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
1187 option will adjust the superblock of an array what was created on a Sparc
1188 machine running a patched 2.2 Linux kernel. This kernel got the
1189 alignment of part of the superblock wrong. You can use the
1190 .B "\-\-examine \-\-sparc2.2"
1193 to see what effect this would have.
1197 option will update the
1198 .B "preferred minor"
1199 field on each superblock to match the minor number of the array being
1201 This can be useful if
1203 reports a different "Preferred Minor" to
1205 In some cases this update will be performed automatically
1206 by the kernel driver. In particular the update happens automatically
1207 at the first write to an array with redundancy (RAID level 1 or
1208 greater) on a 2.6 (or later) kernel.
1212 option will change the uuid of the array. If a UUID is given with the
1214 option that UUID will be used as a new UUID and will
1216 be used to help identify the devices in the array.
1219 is given, a random UUID is chosen.
1223 option will change the
1225 of the array as stored in the superblock. This is only supported for
1226 version-1 superblocks.
1230 option will change the
1232 of the array as stored in the bitmap superblock. This option only
1233 works for a clustered environment.
1237 option will change the
1239 as recorded in the superblock. For version-0 superblocks, this is the
1240 same as updating the UUID.
1241 For version-1 superblocks, this involves updating the name.
1245 option will change the cluster name as recorded in the superblock and
1246 bitmap. This option only works for clustered environment.
1250 option will cause the array to be marked
1252 meaning that any redundancy in the array (e.g. parity for RAID5,
1253 copies for RAID1) may be incorrect. This will cause the RAID system
1254 to perform a "resync" pass to make sure that all redundant information
1259 option allows arrays to be moved between machines with different
1261 When assembling such an array for the first time after a move, giving
1262 .B "\-\-update=byteorder"
1265 to expect superblocks to have their byteorder reversed, and will
1266 correct that order before assembling the array. This is only valid
1267 with original (Version 0.90) superblocks.
1271 option will correct the summaries in the superblock. That is the
1272 counts of total, working, active, failed, and spare devices.
1276 option will rarely be of use. It applies to version 1.1 and 1.2 metadata
1277 only (where the metadata is at the start of the device) and is only
1278 useful when the component device has changed size (typically become
1279 larger). The version 1 metadata records the amount of the device that
1280 can be used to store data, so if a device in a version 1.1 or 1.2
1281 array becomes larger, the metadata will still be visible, but the
1282 extra space will not. In this case it might be useful to assemble the
1284 .BR \-\-update=devicesize .
1287 to determine the maximum usable amount of space on each device and
1288 update the relevant field in the metadata.
1292 option only works on v0.90 metadata arrays and will convert them to
1293 v1.0 metadata. The array must not be dirty (i.e. it must not need a
1294 sync) and it must not have a write-intent bitmap.
1296 The old metadata will remain on the devices, but will appear older
1297 than the new metadata and so will usually be ignored. The old metadata
1298 (or indeed the new metadata) can be removed by giving the appropriate
1301 .BR \-\-zero\-superblock .
1305 option can be used when an array has an internal bitmap which is
1306 corrupt in some way so that assembling the array normally fails. It
1307 will cause any internal bitmap to be ignored.
1311 option will reserve space in each device for a bad block list. This
1312 will be 4K in size and positioned near the end of any free space
1313 between the superblock and the data.
1317 option will cause any reservation of space for a bad block list to be
1318 removed. If the bad block list contains entries, this will fail, as
1319 removing the list could cause data corruption.
1323 option will enable PPL for a RAID5 array and reserve space for PPL on each
1324 device. There must be enough free space between the data and superblock and a
1325 write-intent bitmap or journal must not be used.
1329 option will disable PPL in the superblock.
1332 .BR \-\-freeze\-reshape
1333 Option is intended to be used in start-up scripts during initrd boot phase.
1334 When array under reshape is assembled during initrd phase, this option
1335 stops reshape after reshape critical section is being restored. This happens
1336 before file system pivot operation and avoids loss of file system context.
1337 Losing file system context would cause reshape to be broken.
1339 Reshape can be continued later using the
1341 option for the grow command.
1345 See this option under Create and Build options.
1347 .SH For Manage mode:
1350 .BR \-t ", " \-\-test
1351 Unless a more serious error occurred,
1353 will exit with a status of 2 if no changes were made to the array and
1354 0 if at least one change was made.
1355 This can be useful when an indirect specifier such as
1360 is used in requesting an operation on the array.
1362 will report failure if these specifiers didn't find any match.
1365 .BR \-a ", " \-\-add
1366 hot-add listed devices.
1367 If a device appears to have recently been part of the array
1368 (possibly it failed or was removed) the device is re\-added as described
1370 If that fails or the device was never part of the array, the device is
1371 added as a hot-spare.
1372 If the array is degraded, it will immediately start to rebuild data
1375 Note that this and the following options are only meaningful on array
1376 with redundancy. They don't apply to RAID0 or Linear.
1380 re\-add a device that was previously removed from an array.
1381 If the metadata on the device reports that it is a member of the
1382 array, and the slot that it used is still vacant, then the device will
1383 be added back to the array in the same position. This will normally
1384 cause the data for that device to be recovered. However based on the
1385 event count on the device, the recovery may only require sections that
1386 are flagged a write-intent bitmap to be recovered or may not require
1387 any recovery at all.
1389 When used on an array that has no metadata (i.e. it was built with
1391 it will be assumed that bitmap-based recovery is enough to make the
1392 device fully consistent with the array.
1394 When used with v1.x metadata,
1396 can be accompanied by
1397 .BR \-\-update=devicesize ,
1398 .BR \-\-update=bbl ", or"
1399 .BR \-\-update=no\-bbl .
1400 See the description of these option when used in Assemble mode for an
1401 explanation of their use.
1403 If the device name given is
1407 will try to find any device that looks like it should be
1408 part of the array but isn't and will try to re\-add all such devices.
1410 If the device name given is
1414 will find all devices in the array that are marked
1416 remove them and attempt to immediately re\-add them. This can be
1417 useful if you are certain that the reason for failure has been
1422 Add a device as a spare. This is similar to
1424 except that it does not attempt
1426 first. The device will be added as a spare even if it looks like it
1427 could be an recent member of the array.
1430 .BR \-r ", " \-\-remove
1431 remove listed devices. They must not be active. i.e. they should
1432 be failed or spare devices.
1434 As well as the name of a device file
1444 The first causes all failed device to be removed. The second causes
1445 any device which is no longer connected to the system (i.e an 'open'
1449 The third will remove a set as describe below under
1453 .BR \-f ", " \-\-fail
1454 Mark listed devices as faulty.
1455 As well as the name of a device file, the word
1459 can be given. The former will cause any device that has been detached from
1460 the system to be marked as failed. It can then be removed.
