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 0,4,5,6,10 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
225 then the MANAGE mode is assumed.
226 Anything other than these will cause the
230 .SH Options that are not mode-specific are:
233 .BR \-h ", " \-\-help
234 Display general help message or, after one of the above options, a
235 mode-specific help message.
239 Display more detailed help about command line parsing and some commonly
243 .BR \-V ", " \-\-version
244 Print version information for mdadm.
247 .BR \-v ", " \-\-verbose
248 Be more verbose about what is happening. This can be used twice to be
250 The extra verbosity currently only affects
251 .B \-\-detail \-\-scan
253 .BR "\-\-examine \-\-scan" .
256 .BR \-q ", " \-\-quiet
257 Avoid printing purely informative messages. With this,
259 will be silent unless there is something really important to report.
263 .BR \-f ", " \-\-force
264 Be more forceful about certain operations. See the various modes for
265 the exact meaning of this option in different contexts.
268 .BR \-c ", " \-\-config=
269 Specify the config file or directory. Default is to use
272 .BR /etc/mdadm.conf.d ,
273 or if those are missing then
274 .B /etc/mdadm/mdadm.conf
276 .BR /etc/mdadm/mdadm.conf.d .
277 If the config file given is
279 then nothing will be read, but
281 will act as though the config file contained exactly
283 .B " DEVICE partitions containers"
287 to find a list of devices to scan, and
289 to find a list of containers to examine.
292 is given for the config file, then
294 will act as though the config file were empty.
296 If the name given is of a directory, then
298 will collect all the files contained in the directory with a name ending
301 sort them lexically, and process all of those files as config files.
304 .BR \-s ", " \-\-scan
307 for missing information.
308 In general, this option gives
310 permission to get any missing information (like component devices,
311 array devices, array identities, and alert destination) from the
312 configuration file (see previous option);
313 one exception is MISC mode when using
319 says to get a list of array devices from
323 .BR \-e ", " \-\-metadata=
324 Declare the style of RAID metadata (superblock) to be used. The
325 default is {DEFAULT_METADATA} for
327 and to guess for other operations.
328 The default can be overridden by setting the
337 .ie '{DEFAULT_METADATA}'0.90'
338 .IP "0, 0.90, default"
341 Use the original 0.90 format superblock. This format limits arrays to
342 28 component devices and limits component devices of levels 1 and
343 greater to 2 terabytes. It is also possible for there to be confusion
344 about whether the superblock applies to a whole device or just the
345 last partition, if that partition starts on a 64K boundary.
346 .ie '{DEFAULT_METADATA}'0.90'
347 .IP "1, 1.0, 1.1, 1.2"
349 .IP "1, 1.0, 1.1, 1.2 default"
350 Use the new version-1 format superblock. This has fewer restrictions.
351 It can easily be moved between hosts with different endian-ness, and a
352 recovery operation can be checkpointed and restarted. The different
353 sub-versions store the superblock at different locations on the
354 device, either at the end (for 1.0), at the start (for 1.1) or 4K from
355 the start (for 1.2). "1" is equivalent to "1.2" (the commonly
356 preferred 1.x format).
357 'if '{DEFAULT_METADATA}'1.2' "default" is equivalent to "1.2".
359 Use the "Industry Standard" DDF (Disk Data Format) format defined by
361 When creating a DDF array a
363 will be created, and normal arrays can be created in that container.
365 Use the Intel(R) Matrix Storage Manager metadata format. This creates a
367 which is managed in a similar manner to DDF, and is supported by an
368 option-rom on some platforms:
370 .B http://www.intel.com/design/chipsets/matrixstorage_sb.htm
376 This will override any
378 setting in the config file and provides the identity of the host which
379 should be considered the home for any arrays.
381 When creating an array, the
383 will be recorded in the metadata. For version-1 superblocks, it will
384 be prefixed to the array name. For version-0.90 superblocks, part of
385 the SHA1 hash of the hostname will be stored in the later half of the
388 When reporting information about an array, any array which is tagged
389 for the given homehost will be reported as such.
391 When using Auto-Assemble, only arrays tagged for the given homehost
392 will be allowed to use 'local' names (i.e. not ending in '_' followed
393 by a digit string). See below under
394 .BR "Auto Assembly" .
396 The special name "\fBany\fP" can be used as a wild card. If an array
399 then the name "\fBany\fP" will be stored in the array and it can be
400 assembled in the same way on any host. If an array is assembled with
401 this option, then the homehost recorded on the array will be ignored.
407 needs to print the name for a device it normally finds the name in
409 which refers to the device and is shortest. When a path component is
413 will prefer a longer name if it contains that component. For example
414 .B \-\-prefer=by-uuid
415 will prefer a name in a subdirectory of
420 This functionality is currently only provided by
426 .B \-\-home\-cluster=
427 specifies the cluster name for the md device. The md device can be assembled
428 only on the cluster which matches the name specified. If this option is not
429 provided, mdadm tries to detect the cluster name automatically.
431 .SH For create, build, or grow:
434 .BR \-n ", " \-\-raid\-devices=
435 Specify the number of active devices in the array. This, plus the
436 number of spare devices (see below) must equal the number of
438 (including "\fBmissing\fP" devices)
439 that are listed on the command line for
441 Setting a value of 1 is probably
442 a mistake and so requires that
444 be specified first. A value of 1 will then be allowed for linear,
445 multipath, RAID0 and RAID1. It is never allowed for RAID4, RAID5 or RAID6.
447 This number can only be changed using
449 for RAID1, RAID4, RAID5 and RAID6 arrays, and only on kernels which provide
450 the necessary support.
453 .BR \-x ", " \-\-spare\-devices=
454 Specify the number of spare (eXtra) devices in the initial array.
455 Spares can also be added
456 and removed later. The number of component devices listed
457 on the command line must equal the number of RAID devices plus the
458 number of spare devices.
461 .BR \-z ", " \-\-size=
462 Amount (in Kilobytes) of space to use from each drive in RAID levels 1/4/5/6.
463 This must be a multiple of the chunk size, and must leave about 128Kb
464 of space at the end of the drive for the RAID superblock.
465 If this is not specified
466 (as it normally is not) the smallest drive (or partition) sets the
467 size, though if there is a variance among the drives of greater than 1%, a warning is
470 A suffix of 'K', 'M' or 'G' can be given to indicate Kilobytes, Megabytes or
471 Gigabytes respectively.
473 Sometimes a replacement drive can be a little smaller than the
474 original drives though this should be minimised by IDEMA standards.
475 Such a replacement drive will be rejected by
477 To guard against this it can be useful to set the initial size
478 slightly smaller than the smaller device with the aim that it will
479 still be larger than any replacement.
481 This value can be set with
483 for RAID level 1/4/5/6 though
485 based arrays such as those with IMSM metadata may not be able to
487 If the array was created with a size smaller than the currently
488 active drives, the extra space can be accessed using
490 The size can be given as
492 which means to choose the largest size that fits on all current drives.
494 Before reducing the size of the array (with
495 .BR "\-\-grow \-\-size=" )
496 you should make sure that space isn't needed. If the device holds a
497 filesystem, you would need to resize the filesystem to use less space.
499 After reducing the array size you should check that the data stored in
500 the device is still available. If the device holds a filesystem, then
501 an 'fsck' of the filesystem is a minimum requirement. If there are
502 problems the array can be made bigger again with no loss with another
503 .B "\-\-grow \-\-size="
506 This value cannot be used when creating a
508 such as with DDF and IMSM metadata, though it perfectly valid when
509 creating an array inside a container.
512 .BR \-Z ", " \-\-array\-size=
513 This is only meaningful with
515 and its effect is not persistent: when the array is stopped and
516 restarted the default array size will be restored.
518 Setting the array-size causes the array to appear smaller to programs
519 that access the data. This is particularly needed before reshaping an
520 array so that it will be smaller. As the reshape is not reversible,
521 but setting the size with
523 is, it is required that the array size is reduced as appropriate
524 before the number of devices in the array is reduced.
526 Before reducing the size of the array you should make sure that space
527 isn't needed. If the device holds a filesystem, you would need to
528 resize the filesystem to use less space.
530 After reducing the array size you should check that the data stored in
531 the device is still available. If the device holds a filesystem, then
532 an 'fsck' of the filesystem is a minimum requirement. If there are
533 problems the array can be made bigger again with no loss with another
534 .B "\-\-grow \-\-array\-size="
537 A suffix of 'K', 'M' or 'G' can be given to indicate Kilobytes, Megabytes or
538 Gigabytes respectively.
541 restores the apparent size of the array to be whatever the real
542 amount of available space is.
545 .BR \-c ", " \-\-chunk=
546 Specify chunk size of kilobytes. The default when creating an
547 array is 512KB. To ensure compatibility with earlier versions, the
548 default when building an array with no persistent metadata is 64KB.
549 This is only meaningful for RAID0, RAID4, RAID5, RAID6, and RAID10.
551 RAID4, RAID5, RAID6, and RAID10 require the chunk size to be a power
552 of 2. In any case it must be a multiple of 4KB.
554 A suffix of 'K', 'M' or 'G' can be given to indicate Kilobytes, Megabytes or
555 Gigabytes respectively.
559 Specify rounding factor for a Linear array. The size of each
560 component will be rounded down to a multiple of this size.
561 This is a synonym for
563 but highlights the different meaning for Linear as compared to other
564 RAID levels. The default is 64K if a kernel earlier than 2.6.16 is in
565 use, and is 0K (i.e. no rounding) in later kernels.
568 .BR \-l ", " \-\-level=
569 Set RAID level. When used with
571 options are: linear, raid0, 0, stripe, raid1, 1, mirror, raid4, 4,
572 raid5, 5, raid6, 6, raid10, 10, multipath, mp, faulty, container.
