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
727 .B "\-\-bitmap=none".
730 .BR \-\-bitmap\-chunk=
731 Set the chunksize of the bitmap. Each bit corresponds to that many
732 Kilobytes of storage.
733 When using a file based bitmap, the default is to use the smallest
734 size that is at-least 4 and requires no more than 2^21 chunks.
737 bitmap, the chunksize defaults to 64Meg, or larger if necessary to
738 fit the bitmap into the available space.
740 A suffix of 'K', 'M' or 'G' can be given to indicate Kilobytes, Megabytes or
741 Gigabytes respectively.
744 .BR \-W ", " \-\-write\-mostly
745 subsequent devices listed in a
750 command will be flagged as 'write\-mostly'. This is valid for RAID1
751 only and means that the 'md' driver will avoid reading from these
752 devices if at all possible. This can be useful if mirroring over a
756 .BR \-\-write\-behind=
757 Specify that write-behind mode should be enabled (valid for RAID1
758 only). If an argument is specified, it will set the maximum number
759 of outstanding writes allowed. The default value is 256.
760 A write-intent bitmap is required in order to use write-behind
761 mode, and write-behind is only attempted on drives marked as
766 subsequent devices listed in a
770 command will be flagged as 'failfast'. This is valid for RAID1 and
771 RAID10 only. IO requests to these devices will be encouraged to fail
772 quickly rather than cause long delays due to error handling. Also no
773 attempt is made to repair a read error on these devices.
775 If an array becomes degraded so that the 'failfast' device is the only
776 usable device, the 'failfast' flag will then be ignored and extended
777 delays will be preferred to complete failure.
779 The 'failfast' flag is appropriate for storage arrays which have a
780 low probability of true failure, but which may sometimes
781 cause unacceptable delays due to internal maintenance functions.
784 .BR \-\-assume\-clean
787 that the array pre-existed and is known to be clean. It can be useful
788 when trying to recover from a major failure as you can be sure that no
789 data will be affected unless you actually write to the array. It can
790 also be used when creating a RAID1 or RAID10 if you want to avoid the
791 initial resync, however this practice \(em while normally safe \(em is not
792 recommended. Use this only if you really know what you are doing.
794 When the devices that will be part of a new array were filled
795 with zeros before creation the operator knows the array is
796 actually clean. If that is the case, such as after running
797 badblocks, this argument can be used to tell mdadm the
798 facts the operator knows.
800 When an array is resized to a larger size with
801 .B "\-\-grow \-\-size="
802 the new space is normally resynced in that same way that the whole
803 array is resynced at creation. From Linux version 3.0,
805 can be used with that command to avoid the automatic resync.
808 .BR \-\-backup\-file=
811 is used to increase the number of raid-devices in a RAID5 or RAID6 if
812 there are no spare devices available, or to shrink, change RAID level
813 or layout. See the GROW MODE section below on RAID\-DEVICES CHANGES.
814 The file must be stored on a separate device, not on the RAID array
819 Arrays with 1.x metadata can leave a gap between the start of the
820 device and the start of array data. This gap can be used for various
821 metadata. The start of data is known as the
823 Normally an appropriate data offset is computed automatically.
824 However it can be useful to set it explicitly such as when re-creating
825 an array which was originally created using a different version of
827 which computed a different offset.
829 Setting the offset explicitly over-rides the default. The value given
830 is in Kilobytes unless a suffix of 'K', 'M' or 'G' is used to explicitly
831 indicate Kilobytes, Megabytes or Gigabytes respectively.
835 can also be used with
837 for some RAID levels (initially on RAID10). This allows the
838 data\-offset to be changed as part of the reshape process. When the
839 data offset is changed, no backup file is required as the difference
840 in offsets is used to provide the same functionality.
842 When the new offset is earlier than the old offset, the number of
843 devices in the array cannot shrink. When it is after the old offset,
844 the number of devices in the array cannot increase.
846 When creating an array,
850 In the case each member device is expected to have a offset appended
851 to the name, separated by a colon. This makes it possible to recreate
852 exactly an array which has varying data offsets (as can happen when
853 different versions of
855 are used to add different devices).
859 This option is complementary to the
860 .B \-\-freeze-reshape
861 option for assembly. It is needed when
863 operation is interrupted and it is not restarted automatically due to
864 .B \-\-freeze-reshape
865 usage during array assembly. This option is used together with
869 ) command and device for a pending reshape to be continued.
870 All parameters required for reshape continuation will be read from array metadata.
874 .BR \-\-backup\-file=
875 option to be set, continuation option will require to have exactly the same
876 backup file given as well.
878 Any other parameter passed together with
880 option will be ignored.
883 .BR \-N ", " \-\-name=
886 for the array. This is currently only effective when creating an
887 array with a version-1 superblock, or an array in a DDF container.
888 The name is a simple textual string that can be used to identify array
889 components when assembling. If name is needed but not specified, it
890 is taken from the basename of the device that is being created.
902 run the array, even if some of the components
903 appear to be active in another array or filesystem. Normally
905 will ask for confirmation before including such components in an
906 array. This option causes that question to be suppressed.
909 .BR \-f ", " \-\-force
912 accept the geometry and layout specified without question. Normally
914 will not allow creation of an array with only one device, and will try
915 to create a RAID5 array with one missing drive (as this makes the
916 initial resync work faster). With
919 will not try to be so clever.
922 .BR \-o ", " \-\-readonly
925 rather than read-write as normal. No writes will be allowed to the
926 array, and no resync, recovery, or reshape will be started.