1462 For RAID10 arrays where the number of copies evenly divides the number
1463 of devices, the devices can be conceptually divided into sets where
1464 each set contains a single complete copy of the data on the array.
1465 Sometimes a RAID10 array will be configured so that these sets are on
1466 separate controllers. In this case all the devices in one set can be
1467 failed by giving a name like
1473 The appropriate set names are reported by
1483 Mark listed devices as requiring replacement. As soon as a spare is
1484 available, it will be rebuilt and will replace the marked device.
1485 This is similar to marking a device as faulty, but the device remains
1486 in service during the recovery process to increase resilience against
1487 multiple failures. When the replacement process finishes, the
1488 replaced device will be marked as faulty.
1492 This can follow a list of
1494 devices. The devices listed after
1496 will be preferentially used to replace the devices listed after
1498 These device must already be spare devices in the array.
1501 .BR \-\-write\-mostly
1502 Subsequent devices that are added or re\-added will have the 'write-mostly'
1503 flag set. This is only valid for RAID1 and means that the 'md' driver
1504 will avoid reading from these devices if possible.
1507 Subsequent devices that are added or re\-added will have the 'write-mostly'
1510 .BR \-\-cluster\-confirm
1511 Confirm the existence of the device. This is issued in response to an \-\-add
1512 request by a node in a cluster. When a node adds a device it sends a message
1513 to all nodes in the cluster to look for a device with a UUID. This translates
1514 to a udev notification with the UUID of the device to be added and the slot
1515 number. The receiving node must acknowledge this message
1516 with \-\-cluster\-confirm. Valid arguments are <slot>:<devicename> in case
1517 the device is found or <slot>:missing in case the device is not found.
1521 Recreate journal for RAID-4/5/6 array that lost a journal device. In the
1522 current implementation, this command cannot add a journal to an array
1523 that had a failed journal. To avoid interrupting on-going write opertions,
1525 only works for array in Read-Only state.
1529 Subsequent devices that are added or re\-added will have
1530 the 'failfast' flag set. This is only valid for RAID1 and RAID10 and
1531 means that the 'md' driver will avoid long timeouts on error handling
1535 Subsequent devices that are re\-added will be re\-added without
1536 the 'failfast' flag set.
1539 Each of these options requires that the first device listed is the array
1540 to be acted upon, and the remainder are component devices to be added,
1541 removed, marked as faulty, etc. Several different operations can be
1542 specified for different devices, e.g.
1544 mdadm /dev/md0 \-\-add /dev/sda1 \-\-fail /dev/sdb1 \-\-remove /dev/sdb1
1546 Each operation applies to all devices listed until the next
1549 If an array is using a write-intent bitmap, then devices which have
1550 been removed can be re\-added in a way that avoids a full
1551 reconstruction but instead just updates the blocks that have changed
1552 since the device was removed. For arrays with persistent metadata
1553 (superblocks) this is done automatically. For arrays created with
1555 mdadm needs to be told that this device we removed recently with
1558 Devices can only be removed from an array if they are not in active
1559 use, i.e. that must be spares or failed devices. To remove an active
1560 device, it must first be marked as
1566 .BR \-Q ", " \-\-query
1567 Examine a device to see
1568 (1) if it is an md device and (2) if it is a component of an md
1570 Information about what is discovered is presented.
1573 .BR \-D ", " \-\-detail
1574 Print details of one or more md devices.
1577 .BR \-\-detail\-platform
1578 Print details of the platform's RAID capabilities (firmware / hardware
1579 topology) for a given metadata format. If used without argument, mdadm
1580 will scan all controllers looking for their capabilities. Otherwise, mdadm
1581 will only look at the controller specified by the argument in form of an
1582 absolute filepath or a link, e.g.
1583 .IR /sys/devices/pci0000:00/0000:00:1f.2 .
1586 .BR \-Y ", " \-\-export
1589 .BR \-\-detail-platform ,
1593 output will be formatted as
1595 pairs for easy import into the environment.
1601 indicates whether an array was started
1603 or not, which may include a reason
1604 .RB ( unsafe ", " nothing ", " no ).
1607 indicates if the array is expected on this host
1609 or seems to be from elsewhere
1613 .BR \-E ", " \-\-examine
1614 Print contents of the metadata stored on the named device(s).
1615 Note the contrast between
1620 applies to devices which are components of an array, while
1622 applies to a whole array which is currently active.
1625 If an array was created on a SPARC machine with a 2.2 Linux kernel
1626 patched with RAID support, the superblock will have been created
1627 incorrectly, or at least incompatibly with 2.4 and later kernels.
1632 will fix the superblock before displaying it. If this appears to do
1633 the right thing, then the array can be successfully assembled using
1634 .BR "\-\-assemble \-\-update=sparc2.2" .
1637 .BR \-X ", " \-\-examine\-bitmap
1638 Report information about a bitmap file.
1639 The argument is either an external bitmap file or an array component
1640 in case of an internal bitmap. Note that running this on an array
1643 does not report the bitmap for that array.
1646 .B \-\-examine\-badblocks
1647 List the bad-blocks recorded for the device, if a bad-blocks list has
1648 been configured. Currently only
1650 metadata supports bad-blocks lists.
1653 .BI \-\-dump= directory
1655 .BI \-\-restore= directory
1656 Save metadata from lists devices, or restore metadata to listed devices.
1659 .BR \-R ", " \-\-run
1660 start a partially assembled array. If
1662 did not find enough devices to fully start the array, it might leaving
1663 it partially assembled. If you wish, you can then use
1665 to start the array in degraded mode.
1668 .BR \-S ", " \-\-stop
1669 deactivate array, releasing all resources.
1672 .BR \-o ", " \-\-readonly
1673 mark array as readonly.
1676 .BR \-w ", " \-\-readwrite
1677 mark array as readwrite.
1680 .B \-\-zero\-superblock
1681 If the device contains a valid md superblock, the block is
1682 overwritten with zeros. With
1684 the block where the superblock would be is overwritten even if it
1685 doesn't appear to be valid.
1688 .B \-\-kill\-subarray=
1689 If the device is a container and the argument to \-\-kill\-subarray
1690 specifies an inactive subarray in the container, then the subarray is
1691 deleted. Deleting all subarrays will leave an 'empty-container' or
1692 spare superblock on the drives. See
1693 .B \-\-zero\-superblock
1695 removing a superblock. Note that some formats depend on the subarray
1696 index for generating a UUID, this command will fail if it would change
1697 the UUID of an active subarray.
