs
501 that access the data. This is particularly needed before reshaping an
502 array so that it will be smaller. As the reshape is not reversible,
503 but setting the size with
505 is, it is required that the array size is reduced as appropriate
506 before the number of devices in the array is reduced.
508 Before reducing the size of the array you should make sure that space
509 isn't needed. If the device holds a filesystem, you would need to
510 resize the filesystem to use less space.
512 After reducing the array size you should check that the data stored in
513 the device is still available. If the device holds a filesystem, then
514 an 'fsck' of the filesystem is a minimum requirement. If there are
515 problems the array can be made bigger again with no loss with another
516 .B "\-\-grow \-\-array\-size="
519 A suffix of 'M' or 'G' can be given to indicate Megabytes or
520 Gigabytes respectively.
523 restores the apparent size of the array to be whatever the real
524 amount of available space is.
527 .BR \-c ", " \-\-chunk=
528 Specify chunk size of kibibytes. The default when creating an
529 array is 512KB. To ensure compatibility with earlier versions, the
530 default when Building and array with no persistent metadata is 64KB.
531 This is only meaningful for RAID0, RAID4, RAID5, RAID6, and RAID10.
533 RAID4, RAID5, RAID6, and RAID10 require the chunk size to be a power
534 of 2. In any case it must be a multiple of 4KB.
536 A suffix of 'M' or 'G' can be given to indicate Megabytes or
537 Gigabytes respectively.
541 Specify rounding factor for a Linear array. The size of each
542 component will be rounded down to a multiple of this size.
543 This is a synonym for
545 but highlights the different meaning for Linear as compared to other
546 RAID levels. The default is 64K if a kernel earlier than 2.6.16 is in
547 use, and is 0K (i.e. no rounding) in later kernels.
550 .BR \-l ", " \-\-level=
551 Set RAID level. When used with
553 options are: linear, raid0, 0, stripe, raid1, 1, mirror, raid4, 4,
554 raid5, 5, raid6, 6, raid10, 10, multipath, mp, faulty, container.
555 Obviously some of these are synonymous.
559 metadata type is requested, only the
561 level is permitted, and it does not need to be explicitly given.
565 only linear, stripe, raid0, 0, raid1, multipath, mp, and faulty are valid.
569 to change the RAID level in some cases. See LEVEL CHANGES below.
572 .BR \-p ", " \-\-layout=
573 This option configures the fine details of data layout for RAID5, RAID6,
574 and RAID10 arrays, and controls the failure modes for
577 The layout of the RAID5 parity block can be one of
578 .BR left\-asymmetric ,
579 .BR left\-symmetric ,
580 .BR right\-asymmetric ,
581 .BR right\-symmetric ,
582 .BR la ", " ra ", " ls ", " rs .
584 .BR left\-symmetric .
586 It is also possible to cause RAID5 to use a RAID4-like layout by
592 Finally for RAID5 there are DDF\-compatible layouts,
593 .BR ddf\-zero\-restart ,
594 .BR ddf\-N\-restart ,
596 .BR ddf\-N\-continue .
598 These same layouts are available for RAID6. There are also 4 layouts
599 that will provide an intermediate stage for converting between RAID5
600 and RAID6. These provide a layout which is identical to the
601 corresponding RAID5 layout on the first N\-1 devices, and has the 'Q'
602 syndrome (the second 'parity' block used by RAID6) on the last device.
604 .BR left\-symmetric\-6 ,
605 .BR right\-symmetric\-6 ,
606 .BR left\-asymmetric\-6 ,
607 .BR right\-asymmetric\-6 ,
609 .BR parity\-first\-6 .
611 When setting the failure mode for level
614 .BR write\-transient ", " wt ,
615 .BR read\-transient ", " rt ,
616 .BR write\-persistent ", " wp ,
617 .BR read\-persistent ", " rp ,
619 .BR read\-fixable ", " rf ,
620 .BR clear ", " flush ", " none .
622 Each failure mode can be followed by a number, which is used as a period
623 between fault generation. Without a number, the fault is generated
624 once on the first relevant request. With a number, the fault will be
625 generated after that many requests, and will continue to be generated
626 every time the period elapses.
628 Multiple failure modes can be current simultaneously by using the
630 option to set subsequent failure modes.
632 "clear" or "none" will remove any pending or periodic failure modes,
633 and "flush" will clear any persistent faults.
635 Finally, the layout options for RAID10 are one of 'n', 'o' or 'f' followed
636 by a small number. The default is 'n2'. The supported options are:
639 signals 'near' copies. Multiple copies of one data block are at
640 similar offsets in different devices.
643 signals 'offset' copies. Rather than the chunks being duplicated
644 within a stripe, whole stripes are duplicated but are rotated by one
645 device so duplicate blocks are on different devices. Thus subsequent
646 copies of a block are in the next drive, and are one chunk further
651 (multiple copies have very different offsets).
652 See md(4) for more detail about 'near', 'offset', and 'far'.
654 The number is the number of copies of each datablock. 2 is normal, 3
655 can be useful. This number can be at most equal to the number of
656 devices in the array. It does not need to divide evenly into that
657 number (e.g. it is perfectly legal to have an 'n2' layout for an array
658 with an odd number of devices).
660 When an array is converted between RAID5 and RAID6 an intermediate
661 RAID6 layout is used in which the second parity block (Q) is always on
662 the last device. To convert a RAID5 to RAID6 and leave it in this new
663 layout (which does not require re-striping) use
664 .BR \-\-layout=preserve .
665 This will try to avoid any restriping.
667 The converse of this is
668 .B \-\-layout=normalise
669 which will change a non-standard RAID6 layout into a more standard
676 (thus explaining the p of
680 .BR \-b ", " \-\-bitmap=
681 Specify a file to store a write-intent bitmap in. The file should not
684 is also given. The same file should be provided
685 when assembling the array. If the word
687 is given, then the bitmap is stored with the metadata on the array,
688 and so is replicated on all devices. If the word
692 mode, then any bitmap that is present is removed.
694 To help catch typing errors, the filename must contain at least one
695 slash ('/') if it is a real file (not 'internal' or 'none').
697 Note: external bitmaps are only known to work on ext2 and ext3.
698 Storing bitmap files on other filesystems may result in serious problems.
701 .BR \-\-bitmap\-chunk=
702 Set the chunksize of the bitmap. Each bit corresponds to that many
703 Kilobytes of storage.
704 When using a file based bitmap, the default is to use the smallest
705 size that is at-least 4 and requires no more than 2^21 chunks.
708 bitmap, the chunksize defaults to 64Meg, or larger if necessary to
709 fit the bitmap into the available space.
711 A suffix of 'M' or 'G' can be given to indicate Megabytes or
712 Gigabytes respectively.
715 .BR \-W ", " \-\-write\-mostly
716 subsequent devices listed in a
721 command will be flagged as 'write-mostly'. This is valid for RAID1
722 only and means that the 'md' driver will avoid reading from these
723 devices if at all possible. This can be useful if mirroring over a
727 .BR \-\-write\-behind=
728 Specify that write-behind mode should be enabled (valid for RAID1
729 only). If an argument is specified, it will set the maximum number
730 of outstanding writes allowed. The default value is 256.
731 A write-intent bitmap is required in order to use write-behind
732 mode, and write-behind is only attempted on drives marked as
736 .BR \-\-assume\-clean
739 that the array pre-existed and is known to be clean. It can be useful
740 when trying to recover from a major failure as you can be sure that no
741 data will be affected unless you actually write to the array. It can
742 also be used when creating a RAID1 or RAID10 if you want to avoid the
743 initial resync, however this practice \(em while normally safe \(em is not
744 recommended. Use this only if you really know what you are doing.