573 Obviously some of these are synonymous.
577 metadata type is requested, only the
579 level is permitted, and it does not need to be explicitly given.
583 only linear, stripe, raid0, 0, raid1, multipath, mp, and faulty are valid.
587 to change the RAID level in some cases. See LEVEL CHANGES below.
590 .BR \-p ", " \-\-layout=
591 This option configures the fine details of data layout for RAID5, RAID6,
592 and RAID10 arrays, and controls the failure modes for
595 The layout of the RAID5 parity block can be one of
596 .BR left\-asymmetric ,
597 .BR left\-symmetric ,
598 .BR right\-asymmetric ,
599 .BR right\-symmetric ,
600 .BR la ", " ra ", " ls ", " rs .
602 .BR left\-symmetric .
604 It is also possible to cause RAID5 to use a RAID4-like layout by
610 Finally for RAID5 there are DDF\-compatible layouts,
611 .BR ddf\-zero\-restart ,
612 .BR ddf\-N\-restart ,
614 .BR ddf\-N\-continue .
616 These same layouts are available for RAID6. There are also 4 layouts
617 that will provide an intermediate stage for converting between RAID5
618 and RAID6. These provide a layout which is identical to the
619 corresponding RAID5 layout on the first N\-1 devices, and has the 'Q'
620 syndrome (the second 'parity' block used by RAID6) on the last device.
622 .BR left\-symmetric\-6 ,
623 .BR right\-symmetric\-6 ,
624 .BR left\-asymmetric\-6 ,
625 .BR right\-asymmetric\-6 ,
627 .BR parity\-first\-6 .
629 When setting the failure mode for level
632 .BR write\-transient ", " wt ,
633 .BR read\-transient ", " rt ,
634 .BR write\-persistent ", " wp ,
635 .BR read\-persistent ", " rp ,
637 .BR read\-fixable ", " rf ,
638 .BR clear ", " flush ", " none .
640 Each failure mode can be followed by a number, which is used as a period
641 between fault generation. Without a number, the fault is generated
642 once on the first relevant request. With a number, the fault will be
643 generated after that many requests, and will continue to be generated
644 every time the period elapses.
646 Multiple failure modes can be current simultaneously by using the
648 option to set subsequent failure modes.
650 "clear" or "none" will remove any pending or periodic failure modes,
651 and "flush" will clear any persistent faults.
653 Finally, the layout options for RAID10 are one of 'n', 'o' or 'f' followed
654 by a small number. The default is 'n2'. The supported options are:
657 signals 'near' copies. Multiple copies of one data block are at
658 similar offsets in different devices.
661 signals 'offset' copies. Rather than the chunks being duplicated
662 within a stripe, whole stripes are duplicated but are rotated by one
663 device so duplicate blocks are on different devices. Thus subsequent
664 copies of a block are in the next drive, and are one chunk further
669 (multiple copies have very different offsets).
670 See md(4) for more detail about 'near', 'offset', and 'far'.
672 The number is the number of copies of each datablock. 2 is normal, 3
673 can be useful. This number can be at most equal to the number of
674 devices in the array. It does not need to divide evenly into that
675 number (e.g. it is perfectly legal to have an 'n2' layout for an array
676 with an odd number of devices).
678 When an array is converted between RAID5 and RAID6 an intermediate
679 RAID6 layout is used in which the second parity block (Q) is always on
680 the last device. To convert a RAID5 to RAID6 and leave it in this new
681 layout (which does not require re-striping) use
682 .BR \-\-layout=preserve .
683 This will try to avoid any restriping.
685 The converse of this is
686 .B \-\-layout=normalise
687 which will change a non-standard RAID6 layout into a more standard
694 (thus explaining the p of
698 .BR \-b ", " \-\-bitmap=
699 Specify a file to store a write-intent bitmap in. The file should not
702 is also given. The same file should be provided
703 when assembling the array. If the word
705 is given, then the bitmap is stored with the metadata on the array,
706 and so is replicated on all devices. If the word
710 mode, then any bitmap that is present is removed. If the word
712 is given, the array is created for a clustered environment. One bitmap
713 is created for each node as defined by the
715 parameter and are stored internally.
717 To help catch typing errors, the filename must contain at least one
718 slash ('/') if it is a real file (not 'internal' or 'none').
720 Note: external bitmaps are only known to work on ext2 and ext3.
721 Storing bitmap files on other filesystems may result in serious problems.
723 When creating an array on devices which are 100G or larger,
725 automatically adds an internal bitmap as it will usually be
726 beneficial. This can be suppressed with
728 or by selecting a different consistency policy with
729 .BR \-\-consistency\-policy .
732 .BR \-\-bitmap\-chunk=
733 Set the chunksize of the bitmap. Each bit corresponds to that many
734 Kilobytes of storage.
735 When using a file based bitmap, the default is to use the smallest
736 size that is at-least 4 and requires no more than 2^21 chunks.
739 bitmap, the chunksize defaults to 64Meg, or larger if necessary to
740 fit the bitmap into the available space.
742 A suffix of 'K', 'M' or 'G' can be given to indicate Kilobytes, Megabytes or
743 Gigabytes respectively.
746 .BR \-W ", " \-\-write\-mostly
747 subsequent devices listed in a
752 command will be flagged as 'write\-mostly'. This is valid for RAID1
753 only and means that the 'md' driver will avoid reading from these
754 devices if at all possible. This can be useful if mirroring over a
758 .BR \-\-write\-behind=
759 Specify that write-behind mode should be enabled (valid for RAID1
760 only). If an argument is specified, it will set the maximum number
761 of outstanding writes allowed. The default value is 256.
762 A write-intent bitmap is required in order to use write-behind
763 mode, and write-behind is only attempted on drives marked as
768 subsequent devices listed in a
772 command will be flagged as 'failfast'. This is valid for RAID1 and
773 RAID10 only. IO requests to these devices will be encouraged to fail
774 quickly rather than cause long delays due to error handling. Also no
775 attempt is made to repair a read error on these devices.
777 If an array becomes degraded so that the 'failfast' device is the only
778 usable device, the 'failfast' flag will then be ignored and extended
779 delays will be preferred to complete failure.
781 The 'failfast' flag is appropriate for storage arrays which have a
782 low probability of true failure, but which may sometimes
783 cause unacceptable delays due to internal maintenance functions.
786 .BR \-\-assume\-clean
789 that the array pre-existed and is known to be clean. It can be useful
790 when trying to recover from a major failure as you can be sure that no
791 data will be affected unless you actually write to the array. It can
792 also be used when creating a RAID1 or RAID10 if you want to avoid the
793 initial resync, however this practice \(em while normally safe \(em is not
794 recommended. Use this only if you really know what you are doing.
796 When the devices that will be part of a new array were filled
797 with zeros before creation the operator knows the array is
798 actually clean. If that is the case, such as after running
799 badblocks, this argument can be used to tell mdadm the
800 facts the operator knows.
802 When an array is resized to a larger size with
803 .B "\-\-grow \-\-size="
804 the new space is normally resynced in that same way that the whole
805 array is resynced at creation. From Linux version 3.0,
807 can be used with that command to avoid the automatic resync.
810 .BR \-\-backup\-file=
813 is used to increase the number of raid-devices in a RAID5 or RAID6 if
814 there are no spare devices available, or to shrink, change RAID level
815 or layout. See the GROW MODE section below on RAID\-DEVICES CHANGES.
816 The file must be stored on a separate device, not on the RAID array
821 Arrays with 1.x metadata can leave a gap between the start of the
822 device and the start of array data. This gap can be used for various
823 metadata. The start of data is known as the
825 Normally an appropriate data offset is computed automatically.
826 However it can be useful to set it explicitly such as when re-creating
827 an array which was originally created using a different version of
829 which computed a different offset.
831 Setting the offset explicitly over-rides the default. The value given
832 is in Kilobytes unless a suffix of 'K', 'M' or 'G' is used to explicitly
833 indicate Kilobytes, Megabytes or Gigabytes respectively.
837 can also be used with
839 for some RAID levels (initially on RAID10). This allows the
840 data\-offset to be changed as part of the reshape process. When the
841 data offset is changed, no backup file is required as the difference
842 in offsets is used to provide the same functionality.
844 When the new offset is earlier than the old offset, the number of
845 devices in the array cannot shrink. When it is after the old offset,
846 the number of devices in the array cannot increase.
848 When creating an array,
852 In the case each member device is expected to have a offset appended
853 to the name, separated by a colon. This makes it possible to recreate
854 exactly an array which has varying data offsets (as can happen when
855 different versions of
857 are used to add different devices).
861 This option is complementary to the
862 .B \-\-freeze-reshape
863 option for assembly. It is needed when
865 operation is interrupted and it is not restarted automatically due to
866 .B \-\-freeze-reshape
867 usage during array assembly. This option is used together with
871 ) command and device for a pending reshape to be continued.
872 All parameters required for reshape continuation will be read from array metadata.
876 .BR \-\-backup\-file=
877 option to be set, continuation option will require to have exactly the same
878 backup file given as well.
880 Any other parameter passed together with
882 option will be ignored.
885 .BR \-N ", " \-\-name=
888 for the array. This is currently only effective when creating an
889 array with a version-1 superblock, or an array in a DDF container.
890 The name is a simple textual string that can be used to identify array
891 components when assembling. If name is needed but not specified, it
892 is taken from the basename of the device that is being created.
904 run the array, even if some of the components
905 appear to be active in another array or filesystem. Normally
907 will ask for confirmation before including such components in an
908 array. This option causes that question to be suppressed.
911 .BR \-f ", " \-\-force
914 accept the geometry and layout specified without question. Normally
916 will not allow creation of an array with only one device, and will try
917 to create a RAID5 array with one missing drive (as this makes the
918 initial resync work faster). With
921 will not try to be so clever.