1700 .B \-\-update\-subarray=
1701 If the device is a container and the argument to \-\-update\-subarray
1702 specifies a subarray in the container, then attempt to update the given
1703 superblock field in the subarray. See below in
1708 .BR \-t ", " \-\-test
1713 is set to reflect the status of the device. See below in
1718 .BR \-W ", " \-\-wait
1719 For each md device given, wait for any resync, recovery, or reshape
1720 activity to finish before returning.
1722 will return with success if it actually waited for every device
1723 listed, otherwise it will return failure.
1727 For each md device given, or each device in /proc/mdstat if
1729 is given, arrange for the array to be marked clean as soon as possible.
1731 will return with success if the array uses external metadata and we
1732 successfully waited. For native arrays this returns immediately as the
1733 kernel handles dirty-clean transitions at shutdown. No action is taken
1734 if safe-mode handling is disabled.
1738 Set the "sync_action" for all md devices given to one of
1745 will abort any currently running action though some actions will
1746 automatically restart.
1749 will abort any current action and ensure no other action starts
1759 .BR "SCRUBBING AND MISMATCHES" .
1761 .SH For Incremental Assembly mode:
1763 .BR \-\-rebuild\-map ", " \-r
1764 Rebuild the map file
1768 uses to help track which arrays are currently being assembled.
1771 .BR \-\-run ", " \-R
1772 Run any array assembled as soon as a minimal number of devices are
1773 available, rather than waiting until all expected devices are present.
1776 .BR \-\-scan ", " \-s
1777 Only meaningful with
1781 file for arrays that are being incrementally assembled and will try to
1782 start any that are not already started. If any such array is listed
1785 as requiring an external bitmap, that bitmap will be attached first.
1788 .BR \-\-fail ", " \-f
1789 This allows the hot-plug system to remove devices that have fully disappeared
1790 from the kernel. It will first fail and then remove the device from any
1791 array it belongs to.
1792 The device name given should be a kernel device name such as "sda",
1798 Only used with \-\-fail. The 'path' given will be recorded so that if
1799 a new device appears at the same location it can be automatically
1800 added to the same array. This allows the failed device to be
1801 automatically replaced by a new device without metadata if it appears
1802 at specified path. This option is normally only set by a
1806 .SH For Monitor mode:
1808 .BR \-m ", " \-\-mail
1809 Give a mail address to send alerts to.
1812 .BR \-p ", " \-\-program ", " \-\-alert
1813 Give a program to be run whenever an event is detected.
1816 .BR \-y ", " \-\-syslog
1817 Cause all events to be reported through 'syslog'. The messages have
1818 facility of 'daemon' and varying priorities.
1821 .BR \-d ", " \-\-delay
1822 Give a delay in seconds.
1824 polls the md arrays and then waits this many seconds before polling
1825 again. The default is 60 seconds. Since 2.6.16, there is no need to
1826 reduce this as the kernel alerts
1828 immediately when there is any change.
1831 .BR \-r ", " \-\-increment
1832 Give a percentage increment.
1834 will generate RebuildNN events with the given percentage increment.
1837 .BR \-f ", " \-\-daemonise
1840 to run as a background daemon if it decides to monitor anything. This
1841 causes it to fork and run in the child, and to disconnect from the
1842 terminal. The process id of the child is written to stdout.
1845 which will only continue monitoring if a mail address or alert program
1846 is found in the config file.
1849 .BR \-i ", " \-\-pid\-file
1852 is running in daemon mode, write the pid of the daemon process to
1853 the specified file, instead of printing it on standard output.
1856 .BR \-1 ", " \-\-oneshot
1857 Check arrays only once. This will generate
1859 events and more significantly
1865 .B " mdadm \-\-monitor \-\-scan \-1"
1867 from a cron script will ensure regular notification of any degraded arrays.
1870 .BR \-t ", " \-\-test
1873 alert for every array found at startup. This alert gets mailed and
1874 passed to the alert program. This can be used for testing that alert
1875 message do get through successfully.
1879 This inhibits the functionality for moving spares between arrays.
1880 Only one monitoring process started with
1882 but without this flag is allowed, otherwise the two could interfere
1889 .B mdadm \-\-assemble
1890 .I md-device options-and-component-devices...
1893 .B mdadm \-\-assemble \-\-scan
1894 .I md-devices-and-options...
1897 .B mdadm \-\-assemble \-\-scan
1901 This usage assembles one or more RAID arrays from pre-existing components.
1902 For each array, mdadm needs to know the md device, the identity of the
1903 array, and a number of component-devices. These can be found in a number of ways.
1905 In the first usage example (without the
1907 the first device given is the md device.
1908 In the second usage example, all devices listed are treated as md
1909 devices and assembly is attempted.
1910 In the third (where no devices are listed) all md devices that are
1911 listed in the configuration file are assembled. If no arrays are
1912 described by the configuration file, then any arrays that
1913 can be found on unused devices will be assembled.
1915 If precisely one device is listed, but
1921 was given and identity information is extracted from the configuration file.
1923 The identity can be given with the
1929 option, will be taken from the md-device record in the config file, or
1930 will be taken from the super block of the first component-device
1931 listed on the command line.
1933 Devices can be given on the
1935 command line or in the config file. Only devices which have an md
1936 superblock which contains the right identity will be considered for
1939 The config file is only used if explicitly named with
1941 or requested with (a possibly implicit)
1946 .B /etc/mdadm/mdadm.conf
1951 is not given, then the config file will only be used to find the
1952 identity of md arrays.
1954 Normally the array will be started after it is assembled. However if
1956 is not given and not all expected drives were listed, then the array
1957 is not started (to guard against usage errors). To insist that the
1958 array be started in this case (as may work for RAID1, 4, 5, 6, or 10),
1967 does not create any entries in
1971 It does record information in
1975 to choose the correct name.
1979 detects that udev is not configured, it will create the devices in
1983 In Linux kernels prior to version 2.6.28 there were two distinctly
1984 different types of md devices that could be created: one that could be
1985 partitioned using standard partitioning tools and one that could not.
1986 Since 2.6.28 that distinction is no longer relevant as both type of
1987 devices can be partitioned.
1989 will normally create the type that originally could not be partitioned
1990 as it has a well defined major number (9).
1992 Prior to 2.6.28, it is important that mdadm chooses the correct type
1993 of array device to use. This can be controlled with the
1995 option. In particular, a value of "mdp" or "part" or "p" tells mdadm
1996 to use a partitionable device rather than the default.
1998 In the no-udev case, the value given to
2000 can be suffixed by a number. This tells
2002 to create that number of partition devices rather than the default of 4.