746 When the devices that will be part of a new array were filled
747 with zeros before creation the operator knows the array is
748 actually clean. If that is the case, such as after running
749 badblocks, this argument can be used to tell mdadm the
750 facts the operator knows.
752 When an array is resized to a larger size with
753 .B "\-\-grow \-\-size="
754 the new space is normally resynced in that same way that the whole
755 array is resynced at creation. From Linux version 3.0,
757 can be used with that command to avoid the automatic resync.
760 .BR \-\-backup\-file=
763 is used to increase the number of raid-devices in a RAID5 or RAID6 if
764 there are no spare devices available, or to shrink, change RAID level
765 or layout. See the GROW MODE section below on RAID\-DEVICES CHANGES.
766 The file must be stored on a separate device, not on the RAID array
771 Arrays with 1.x metadata can leave a gap between the start of the
772 device and the start of array data. This gap can be used for various
773 metadata. The start of data is known as the
775 Normally an appropriate data offset is computed automatically.
776 However it can be useful to set it explicitly such as when re-creating
777 an array which was originally created using a different version of
779 which computed a different offset.
781 Setting the offset explicitly over-rides the default. The value given
782 is in Kilobytes unless an 'M' or 'G' suffix is given.
786 can also be used with
788 for some RAID levels (initially on RAID10). This allows the
789 data\-offset to be changed as part of the reshape process. When the
790 data offset is changed, no backup file is required as the difference
791 in offsets is used to provide the same functionality.
793 When the new offset is earlier than the old offset, the number of
794 devices in the array cannot shrink. When it is after the old offset,
795 the number of devices in the array cannot increase.
797 When creating an array,
801 In the case each member device is expected to have a offset appended
802 to the name, separated by a colon. This makes it possible to recreate
803 exactly an array which has varying data offsets (as can happen when
804 different versions of
806 are used to add different devices).
810 This option is complementary to the
811 .B \-\-freeze-reshape
812 option for assembly. It is needed when
814 operation is interrupted and it is not restarted automatically due to
815 .B \-\-freeze-reshape
816 usage during array assembly. This option is used together with
820 ) command and device for a pending reshape to be continued.
821 All parameters required for reshape continuation will be read from array metadata.
825 .BR \-\-backup\-file=
826 option to be set, continuation option will require to have exactly the same
827 backup file given as well.
829 Any other parameter passed together with
831 option will be ignored.
834 .BR \-N ", " \-\-name=
837 for the array. This is currently only effective when creating an
838 array with a version-1 superblock, or an array in a DDF container.
839 The name is a simple textual string that can be used to identify array
840 components when assembling. If name is needed but not specified, it
841 is taken from the basename of the device that is being created.
853 run the array, even if some of the components
854 appear to be active in another array or filesystem. Normally
856 will ask for confirmation before including such components in an
857 array. This option causes that question to be suppressed.
860 .BR \-f ", " \-\-force
863 accept the geometry and layout specified without question. Normally
865 will not allow creation of an array with only one device, and will try
866 to create a RAID5 array with one missing drive (as this makes the
867 initial resync work faster). With
870 will not try to be so clever.
873 .BR \-o ", " \-\-readonly
876 rather than read-write as normal. No writes will be allowed to the
877 array, and no resync, recovery, or reshape will be started.
880 .BR \-a ", " "\-\-auto{=yes,md,mdp,part,p}{NN}"
881 Instruct mdadm how to create the device file if needed, possibly allocating
882 an unused minor number. "md" causes a non-partitionable array
883 to be used (though since Linux 2.6.28, these array devices are in fact
884 partitionable). "mdp", "part" or "p" causes a partitionable array (2.6 and
885 later) to be used. "yes" requires the named md device to have
886 a 'standard' format, and the type and minor number will be determined
887 from this. With mdadm 3.0, device creation is normally left up to
889 so this option is unlikely to be needed.
890 See DEVICE NAMES below.
892 The argument can also come immediately after
897 is not given on the command line or in the config file, then
903 is also given, then any
905 entries in the config file will override the
907 instruction given on the command line.
909 For partitionable arrays,
911 will create the device file for the whole array and for the first 4
912 partitions. A different number of partitions can be specified at the
913 end of this option (e.g.
915 If the device name ends with a digit, the partition names add a 'p',
917 .IR /dev/md/home1p3 .
918 If there is no trailing digit, then the partition names just have a
920 .IR /dev/md/scratch3 .
922 If the md device name is in a 'standard' format as described in DEVICE
923 NAMES, then it will be created, if necessary, with the appropriate
924 device number based on that name. If the device name is not in one of these
925 formats, then a unused device number will be allocated. The device
926 number will be considered unused if there is no active array for that
927 number, and there is no entry in /dev for that number and with a
928 non-standard name. Names that are not in 'standard' format are only
929 allowed in "/dev/md/".
931 This is meaningful with
937 .BR \-a ", " "\-\-add"
938 This option can be used in Grow mode in two cases.
940 If the target array is a Linear array, then
942 can be used to add one or more devices to the array. They
943 are simply catenated on to the end of the array. Once added, the
944 devices cannot be removed.
948 option is being used to increase the number of devices in an array,
951 can be used to add some extra devices to be included in the array.
952 In most cases this is not needed as the extra devices can be added as
953 spares first, and then the number of raid-disks can be changed.
954 However for RAID0, it is not possible to add spares. So to increase
955 the number of devices in a RAID0, it is necessary to set the new
956 number of devices, and to add the new devices, in the same command.
961 .BR \-u ", " \-\-uuid=
962 uuid of array to assemble. Devices which don't have this uuid are
966 .BR \-m ", " \-\-super\-minor=
967 Minor number of device that array was created for. Devices which
968 don't have this minor number are excluded. If you create an array as
969 /dev/md1, then all superblocks will contain the minor number 1, even if
970 the array is later assembled as /dev/md2.
972 Giving the literal word "dev" for
976 to use the minor number of the md device that is being assembled.
979 .B \-\-super\-minor=dev
980 will look for super blocks with a minor number of 0.
983 is only relevant for v0.90 metadata, and should not normally be used.
989 .BR \-N ", " \-\-name=
990 Specify the name of the array to assemble. This must be the name
991 that was specified when creating the array. It must either match
992 the name stored in the superblock exactly, or it must match
995 prefixed to the start of the given name.
998 .BR \-f ", " \-\-force
999 Assemble the array even if the metadata on some devices appears to be
1002 cannot find enough working devices to start the array, but can find
1003 some devices that are recorded as having failed, then it will mark
1004 those devices as working so that the array can be started.
1005 An array which requires
1007 to be started may contain data corruption. Use it carefully.
1010 .BR \-R ", " \-\-run
1011 Attempt to start the array even if fewer drives were given than were
1012 present last time the array was active. Normally if not all the
1013 expected drives are found and
1015 is not used, then the array will be assembled but not started.
1018 an attempt will be made to start it anyway.
1022 This is the reverse of
1024 in that it inhibits the startup of array unless all expected drives
1025 are present. This is only needed with
1027 and can be used if the physical connections to devices are
1028 not as reliable as you would like.
1031 .BR \-a ", " "\-\-auto{=no,yes,md,mdp,part}"
1032 See this option under Create and Build options.
1035 .BR \-b ", " \-\-bitmap=
1036 Specify the bitmap file that was given when the array was created. If
1039 bitmap, there is no need to specify this when assembling the array.