924 .BR \-o ", " \-\-readonly
927 rather than read-write as normal. No writes will be allowed to the
928 array, and no resync, recovery, or reshape will be started.
931 .BR \-a ", " "\-\-auto{=yes,md,mdp,part,p}{NN}"
932 Instruct mdadm how to create the device file if needed, possibly allocating
933 an unused minor number. "md" causes a non-partitionable array
934 to be used (though since Linux 2.6.28, these array devices are in fact
935 partitionable). "mdp", "part" or "p" causes a partitionable array (2.6 and
936 later) to be used. "yes" requires the named md device to have
937 a 'standard' format, and the type and minor number will be determined
938 from this. With mdadm 3.0, device creation is normally left up to
940 so this option is unlikely to be needed.
941 See DEVICE NAMES below.
943 The argument can also come immediately after
948 is not given on the command line or in the config file, then
954 is also given, then any
956 entries in the config file will override the
958 instruction given on the command line.
960 For partitionable arrays,
962 will create the device file for the whole array and for the first 4
963 partitions. A different number of partitions can be specified at the
964 end of this option (e.g.
966 If the device name ends with a digit, the partition names add a 'p',
968 .IR /dev/md/home1p3 .
969 If there is no trailing digit, then the partition names just have a
971 .IR /dev/md/scratch3 .
973 If the md device name is in a 'standard' format as described in DEVICE
974 NAMES, then it will be created, if necessary, with the appropriate
975 device number based on that name. If the device name is not in one of these
976 formats, then a unused device number will be allocated. The device
977 number will be considered unused if there is no active array for that
978 number, and there is no entry in /dev for that number and with a
979 non-standard name. Names that are not in 'standard' format are only
980 allowed in "/dev/md/".
982 This is meaningful with
988 .BR \-a ", " "\-\-add"
989 This option can be used in Grow mode in two cases.
991 If the target array is a Linear array, then
993 can be used to add one or more devices to the array. They
994 are simply catenated on to the end of the array. Once added, the
995 devices cannot be removed.
999 option is being used to increase the number of devices in an array,
1002 can be used to add some extra devices to be included in the array.
1003 In most cases this is not needed as the extra devices can be added as
1004 spares first, and then the number of raid-disks can be changed.
1005 However for RAID0, it is not possible to add spares. So to increase
1006 the number of devices in a RAID0, it is necessary to set the new
1007 number of devices, and to add the new devices, in the same command.
1011 Only works when the array is for clustered environment. It specifies
1012 the maximum number of nodes in the cluster that will use this device
1013 simultaneously. If not specified, this defaults to 4.
1016 .BR \-\-write-journal
1017 Specify journal device for the RAID-4/5/6 array. The journal device
1018 should be a SSD with reasonable lifetime.
1022 Auto creation of symlinks in /dev to /dev/md, option --symlinks must
1023 be 'no' or 'yes' and work with --create and --build.
1026 .BR \-k ", " \-\-consistency\-policy=
1027 Specify how the array maintains consistency in case of unexpected shutdown.
1028 Only relevant for RAID levels with redundancy.
1029 Currently supported options are:
1034 Full resync is performed and all redundancy is regenerated when the array is
1035 started after unclean shutdown.
1039 Resync assisted by a write-intent bitmap. Implicitly selected when using
1044 For RAID levels 4/5/6, journal device is used to log transactions and replay
1045 after unclean shutdown. Implicitly selected when using
1046 .BR \-\-write\-journal .
1050 For RAID5 only, Partial Parity Log is used to close the write hole and
1051 eliminate resync. PPL is stored in the metadata region of RAID member drives,
1052 no additional journal drive is needed.
1059 .BR \-u ", " \-\-uuid=
1060 uuid of array to assemble. Devices which don't have this uuid are
1064 .BR \-m ", " \-\-super\-minor=
1065 Minor number of device that array was created for. Devices which
1066 don't have this minor number are excluded. If you create an array as
1067 /dev/md1, then all superblocks will contain the minor number 1, even if
1068 the array is later assembled as /dev/md2.
1070 Giving the literal word "dev" for
1074 to use the minor number of the md device that is being assembled.
1075 e.g. when assembling
1077 .B \-\-super\-minor=dev
1078 will look for super blocks with a minor number of 0.
1081 is only relevant for v0.90 metadata, and should not normally be used.
1087 .BR \-N ", " \-\-name=
1088 Specify the name of the array to assemble. This must be the name
1089 that was specified when creating the array. It must either match
1090 the name stored in the superblock exactly, or it must match
1093 prefixed to the start of the given name.
1096 .BR \-f ", " \-\-force
1097 Assemble the array even if the metadata on some devices appears to be
1100 cannot find enough working devices to start the array, but can find
1101 some devices that are recorded as having failed, then it will mark
1102 those devices as working so that the array can be started.
1103 An array which requires
1105 to be started may contain data corruption. Use it carefully.
1108 .BR \-R ", " \-\-run
1109 Attempt to start the array even if fewer drives were given than were
1110 present last time the array was active. Normally if not all the
1111 expected drives are found and
1113 is not used, then the array will be assembled but not started.
1116 an attempt will be made to start it anyway.
1120 This is the reverse of
1122 in that it inhibits the startup of array unless all expected drives
1123 are present. This is only needed with
1125 and can be used if the physical connections to devices are
1126 not as reliable as you would like.
1129 .BR \-a ", " "\-\-auto{=no,yes,md,mdp,part}"
1130 See this option under Create and Build options.
1133 .BR \-b ", " \-\-bitmap=
1134 Specify the bitmap file that was given when the array was created. If
1137 bitmap, there is no need to specify this when assembling the array.
1140 .BR \-\-backup\-file=
1143 was used while reshaping an array (e.g. changing number of devices or
1144 chunk size) and the system crashed during the critical section, then the same
1146 must be presented to
1148 to allow possibly corrupted data to be restored, and the reshape
1152 .BR \-\-invalid\-backup
1153 If the file needed for the above option is not available for any
1154 reason an empty file can be given together with this option to
1155 indicate that the backup file is invalid. In this case the data that
1156 was being rearranged at the time of the crash could be irrecoverably
1157 lost, but the rest of the array may still be recoverable. This option
1158 should only be used as a last resort if there is no way to recover the
1163 .BR \-U ", " \-\-update=
1164 Update the superblock on each device while assembling the array. The
1165 argument given to this flag can be one of
1185 option will adjust the superblock of an array what was created on a Sparc
1186 machine running a patched 2.2 Linux kernel. This kernel got the
1187 alignment of part of the superblock wrong. You can use the
1188 .B "\-\-examine \-\-sparc2.2"
1191 to see what effect this would have.
1195 option will update the
1196 .B "preferred minor"
1197 field on each superblock to match the minor number of the array being
1199 This can be useful if
1201 reports a different "Preferred Minor" to
1203 In some cases this update will be performed automatically
1204 by the kernel driver. In particular the update happens automatically
1205 at the first write to an array with redundancy (RAID level 1 or
1206 greater) on a 2.6 (or later) kernel.
1210 option will change the uuid of the array. If a UUID is given with the
1212 option that UUID will be used as a new UUID and will
1214 be used to help identify the devices in the array.
1217 is given, a random UUID is chosen.
1221 option will change the
1223 of the array as stored in the superblock. This is only supported for
1224 version-1 superblocks.
1228 option will change the
1230 of the array as stored in the bitmap superblock. This option only
1231 works for a clustered environment.
1235 option will change the
1237 as recorded in the superblock. For version-0 superblocks, this is the
1238 same as updating the UUID.
1239 For version-1 superblocks, this involves updating the name.
1243 option will change the cluster name as recorded in the superblock and
1244 bitmap. This option only works for clustered environment.
1248 option will cause the array to be marked
1250 meaning that any redundancy in the array (e.g. parity for RAID5,
1251 copies for RAID1) may be incorrect. This will cause the RAID system
1252 to perform a "resync" pass to make sure that all redundant information
1257 option allows arrays to be moved between machines with different
1259 When assembling such an array for the first time after a move, giving
1260 .B "\-\-update=byteorder"
1263 to expect superblocks to have their byteorder reversed, and will
1264 correct that order before assembling the array. This is only valid
1265 with original (Version 0.90) superblocks.
1269 option will correct the summaries in the superblock. That is the
1270 counts of total, working, active, failed, and spare devices.
1274 option will rarely be of use. It applies to version 1.1 and 1.2 metadata
1275 only (where the metadata is at the start of the device) and is only
1276 useful when the component device has changed size (typically become
1277 larger). The version 1 metadata records the amount of the device that
1278 can be used to store data, so if a device in a version 1.1 or 1.2
1279 array becomes larger, the metadata will still be visible, but the
1280 extra space will not. In this case it might be useful to assemble the
1282 .BR \-\-update=devicesize .
1285 to determine the maximum usable amount of space on each device and
1286 update the relevant field in the metadata.
1290 option only works on v0.90 metadata arrays and will convert them to
1291 v1.0 metadata. The array must not be dirty (i.e. it must not need a
1292 sync) and it must not have a write-intent bitmap.
1294 The old metadata will remain on the devices, but will appear older
1295 than the new metadata and so will usually be ignored. The old metadata
1296 (or indeed the new metadata) can be removed by giving the appropriate
1299 .BR \-\-zero\-superblock .
1303 option can be used when an array has an internal bitmap which is
1304 corrupt in some way so that assembling the array normally fails. It
1305 will cause any internal bitmap to be ignored.
1309 option will reserve space in each device for a bad block list. This
1310 will be 4K in size and positioned near the end of any free space
1311 between the superblock and the data.
1315 option will cause any reservation of space for a bad block list to be
1316 removed. If the bad block list contains entries, this will fail, as
1317 removing the list could cause data corruption.