2006 can also be given in the configuration file as a word starting
2008 on the ARRAY line for the relevant array.
2015 and no devices are listed,
2017 will first attempt to assemble all the arrays listed in the config
2020 If no arrays are listed in the config (other than those marked
2022 it will look through the available devices for possible arrays and
2023 will try to assemble anything that it finds. Arrays which are tagged
2024 as belonging to the given homehost will be assembled and started
2025 normally. Arrays which do not obviously belong to this host are given
2026 names that are expected not to conflict with anything local, and are
2027 started "read-auto" so that nothing is written to any device until the
2028 array is written to. i.e. automatic resync etc is delayed.
2032 finds a consistent set of devices that look like they should comprise
2033 an array, and if the superblock is tagged as belonging to the given
2034 home host, it will automatically choose a device name and try to
2035 assemble the array. If the array uses version-0.90 metadata, then the
2037 number as recorded in the superblock is used to create a name in
2041 If the array uses version-1 metadata, then the
2043 from the superblock is used to similarly create a name in
2045 (the name will have any 'host' prefix stripped first).
2047 This behaviour can be modified by the
2051 configuration file. This line can indicate that specific metadata
2052 type should, or should not, be automatically assembled. If an array
2053 is found which is not listed in
2055 and has a metadata format that is denied by the
2057 line, then it will not be assembled.
2060 line can also request that all arrays identified as being for this
2061 homehost should be assembled regardless of their metadata type.
2064 for further details.
2066 Note: Auto assembly cannot be used for assembling and activating some
2067 arrays which are undergoing reshape. In particular as the
2069 cannot be given, any reshape which requires a backup-file to continue
2070 cannot be started by auto assembly. An array which is growing to more
2071 devices and has passed the critical section can be assembled using
2082 .BI \-\-raid\-devices= Z
2086 This usage is similar to
2088 The difference is that it creates an array without a superblock. With
2089 these arrays there is no difference between initially creating the array and
2090 subsequently assembling the array, except that hopefully there is useful
2091 data there in the second case.
2093 The level may raid0, linear, raid1, raid10, multipath, or faulty, or
2094 one of their synonyms. All devices must be listed and the array will
2095 be started once complete. It will often be appropriate to use
2096 .B \-\-assume\-clean
2097 with levels raid1 or raid10.
2108 .BI \-\-raid\-devices= Z
2112 This usage will initialise a new md array, associate some devices with
2113 it, and activate the array.
2115 The named device will normally not exist when
2116 .I "mdadm \-\-create"
2117 is run, but will be created by
2119 once the array becomes active.
2121 As devices are added, they are checked to see if they contain RAID
2122 superblocks or filesystems. They are also checked to see if the variance in
2123 device size exceeds 1%.
2125 If any discrepancy is found, the array will not automatically be run, though
2128 can override this caution.
2130 To create a "degraded" array in which some devices are missing, simply
2131 give the word "\fBmissing\fP"
2132 in place of a device name. This will cause
2134 to leave the corresponding slot in the array empty.
2135 For a RAID4 or RAID5 array at most one slot can be
2136 "\fBmissing\fP"; for a RAID6 array at most two slots.
2137 For a RAID1 array, only one real device needs to be given. All of the
2141 When creating a RAID5 array,
2143 will automatically create a degraded array with an extra spare drive.
2144 This is because building the spare into a degraded array is in general
2145 faster than resyncing the parity on a non-degraded, but not clean,
2146 array. This feature can be overridden with the
2150 When creating an array with version-1 metadata a name for the array is
2152 If this is not given with the
2156 will choose a name based on the last component of the name of the
2157 device being created. So if
2159 is being created, then the name
2164 is being created, then the name
2168 When creating a partition based array, using
2170 with version-1.x metadata, the partition type should be set to
2172 (non fs-data). This type selection allows for greater precision since
2173 using any other [RAID auto-detect (0xFD) or a GNU/Linux partition (0x83)],
2174 might create problems in the event of array recovery through a live cdrom.
2176 A new array will normally get a randomly assigned 128bit UUID which is
2177 very likely to be unique. If you have a specific need, you can choose
2178 a UUID for the array by giving the
2180 option. Be warned that creating two arrays with the same UUID is a
2181 recipe for disaster. Also, using
2183 when creating a v0.90 array will silently override any
2188 .\"option is given, it is not necessary to list any component-devices in this command.
2189 .\"They can be added later, before a
2193 .\"is given, the apparent size of the smallest drive given is used.
2195 If the array type supports a write-intent bitmap, and if the devices
2196 in the array exceed 100G is size, an internal write-intent bitmap
2197 will automatically be added unless some other option is explicitly
2200 option or a different consistency policy is selected with the
2201 .B \-\-consistency\-policy
2202 option. In any case space for a bitmap will be reserved so that one
2203 can be added later with
2204 .BR "\-\-grow \-\-bitmap=internal" .
2206 If the metadata type supports it (currently only 1.x metadata), space
2207 will be allocated to store a bad block list. This allows a modest
2208 number of bad blocks to be recorded, allowing the drive to remain in
2209 service while only partially functional.
2211 When creating an array within a
2214 can be given either the list of devices to use, or simply the name of
2215 the container. The former case gives control over which devices in
2216 the container will be used for the array. The latter case allows
2218 to automatically choose which devices to use based on how much spare
2221 The General Management options that are valid with
2226 insist on running the array even if some devices look like they might
2231 start the array readonly \(em not supported yet.
2238 .I options... devices...
2241 This usage will allow individual devices in an array to be failed,
2242 removed or added. It is possible to perform multiple operations with
2243 on command. For example:
2245 .B " mdadm /dev/md0 \-f /dev/hda1 \-r /dev/hda1 \-a /dev/hda1"
2251 and will then remove it from the array and finally add it back
2252 in as a spare. However only one md array can be affected by a single
2255 When a device is added to an active array, mdadm checks to see if it
2256 has metadata on it which suggests that it was recently a member of the
2257 array. If it does, it tries to "re\-add" the device. If there have
2258 been no changes since the device was removed, or if the array has a
2259 write-intent bitmap which has recorded whatever changes there were,
2260 then the device will immediately become a full member of the array and
2261 those differences recorded in the bitmap will be resolved.
2271 MISC mode includes a number of distinct operations that
2272 operate on distinct devices. The operations are:
2275 The device is examined to see if it is
2276 (1) an active md array, or
2277 (2) a component of an md array.
2278 The information discovered is reported.
2282 The device should be an active md device.
2284 will display a detailed description of the array.