1042 .BR \-\-backup\-file=
1045 was used while reshaping an array (e.g. changing number of devices or
1046 chunk size) and the system crashed during the critical section, then the same
1048 must be presented to
1050 to allow possibly corrupted data to be restored, and the reshape
1054 .BR \-\-invalid\-backup
1055 If the file needed for the above option is not available for any
1056 reason an empty file can be given together with this option to
1057 indicate that the backup file is invalid. In this case the data that
1058 was being rearranged at the time of the crash could be irrecoverably
1059 lost, but the rest of the array may still be recoverable. This option
1060 should only be used as a last resort if there is no way to recover the
1065 .BR \-U ", " \-\-update=
1066 Update the superblock on each device while assembling the array. The
1067 argument given to this flag can be one of
1084 option will adjust the superblock of an array what was created on a Sparc
1085 machine running a patched 2.2 Linux kernel. This kernel got the
1086 alignment of part of the superblock wrong. You can use the
1087 .B "\-\-examine \-\-sparc2.2"
1090 to see what effect this would have.
1094 option will update the
1095 .B "preferred minor"
1096 field on each superblock to match the minor number of the array being
1098 This can be useful if
1100 reports a different "Preferred Minor" to
1102 In some cases this update will be performed automatically
1103 by the kernel driver. In particular the update happens automatically
1104 at the first write to an array with redundancy (RAID level 1 or
1105 greater) on a 2.6 (or later) kernel.
1109 option will change the uuid of the array. If a UUID is given with the
1111 option that UUID will be used as a new UUID and will
1113 be used to help identify the devices in the array.
1116 is given, a random UUID is chosen.
1120 option will change the
1122 of the array as stored in the superblock. This is only supported for
1123 version-1 superblocks.
1127 option will change the
1129 as recorded in the superblock. For version-0 superblocks, this is the
1130 same as updating the UUID.
1131 For version-1 superblocks, this involves updating the name.
1135 option will cause the array to be marked
1137 meaning that any redundancy in the array (e.g. parity for RAID5,
1138 copies for RAID1) may be incorrect. This will cause the RAID system
1139 to perform a "resync" pass to make sure that all redundant information
1144 option allows arrays to be moved between machines with different
1146 When assembling such an array for the first time after a move, giving
1147 .B "\-\-update=byteorder"
1150 to expect superblocks to have their byteorder reversed, and will
1151 correct that order before assembling the array. This is only valid
1152 with original (Version 0.90) superblocks.
1156 option will correct the summaries in the superblock. That is the
1157 counts of total, working, active, failed, and spare devices.
1161 option will rarely be of use. It applies to version 1.1 and 1.2 metadata
1162 only (where the metadata is at the start of the device) and is only
1163 useful when the component device has changed size (typically become
1164 larger). The version 1 metadata records the amount of the device that
1165 can be used to store data, so if a device in a version 1.1 or 1.2
1166 array becomes larger, the metadata will still be visible, but the
1167 extra space will not. In this case it might be useful to assemble the
1169 .BR \-\-update=devicesize .
1172 to determine the maximum usable amount of space on each device and
1173 update the relevant field in the metadata.
1177 option can be used when an array has an internal bitmap which is
1178 corrupt in some way so that assembling the array normally fails. It
1179 will cause any internal bitmap to be ignored.
1183 option will reserve space in each device for a bad block list. This
1184 will be 4K in size and positioned near the end of any free space
1185 between the superblock and the data.
1189 option will cause any reservation of space for a bad block list to be
1190 removed. If the bad block list contains entries, this will fail, as
1191 removing the list could cause data corruption.
1194 .BR \-\-freeze\-reshape
1195 Option is intended to be used in start-up scripts during initrd boot phase.
1196 When array under reshape is assembled during initrd phase, this option
1197 stops reshape after reshape critical section is being restored. This happens
1198 before file system pivot operation and avoids loss of file system context.
1199 Losing file system context would cause reshape to be broken.
1201 Reshape can be continued later using the
1203 option for the grow command.
1205 .SH For Manage mode:
1208 .BR \-t ", " \-\-test
1209 Unless a more serious error occurred,
1211 will exit with a status of 2 if no changes were made to the array and
1212 0 if at least one change was made.
1213 This can be useful when an indirect specifier such as
1218 is used in requesting an operation on the array.
1220 will report failure if these specifiers didn't find any match.
1223 .BR \-a ", " \-\-add
1224 hot-add listed devices.
1225 If a device appears to have recently been part of the array
1226 (possibly it failed or was removed) the device is re\-added as described
1228 If that fails or the device was never part of the array, the device is
1229 added as a hot-spare.
1230 If the array is degraded, it will immediately start to rebuild data
1233 Note that this and the following options are only meaningful on array
1234 with redundancy. They don't apply to RAID0 or Linear.
1238 re\-add a device that was previous removed from an array.
1239 If the metadata on the device reports that it is a member of the
1240 array, and the slot that it used is still vacant, then the device will
1241 be added back to the array in the same position. This will normally
1242 cause the data for that device to be recovered. However based on the
1243 event count on the device, the recovery may only require sections that
1244 are flagged a write-intent bitmap to be recovered or may not require
1245 any recovery at all.
1247 When used on an array that has no metadata (i.e. it was built with
1249 it will be assumed that bitmap-based recovery is enough to make the
1250 device fully consistent with the array.
1252 When used with v1.x metadata,
1254 can be accompanied by
1255 .BR \-\-update=devicesize ,
1256 .BR \-\-update=bbl ", or"
1257 .BR \-\-update=no\-bbl .
1258 See the description of these option when used in Assemble mode for an
1259 explanation of their use.
1261 If the device name given is
1263 then mdadm will try to find any device that looks like it should be
1264 part of the array but isn't and will try to re\-add all such devices.
1267 .BR \-r ", " \-\-remove
1268 remove listed devices. They must not be active. i.e. they should
1269 be failed or spare devices. As well as the name of a device file
1278 The first causes all failed device to be removed. The second causes
1279 any device which is no longer connected to the system (i.e an 'open'
1282 to be removed. This will only succeed for devices that are spares or
1283 have already been marked as failed.
1286 .BR \-f ", " \-\-fail
1287 Mark listed devices as faulty.
1288 As well as the name of a device file, the word
1290 can be given. This will cause any device that has been detached from
1291 the system to be marked as failed. It can then be removed.
1300 Mark listed devices as requiring replacement. As soon as a spare is
1301 available, it will be rebuilt and will replace the marked device.
1302 This is similar to marking a device as faulty, but the device remains
1303 in service during the recovery process to increase resilience against
1304 multiple failures. When the replacement process finishes, the
1305 replaced device will be marked as faulty.
1309 This can follow a list of
1311 devices. The devices listed after
1313 will be preferentially used to replace the devices listed after
1315 These device must already be spare devices in the array.
1318 .BR \-\-write\-mostly
1319 Subsequent devices that are added or re\-added will have the 'write-mostly'
1320 flag set. This is only valid for RAID1 and means that the 'md' driver
1321 will avoid reading from these devices if possible.
1324 Subsequent devices that are added or re\-added will have the 'write-mostly'
1328 Each of these options requires that the first device listed is the array
1329 to be acted upon, and the remainder are component devices to be added,
1330 removed, marked as faulty, etc. Several different operations can be
1331 specified for different devices, e.g.
1333 mdadm /dev/md0 \-\-add /dev/sda1 \-\-fail /dev/sdb1 \-\-remove /dev/sdb1
1335 Each operation applies to all devices listed until the next
1338 If an array is using a write-intent bitmap, then devices which have
1339 been removed can be re\-added in a way that avoids a full
1340 reconstruction but instead just updates the blocks that have changed
1341 since the device was removed. For arrays with persistent metadata
1342 (superblocks) this is done automatically. For arrays created with
1344 mdadm needs to be told that this device we removed recently with
1347 Devices can only be removed from an array if they are not in active
1348 use, i.e. that must be spares or failed devices. To remove an active
1349 device, it must first be marked as
1355 .BR \-Q ", " \-\-query
1356 Examine a device to see
1357 (1) if it is an md device and (2) if it is a component of an md
1359 Information about what is discovered is presented.
1362 .BR \-D ", " \-\-detail
1363 Print details of one or more md devices.
1366 .BR \-\-detail\-platform
1367 Print details of the platform's RAID capabilities (firmware / hardware
1368 topology) for a given metadata format. If used without argument, mdadm
1369 will scan all controllers looking for their capabilities. Otherwise, mdadm
1370 will only look at the controller specified by the argument in form of an
1371 absolute filepath or a link, e.g.