1320 .BR \-\-freeze\-reshape
1321 Option is intended to be used in start-up scripts during initrd boot phase.
1322 When array under reshape is assembled during initrd phase, this option
1323 stops reshape after reshape critical section is being restored. This happens
1324 before file system pivot operation and avoids loss of file system context.
1325 Losing file system context would cause reshape to be broken.
1327 Reshape can be continued later using the
1329 option for the grow command.
1333 See this option under Create and Build options.
1335 .SH For Manage mode:
1338 .BR \-t ", " \-\-test
1339 Unless a more serious error occurred,
1341 will exit with a status of 2 if no changes were made to the array and
1342 0 if at least one change was made.
1343 This can be useful when an indirect specifier such as
1348 is used in requesting an operation on the array.
1350 will report failure if these specifiers didn't find any match.
1353 .BR \-a ", " \-\-add
1354 hot-add listed devices.
1355 If a device appears to have recently been part of the array
1356 (possibly it failed or was removed) the device is re\-added as described
1358 If that fails or the device was never part of the array, the device is
1359 added as a hot-spare.
1360 If the array is degraded, it will immediately start to rebuild data
1363 Note that this and the following options are only meaningful on array
1364 with redundancy. They don't apply to RAID0 or Linear.
1368 re\-add a device that was previously removed from an array.
1369 If the metadata on the device reports that it is a member of the
1370 array, and the slot that it used is still vacant, then the device will
1371 be added back to the array in the same position. This will normally
1372 cause the data for that device to be recovered. However based on the
1373 event count on the device, the recovery may only require sections that
1374 are flagged a write-intent bitmap to be recovered or may not require
1375 any recovery at all.
1377 When used on an array that has no metadata (i.e. it was built with
1379 it will be assumed that bitmap-based recovery is enough to make the
1380 device fully consistent with the array.
1382 When used with v1.x metadata,
1384 can be accompanied by
1385 .BR \-\-update=devicesize ,
1386 .BR \-\-update=bbl ", or"
1387 .BR \-\-update=no\-bbl .
1388 See the description of these option when used in Assemble mode for an
1389 explanation of their use.
1391 If the device name given is
1395 will try to find any device that looks like it should be
1396 part of the array but isn't and will try to re\-add all such devices.
1398 If the device name given is
1402 will find all devices in the array that are marked
1404 remove them and attempt to immediately re\-add them. This can be
1405 useful if you are certain that the reason for failure has been
1410 Add a device as a spare. This is similar to
1412 except that it does not attempt
1414 first. The device will be added as a spare even if it looks like it
1415 could be an recent member of the array.
1418 .BR \-r ", " \-\-remove
1419 remove listed devices. They must not be active. i.e. they should
1420 be failed or spare devices.
1422 As well as the name of a device file
1432 The first causes all failed device to be removed. The second causes
1433 any device which is no longer connected to the system (i.e an 'open'
1437 The third will remove a set as describe below under
1441 .BR \-f ", " \-\-fail
1442 Mark listed devices as faulty.
1443 As well as the name of a device file, the word
1447 can be given. The former will cause any device that has been detached from
1448 the system to be marked as failed. It can then be removed.
1450 For RAID10 arrays where the number of copies evenly divides the number
1451 of devices, the devices can be conceptually divided into sets where
1452 each set contains a single complete copy of the data on the array.
1453 Sometimes a RAID10 array will be configured so that these sets are on
1454 separate controllers. In this case all the devices in one set can be
1455 failed by giving a name like
1461 The appropriate set names are reported by
1471 Mark listed devices as requiring replacement. As soon as a spare is
1472 available, it will be rebuilt and will replace the marked device.
1473 This is similar to marking a device as faulty, but the device remains
1474 in service during the recovery process to increase resilience against
1475 multiple failures. When the replacement process finishes, the
1476 replaced device will be marked as faulty.
1480 This can follow a list of
1482 devices. The devices listed after
1484 will be preferentially used to replace the devices listed after
1486 These device must already be spare devices in the array.
1489 .BR \-\-write\-mostly
1490 Subsequent devices that are added or re\-added will have the 'write-mostly'
1491 flag set. This is only valid for RAID1 and means that the 'md' driver
1492 will avoid reading from these devices if possible.
1495 Subsequent devices that are added or re\-added will have the 'write-mostly'
1498 .BR \-\-cluster\-confirm
1499 Confirm the existence of the device. This is issued in response to an \-\-add
1500 request by a node in a cluster. When a node adds a device it sends a message
1501 to all nodes in the cluster to look for a device with a UUID. This translates
1502 to a udev notification with the UUID of the device to be added and the slot
1503 number. The receiving node must acknowledge this message
1504 with \-\-cluster\-confirm. Valid arguments are <slot>:<devicename> in case
1505 the device is found or <slot>:missing in case the device is not found.
1509 Recreate journal for RAID-4/5/6 array that lost a journal device. In the
1510 current implementation, this command cannot add a journal to an array
1511 that had a failed journal. To avoid interrupting on-going write opertions,
1513 only works for array in Read-Only state.
1517 Subsequent devices that are added or re\-added will have
1518 the 'failfast' flag set. This is only valid for RAID1 and RAID10 and
1519 means that the 'md' driver will avoid long timeouts on error handling
1523 Subsequent devices that are re\-added will be re\-added without
1524 the 'failfast' flag set.
1527 Each of these options requires that the first device listed is the array
1528 to be acted upon, and the remainder are component devices to be added,
1529 removed, marked as faulty, etc. Several different operations can be
1530 specified for different devices, e.g.
1532 mdadm /dev/md0 \-\-add /dev/sda1 \-\-fail /dev/sdb1 \-\-remove /dev/sdb1
1534 Each operation applies to all devices listed until the next
1537 If an array is using a write-intent bitmap, then devices which have
1538 been removed can be re\-added in a way that avoids a full
1539 reconstruction but instead just updates the blocks that have changed
1540 since the device was removed. For arrays with persistent metadata
1541 (superblocks) this is done automatically. For arrays created with
1543 mdadm needs to be told that this device we removed recently with
1546 Devices can only be removed from an array if they are not in active
1547 use, i.e. that must be spares or failed devices. To remove an active
1548 device, it must first be marked as
1554 .BR \-Q ", " \-\-query
1555 Examine a device to see
1556 (1) if it is an md device and (2) if it is a component of an md
1558 Information about what is discovered is presented.
1561 .BR \-D ", " \-\-detail
1562 Print details of one or more md devices.
1565 .BR \-\-detail\-platform
1566 Print details of the platform's RAID capabilities (firmware / hardware
1567 topology) for a given metadata format. If used without argument, mdadm
1568 will scan all controllers looking for their capabilities. Otherwise, mdadm
1569 will only look at the controller specified by the argument in form of an
1570 absolute filepath or a link, e.g.
1571 .IR /sys/devices/pci0000:00/0000:00:1f.2 .
1574 .BR \-Y ", " \-\-export
1577 .BR \-\-detail-platform ,
1581 output will be formatted as
1583 pairs for easy import into the environment.
1589 indicates whether an array was started
1591 or not, which may include a reason
1592 .RB ( unsafe ", " nothing ", " no ).
1595 indicates if the array is expected on this host
1597 or seems to be from elsewhere
1601 .BR \-E ", " \-\-examine
1602 Print contents of the metadata stored on the named device(s).
1603 Note the contrast between
1608 applies to devices which are components of an array, while
1610 applies to a whole array which is currently active.
1613 If an array was created on a SPARC machine with a 2.2 Linux kernel
1614 patched with RAID support, the superblock will have been created
1615 incorrectly, or at least incompatibly with 2.4 and later kernels.
1620 will fix the superblock before displaying it. If this appears to do
1621 the right thing, then the array can be successfully assembled using
1622 .BR "\-\-assemble \-\-update=sparc2.2" .
1625 .BR \-X ", " \-\-examine\-bitmap
1626 Report information about a bitmap file.
1627 The argument is either an external bitmap file or an array component
1628 in case of an internal bitmap. Note that running this on an array
1631 does not report the bitmap for that array.
1634 .B \-\-examine\-badblocks
1635 List the bad-blocks recorded for the device, if a bad-blocks list has
1636 been configured. Currently only
1638 metadata supports bad-blocks lists.
1641 .BI \-\-dump= directory
1643 .BI \-\-restore= directory
1644 Save metadata from lists devices, or restore metadata to listed devices.
1647 .BR \-R ", " \-\-run
1648 start a partially assembled array. If
1650 did not find enough devices to fully start the array, it might leaving
1651 it partially assembled. If you wish, you can then use
1653 to start the array in degraded mode.
1656 .BR \-S ", " \-\-stop
1657 deactivate array, releasing all resources.
1660 .BR \-o ", " \-\-readonly
1661 mark array as readonly.
1664 .BR \-w ", " \-\-readwrite
1665 mark array as readwrite.
1668 .B \-\-zero\-superblock
1669 If the device contains a valid md superblock, the block is
1670 overwritten with zeros. With
1672 the block where the superblock would be is overwritten even if it
1673 doesn't appear to be valid.
1676 .B \-\-kill\-subarray=
1677 If the device is a container and the argument to \-\-kill\-subarray
1678 specifies an inactive subarray in the container, then the subarray is
1679 deleted. Deleting all subarrays will leave an 'empty-container' or
1680 spare superblock on the drives. See
1681 .B \-\-zero\-superblock
1683 removing a superblock. Note that some formats depend on the subarray
1684 index for generating a UUID, this command will fail if it would change
1685 the UUID of an active subarray.
1688 .B \-\-update\-subarray=
1689 If the device is a container and the argument to \-\-update\-subarray
1690 specifies a subarray in the container, then attempt to update the given
1691 superblock field in the subarray. See below in
1696 .BR \-t ", " \-\-test
1701 is set to reflect the status of the device. See below in
1706 .BR \-W ", " \-\-wait
1707 For each md device given, wait for any resync, recovery, or reshape
1708 activity to finish before returning.