2288 will cause the output to be less detailed and the format to be
2289 suitable for inclusion in
2293 will normally be 0 unless
2295 failed to get useful information about the device(s); however, if the
2297 option is given, then the exit status will be:
2301 The array is functioning normally.
2304 The array has at least one failed device.
2307 The array has multiple failed devices such that it is unusable.
2310 There was an error while trying to get information about the device.
2314 .B \-\-detail\-platform
2315 Print detail of the platform's RAID capabilities (firmware / hardware
2316 topology). If the metadata is specified with
2320 then the return status will be:
2324 metadata successfully enumerated its platform components on this system
2327 metadata is platform independent
2330 metadata failed to find its platform components on this system
2334 .B \-\-update\-subarray=
2335 If the device is a container and the argument to \-\-update\-subarray
2336 specifies a subarray in the container, then attempt to update the given
2337 superblock field in the subarray. Similar to updating an array in
2338 "assemble" mode, the field to update is selected by
2342 option. The supported options are
2350 option updates the subarray name in the metadata, it may not affect the
2351 device node name or the device node symlink until the subarray is
2352 re\-assembled. If updating
2354 would change the UUID of an active subarray this operation is blocked,
2355 and the command will end in an error.
2361 options enable and disable PPL in the metadata. Currently supported only for
2366 The device should be a component of an md array.
2368 will read the md superblock of the device and display the contents.
2373 is given, then multiple devices that are components of the one array
2374 are grouped together and reported in a single entry suitable
2380 without listing any devices will cause all devices listed in the
2381 config file to be examined.
2384 .BI \-\-dump= directory
2385 If the device contains RAID metadata, a file will be created in the
2387 and the metadata will be written to it. The file will be the same
2388 size as the device and have the metadata written in the file at the
2389 same locate that it exists in the device. However the file will be "sparse" so
2390 that only those blocks containing metadata will be allocated. The
2391 total space used will be small.
2393 The file name used in the
2395 will be the base name of the device. Further if any links appear in
2397 which point to the device, then hard links to the file will be created
2404 Multiple devices can be listed and their metadata will all be stored
2405 in the one directory.
2408 .BI \-\-restore= directory
2409 This is the reverse of
2412 will locate a file in the directory that has a name appropriate for
2413 the given device and will restore metadata from it. Names that match
2415 names are preferred, however if two of those refer to different files,
2417 will not choose between them but will abort the operation.
2419 If a file name is given instead of a
2423 will restore from that file to a single device, always provided the
2424 size of the file matches that of the device, and the file contains
2428 The devices should be active md arrays which will be deactivated, as
2429 long as they are not currently in use.
2433 This will fully activate a partially assembled md array.
2437 This will mark an active array as read-only, providing that it is
2438 not currently being used.
2444 array back to being read/write.
2448 For all operations except
2451 will cause the operation to be applied to all arrays listed in
2456 causes all devices listed in the config file to be examined.
2459 .BR \-b ", " \-\-brief
2460 Be less verbose. This is used with
2468 gives an intermediate level of verbosity.
2474 .B mdadm \-\-monitor
2475 .I options... devices...
2480 to periodically poll a number of md arrays and to report on any events
2483 will never exit once it decides that there are arrays to be checked,
2484 so it should normally be run in the background.
2486 As well as reporting events,
2488 may move a spare drive from one array to another if they are in the
2493 and if the destination array has a failed drive but no spares.
2495 If any devices are listed on the command line,
2497 will only monitor those devices. Otherwise all arrays listed in the
2498 configuration file will be monitored. Further, if
2500 is given, then any other md devices that appear in
2502 will also be monitored.
2504 The result of monitoring the arrays is the generation of events.
2505 These events are passed to a separate program (if specified) and may
2506 be mailed to a given E-mail address.
2508 When passing events to a program, the program is run once for each event,
2509 and is given 2 or 3 command-line arguments: the first is the
2510 name of the event (see below), the second is the name of the
2511 md device which is affected, and the third is the name of a related
2512 device if relevant (such as a component device that has failed).
2516 is given, then a program or an E-mail address must be specified on the
2517 command line or in the config file. If neither are available, then
2519 will not monitor anything.
2523 will continue monitoring as long as something was found to monitor. If
2524 no program or email is given, then each event is reported to
2527 The different events are:
2531 .B DeviceDisappeared
2532 An md array which previously was configured appears to no longer be
2533 configured. (syslog priority: Critical)
2537 was told to monitor an array which is RAID0 or Linear, then it will
2539 .B DeviceDisappeared
2540 with the extra information
2542 This is because RAID0 and Linear do not support the device-failed,
2543 hot-spare and resync operations which are monitored.
2547 An md array started reconstruction (e.g. recovery, resync, reshape,
2548 check, repair). (syslog priority: Warning)
2554 is a two-digit number (ie. 05, 48). This indicates that rebuild
2555 has passed that many percent of the total. The events are generated
2556 with fixed increment since 0. Increment size may be specified with
2557 a commandline option (default is 20). (syslog priority: Warning)
2561 An md array that was rebuilding, isn't any more, either because it
2562 finished normally or was aborted. (syslog priority: Warning)
2566 An active component device of an array has been marked as
2567 faulty. (syslog priority: Critical)
2571 A spare component device which was being rebuilt to replace a faulty
2572 device has failed. (syslog priority: Critical)
2576 A spare component device which was being rebuilt to replace a faulty
2577 device has been successfully rebuilt and has been made active.
2578 (syslog priority: Info)
2582 A new md array has been detected in the
2584 file. (syslog priority: Info)
2588 A newly noticed array appears to be degraded. This message is not
2591 notices a drive failure which causes degradation, but only when
2593 notices that an array is degraded when it first sees the array.
2594 (syslog priority: Critical)
2598 A spare drive has been moved from one array in a
2602 to another to allow a failed drive to be replaced.
2603 (syslog priority: Info)
2609 has been told, via the config file, that an array should have a certain
2610 number of spare devices, and
2612 detects that it has fewer than this number when it first sees the
2613 array, it will report a
2616 (syslog priority: Warning)
2620 An array was found at startup, and the
2623 (syslog priority: Info)
2633 cause Email to be sent. All events cause the program to be run.
2634 The program is run with two or three arguments: the event
2635 name, the array device and possibly a second device.
2637 Each event has an associated array device (e.g.
2639 and possibly a second device. For
2644 the second device is the relevant component device.
2647 the second device is the array that the spare was moved from.
2651 to move spares from one array to another, the different arrays need to
2652 be labeled with the same
2654 or the spares must be allowed to migrate through matching POLICY domains
2655 in the configuration file. The
2657 name can be any string; it is only necessary that different spare
2658 groups use different names.