1372 .IR /sys/devices/pci0000:00/0000:00:1f.2 .
1375 .BR \-Y ", " \-\-export
1377 .B \-\-detail , \-\-detail-platform
1380 output will be formatted as
1382 pairs for easy import into the environment.
1385 .BR \-E ", " \-\-examine
1386 Print contents of the metadata stored on the named device(s).
1387 Note the contrast between
1392 applies to devices which are components of an array, while
1394 applies to a whole array which is currently active.
1397 If an array was created on a SPARC machine with a 2.2 Linux kernel
1398 patched with RAID support, the superblock will have been created
1399 incorrectly, or at least incompatibly with 2.4 and later kernels.
1404 will fix the superblock before displaying it. If this appears to do
1405 the right thing, then the array can be successfully assembled using
1406 .BR "\-\-assemble \-\-update=sparc2.2" .
1409 .BR \-X ", " \-\-examine\-bitmap
1410 Report information about a bitmap file.
1411 The argument is either an external bitmap file or an array component
1412 in case of an internal bitmap. Note that running this on an array
1415 does not report the bitmap for that array.
1418 .BR \-R ", " \-\-run
1419 start a partially assembled array. If
1421 did not find enough devices to fully start the array, it might leaving
1422 it partially assembled. If you wish, you can then use
1424 to start the array in degraded mode.
1427 .BR \-S ", " \-\-stop
1428 deactivate array, releasing all resources.
1431 .BR \-o ", " \-\-readonly
1432 mark array as readonly.
1435 .BR \-w ", " \-\-readwrite
1436 mark array as readwrite.
1439 .B \-\-zero\-superblock
1440 If the device contains a valid md superblock, the block is
1441 overwritten with zeros. With
1443 the block where the superblock would be is overwritten even if it
1444 doesn't appear to be valid.
1447 .B \-\-kill\-subarray=
1448 If the device is a container and the argument to \-\-kill\-subarray
1449 specifies an inactive subarray in the container, then the subarray is
1450 deleted. Deleting all subarrays will leave an 'empty-container' or
1451 spare superblock on the drives. See \-\-zero\-superblock for completely
1452 removing a superblock. Note that some formats depend on the subarray
1453 index for generating a UUID, this command will fail if it would change
1454 the UUID of an active subarray.
1457 .B \-\-update\-subarray=
1458 If the device is a container and the argument to \-\-update\-subarray
1459 specifies a subarray in the container, then attempt to update the given
1460 superblock field in the subarray. See below in
1465 .BR \-t ", " \-\-test
1470 is set to reflect the status of the device. See below in
1475 .BR \-W ", " \-\-wait
1476 For each md device given, wait for any resync, recovery, or reshape
1477 activity to finish before returning.
1479 will return with success if it actually waited for every device
1480 listed, otherwise it will return failure.
1484 For each md device given, or each device in /proc/mdstat if
1486 is given, arrange for the array to be marked clean as soon as possible.
1488 will return with success if the array uses external metadata and we
1489 successfully waited. For native arrays this returns immediately as the
1490 kernel handles dirty-clean transitions at shutdown. No action is taken
1491 if safe-mode handling is disabled.
1493 .SH For Incremental Assembly mode:
1495 .BR \-\-rebuild\-map ", " \-r
1496 Rebuild the map file
1500 uses to help track which arrays are currently being assembled.
1503 .BR \-\-run ", " \-R
1504 Run any array assembled as soon as a minimal number of devices are
1505 available, rather than waiting until all expected devices are present.
1508 .BR \-\-scan ", " \-s
1509 Only meaningful with
1513 file for arrays that are being incrementally assembled and will try to
1514 start any that are not already started. If any such array is listed
1517 as requiring an external bitmap, that bitmap will be attached first.
1520 .BR \-\-fail ", " \-f
1521 This allows the hot-plug system to remove devices that have fully disappeared
1522 from the kernel. It will first fail and then remove the device from any
1523 array it belongs to.
1524 The device name given should be a kernel device name such as "sda",
1530 Only used with \-\-fail. The 'path' given will be recorded so that if
1531 a new device appears at the same location it can be automatically
1532 added to the same array. This allows the failed device to be
1533 automatically replaced by a new device without metadata if it appears
1534 at specified path. This option is normally only set by a
1538 .SH For Monitor mode:
1540 .BR \-m ", " \-\-mail
1541 Give a mail address to send alerts to.
1544 .BR \-p ", " \-\-program ", " \-\-alert
1545 Give a program to be run whenever an event is detected.
1548 .BR \-y ", " \-\-syslog
1549 Cause all events to be reported through 'syslog'. The messages have
1550 facility of 'daemon' and varying priorities.
1553 .BR \-d ", " \-\-delay
1554 Give a delay in seconds.
1556 polls the md arrays and then waits this many seconds before polling
1557 again. The default is 60 seconds. Since 2.6.16, there is no need to
1558 reduce this as the kernel alerts
1560 immediately when there is any change.
1563 .BR \-r ", " \-\-increment
1564 Give a percentage increment.
1566 will generate RebuildNN events with the given percentage increment.
1569 .BR \-f ", " \-\-daemonise
1572 to run as a background daemon if it decides to monitor anything. This
1573 causes it to fork and run in the child, and to disconnect from the
1574 terminal. The process id of the child is written to stdout.
1577 which will only continue monitoring if a mail address or alert program
1578 is found in the config file.
1581 .BR \-i ", " \-\-pid\-file
1584 is running in daemon mode, write the pid of the daemon process to
1585 the specified file, instead of printing it on standard output.
1588 .BR \-1 ", " \-\-oneshot
1589 Check arrays only once. This will generate
1591 events and more significantly
1597 .B " mdadm \-\-monitor \-\-scan \-1"
1599 from a cron script will ensure regular notification of any degraded arrays.
1602 .BR \-t ", " \-\-test
1605 alert for every array found at startup. This alert gets mailed and
1606 passed to the alert program. This can be used for testing that alert
1607 message do get through successfully.
1611 This inhibits the functionality for moving spares between arrays.
1612 Only one monitoring process started with
1614 but without this flag is allowed, otherwise the two could interfere
1621 .B mdadm \-\-assemble
1622 .I md-device options-and-component-devices...
1625 .B mdadm \-\-assemble \-\-scan
1626 .I md-devices-and-options...
1629 .B mdadm \-\-assemble \-\-scan
1633 This usage assembles one or more RAID arrays from pre-existing components.
1634 For each array, mdadm needs to know the md device, the identity of the
1635 array, and a number of component-devices. These can be found in a number of ways.
1637 In the first usage example (without the
1639 the first device given is the md device.
1640 In the second usage example, all devices listed are treated as md
1641 devices and assembly is attempted.
1642 In the third (where no devices are listed) all md devices that are
1643 listed in the configuration file are assembled. If no arrays are
1644 described by the configuration file, then any arrays that
1645 can be found on unused devices will be assembled.
1647 If precisely one device is listed, but
1653 was given and identity information is extracted from the configuration file.
1655 The identity can be given with the
1661 option, will be taken from the md-device record in the config file, or
1662 will be taken from the super block of the first component-device
1663 listed on the command line.
1665 Devices can be given on the
1667 command line or in the config file. Only devices which have an md
1668 superblock which contains the right identity will be considered for
1671 The config file is only used if explicitly named with
1673 or requested with (a possibly implicit)
1678 .B /etc/mdadm/mdadm.conf
1683 is not given, then the config file will only be used to find the
1684 identity of md arrays.