1710 will return with success if it actually waited for every device
1711 listed, otherwise it will return failure.
1715 For each md device given, or each device in /proc/mdstat if
1717 is given, arrange for the array to be marked clean as soon as possible.
1719 will return with success if the array uses external metadata and we
1720 successfully waited. For native arrays this returns immediately as the
1721 kernel handles dirty-clean transitions at shutdown. No action is taken
1722 if safe-mode handling is disabled.
1726 Set the "sync_action" for all md devices given to one of
1733 will abort any currently running action though some actions will
1734 automatically restart.
1737 will abort any current action and ensure no other action starts
1747 .BR "SCRUBBING AND MISMATCHES" .
1749 .SH For Incremental Assembly mode:
1751 .BR \-\-rebuild\-map ", " \-r
1752 Rebuild the map file
1756 uses to help track which arrays are currently being assembled.
1759 .BR \-\-run ", " \-R
1760 Run any array assembled as soon as a minimal number of devices are
1761 available, rather than waiting until all expected devices are present.
1764 .BR \-\-scan ", " \-s
1765 Only meaningful with
1769 file for arrays that are being incrementally assembled and will try to
1770 start any that are not already started. If any such array is listed
1773 as requiring an external bitmap, that bitmap will be attached first.
1776 .BR \-\-fail ", " \-f
1777 This allows the hot-plug system to remove devices that have fully disappeared
1778 from the kernel. It will first fail and then remove the device from any
1779 array it belongs to.
1780 The device name given should be a kernel device name such as "sda",
1786 Only used with \-\-fail. The 'path' given will be recorded so that if
1787 a new device appears at the same location it can be automatically
1788 added to the same array. This allows the failed device to be
1789 automatically replaced by a new device without metadata if it appears
1790 at specified path. This option is normally only set by a
1794 .SH For Monitor mode:
1796 .BR \-m ", " \-\-mail
1797 Give a mail address to send alerts to.
1800 .BR \-p ", " \-\-program ", " \-\-alert
1801 Give a program to be run whenever an event is detected.
1804 .BR \-y ", " \-\-syslog
1805 Cause all events to be reported through 'syslog'. The messages have
1806 facility of 'daemon' and varying priorities.
1809 .BR \-d ", " \-\-delay
1810 Give a delay in seconds.
1812 polls the md arrays and then waits this many seconds before polling
1813 again. The default is 60 seconds. Since 2.6.16, there is no need to
1814 reduce this as the kernel alerts
1816 immediately when there is any change.
1819 .BR \-r ", " \-\-increment
1820 Give a percentage increment.
1822 will generate RebuildNN events with the given percentage increment.
1825 .BR \-f ", " \-\-daemonise
1828 to run as a background daemon if it decides to monitor anything. This
1829 causes it to fork and run in the child, and to disconnect from the
1830 terminal. The process id of the child is written to stdout.
1833 which will only continue monitoring if a mail address or alert program
1834 is found in the config file.
1837 .BR \-i ", " \-\-pid\-file
1840 is running in daemon mode, write the pid of the daemon process to
1841 the specified file, instead of printing it on standard output.
1844 .BR \-1 ", " \-\-oneshot
1845 Check arrays only once. This will generate
1847 events and more significantly
1853 .B " mdadm \-\-monitor \-\-scan \-1"
1855 from a cron script will ensure regular notification of any degraded arrays.
1858 .BR \-t ", " \-\-test
1861 alert for every array found at startup. This alert gets mailed and
1862 passed to the alert program. This can be used for testing that alert
1863 message do get through successfully.
1867 This inhibits the functionality for moving spares between arrays.
1868 Only one monitoring process started with
1870 but without this flag is allowed, otherwise the two could interfere
1877 .B mdadm \-\-assemble
1878 .I md-device options-and-component-devices...
1881 .B mdadm \-\-assemble \-\-scan
1882 .I md-devices-and-options...
1885 .B mdadm \-\-assemble \-\-scan
1889 This usage assembles one or more RAID arrays from pre-existing components.
1890 For each array, mdadm needs to know the md device, the identity of the
1891 array, and a number of component-devices. These can be found in a number of ways.
1893 In the first usage example (without the
1895 the first device given is the md device.
1896 In the second usage example, all devices listed are treated as md
1897 devices and assembly is attempted.
1898 In the third (where no devices are listed) all md devices that are
1899 listed in the configuration file are assembled. If no arrays are
1900 described by the configuration file, then any arrays that
1901 can be found on unused devices will be assembled.
1903 If precisely one device is listed, but
1909 was given and identity information is extracted from the configuration file.
1911 The identity can be given with the
1917 option, will be taken from the md-device record in the config file, or
1918 will be taken from the super block of the first component-device
1919 listed on the command line.
1921 Devices can be given on the
1923 command line or in the config file. Only devices which have an md
1924 superblock which contains the right identity will be considered for
1927 The config file is only used if explicitly named with
1929 or requested with (a possibly implicit)
1934 .B /etc/mdadm/mdadm.conf
1939 is not given, then the config file will only be used to find the
1940 identity of md arrays.
1942 Normally the array will be started after it is assembled. However if
1944 is not given and not all expected drives were listed, then the array
1945 is not started (to guard against usage errors). To insist that the
1946 array be started in this case (as may work for RAID1, 4, 5, 6, or 10),
1955 does not create any entries in
1959 It does record information in
1963 to choose the correct name.
1967 detects that udev is not configured, it will create the devices in
1971 In Linux kernels prior to version 2.6.28 there were two distinctly
1972 different types of md devices that could be created: one that could be
1973 partitioned using standard partitioning tools and one that could not.
1974 Since 2.6.28 that distinction is no longer relevant as both type of
1975 devices can be partitioned.
1977 will normally create the type that originally could not be partitioned
1978 as it has a well defined major number (9).
1980 Prior to 2.6.28, it is important that mdadm chooses the correct type
1981 of array device to use. This can be controlled with the
1983 option. In particular, a value of "mdp" or "part" or "p" tells mdadm
1984 to use a partitionable device rather than the default.
1986 In the no-udev case, the value given to
1988 can be suffixed by a number. This tells
1990 to create that number of partition devices rather than the default of 4.
1994 can also be given in the configuration file as a word starting
1996 on the ARRAY line for the relevant array.
2003 and no devices are listed,
2005 will first attempt to assemble all the arrays listed in the config
2008 If no arrays are listed in the config (other than those marked
2010 it will look through the available devices for possible arrays and
2011 will try to assemble anything that it finds. Arrays which are tagged
2012 as belonging to the given homehost will be assembled and started
2013 normally. Arrays which do not obviously belong to this host are given
2014 names that are expected not to conflict with anything local, and are
2015 started "read-auto" so that nothing is written to any device until the
2016 array is written to. i.e. automatic resync etc is delayed.
2020 finds a consistent set of devices that look like they should comprise
2021 an array, and if the superblock is tagged as belonging to the given
2022 home host, it will automatically choose a device name and try to
2023 assemble the array. If the array uses version-0.90 metadata, then the
2025 number as recorded in the superblock is used to create a name in
2029 If the array uses version-1 metadata, then the
2031 from the superblock is used to similarly create a name in
2033 (the name will have any 'host' prefix stripped first).
2035 This behaviour can be modified by the
2039 configuration file. This line can indicate that specific metadata
2040 type should, or should not, be automatically assembled. If an array
2041 is found which is not listed in
2043 and has a metadata format that is denied by the
2045 line, then it will not be assembled.
2048 line can also request that all arrays identified as being for this
2049 homehost should be assembled regardless of their metadata type.
2052 for further details.
2054 Note: Auto assembly cannot be used for assembling and activating some
2055 arrays which are undergoing reshape. In particular as the
2057 cannot be given, any reshape which requires a backup-file to continue
2058 cannot be started by auto assembly. An array which is growing to more
2059 devices and has passed the critical section can be assembled using
2070 .BI \-\-raid\-devices= Z
2074 This usage is similar to
2076 The difference is that it creates an array without a superblock. With
2077 these arrays there is no difference between initially creating the array and
2078 subsequently assembling the array, except that hopefully there is useful
2079 data there in the second case.
2081 The level may raid0, linear, raid1, raid10, multipath, or faulty, or
2082 one of their synonyms. All devices must be listed and the array will
2083 be started once complete. It will often be appropriate to use
2084 .B \-\-assume\-clean
2085 with levels raid1 or raid10.
2096 .BI \-\-raid\-devices= Z
2100 This usage will initialise a new md array, associate some devices with
2101 it, and activate the array.
2103 The named device will normally not exist when
2104 .I "mdadm \-\-create"
2105 is run, but will be created by
2107 once the array becomes active.
2109 As devices are added, they are checked to see if they contain RAID
2110 superblocks or filesystems. They are also checked to see if the variance in
2111 device size exceeds 1%.
2113 If any discrepancy is found, the array will not automatically be run, though
2116 can override this caution.
2118 To create a "degraded" array in which some devices are missing, simply
2119 give the word "\fBmissing\fP"
2120 in place of a device name. This will cause
2122 to leave the corresponding slot in the array empty.
2123 For a RAID4 or RAID5 array at most one slot can be
2124 "\fBmissing\fP"; for a RAID6 array at most two slots.
2125 For a RAID1 array, only one real device needs to be given. All of the
2129 When creating a RAID5 array,
2131 will automatically create a degraded array with an extra spare drive.