2662 detects that an array in a spare group has fewer active
2663 devices than necessary for the complete array, and has no spare
2664 devices, it will look for another array in the same spare group that
2665 has a full complement of working drive and a spare. It will then
2666 attempt to remove the spare from the second drive and add it to the
2668 If the removal succeeds but the adding fails, then it is added back to
2671 If the spare group for a degraded array is not defined,
2673 will look at the rules of spare migration specified by POLICY lines in
2675 and then follow similar steps as above if a matching spare is found.
2678 The GROW mode is used for changing the size or shape of an active
2680 For this to work, the kernel must support the necessary change.
2681 Various types of growth are being added during 2.6 development.
2683 Currently the supported changes include
2685 change the "size" attribute for RAID1, RAID4, RAID5 and RAID6.
2687 increase or decrease the "raid\-devices" attribute of RAID0, RAID1, RAID4,
2690 change the chunk-size and layout of RAID0, RAID4, RAID5, RAID6 and RAID10.
2692 convert between RAID1 and RAID5, between RAID5 and RAID6, between
2693 RAID0, RAID4, and RAID5, and between RAID0 and RAID10 (in the near-2 mode).
2695 add a write-intent bitmap to any array which supports these bitmaps, or
2696 remove a write-intent bitmap from such an array.
2699 Using GROW on containers is currently supported only for Intel's IMSM
2700 container format. The number of devices in a container can be
2701 increased - which affects all arrays in the container - or an array
2702 in a container can be converted between levels where those levels are
2703 supported by the container, and the conversion is on of those listed
2704 above. Resizing arrays in an IMSM container with
2706 is not yet supported.
2708 Grow functionality (e.g. expand a number of raid devices) for Intel's
2709 IMSM container format has an experimental status. It is guarded by the
2710 .B MDADM_EXPERIMENTAL
2711 environment variable which must be set to '1' for a GROW command to
2713 This is for the following reasons:
2716 Intel's native IMSM check-pointing is not fully tested yet.
2717 This can causes IMSM incompatibility during the grow process: an array
2718 which is growing cannot roam between Microsoft Windows(R) and Linux
2722 Interrupting a grow operation is not recommended, because it
2723 has not been fully tested for Intel's IMSM container format yet.
2726 Note: Intel's native checkpointing doesn't use
2728 option and it is transparent for assembly feature.
2731 Normally when an array is built the "size" is taken from the smallest
2732 of the drives. If all the small drives in an arrays are, one at a
2733 time, removed and replaced with larger drives, then you could have an
2734 array of large drives with only a small amount used. In this
2735 situation, changing the "size" with "GROW" mode will allow the extra
2736 space to start being used. If the size is increased in this way, a
2737 "resync" process will start to make sure the new parts of the array
2740 Note that when an array changes size, any filesystem that may be
2741 stored in the array will not automatically grow or shrink to use or
2742 vacate the space. The
2743 filesystem will need to be explicitly told to use the extra space
2744 after growing, or to reduce its size
2746 to shrinking the array.
2748 Also the size of an array cannot be changed while it has an active
2749 bitmap. If an array has a bitmap, it must be removed before the size
2750 can be changed. Once the change is complete a new bitmap can be created.
2752 .SS RAID\-DEVICES CHANGES
2754 A RAID1 array can work with any number of devices from 1 upwards
2755 (though 1 is not very useful). There may be times which you want to
2756 increase or decrease the number of active devices. Note that this is
2757 different to hot-add or hot-remove which changes the number of
2760 When reducing the number of devices in a RAID1 array, the slots which
2761 are to be removed from the array must already be vacant. That is, the
2762 devices which were in those slots must be failed and removed.
2764 When the number of devices is increased, any hot spares that are
2765 present will be activated immediately.
2767 Changing the number of active devices in a RAID5 or RAID6 is much more
2768 effort. Every block in the array will need to be read and written
2769 back to a new location. From 2.6.17, the Linux Kernel is able to
2770 increase the number of devices in a RAID5 safely, including restarting
2771 an interrupted "reshape". From 2.6.31, the Linux Kernel is able to
2772 increase or decrease the number of devices in a RAID5 or RAID6.
2774 From 2.6.35, the Linux Kernel is able to convert a RAID0 in to a RAID4
2777 uses this functionality and the ability to add
2778 devices to a RAID4 to allow devices to be added to a RAID0. When
2779 requested to do this,
2781 will convert the RAID0 to a RAID4, add the necessary disks and make
2782 the reshape happen, and then convert the RAID4 back to RAID0.
2784 When decreasing the number of devices, the size of the array will also
2785 decrease. If there was data in the array, it could get destroyed and
2786 this is not reversible, so you should firstly shrink the filesystem on
2787 the array to fit within the new size. To help prevent accidents,
2789 requires that the size of the array be decreased first with
2790 .BR "mdadm --grow --array-size" .
2791 This is a reversible change which simply makes the end of the array
2792 inaccessible. The integrity of any data can then be checked before
2793 the non-reversible reduction in the number of devices is request.
2795 When relocating the first few stripes on a RAID5 or RAID6, it is not
2796 possible to keep the data on disk completely consistent and
2797 crash-proof. To provide the required safety, mdadm disables writes to
2798 the array while this "critical section" is reshaped, and takes a
2799 backup of the data that is in that section. For grows, this backup may be
2800 stored in any spare devices that the array has, however it can also be
2801 stored in a separate file specified with the
2803 option, and is required to be specified for shrinks, RAID level
2804 changes and layout changes. If this option is used, and the system
2805 does crash during the critical period, the same file must be passed to
2807 to restore the backup and reassemble the array. When shrinking rather
2808 than growing the array, the reshape is done from the end towards the
2809 beginning, so the "critical section" is at the end of the reshape.
2813 Changing the RAID level of any array happens instantaneously. However
2814 in the RAID5 to RAID6 case this requires a non-standard layout of the
2815 RAID6 data, and in the RAID6 to RAID5 case that non-standard layout is
2816 required before the change can be accomplished. So while the level
2817 change is instant, the accompanying layout change can take quite a
2820 is required. If the array is not simultaneously being grown or
2821 shrunk, so that the array size will remain the same - for example,
2822 reshaping a 3-drive RAID5 into a 4-drive RAID6 - the backup file will
2823 be used not just for a "cricital section" but throughout the reshape
2824 operation, as described below under LAYOUT CHANGES.
2826 .SS CHUNK-SIZE AND LAYOUT CHANGES
2828 Changing the chunk-size of layout without also changing the number of
2829 devices as the same time will involve re-writing all blocks in-place.