1686 Normally the array will be started after it is assembled. However if
1688 is not given and not all expected drives were listed, then the array
1689 is not started (to guard against usage errors). To insist that the
1690 array be started in this case (as may work for RAID1, 4, 5, 6, or 10),
1699 does not create any entries in
1703 It does record information in
1707 to choose the correct name.
1711 detects that udev is not configured, it will create the devices in
1715 In Linux kernels prior to version 2.6.28 there were two distinctly
1716 different types of md devices that could be created: one that could be
1717 partitioned using standard partitioning tools and one that could not.
1718 Since 2.6.28 that distinction is no longer relevant as both type of
1719 devices can be partitioned.
1721 will normally create the type that originally could not be partitioned
1722 as it has a well defined major number (9).
1724 Prior to 2.6.28, it is important that mdadm chooses the correct type
1725 of array device to use. This can be controlled with the
1727 option. In particular, a value of "mdp" or "part" or "p" tells mdadm
1728 to use a partitionable device rather than the default.
1730 In the no-udev case, the value given to
1732 can be suffixed by a number. This tells
1734 to create that number of partition devices rather than the default of 4.
1738 can also be given in the configuration file as a word starting
1740 on the ARRAY line for the relevant array.
1747 and no devices are listed,
1749 will first attempt to assemble all the arrays listed in the config
1752 If no arrays are listed in the config (other than those marked
1754 it will look through the available devices for possible arrays and
1755 will try to assemble anything that it finds. Arrays which are tagged
1756 as belonging to the given homehost will be assembled and started
1757 normally. Arrays which do not obviously belong to this host are given
1758 names that are expected not to conflict with anything local, and are
1759 started "read-auto" so that nothing is written to any device until the
1760 array is written to. i.e. automatic resync etc is delayed.
1764 finds a consistent set of devices that look like they should comprise
1765 an array, and if the superblock is tagged as belonging to the given
1766 home host, it will automatically choose a device name and try to
1767 assemble the array. If the array uses version-0.90 metadata, then the
1769 number as recorded in the superblock is used to create a name in
1773 If the array uses version-1 metadata, then the
1775 from the superblock is used to similarly create a name in
1777 (the name will have any 'host' prefix stripped first).
1779 This behaviour can be modified by the
1783 configuration file. This line can indicate that specific metadata
1784 type should, or should not, be automatically assembled. If an array
1785 is found which is not listed in
1787 and has a metadata format that is denied by the
1789 line, then it will not be assembled.
1792 line can also request that all arrays identified as being for this
1793 homehost should be assembled regardless of their metadata type.
1796 for further details.
1798 Note: Auto assembly cannot be used for assembling and activating some
1799 arrays which are undergoing reshape. In particular as the
1801 cannot be given, any reshape which requires a backup-file to continue
1802 cannot be started by auto assembly. An array which is growing to more
1803 devices and has passed the critical section can be assembled using
1814 .BI \-\-raid\-devices= Z
1818 This usage is similar to
1820 The difference is that it creates an array without a superblock. With
1821 these arrays there is no difference between initially creating the array and
1822 subsequently assembling the array, except that hopefully there is useful
1823 data there in the second case.
1825 The level may raid0, linear, raid1, raid10, multipath, or faulty, or
1826 one of their synonyms. All devices must be listed and the array will
1827 be started once complete. It will often be appropriate to use
1828 .B \-\-assume\-clean
1829 with levels raid1 or raid10.
1840 .BI \-\-raid\-devices= Z
1844 This usage will initialise a new md array, associate some devices with
1845 it, and activate the array.
1847 The named device will normally not exist when
1848 .I "mdadm \-\-create"
1849 is run, but will be created by
1851 once the array becomes active.
1853 As devices are added, they are checked to see if they contain RAID
1854 superblocks or filesystems. They are also checked to see if the variance in
1855 device size exceeds 1%.
1857 If any discrepancy is found, the array will not automatically be run, though
1860 can override this caution.
1862 To create a "degraded" array in which some devices are missing, simply
1863 give the word "\fBmissing\fP"
1864 in place of a device name. This will cause
1866 to leave the corresponding slot in the array empty.
1867 For a RAID4 or RAID5 array at most one slot can be
1868 "\fBmissing\fP"; for a RAID6 array at most two slots.
1869 For a RAID1 array, only one real device needs to be given. All of the
1873 When creating a RAID5 array,
1875 will automatically create a degraded array with an extra spare drive.
1876 This is because building the spare into a degraded array is in general
1877 faster than resyncing the parity on a non-degraded, but not clean,
1878 array. This feature can be overridden with the
1882 When creating an array with version-1 metadata a name for the array is
1884 If this is not given with the
1888 will choose a name based on the last component of the name of the
1889 device being created. So if
1891 is being created, then the name
1896 is being created, then the name
1900 When creating a partition based array, using
1902 with version-1.x metadata, the partition type should be set to
1904 (non fs-data). This type selection allows for greater precision since
1905 using any other [RAID auto-detect (0xFD) or a GNU/Linux partition (0x83)],
1906 might create problems in the event of array recovery through a live cdrom.
1908 A new array will normally get a randomly assigned 128bit UUID which is
1909 very likely to be unique. If you have a specific need, you can choose
1910 a UUID for the array by giving the
1912 option. Be warned that creating two arrays with the same UUID is a
1913 recipe for disaster. Also, using
1915 when creating a v0.90 array will silently override any
1920 .\"option is given, it is not necessary to list any component-devices in this command.
1921 .\"They can be added later, before a
1925 .\"is given, the apparent size of the smallest drive given is used.
1927 If the metadata type supports it (currently only 1.x metadata), space
1928 will be allocated to store a bad block list. This allows a modest
1929 number of bad blocks to be recorded, allowing the drive to remain in
1930 service while only partially functional.
1932 When creating an array within a
1935 can be given either the list of devices to use, or simply the name of
1936 the container. The former case gives control over which devices in
1937 the container will be used for the array. The latter case allows
1939 to automatically choose which devices to use based on how much spare
1942 The General Management options that are valid with
1947 insist on running the array even if some devices look like they might
1952 start the array readonly \(em not supported yet.
1959 .I options... devices...
1962 This usage will allow individual devices in an array to be failed,
1963 removed or added. It is possible to perform multiple operations with
1964 on command. For example:
1966 .B " mdadm /dev/md0 \-f /dev/hda1 \-r /dev/hda1 \-a /dev/hda1"
1972 and will then remove it from the array and finally add it back
1973 in as a spare. However only one md array can be affected by a single
1976 When a device is added to an active array, mdadm checks to see if it
1977 has metadata on it which suggests that it was recently a member of the
1978 array. If it does, it tries to "re\-add" the device. If there have
1979 been no changes since the device was removed, or if the array has a
1980 write-intent bitmap which has recorded whatever changes there were,
1981 then the device will immediately become a full member of the array and
1982 those differences recorded in the bitmap will be resolved.
1992 MISC mode includes a number of distinct operations that
1993 operate on distinct devices. The operations are:
1996 The device is examined to see if it is
1997 (1) an active md array, or
1998 (2) a component of an md array.
1999 The information discovered is reported.
2003 The device should be an active md device.
2005 will display a detailed description of the array.