2132 This is because building the spare into a degraded array is in general
2133 faster than resyncing the parity on a non-degraded, but not clean,
2134 array. This feature can be overridden with the
2138 When creating an array with version-1 metadata a name for the array is
2140 If this is not given with the
2144 will choose a name based on the last component of the name of the
2145 device being created. So if
2147 is being created, then the name
2152 is being created, then the name
2156 When creating a partition based array, using
2158 with version-1.x metadata, the partition type should be set to
2160 (non fs-data). This type selection allows for greater precision since
2161 using any other [RAID auto-detect (0xFD) or a GNU/Linux partition (0x83)],
2162 might create problems in the event of array recovery through a live cdrom.
2164 A new array will normally get a randomly assigned 128bit UUID which is
2165 very likely to be unique. If you have a specific need, you can choose
2166 a UUID for the array by giving the
2168 option. Be warned that creating two arrays with the same UUID is a
2169 recipe for disaster. Also, using
2171 when creating a v0.90 array will silently override any
2176 .\"option is given, it is not necessary to list any component-devices in this command.
2177 .\"They can be added later, before a
2181 .\"is given, the apparent size of the smallest drive given is used.
2183 If the array type supports a write-intent bitmap, and if the devices
2184 in the array exceed 100G is size, an internal write-intent bitmap
2185 will automatically be added unless some other option is explicitly
2188 option or a different consistency policy is selected with the
2189 .B \-\-consistency\-policy
2190 option. In any case space for a bitmap will be reserved so that one
2191 can be added later with
2192 .BR "\-\-grow \-\-bitmap=internal" .
2194 If the metadata type supports it (currently only 1.x metadata), space
2195 will be allocated to store a bad block list. This allows a modest
2196 number of bad blocks to be recorded, allowing the drive to remain in
2197 service while only partially functional.
2199 When creating an array within a
2202 can be given either the list of devices to use, or simply the name of
2203 the container. The former case gives control over which devices in
2204 the container will be used for the array. The latter case allows
2206 to automatically choose which devices to use based on how much spare
2209 The General Management options that are valid with
2214 insist on running the array even if some devices look like they might
2219 start the array readonly \(em not supported yet.
2226 .I options... devices...
2229 This usage will allow individual devices in an array to be failed,
2230 removed or added. It is possible to perform multiple operations with
2231 on command. For example:
2233 .B " mdadm /dev/md0 \-f /dev/hda1 \-r /dev/hda1 \-a /dev/hda1"
2239 and will then remove it from the array and finally add it back
2240 in as a spare. However only one md array can be affected by a single
2243 When a device is added to an active array, mdadm checks to see if it
2244 has metadata on it which suggests that it was recently a member of the
2245 array. If it does, it tries to "re\-add" the device. If there have
2246 been no changes since the device was removed, or if the array has a
2247 write-intent bitmap which has recorded whatever changes there were,
2248 then the device will immediately become a full member of the array and
2249 those differences recorded in the bitmap will be resolved.
2259 MISC mode includes a number of distinct operations that
2260 operate on distinct devices. The operations are:
2263 The device is examined to see if it is
2264 (1) an active md array, or
2265 (2) a component of an md array.
2266 The information discovered is reported.
2270 The device should be an active md device.
2272 will display a detailed description of the array.
2276 will cause the output to be less detailed and the format to be
2277 suitable for inclusion in
2281 will normally be 0 unless
2283 failed to get useful information about the device(s); however, if the
2285 option is given, then the exit status will be:
2289 The array is functioning normally.
2292 The array has at least one failed device.
2295 The array has multiple failed devices such that it is unusable.
2298 There was an error while trying to get information about the device.
2302 .B \-\-detail\-platform
2303 Print detail of the platform's RAID capabilities (firmware / hardware
2304 topology). If the metadata is specified with
2308 then the return status will be:
2312 metadata successfully enumerated its platform components on this system
2315 metadata is platform independent
2318 metadata failed to find its platform components on this system
2322 .B \-\-update\-subarray=
2323 If the device is a container and the argument to \-\-update\-subarray
2324 specifies a subarray in the container, then attempt to update the given
2325 superblock field in the subarray. Similar to updating an array in
2326 "assemble" mode, the field to update is selected by
2330 option. Currently only
2336 option updates the subarray name in the metadata, it may not affect the
2337 device node name or the device node symlink until the subarray is
2338 re\-assembled. If updating
2340 would change the UUID of an active subarray this operation is blocked,
2341 and the command will end in an error.
2345 The device should be a component of an md array.
2347 will read the md superblock of the device and display the contents.
2352 is given, then multiple devices that are components of the one array
2353 are grouped together and reported in a single entry suitable
2359 without listing any devices will cause all devices listed in the
2360 config file to be examined.
2363 .BI \-\-dump= directory
2364 If the device contains RAID metadata, a file will be created in the
2366 and the metadata will be written to it. The file will be the same
2367 size as the device and have the metadata written in the file at the
2368 same locate that it exists in the device. However the file will be "sparse" so
2369 that only those blocks containing metadata will be allocated. The
2370 total space used will be small.
2372 The file name used in the
2374 will be the base name of the device. Further if any links appear in
2376 which point to the device, then hard links to the file will be created
2383 Multiple devices can be listed and their metadata will all be stored
2384 in the one directory.
2387 .BI \-\-restore= directory
2388 This is the reverse of
2391 will locate a file in the directory that has a name appropriate for
2392 the given device and will restore metadata from it. Names that match
2394 names are preferred, however if two of those refer to different files,
2396 will not choose between them but will abort the operation.
2398 If a file name is given instead of a
2402 will restore from that file to a single device, always provided the
2403 size of the file matches that of the device, and the file contains
2407 The devices should be active md arrays which will be deactivated, as
2408 long as they are not currently in use.
2412 This will fully activate a partially assembled md array.
2416 This will mark an active array as read-only, providing that it is
2417 not currently being used.
2423 array back to being read/write.
2427 For all operations except
2430 will cause the operation to be applied to all arrays listed in
2435 causes all devices listed in the config file to be examined.
2438 .BR \-b ", " \-\-brief
2439 Be less verbose. This is used with
2447 gives an intermediate level of verbosity.
2453 .B mdadm \-\-monitor
2454 .I options... devices...
2459 to periodically poll a number of md arrays and to report on any events
2462 will never exit once it decides that there are arrays to be checked,
2463 so it should normally be run in the background.
2465 As well as reporting events,
2467 may move a spare drive from one array to another if they are in the
2472 and if the destination array has a failed drive but no spares.
2474 If any devices are listed on the command line,
2476 will only monitor those devices. Otherwise all arrays listed in the
2477 configuration file will be monitored. Further, if
2479 is given, then any other md devices that appear in
2481 will also be monitored.
2483 The result of monitoring the arrays is the generation of events.
2484 These events are passed to a separate program (if specified) and may
2485 be mailed to a given E-mail address.
2487 When passing events to a program, the program is run once for each event,
2488 and is given 2 or 3 command-line arguments: the first is the
2489 name of the event (see below), the second is the name of the
2490 md device which is affected, and the third is the name of a related
2491 device if relevant (such as a component device that has failed).
2495 is given, then a program or an E-mail address must be specified on the
2496 command line or in the config file. If neither are available, then
2498 will not monitor anything.
2502 will continue monitoring as long as something was found to monitor. If
2503 no program or email is given, then each event is reported to
2506 The different events are:
2510 .B DeviceDisappeared
2511 An md array which previously was configured appears to no longer be
2512 configured. (syslog priority: Critical)
2516 was told to monitor an array which is RAID0 or Linear, then it will
2518 .B DeviceDisappeared
2519 with the extra information
2521 This is because RAID0 and Linear do not support the device-failed,
2522 hot-spare and resync operations which are monitored.
2526 An md array started reconstruction (e.g. recovery, resync, reshape,
2527 check, repair). (syslog priority: Warning)
2533 is a two-digit number (ie. 05, 48). This indicates that rebuild
2534 has passed that many percent of the total. The events are generated
2535 with fixed increment since 0. Increment size may be specified with
2536 a commandline option (default is 20). (syslog priority: Warning)
2540 An md array that was rebuilding, isn't any more, either because it
2541 finished normally or was aborted. (syslog priority: Warning)
2545 An active component device of an array has been marked as
2546 faulty. (syslog priority: Critical)
2550 A spare component device which was being rebuilt to replace a faulty
2551 device has failed. (syslog priority: Critical)
2555 A spare component device which was being rebuilt to replace a faulty
2556 device has been successfully rebuilt and has been made active.
2557 (syslog priority: Info)
2561 A new md array has been detected in the
2563 file. (syslog priority: Info)
2567 A newly noticed array appears to be degraded. This message is not
2570 notices a drive failure which causes degradation, but only when
2572 notices that an array is degraded when it first sees the array.
2573 (syslog priority: Critical)
2577 A spare drive has been moved from one array in a
2581 to another to allow a failed drive to be replaced.
2582 (syslog priority: Info)
2588 has been told, via the config file, that an array should have a certain
2589 number of spare devices, and
2591 detects that it has fewer than this number when it first sees the
2592 array, it will report a
2595 (syslog priority: Warning)
2599 An array was found at startup, and the
2602 (syslog priority: Info)
2612 cause Email to be sent. All events cause the program to be run.
2613 The program is run with two or three arguments: the event
2614 name, the array device and possibly a second device.
2616 Each event has an associated array device (e.g.
2618 and possibly a second device. For
2623 the second device is the relevant component device.
2626 the second device is the array that the spare was moved from.
2630 to move spares from one array to another, the different arrays need to
2631 be labeled with the same
2633 or the spares must be allowed to migrate through matching POLICY domains
2634 in the configuration file. The
2636 name can be any string; it is only necessary that different spare
2637 groups use different names.