2830 To ensure against data loss in the case of a crash, a
2832 must be provided for these changes. Small sections of the array will
2833 be copied to the backup file while they are being rearranged. This
2834 means that all the data is copied twice, once to the backup and once
2835 to the new layout on the array, so this type of reshape will go very
2838 If the reshape is interrupted for any reason, this backup file must be
2840 .B "mdadm --assemble"
2841 so the array can be reassembled. Consequently the file cannot be
2842 stored on the device being reshaped.
2847 A write-intent bitmap can be added to, or removed from, an active
2848 array. Either internal bitmaps, or bitmaps stored in a separate file,
2849 can be added. Note that if you add a bitmap stored in a file which is
2850 in a filesystem that is on the RAID array being affected, the system
2851 will deadlock. The bitmap must be on a separate filesystem.
2853 .SH INCREMENTAL MODE
2857 .B mdadm \-\-incremental
2861 .RI [ optional-aliases-for-device ]
2864 .B mdadm \-\-incremental \-\-fail
2868 .B mdadm \-\-incremental \-\-rebuild\-map
2871 .B mdadm \-\-incremental \-\-run \-\-scan
2874 This mode is designed to be used in conjunction with a device
2875 discovery system. As devices are found in a system, they can be
2877 .B "mdadm \-\-incremental"
2878 to be conditionally added to an appropriate array.
2880 Conversely, it can also be used with the
2882 flag to do just the opposite and find whatever array a particular device
2883 is part of and remove the device from that array.
2885 If the device passed is a
2887 device created by a previous call to
2889 then rather than trying to add that device to an array, all the arrays
2890 described by the metadata of the container will be started.
2893 performs a number of tests to determine if the device is part of an
2894 array, and which array it should be part of. If an appropriate array
2895 is found, or can be created,
2897 adds the device to the array and conditionally starts the array.
2901 will normally only add devices to an array which were previously working
2902 (active or spare) parts of that array. The support for automatic
2903 inclusion of a new drive as a spare in some array requires
2904 a configuration through POLICY in config file.
2908 makes are as follow:
2910 Is the device permitted by
2912 That is, is it listed in a
2914 line in that file. If
2916 is absent then the default it to allow any device. Similarly if
2918 contains the special word
2920 then any device is allowed. Otherwise the device name given to
2922 or one of the aliases given, or an alias found in the filesystem,
2923 must match one of the names or patterns in a
2927 This is the only context where the aliases are used. They are
2928 usually provided by a
2934 Does the device have a valid md superblock? If a specific metadata
2935 version is requested with
2939 then only that style of metadata is accepted, otherwise
2941 finds any known version of metadata. If no
2943 metadata is found, the device may be still added to an array
2944 as a spare if POLICY allows.
2948 Does the metadata match an expected array?
2949 The metadata can match in two ways. Either there is an array listed
2952 which identifies the array (either by UUID, by name, by device list,
2953 or by minor-number), or the array was created with a
2959 or on the command line.
2962 is not able to positively identify the array as belonging to the
2963 current host, the device will be rejected.
2968 keeps a list of arrays that it has partially assembled in
2970 If no array exists which matches
2971 the metadata on the new device,
2973 must choose a device name and unit number. It does this based on any
2976 or any name information stored in the metadata. If this name
2977 suggests a unit number, that number will be used, otherwise a free
2978 unit number will be chosen. Normally
2980 will prefer to create a partitionable array, however if the
2984 suggests that a non-partitionable array is preferred, that will be
2987 If the array is not found in the config file and its metadata does not
2988 identify it as belonging to the "homehost", then
2990 will choose a name for the array which is certain not to conflict with
2991 any array which does belong to this host. It does this be adding an
2992 underscore and a small number to the name preferred by the metadata.
2994 Once an appropriate array is found or created and the device is added,
2996 must decide if the array is ready to be started. It will
2997 normally compare the number of available (non-spare) devices to the
2998 number of devices that the metadata suggests need to be active. If
2999 there are at least that many, the array will be started. This means
3000 that if any devices are missing the array will not be restarted.
3006 in which case the array will be run as soon as there are enough
3007 devices present for the data to be accessible. For a RAID1, that
3008 means one device will start the array. For a clean RAID5, the array
3009 will be started as soon as all but one drive is present.
3011 Note that neither of these approaches is really ideal. If it can
3012 be known that all device discovery has completed, then
3016 can be run which will try to start all arrays that are being
3017 incrementally assembled. They are started in "read-auto" mode in
3018 which they are read-only until the first write request. This means
3019 that no metadata updates are made and no attempt at resync or recovery
3020 happens. Further devices that are found before the first write can
3021 still be added safely.
3024 This section describes environment variables that affect how mdadm
3029 Setting this value to 1 will prevent mdadm from automatically launching
3030 mdmon. This variable is intended primarily for debugging mdadm/mdmon.
3036 does not create any device nodes in /dev, but leaves that task to
3040 appears not to be configured, or if this environment variable is set
3043 will create and devices that are needed.
3046 .B MDADM_NO_SYSTEMCTL
3051 is in use it will normally request
3053 to start various background tasks (particularly
3055 rather than forking and running them in the background. This can be
3056 suppressed by setting
3057 .BR MDADM_NO_SYSTEMCTL=1 .
3061 A key value of IMSM metadata is that it allows interoperability with
3062 boot ROMs on Intel platforms, and with other major operating systems.
3065 will only allow an IMSM array to be created or modified if detects
3066 that it is running on an Intel platform which supports IMSM, and
3067 supports the particular configuration of IMSM that is being requested
3068 (some functionality requires newer OROM support).
3070 These checks can be suppressed by setting IMSM_NO_PLATFORM=1 in the
3071 environment. This can be useful for testing or for disaster
3072 recovery. You should be aware that interoperability may be
3073 compromised by setting this value.
3076 .B MDADM_GROW_ALLOW_OLD
3077 If an array is stopped while it is performing a reshape and that
3078 reshape was making use of a backup file, then when the array is
3081 will sometimes complain that the backup file is too old. If this
3082 happens and you are certain it is the right backup file, you can
3083 over-ride this check by setting
3084 .B MDADM_GROW_ALLOW_OLD=1
3089 Any string given in this variable is added to the start of the
3091 line in the config file, or treated as the whole
3093 line if none is given. It can be used to disable certain metadata
3096 is called from a boot script. For example
3098 .B " export MDADM_CONF_AUTO='-ddf -imsm'
3102 does not automatically assemble any DDF or
3103 IMSM arrays that are found. This can be useful on systems configured
3104 to manage such arrays with
3110 .B " mdadm \-\-query /dev/name-of-device"
3112 This will find out if a given device is a RAID array, or is part of
3113 one, and will provide brief information about the device.