2009 will cause the output to be less detailed and the format to be
2010 suitable for inclusion in
2014 will normally be 0 unless
2016 failed to get useful information about the device(s); however, if the
2018 option is given, then the exit status will be:
2022 The array is functioning normally.
2025 The array has at least one failed device.
2028 The array has multiple failed devices such that it is unusable.
2031 There was an error while trying to get information about the device.
2035 .B \-\-detail\-platform
2036 Print detail of the platform's RAID capabilities (firmware / hardware
2037 topology). If the metadata is specified with
2041 then the return status will be:
2045 metadata successfully enumerated its platform components on this system
2048 metadata is platform independent
2051 metadata failed to find its platform components on this system
2055 .B \-\-update\-subarray=
2056 If the device is a container and the argument to \-\-update\-subarray
2057 specifies a subarray in the container, then attempt to update the given
2058 superblock field in the subarray. Similar to updating an array in
2059 "assemble" mode, the field to update is selected by
2063 option. Currently only
2069 option updates the subarray name in the metadata, it may not affect the
2070 device node name or the device node symlink until the subarray is
2071 re\-assembled. If updating
2073 would change the UUID of an active subarray this operation is blocked,
2074 and the command will end in an error.
2078 The device should be a component of an md array.
2080 will read the md superblock of the device and display the contents.
2085 is given, then multiple devices that are components of the one array
2086 are grouped together and reported in a single entry suitable
2092 without listing any devices will cause all devices listed in the
2093 config file to be examined.
2097 The devices should be active md arrays which will be deactivated, as
2098 long as they are not currently in use.
2102 This will fully activate a partially assembled md array.
2106 This will mark an active array as read-only, providing that it is
2107 not currently being used.
2113 array back to being read/write.
2117 For all operations except
2120 will cause the operation to be applied to all arrays listed in
2125 causes all devices listed in the config file to be examined.
2128 .BR \-b ", " \-\-brief
2129 Be less verbose. This is used with
2137 gives an intermediate level of verbosity.
2143 .B mdadm \-\-monitor
2144 .I options... devices...
2149 to periodically poll a number of md arrays and to report on any events
2152 will never exit once it decides that there are arrays to be checked,
2153 so it should normally be run in the background.
2155 As well as reporting events,
2157 may move a spare drive from one array to another if they are in the
2162 and if the destination array has a failed drive but no spares.
2164 If any devices are listed on the command line,
2166 will only monitor those devices. Otherwise all arrays listed in the
2167 configuration file will be monitored. Further, if
2169 is given, then any other md devices that appear in
2171 will also be monitored.
2173 The result of monitoring the arrays is the generation of events.
2174 These events are passed to a separate program (if specified) and may
2175 be mailed to a given E-mail address.
2177 When passing events to a program, the program is run once for each event,
2178 and is given 2 or 3 command-line arguments: the first is the
2179 name of the event (see below), the second is the name of the
2180 md device which is affected, and the third is the name of a related
2181 device if relevant (such as a component device that has failed).
2185 is given, then a program or an E-mail address must be specified on the
2186 command line or in the config file. If neither are available, then
2188 will not monitor anything.
2192 will continue monitoring as long as something was found to monitor. If
2193 no program or email is given, then each event is reported to
2196 The different events are:
2200 .B DeviceDisappeared
2201 An md array which previously was configured appears to no longer be
2202 configured. (syslog priority: Critical)
2206 was told to monitor an array which is RAID0 or Linear, then it will
2208 .B DeviceDisappeared
2209 with the extra information
2211 This is because RAID0 and Linear do not support the device-failed,
2212 hot-spare and resync operations which are monitored.
2216 An md array started reconstruction. (syslog priority: Warning)
2222 is a two-digit number (ie. 05, 48). This indicates that rebuild
2223 has passed that many percent of the total. The events are generated
2224 with fixed increment since 0. Increment size may be specified with
2225 a commandline option (default is 20). (syslog priority: Warning)
2229 An md array that was rebuilding, isn't any more, either because it
2230 finished normally or was aborted. (syslog priority: Warning)
2234 An active component device of an array has been marked as
2235 faulty. (syslog priority: Critical)
2239 A spare component device which was being rebuilt to replace a faulty
2240 device has failed. (syslog priority: Critical)
2244 A spare component device which was being rebuilt to replace a faulty
2245 device has been successfully rebuilt and has been made active.
2246 (syslog priority: Info)
2250 A new md array has been detected in the
2252 file. (syslog priority: Info)
2256 A newly noticed array appears to be degraded. This message is not
2259 notices a drive failure which causes degradation, but only when
2261 notices that an array is degraded when it first sees the array.
2262 (syslog priority: Critical)
2266 A spare drive has been moved from one array in a
2270 to another to allow a failed drive to be replaced.
2271 (syslog priority: Info)
2277 has been told, via the config file, that an array should have a certain
2278 number of spare devices, and
2280 detects that it has fewer than this number when it first sees the
2281 array, it will report a
2284 (syslog priority: Warning)
2288 An array was found at startup, and the
2291 (syslog priority: Info)
2301 cause Email to be sent. All events cause the program to be run.
2302 The program is run with two or three arguments: the event
2303 name, the array device and possibly a second device.
2305 Each event has an associated array device (e.g.
2307 and possibly a second device. For
2312 the second device is the relevant component device.
2315 the second device is the array that the spare was moved from.
2319 to move spares from one array to another, the different arrays need to
2320 be labeled with the same
2322 or the spares must be allowed to migrate through matching POLICY domains
2323 in the configuration file. The
2325 name can be any string; it is only necessary that different spare
2326 groups use different names.
2330 detects that an array in a spare group has fewer active
2331 devices than necessary for the complete array, and has no spare
2332 devices, it will look for another array in the same spare group that
2333 has a full complement of working drive and a spare. It will then
2334 attempt to remove the spare from the second drive and add it to the
2336 If the removal succeeds but the adding fails, then it is added back to
2339 If the spare group for a degraded array is not defined,
2341 will look at the rules of spare migration specified by POLICY lines in
2343 and then follow similar steps as above if a matching spare is found.
2346 The GROW mode is used for changing the size or shape of an active
2348 For this to work, the kernel must support the necessary change.
2349 Various types of growth are being added during 2.6 development.
2351 Currently the supported changes include
2353 change the "size" attribute for RAID1, RAID4, RAID5 and RAID6.
2355 increase or decrease the "raid\-devices" attribute of RAID0, RAID1, RAID4,
2358 change the chunk-size and layout of RAID0, RAID4, RAID5 and RAID6.
2360 convert between RAID1 and RAID5, between RAID5 and RAID6, between
2361 RAID0, RAID4, and RAID5, and between RAID0 and RAID10 (in the near-2 mode).
2363 add a write-intent bitmap to any array which supports these bitmaps, or
2364 remove a write-intent bitmap from such an array.
2367 Using GROW on containers is currently supported only for Intel's IMSM
2368 container format. The number of devices in a container can be
2369 increased - which affects all arrays in the container - or an array
2370 in a container can be converted between levels where those levels are
2371 supported by the container, and the conversion is on of those listed
2372 above. Resizing arrays in an IMSM container with
2374 is not yet supported.
2376 Grow functionality (e.g. expand a number of raid devices) for Intel's
2377 IMSM container format has an experimental status. It is guarded by the
2378 .B MDADM_EXPERIMENTAL
2379 environment variable which must be set to '1' for a GROW command to
2381 This is for the following reasons:
2384 Intel's native IMSM check-pointing is not fully tested yet.
2385 This can causes IMSM incompatibility during the grow process: an array
2386 which is growing cannot roam between Microsoft Windows(R) and Linux
2390 Interrupting a grow operation is not recommended, because it
2391 has not been fully tested for Intel's IMSM container format yet.
2394 Note: Intel's native checkpointing doesn't use
2396 option and it is transparent for assembly feature.
2399 Normally when an array is built the "size" is taken from the smallest
2400 of the drives. If all the small drives in an arrays are, one at a
2401 time, removed and replaced with larger drives, then you could have an
2402 array of large drives with only a small amount used. In this
2403 situation, changing the "size" with "GROW" mode will allow the extra
2404 space to start being used. If the size is increased in this way, a
2405 "resync" process will start to make sure the new parts of the array
2408 Note that when an array changes size, any filesystem that may be
2409 stored in the array will not automatically grow or shrink to use or
2410 vacate the space. The
2411 filesystem will need to be explicitly told to use the extra space
2412 after growing, or to reduce its size
2414 to shrinking the array.