2641 detects that an array in a spare group has fewer active
2642 devices than necessary for the complete array, and has no spare
2643 devices, it will look for another array in the same spare group that
2644 has a full complement of working drive and a spare. It will then
2645 attempt to remove the spare from the second drive and add it to the
2647 If the removal succeeds but the adding fails, then it is added back to
2650 If the spare group for a degraded array is not defined,
2652 will look at the rules of spare migration specified by POLICY lines in
2654 and then follow similar steps as above if a matching spare is found.
2657 The GROW mode is used for changing the size or shape of an active
2659 For this to work, the kernel must support the necessary change.
2660 Various types of growth are being added during 2.6 development.
2662 Currently the supported changes include
2664 change the "size" attribute for RAID1, RAID4, RAID5 and RAID6.
2666 increase or decrease the "raid\-devices" attribute of RAID0, RAID1, RAID4,
2669 change the chunk-size and layout of RAID0, RAID4, RAID5, RAID6 and RAID10.
2671 convert between RAID1 and RAID5, between RAID5 and RAID6, between
2672 RAID0, RAID4, and RAID5, and between RAID0 and RAID10 (in the near-2 mode).
2674 add a write-intent bitmap to any array which supports these bitmaps, or
2675 remove a write-intent bitmap from such an array.
2678 Using GROW on containers is currently supported only for Intel's IMSM
2679 container format. The number of devices in a container can be
2680 increased - which affects all arrays in the container - or an array
2681 in a container can be converted between levels where those levels are
2682 supported by the container, and the conversion is on of those listed
2683 above. Resizing arrays in an IMSM container with
2685 is not yet supported.
2687 Grow functionality (e.g. expand a number of raid devices) for Intel's
2688 IMSM container format has an experimental status. It is guarded by the
2689 .B MDADM_EXPERIMENTAL
2690 environment variable which must be set to '1' for a GROW command to
2692 This is for the following reasons:
2695 Intel's native IMSM check-pointing is not fully tested yet.
2696 This can causes IMSM incompatibility during the grow process: an array
2697 which is growing cannot roam between Microsoft Windows(R) and Linux
2701 Interrupting a grow operation is not recommended, because it
2702 has not been fully tested for Intel's IMSM container format yet.
2705 Note: Intel's native checkpointing doesn't use
2707 option and it is transparent for assembly feature.
2710 Normally when an array is built the "size" is taken from the smallest
2711 of the drives. If all the small drives in an arrays are, one at a
2712 time, removed and replaced with larger drives, then you could have an
2713 array of large drives with only a small amount used. In this
2714 situation, changing the "size" with "GROW" mode will allow the extra
2715 space to start being used. If the size is increased in this way, a
2716 "resync" process will start to make sure the new parts of the array
2719 Note that when an array changes size, any filesystem that may be
2720 stored in the array will not automatically grow or shrink to use or
2721 vacate the space. The
2722 filesystem will need to be explicitly told to use the extra space
2723 after growing, or to reduce its size
2725 to shrinking the array.
2727 Also the size of an array cannot be changed while it has an active
2728 bitmap. If an array has a bitmap, it must be removed before the size
2729 can be changed. Once the change is complete a new bitmap can be created.
2731 .SS RAID\-DEVICES CHANGES
2733 A RAID1 array can work with any number of devices from 1 upwards
2734 (though 1 is not very useful). There may be times which you want to
2735 increase or decrease the number of active devices. Note that this is
2736 different to hot-add or hot-remove which changes the number of
2739 When reducing the number of devices in a RAID1 array, the slots which
2740 are to be removed from the array must already be vacant. That is, the
2741 devices which were in those slots must be failed and removed.
2743 When the number of devices is increased, any hot spares that are
2744 present will be activated immediately.
2746 Changing the number of active devices in a RAID5 or RAID6 is much more
2747 effort. Every block in the array will need to be read and written
2748 back to a new location. From 2.6.17, the Linux Kernel is able to
2749 increase the number of devices in a RAID5 safely, including restarting
2750 an interrupted "reshape". From 2.6.31, the Linux Kernel is able to
2751 increase or decrease the number of devices in a RAID5 or RAID6.
2753 From 2.6.35, the Linux Kernel is able to convert a RAID0 in to a RAID4
2756 uses this functionality and the ability to add
2757 devices to a RAID4 to allow devices to be added to a RAID0. When
2758 requested to do this,
2760 will convert the RAID0 to a RAID4, add the necessary disks and make
2761 the reshape happen, and then convert the RAID4 back to RAID0.
2763 When decreasing the number of devices, the size of the array will also
2764 decrease. If there was data in the array, it could get destroyed and
2765 this is not reversible, so you should firstly shrink the filesystem on
2766 the array to fit within the new size. To help prevent accidents,
2768 requires that the size of the array be decreased first with
2769 .BR "mdadm --grow --array-size" .
2770 This is a reversible change which simply makes the end of the array
2771 inaccessible. The integrity of any data can then be checked before
2772 the non-reversible reduction in the number of devices is request.
2774 When relocating the first few stripes on a RAID5 or RAID6, it is not
2775 possible to keep the data on disk completely consistent and
2776 crash-proof. To provide the required safety, mdadm disables writes to
2777 the array while this "critical section" is reshaped, and takes a
2778 backup of the data that is in that section. For grows, this backup may be
2779 stored in any spare devices that the array has, however it can also be
2780 stored in a separate file specified with the
2782 option, and is required to be specified for shrinks, RAID level
2783 changes and layout changes. If this option is used, and the system
2784 does crash during the critical period, the same file must be passed to
2786 to restore the backup and reassemble the array. When shrinking rather
2787 than growing the array, the reshape is done from the end towards the
2788 beginning, so the "critical section" is at the end of the reshape.
2792 Changing the RAID level of any array happens instantaneously. However
2793 in the RAID5 to RAID6 case this requires a non-standard layout of the
2794 RAID6 data, and in the RAID6 to RAID5 case that non-standard layout is
2795 required before the change can be accomplished. So while the level
2796 change is instant, the accompanying layout change can take quite a
2799 is required. If the array is not simultaneously being grown or
2800 shrunk, so that the array size will remain the same - for example,
2801 reshaping a 3-drive RAID5 into a 4-drive RAID6 - the backup file will
2802 be used not just for a "cricital section" but throughout the reshape
2803 operation, as described below under LAYOUT CHANGES.
2805 .SS CHUNK-SIZE AND LAYOUT CHANGES
2807 Changing the chunk-size of layout without also changing the number of
2808 devices as the same time will involve re-writing all blocks in-place.
2809 To ensure against data loss in the case of a crash, a
2811 must be provided for these changes. Small sections of the array will
2812 be copied to the backup file while they are being rearranged. This
2813 means that all the data is copied twice, once to the backup and once
2814 to the new layout on the array, so this type of reshape will go very
2817 If the reshape is interrupted for any reason, this backup file must be
2819 .B "mdadm --assemble"
2820 so the array can be reassembled. Consequently the file cannot be
2821 stored on the device being reshaped.
2826 A write-intent bitmap can be added to, or removed from, an active
2827 array. Either internal bitmaps, or bitmaps stored in a separate file,
2828 can be added. Note that if you add a bitmap stored in a file which is
2829 in a filesystem that is on the RAID array being affected, the system
2830 will deadlock. The bitmap must be on a separate filesystem.
2832 .SH INCREMENTAL MODE
2836 .B mdadm \-\-incremental
2840 .RI [ optional-aliases-for-device ]
2843 .B mdadm \-\-incremental \-\-fail
2847 .B mdadm \-\-incremental \-\-rebuild\-map
2850 .B mdadm \-\-incremental \-\-run \-\-scan
2853 This mode is designed to be used in conjunction with a device
2854 discovery system. As devices are found in a system, they can be
2856 .B "mdadm \-\-incremental"
2857 to be conditionally added to an appropriate array.
2859 Conversely, it can also be used with the
2861 flag to do just the opposite and find whatever array a particular device
2862 is part of and remove the device from that array.
2864 If the device passed is a
2866 device created by a previous call to
2868 then rather than trying to add that device to an array, all the arrays
2869 described by the metadata of the container will be started.
2872 performs a number of tests to determine if the device is part of an
2873 array, and which array it should be part of. If an appropriate array
2874 is found, or can be created,
2876 adds the device to the array and conditionally starts the array.
2880 will normally only add devices to an array which were previously working
2881 (active or spare) parts of that array. The support for automatic
2882 inclusion of a new drive as a spare in some array requires
2883 a configuration through POLICY in config file.
2887 makes are as follow:
2889 Is the device permitted by
2891 That is, is it listed in a
2893 line in that file. If
2895 is absent then the default it to allow any device. Similarly if
2897 contains the special word
2899 then any device is allowed. Otherwise the device name given to
2901 or one of the aliases given, or an alias found in the filesystem,
2902 must match one of the names or patterns in a
2906 This is the only context where the aliases are used. They are
2907 usually provided by a
2913 Does the device have a valid md superblock? If a specific metadata
2914 version is requested with
2918 then only that style of metadata is accepted, otherwise
2920 finds any known version of metadata. If no
2922 metadata is found, the device may be still added to an array
2923 as a spare if POLICY allows.
2927 Does the metadata match an expected array?
2928 The metadata can match in two ways. Either there is an array listed
2931 which identifies the array (either by UUID, by name, by device list,
2932 or by minor-number), or the array was created with a
2938 or on the command line.
2941 is not able to positively identify the array as belonging to the
2942 current host, the device will be rejected.
2947 keeps a list of arrays that it has partially assembled in
2949 If no array exists which matches
2950 the metadata on the new device,
2952 must choose a device name and unit number. It does this based on any
2955 or any name information stored in the metadata. If this name
2956 suggests a unit number, that number will be used, otherwise a free
2957 unit number will be chosen. Normally
2959 will prefer to create a partitionable array, however if the
2963 suggests that a non-partitionable array is preferred, that will be
2966 If the array is not found in the config file and its metadata does not
2967 identify it as belonging to the "homehost", then
2969 will choose a name for the array which is certain not to conflict with
2970 any array which does belong to this host. It does this be adding an
2971 underscore and a small number to the name preferred by the metadata.