3115 .B " mdadm \-\-assemble \-\-scan"
3117 This will assemble and start all arrays listed in the standard config
3118 file. This command will typically go in a system startup file.
3120 .B " mdadm \-\-stop \-\-scan"
3122 This will shut down all arrays that can be shut down (i.e. are not
3123 currently in use). This will typically go in a system shutdown script.
3125 .B " mdadm \-\-follow \-\-scan \-\-delay=120"
3127 If (and only if) there is an Email address or program given in the
3128 standard config file, then
3129 monitor the status of all arrays listed in that file by
3130 polling them ever 2 minutes.
3132 .B " mdadm \-\-create /dev/md0 \-\-level=1 \-\-raid\-devices=2 /dev/hd[ac]1"
3134 Create /dev/md0 as a RAID1 array consisting of /dev/hda1 and /dev/hdc1.
3137 .B " echo 'DEVICE /dev/hd*[0\-9] /dev/sd*[0\-9]' > mdadm.conf"
3139 .B " mdadm \-\-detail \-\-scan >> mdadm.conf"
3141 This will create a prototype config file that describes currently
3142 active arrays that are known to be made from partitions of IDE or SCSI drives.
3143 This file should be reviewed before being used as it may
3144 contain unwanted detail.
3146 .B " echo 'DEVICE /dev/hd[a\-z] /dev/sd*[a\-z]' > mdadm.conf"
3148 .B " mdadm \-\-examine \-\-scan \-\-config=mdadm.conf >> mdadm.conf"
3150 This will find arrays which could be assembled from existing IDE and
3151 SCSI whole drives (not partitions), and store the information in the
3152 format of a config file.
3153 This file is very likely to contain unwanted detail, particularly
3156 entries. It should be reviewed and edited before being used as an
3159 .B " mdadm \-\-examine \-\-brief \-\-scan \-\-config=partitions"
3161 .B " mdadm \-Ebsc partitions"
3163 Create a list of devices by reading
3164 .BR /proc/partitions ,
3165 scan these for RAID superblocks, and printout a brief listing of all
3168 .B " mdadm \-Ac partitions \-m 0 /dev/md0"
3170 Scan all partitions and devices listed in
3171 .BR /proc/partitions
3174 out of all such devices with a RAID superblock with a minor number of 0.
3176 .B " mdadm \-\-monitor \-\-scan \-\-daemonise > /run/mdadm/mon.pid"
3178 If config file contains a mail address or alert program, run mdadm in
3179 the background in monitor mode monitoring all md devices. Also write
3180 pid of mdadm daemon to
3181 .BR /run/mdadm/mon.pid .
3183 .B " mdadm \-Iq /dev/somedevice"
3185 Try to incorporate newly discovered device into some array as
3188 .B " mdadm \-\-incremental \-\-rebuild\-map \-\-run \-\-scan"
3190 Rebuild the array map from any current arrays, and then start any that
3193 .B " mdadm /dev/md4 --fail detached --remove detached"
3195 Any devices which are components of /dev/md4 will be marked as faulty
3196 and then remove from the array.
3198 .B " mdadm --grow /dev/md4 --level=6 --backup-file=/root/backup-md4"
3202 which is currently a RAID5 array will be converted to RAID6. There
3203 should normally already be a spare drive attached to the array as a
3204 RAID6 needs one more drive than a matching RAID5.
3206 .B " mdadm --create /dev/md/ddf --metadata=ddf --raid-disks 6 /dev/sd[a-f]"
3208 Create a DDF array over 6 devices.
3210 .B " mdadm --create /dev/md/home -n3 -l5 -z 30000000 /dev/md/ddf"
3212 Create a RAID5 array over any 3 devices in the given DDF set. Use
3213 only 30 gigabytes of each device.
3215 .B " mdadm -A /dev/md/ddf1 /dev/sd[a-f]"
3217 Assemble a pre-exist ddf array.
3219 .B " mdadm -I /dev/md/ddf1"
3221 Assemble all arrays contained in the ddf array, assigning names as
3224 .B " mdadm \-\-create \-\-help"
3226 Provide help about the Create mode.
3228 .B " mdadm \-\-config \-\-help"
3230 Provide help about the format of the config file.
3232 .B " mdadm \-\-help"
3234 Provide general help.
3244 lists all active md devices with information about them.
3246 uses this to find arrays when
3248 is given in Misc mode, and to monitor array reconstruction
3253 The config file lists which devices may be scanned to see if
3254 they contain MD super block, and gives identifying information
3255 (e.g. UUID) about known MD arrays. See
3259 .SS /etc/mdadm.conf.d
3261 A directory containing configuration files which are read in lexical
3267 mode is used, this file gets a list of arrays currently being created.
3272 understand two sorts of names for array devices.
3274 The first is the so-called 'standard' format name, which matches the
3275 names used by the kernel and which appear in
3278 The second sort can be freely chosen, but must reside in
3280 When giving a device name to
3282 to create or assemble an array, either full path name such as
3286 can be given, or just the suffix of the second sort of name, such as
3292 chooses device names during auto-assembly or incremental assembly, it
3293 will sometimes add a small sequence number to the end of the name to
3294 avoid conflicted between multiple arrays that have the same name. If
3296 can reasonably determine that the array really is meant for this host,
3297 either by a hostname in the metadata, or by the presence of the array
3300 then it will leave off the suffix if possible.
3301 Also if the homehost is specified as
3304 will only use a suffix if a different array of the same name already
3305 exists or is listed in the config file.
3307 The standard names for non-partitioned arrays (the only sort of md
3308 array available in 2.4 and earlier) are of the form
3312 where NN is a number.
3313 The standard names for partitionable arrays (as available from 2.6
3314 onwards) are of the form:
3318 Partition numbers should be indicated by adding "pMM" to these, thus "/dev/md/d1p2".
3320 From kernel version 2.6.28 the "non-partitioned array" can actually
3321 be partitioned. So the "md_d\fBNN\fP"
3322 names are no longer needed, and
3323 partitions such as "/dev/md\fBNN\fPp\fBXX\fP"
3326 From kernel version 2.6.29 standard names can be non-numeric following
3333 is any string. These names are supported by
3335 since version 3.3 provided they are enabled in
3340 was previously known as
3344 For further information on mdadm usage, MD and the various levels of
3347 .B http://raid.wiki.kernel.org/
3349 (based upon Jakob \(/Ostergaard's Software\-RAID.HOWTO)
3351 The latest version of
3353 should always be available from
3355 .B http://www.kernel.org/pub/linux/utils/raid/mdadm/
projects / thirdparty / mdadm.git / blob