2416 Also the size of an array cannot be changed while it has an active
2417 bitmap. If an array has a bitmap, it must be removed before the size
2418 can be changed. Once the change is complete a new bitmap can be created.
2420 .SS RAID\-DEVICES CHANGES
2422 A RAID1 array can work with any number of devices from 1 upwards
2423 (though 1 is not very useful). There may be times which you want to
2424 increase or decrease the number of active devices. Note that this is
2425 different to hot-add or hot-remove which changes the number of
2428 When reducing the number of devices in a RAID1 array, the slots which
2429 are to be removed from the array must already be vacant. That is, the
2430 devices which were in those slots must be failed and removed.
2432 When the number of devices is increased, any hot spares that are
2433 present will be activated immediately.
2435 Changing the number of active devices in a RAID5 or RAID6 is much more
2436 effort. Every block in the array will need to be read and written
2437 back to a new location. From 2.6.17, the Linux Kernel is able to
2438 increase the number of devices in a RAID5 safely, including restarting
2439 an interrupted "reshape". From 2.6.31, the Linux Kernel is able to
2440 increase or decrease the number of devices in a RAID5 or RAID6.
2442 From 2.6.35, the Linux Kernel is able to convert a RAID0 in to a RAID4
2445 uses this functionality and the ability to add
2446 devices to a RAID4 to allow devices to be added to a RAID0. When
2447 requested to do this,
2449 will convert the RAID0 to a RAID4, add the necessary disks and make
2450 the reshape happen, and then convert the RAID4 back to RAID0.
2452 When decreasing the number of devices, the size of the array will also
2453 decrease. If there was data in the array, it could get destroyed and
2454 this is not reversible, so you should firstly shrink the filesystem on
2455 the array to fit within the new size. To help prevent accidents,
2457 requires that the size of the array be decreased first with
2458 .BR "mdadm --grow --array-size" .
2459 This is a reversible change which simply makes the end of the array
2460 inaccessible. The integrity of any data can then be checked before
2461 the non-reversible reduction in the number of devices is request.
2463 When relocating the first few stripes on a RAID5 or RAID6, it is not
2464 possible to keep the data on disk completely consistent and
2465 crash-proof. To provide the required safety, mdadm disables writes to
2466 the array while this "critical section" is reshaped, and takes a
2467 backup of the data that is in that section. For grows, this backup may be
2468 stored in any spare devices that the array has, however it can also be
2469 stored in a separate file specified with the
2471 option, and is required to be specified for shrinks, RAID level
2472 changes and layout changes. If this option is used, and the system
2473 does crash during the critical period, the same file must be passed to
2475 to restore the backup and reassemble the array. When shrinking rather
2476 than growing the array, the reshape is done from the end towards the
2477 beginning, so the "critical section" is at the end of the reshape.
2481 Changing the RAID level of any array happens instantaneously. However
2482 in the RAID5 to RAID6 case this requires a non-standard layout of the
2483 RAID6 data, and in the RAID6 to RAID5 case that non-standard layout is
2484 required before the change can be accomplished. So while the level
2485 change is instant, the accompanying layout change can take quite a
2488 is required. If the array is not simultaneously being grown or
2489 shrunk, so that the array size will remain the same - for example,
2490 reshaping a 3-drive RAID5 into a 4-drive RAID6 - the backup file will
2491 be used not just for a "cricital section" but throughout the reshape
2492 operation, as described below under LAYOUT CHANGES.
2494 .SS CHUNK-SIZE AND LAYOUT CHANGES
2496 Changing the chunk-size of layout without also changing the number of
2497 devices as the same time will involve re-writing all blocks in-place.
2498 To ensure against data loss in the case of a crash, a
2500 must be provided for these changes. Small sections of the array will
2501 be copied to the backup file while they are being rearranged. This
2502 means that all the data is copied twice, once to the backup and once
2503 to the new layout on the array, so this type of reshape will go very
2506 If the reshape is interrupted for any reason, this backup file must be
2508 .B "mdadm --assemble"
2509 so the array can be reassembled. Consequently the file cannot be
2510 stored on the device being reshaped.
2515 A write-intent bitmap can be added to, or removed from, an active
2516 array. Either internal bitmaps, or bitmaps stored in a separate file,
2517 can be added. Note that if you add a bitmap stored in a file which is
2518 in a filesystem that is on the RAID array being affected, the system
2519 will deadlock. The bitmap must be on a separate filesystem.
2521 .SH INCREMENTAL MODE
2525 .B mdadm \-\-incremental
2531 .B mdadm \-\-incremental \-\-fail
2535 .B mdadm \-\-incremental \-\-rebuild\-map
2538 .B mdadm \-\-incremental \-\-run \-\-scan
2541 This mode is designed to be used in conjunction with a device
2542 discovery system. As devices are found in a system, they can be
2544 .B "mdadm \-\-incremental"
2545 to be conditionally added to an appropriate array.
2547 Conversely, it can also be used with the
2549 flag to do just the opposite and find whatever array a particular device
2550 is part of and remove the device from that array.
2552 If the device passed is a
2554 device created by a previous call to
2556 then rather than trying to add that device to an array, all the arrays
2557 described by the metadata of the container will be started.
2560 performs a number of tests to determine if the device is part of an
2561 array, and which array it should be part of. If an appropriate array
2562 is found, or can be created,
2564 adds the device to the array and conditionally starts the array.
2568 will normally only add devices to an array which were previously working
2569 (active or spare) parts of that array. The support for automatic
2570 inclusion of a new drive as a spare in some array requires
2571 a configuration through POLICY in config file.
2575 makes are as follow:
2577 Is the device permitted by
2579 That is, is it listed in a
2581 line in that file. If
2583 is absent then the default it to allow any device. Similar if
2585 contains the special word
2587 then any device is allowed. Otherwise the device name given to
2589 must match one of the names or patterns in a
2594 Does the device have a valid md superblock? If a specific metadata
2595 version is requested with
2599 then only that style of metadata is accepted, otherwise
2601 finds any known version of metadata. If no
2603 metadata is found, the device may be still added to an array
2604 as a spare if POLICY allows.
2608 Does the metadata match an expected array?
2609 The metadata can match in two ways. Either there is an array listed
2612 which identifies the array (either by UUID, by name, by device list,
2613 or by minor-number), or the array was created with a
2619 or on the command line.
2622 is not able to positively identify the array as belonging to the
2623 current host, the device will be rejected.
2628 keeps a list of arrays that it has partially assembled in
2630 If no array exists which matches
2631 the metadata on the new device,
2633 must choose a device name and unit number. It does this based on any
2636 or any name information stored in the metadata. If this name
2637 suggests a unit number, that number will be used, otherwise a free
2638 unit number will be chosen. Normally
2640 will prefer to create a partitionable array, however if the
2644 suggests that a non-partitionable array is preferred, that will be
2647 If the array is not found in the config file and its metadata does not
2648 identify it as belonging to the "homehost", then
2650 will choose a name for the array which is certain not to conflict with
2651 any array which does belong to this host. It does this be adding an
2652 underscore and a small number to the name preferred by the metadata.
2654 Once an appropriate array is found or created and the device is added,
2656 must decide if the array is ready to be started. It will
2657 normally compare the number of available (non-spare) devices to the
2658 number of devices that the metadata suggests need to be active. If
2659 there are at least that many, the array will be started. This means
2660 that if any devices are missing the array will not be restarted.
2666 in which case the array will be run as soon as there are enough
2667 devices present for the data to be accessible. For a RAID1, that
2668 means one device will start the array. For a clean RAID5, the array
2669 will be started as soon as all but one drive is present.