2973 Once an appropriate array is found or created and the device is added,
2975 must decide if the array is ready to be started. It will
2976 normally compare the number of available (non-spare) devices to the
2977 number of devices that the metadata suggests need to be active. If
2978 there are at least that many, the array will be started. This means
2979 that if any devices are missing the array will not be restarted.
2985 in which case the array will be run as soon as there are enough
2986 devices present for the data to be accessible. For a RAID1, that
2987 means one device will start the array. For a clean RAID5, the array
2988 will be started as soon as all but one drive is present.
2990 Note that neither of these approaches is really ideal. If it can
2991 be known that all device discovery has completed, then
2995 can be run which will try to start all arrays that are being
2996 incrementally assembled. They are started in "read-auto" mode in
2997 which they are read-only until the first write request. This means
2998 that no metadata updates are made and no attempt at resync or recovery
2999 happens. Further devices that are found before the first write can
3000 still be added safely.
3003 This section describes environment variables that affect how mdadm
3008 Setting this value to 1 will prevent mdadm from automatically launching
3009 mdmon. This variable is intended primarily for debugging mdadm/mdmon.
3015 does not create any device nodes in /dev, but leaves that task to
3019 appears not to be configured, or if this environment variable is set
3022 will create and devices that are needed.
3025 .B MDADM_NO_SYSTEMCTL
3030 is in use it will normally request
3032 to start various background tasks (particularly
3034 rather than forking and running them in the background. This can be
3035 suppressed by setting
3036 .BR MDADM_NO_SYSTEMCTL=1 .
3040 A key value of IMSM metadata is that it allows interoperability with
3041 boot ROMs on Intel platforms, and with other major operating systems.
3044 will only allow an IMSM array to be created or modified if detects
3045 that it is running on an Intel platform which supports IMSM, and
3046 supports the particular configuration of IMSM that is being requested
3047 (some functionality requires newer OROM support).
3049 These checks can be suppressed by setting IMSM_NO_PLATFORM=1 in the
3050 environment. This can be useful for testing or for disaster
3051 recovery. You should be aware that interoperability may be
3052 compromised by setting this value.
3055 .B MDADM_GROW_ALLOW_OLD
3056 If an array is stopped while it is performing a reshape and that
3057 reshape was making use of a backup file, then when the array is
3060 will sometimes complain that the backup file is too old. If this
3061 happens and you are certain it is the right backup file, you can
3062 over-ride this check by setting
3063 .B MDADM_GROW_ALLOW_OLD=1
3068 Any string given in this variable is added to the start of the
3070 line in the config file, or treated as the whole
3072 line if none is given. It can be used to disable certain metadata
3075 is called from a boot script. For example
3077 .B " export MDADM_CONF_AUTO='-ddf -imsm'
3081 does not automatically assemble any DDF or
3082 IMSM arrays that are found. This can be useful on systems configured
3083 to manage such arrays with
3089 .B " mdadm \-\-query /dev/name-of-device"
3091 This will find out if a given device is a RAID array, or is part of
3092 one, and will provide brief information about the device.
3094 .B " mdadm \-\-assemble \-\-scan"
3096 This will assemble and start all arrays listed in the standard config
3097 file. This command will typically go in a system startup file.
3099 .B " mdadm \-\-stop \-\-scan"
3101 This will shut down all arrays that can be shut down (i.e. are not
3102 currently in use). This will typically go in a system shutdown script.
3104 .B " mdadm \-\-follow \-\-scan \-\-delay=120"
3106 If (and only if) there is an Email address or program given in the
3107 standard config file, then
3108 monitor the status of all arrays listed in that file by
3109 polling them ever 2 minutes.
3111 .B " mdadm \-\-create /dev/md0 \-\-level=1 \-\-raid\-devices=2 /dev/hd[ac]1"
3113 Create /dev/md0 as a RAID1 array consisting of /dev/hda1 and /dev/hdc1.
3116 .B " echo 'DEVICE /dev/hd*[0\-9] /dev/sd*[0\-9]' > mdadm.conf"
3118 .B " mdadm \-\-detail \-\-scan >> mdadm.conf"
3120 This will create a prototype config file that describes currently
3121 active arrays that are known to be made from partitions of IDE or SCSI drives.
3122 This file should be reviewed before being used as it may
3123 contain unwanted detail.
3125 .B " echo 'DEVICE /dev/hd[a\-z] /dev/sd*[a\-z]' > mdadm.conf"
3127 .B " mdadm \-\-examine \-\-scan \-\-config=mdadm.conf >> mdadm.conf"
3129 This will find arrays which could be assembled from existing IDE and
3130 SCSI whole drives (not partitions), and store the information in the
3131 format of a config file.
3132 This file is very likely to contain unwanted detail, particularly
3135 entries. It should be reviewed and edited before being used as an
3138 .B " mdadm \-\-examine \-\-brief \-\-scan \-\-config=partitions"
3140 .B " mdadm \-Ebsc partitions"
3142 Create a list of devices by reading
3143 .BR /proc/partitions ,
3144 scan these for RAID superblocks, and printout a brief listing of all
3147 .B " mdadm \-Ac partitions \-m 0 /dev/md0"
3149 Scan all partitions and devices listed in
3150 .BR /proc/partitions
3153 out of all such devices with a RAID superblock with a minor number of 0.
3155 .B " mdadm \-\-monitor \-\-scan \-\-daemonise > /run/mdadm/mon.pid"
3157 If config file contains a mail address or alert program, run mdadm in
3158 the background in monitor mode monitoring all md devices. Also write
3159 pid of mdadm daemon to
3160 .BR /run/mdadm/mon.pid .
3162 .B " mdadm \-Iq /dev/somedevice"
3164 Try to incorporate newly discovered device into some array as
3167 .B " mdadm \-\-incremental \-\-rebuild\-map \-\-run \-\-scan"
3169 Rebuild the array map from any current arrays, and then start any that
3172 .B " mdadm /dev/md4 --fail detached --remove detached"
3174 Any devices which are components of /dev/md4 will be marked as faulty
3175 and then remove from the array.
3177 .B " mdadm --grow /dev/md4 --level=6 --backup-file=/root/backup-md4"
3181 which is currently a RAID5 array will be converted to RAID6. There
3182 should normally already be a spare drive attached to the array as a
3183 RAID6 needs one more drive than a matching RAID5.
3185 .B " mdadm --create /dev/md/ddf --metadata=ddf --raid-disks 6 /dev/sd[a-f]"
3187 Create a DDF array over 6 devices.
3189 .B " mdadm --create /dev/md/home -n3 -l5 -z 30000000 /dev/md/ddf"
3191 Create a RAID5 array over any 3 devices in the given DDF set. Use
3192 only 30 gigabytes of each device.
3194 .B " mdadm -A /dev/md/ddf1 /dev/sd[a-f]"
3196 Assemble a pre-exist ddf array.
3198 .B " mdadm -I /dev/md/ddf1"
3200 Assemble all arrays contained in the ddf array, assigning names as
3203 .B " mdadm \-\-create \-\-help"
3205 Provide help about the Create mode.
3207 .B " mdadm \-\-config \-\-help"
3209 Provide help about the format of the config file.
3211 .B " mdadm \-\-help"
3213 Provide general help.
3223 lists all active md devices with information about them.
3225 uses this to find arrays when
3227 is given in Misc mode, and to monitor array reconstruction
3232 The config file lists which devices may be scanned to see if
3233 they contain MD super block, and gives identifying information
3234 (e.g. UUID) about known MD arrays. See
3238 .SS /etc/mdadm.conf.d
3240 A directory containing configuration files which are read in lexical
3246 mode is used, this file gets a list of arrays currently being created.
3251 understand two sorts of names for array devices.
3253 The first is the so-called 'standard' format name, which matches the
3254 names used by the kernel and which appear in
3257 The second sort can be freely chosen, but must reside in
3259 When giving a device name to
3261 to create or assemble an array, either full path name such as
3265 can be given, or just the suffix of the second sort of name, such as
3271 chooses device names during auto-assembly or incremental assembly, it
3272 will sometimes add a small sequence number to the end of the name to
3273 avoid conflicted between multiple arrays that have the same name. If
3275 can reasonably determine that the array really is meant for this host,
3276 either by a hostname in the metadata, or by the presence of the array
3279 then it will leave off the suffix if possible.
3280 Also if the homehost is specified as
3283 will only use a suffix if a different array of the same name already
3284 exists or is listed in the config file.
3286 The standard names for non-partitioned arrays (the only sort of md
3287 array available in 2.4 and earlier) are of the form
3291 where NN is a number.
3292 The standard names for partitionable arrays (as available from 2.6
3293 onwards) are of the form:
3297 Partition numbers should be indicated by adding "pMM" to these, thus "/dev/md/d1p2".
3299 From kernel version 2.6.28 the "non-partitioned array" can actually
3300 be partitioned. So the "md_d\fBNN\fP"
3301 names are no longer needed, and
3302 partitions such as "/dev/md\fBNN\fPp\fBXX\fP"
3305 From kernel version 2.6.29 standard names can be non-numeric following
3312 is any string. These names are supported by
3314 since version 3.3 provided they are enabled in
3319 was previously known as
3323 For further information on mdadm usage, MD and the various levels of
3326 .B http://raid.wiki.kernel.org/
3328 (based upon Jakob \(/Ostergaard's Software\-RAID.HOWTO)
3330 The latest version of
3332 should always be available from
3334 .B http://www.kernel.org/pub/linux/utils/raid/mdadm/
projects / thirdparty / mdadm.git / blob