2671 Note that neither of these approaches is really ideal. If it can
2672 be known that all device discovery has completed, then
2676 can be run which will try to start all arrays that are being
2677 incrementally assembled. They are started in "read-auto" mode in
2678 which they are read-only until the first write request. This means
2679 that no metadata updates are made and no attempt at resync or recovery
2680 happens. Further devices that are found before the first write can
2681 still be added safely.
2684 This section describes environment variables that affect how mdadm
2689 Setting this value to 1 will prevent mdadm from automatically launching
2690 mdmon. This variable is intended primarily for debugging mdadm/mdmon.
2696 does not create any device nodes in /dev, but leaves that task to
2700 appears not to be configured, or if this environment variable is set
2703 will create and devices that are needed.
2707 .B " mdadm \-\-query /dev/name-of-device"
2709 This will find out if a given device is a RAID array, or is part of
2710 one, and will provide brief information about the device.
2712 .B " mdadm \-\-assemble \-\-scan"
2714 This will assemble and start all arrays listed in the standard config
2715 file. This command will typically go in a system startup file.
2717 .B " mdadm \-\-stop \-\-scan"
2719 This will shut down all arrays that can be shut down (i.e. are not
2720 currently in use). This will typically go in a system shutdown script.
2722 .B " mdadm \-\-follow \-\-scan \-\-delay=120"
2724 If (and only if) there is an Email address or program given in the
2725 standard config file, then
2726 monitor the status of all arrays listed in that file by
2727 polling them ever 2 minutes.
2729 .B " mdadm \-\-create /dev/md0 \-\-level=1 \-\-raid\-devices=2 /dev/hd[ac]1"
2731 Create /dev/md0 as a RAID1 array consisting of /dev/hda1 and /dev/hdc1.
2734 .B " echo 'DEVICE /dev/hd*[0\-9] /dev/sd*[0\-9]' > mdadm.conf"
2736 .B " mdadm \-\-detail \-\-scan >> mdadm.conf"
2738 This will create a prototype config file that describes currently
2739 active arrays that are known to be made from partitions of IDE or SCSI drives.
2740 This file should be reviewed before being used as it may
2741 contain unwanted detail.
2743 .B " echo 'DEVICE /dev/hd[a\-z] /dev/sd*[a\-z]' > mdadm.conf"
2745 .B " mdadm \-\-examine \-\-scan \-\-config=mdadm.conf >> mdadm.conf"
2747 This will find arrays which could be assembled from existing IDE and
2748 SCSI whole drives (not partitions), and store the information in the
2749 format of a config file.
2750 This file is very likely to contain unwanted detail, particularly
2753 entries. It should be reviewed and edited before being used as an
2756 .B " mdadm \-\-examine \-\-brief \-\-scan \-\-config=partitions"
2758 .B " mdadm \-Ebsc partitions"
2760 Create a list of devices by reading
2761 .BR /proc/partitions ,
2762 scan these for RAID superblocks, and printout a brief listing of all
2765 .B " mdadm \-Ac partitions \-m 0 /dev/md0"
2767 Scan all partitions and devices listed in
2768 .BR /proc/partitions
2771 out of all such devices with a RAID superblock with a minor number of 0.
2773 .B " mdadm \-\-monitor \-\-scan \-\-daemonise > /run/mdadm/mon.pid"
2775 If config file contains a mail address or alert program, run mdadm in
2776 the background in monitor mode monitoring all md devices. Also write
2777 pid of mdadm daemon to
2778 .BR /run/mdadm/mon.pid .
2780 .B " mdadm \-Iq /dev/somedevice"
2782 Try to incorporate newly discovered device into some array as
2785 .B " mdadm \-\-incremental \-\-rebuild\-map \-\-run \-\-scan"
2787 Rebuild the array map from any current arrays, and then start any that
2790 .B " mdadm /dev/md4 --fail detached --remove detached"
2792 Any devices which are components of /dev/md4 will be marked as faulty
2793 and then remove from the array.
2795 .B " mdadm --grow /dev/md4 --level=6 --backup-file=/root/backup-md4"
2799 which is currently a RAID5 array will be converted to RAID6. There
2800 should normally already be a spare drive attached to the array as a
2801 RAID6 needs one more drive than a matching RAID5.
2803 .B " mdadm --create /dev/md/ddf --metadata=ddf --raid-disks 6 /dev/sd[a-f]"
2805 Create a DDF array over 6 devices.
2807 .B " mdadm --create /dev/md/home -n3 -l5 -z 30000000 /dev/md/ddf"
2809 Create a RAID5 array over any 3 devices in the given DDF set. Use
2810 only 30 gigabytes of each device.
2812 .B " mdadm -A /dev/md/ddf1 /dev/sd[a-f]"
2814 Assemble a pre-exist ddf array.
2816 .B " mdadm -I /dev/md/ddf1"
2818 Assemble all arrays contained in the ddf array, assigning names as
2821 .B " mdadm \-\-create \-\-help"
2823 Provide help about the Create mode.
2825 .B " mdadm \-\-config \-\-help"
2827 Provide help about the format of the config file.
2829 .B " mdadm \-\-help"
2831 Provide general help.
2841 lists all active md devices with information about them.
2843 uses this to find arrays when
2845 is given in Misc mode, and to monitor array reconstruction
2850 The config file lists which devices may be scanned to see if
2851 they contain MD super block, and gives identifying information
2852 (e.g. UUID) about known MD arrays. See
2859 mode is used, this file gets a list of arrays currently being created.
2864 understand two sorts of names for array devices.
2866 The first is the so-called 'standard' format name, which matches the
2867 names used by the kernel and which appear in
2870 The second sort can be freely chosen, but must reside in
2872 When giving a device name to
2874 to create or assemble an array, either full path name such as
2878 can be given, or just the suffix of the second sort of name, such as
2884 chooses device names during auto-assembly or incremental assembly, it
2885 will sometimes add a small sequence number to the end of the name to
2886 avoid conflicted between multiple arrays that have the same name. If
2888 can reasonably determine that the array really is meant for this host,
2889 either by a hostname in the metadata, or by the presence of the array
2892 then it will leave off the suffix if possible.
2893 Also if the homehost is specified as
2896 will only use a suffix if a different array of the same name already
2897 exists or is listed in the config file.
2899 The standard names for non-partitioned arrays (the only sort of md
2900 array available in 2.4 and earlier) are of the form
2904 where NN is a number.
2905 The standard names for partitionable arrays (as available from 2.6
2906 onwards) are of the form
2910 Partition numbers should be indicated by added "pMM" to these, thus "/dev/md/d1p2".
2912 From kernel version, 2.6.28 the "non-partitioned array" can actually
2913 be partitioned. So the "md_dNN" names are no longer needed, and
2914 partitions such as "/dev/mdNNpXX" are possible.
2918 was previously known as
2922 is completely separate from the
2924 package, and does not use the
2926 configuration file at all.
2929 For further information on mdadm usage, MD and the various levels of
2932 .B http://raid.wiki.kernel.org/
2934 (based upon Jakob \(/Ostergaard's Software\-RAID.HOWTO)
2936 .\"for new releases of the RAID driver check out:
2939 .\".UR ftp://ftp.kernel.org/pub/linux/kernel/people/mingo/raid-patches
2940 .\"ftp://ftp.kernel.org/pub/linux/kernel/people/mingo/raid-patches
2945 .\".UR http://www.cse.unsw.edu.au/~neilb/patches/linux-stable/
2946 .\"http://www.cse.unsw.edu.au/~neilb/patches/linux-stable/
2949 The latest version of
2951 should always be available from
2953 .B http://www.kernel.org/pub/linux/utils/raid/mdadm/
projects / thirdparty / mdadm.git / blob