929 .BR \-a ", " "\-\-auto{=yes,md,mdp,part,p}{NN}"
930 Instruct mdadm how to create the device file if needed, possibly allocating
931 an unused minor number. "md" causes a non-partitionable array
932 to be used (though since Linux 2.6.28, these array devices are in fact
933 partitionable). "mdp", "part" or "p" causes a partitionable array (2.6 and
934 later) to be used. "yes" requires the named md device to have
935 a 'standard' format, and the type and minor number will be determined
936 from this. With mdadm 3.0, device creation is normally left up to
938 so this option is unlikely to be needed.
939 See DEVICE NAMES below.
941 The argument can also come immediately after
946 is not given on the command line or in the config file, then
952 is also given, then any
954 entries in the config file will override the
956 instruction given on the command line.
958 For partitionable arrays,
960 will create the device file for the whole array and for the first 4
961 partitions. A different number of partitions can be specified at the
962 end of this option (e.g.
964 If the device name ends with a digit, the partition names add a 'p',
966 .IR /dev/md/home1p3 .
967 If there is no trailing digit, then the partition names just have a
969 .IR /dev/md/scratch3 .
971 If the md device name is in a 'standard' format as described in DEVICE
972 NAMES, then it will be created, if necessary, with the appropriate
973 device number based on that name. If the device name is not in one of these
974 formats, then a unused device number will be allocated. The device
975 number will be considered unused if there is no active array for that
976 number, and there is no entry in /dev for that number and with a
977 non-standard name. Names that are not in 'standard' format are only
978 allowed in "/dev/md/".
980 This is meaningful with
986 .BR \-a ", " "\-\-add"
987 This option can be used in Grow mode in two cases.
989 If the target array is a Linear array, then
991 can be used to add one or more devices to the array. They
992 are simply catenated on to the end of the array. Once added, the
993 devices cannot be removed.
997 option is being used to increase the number of devices in an array,
1000 can be used to add some extra devices to be included in the array.
1001 In most cases this is not needed as the extra devices can be added as
1002 spares first, and then the number of raid-disks can be changed.
1003 However for RAID0, it is not possible to add spares. So to increase
1004 the number of devices in a RAID0, it is necessary to set the new
1005 number of devices, and to add the new devices, in the same command.
1009 Only works when the array is for clustered environment. It specifies
1010 the maximum number of nodes in the cluster that will use this device
1011 simultaneously. If not specified, this defaults to 4.
1014 .BR \-\-write-journal
1015 Specify journal device for the RAID-4/5/6 array. The journal device
1016 should be a SSD with reasonable lifetime.
1022 .BR \-u ", " \-\-uuid=
1023 uuid of array to assemble. Devices which don't have this uuid are
1027 .BR \-m ", " \-\-super\-minor=
1028 Minor number of device that array was created for. Devices which
1029 don't have this minor number are excluded. If you create an array as
1030 /dev/md1, then all superblocks will contain the minor number 1, even if
1031 the array is later assembled as /dev/md2.
1033 Giving the literal word "dev" for
1037 to use the minor number of the md device that is being assembled.
1038 e.g. when assembling
1040 .B \-\-super\-minor=dev
1041 will look for super blocks with a minor number of 0.
1044 is only relevant for v0.90 metadata, and should not normally be used.
1050 .BR \-N ", " \-\-name=
1051 Specify the name of the array to assemble. This must be the name
1052 that was specified when creating the array. It must either match
1053 the name stored in the superblock exactly, or it must match
1056 prefixed to the start of the given name.
1059 .BR \-f ", " \-\-force
1060 Assemble the array even if the metadata on some devices appears to be
1063 cannot find enough working devices to start the array, but can find
1064 some devices that are recorded as having failed, then it will mark
1065 those devices as working so that the array can be started.
1066 An array which requires
1068 to be started may contain data corruption. Use it carefully.
1071 .BR \-R ", " \-\-run
1072 Attempt to start the array even if fewer drives were given than were
1073 present last time the array was active. Normally if not all the
1074 expected drives are found and
1076 is not used, then the array will be assembled but not started.
1079 an attempt will be made to start it anyway.
1083 This is the reverse of
1085 in that it inhibits the startup of array unless all expected drives
1086 are present. This is only needed with
1088 and can be used if the physical connections to devices are
1089 not as reliable as you would like.
1092 .BR \-a ", " "\-\-auto{=no,yes,md,mdp,part}"
1093 See this option under Create and Build options.
1096 .BR \-b ", " \-\-bitmap=
1097 Specify the bitmap file that was given when the array was created. If
1100 bitmap, there is no need to specify this when assembling the array.
1103 .BR \-\-backup\-file=
1106 was used while reshaping an array (e.g. changing number of devices or
1107 chunk size) and the system crashed during the critical section, then the same
1109 must be presented to
1111 to allow possibly corrupted data to be restored, and the reshape
1115 .BR \-\-invalid\-backup
1116 If the file needed for the above option is not available for any
1117 reason an empty file can be given together with this option to
1118 indicate that the backup file is invalid. In this case the data that
1119 was being rearranged at the time of the crash could be irrecoverably
1120 lost, but the rest of the array may still be recoverable. This option
1121 should only be used as a last resort if there is no way to recover the
1126 .BR \-U ", " \-\-update=
1127 Update the superblock on each device while assembling the array. The
1128 argument given to this flag can be one of
1148 option will adjust the superblock of an array what was created on a Sparc
1149 machine running a patched 2.2 Linux kernel. This kernel got the
1150 alignment of part of the superblock wrong. You can use the
1151 .B "\-\-examine \-\-sparc2.2"
1154 to see what effect this would have.
1158 option will update the
1159 .B "preferred minor"
1160 field on each superblock to match the minor number of the array being
1162 This can be useful if
1164 reports a different "Preferred Minor" to
1166 In some cases this update will be performed automatically
1167 by the kernel driver. In particular the update happens automatically
1168 at the first write to an array with redundancy (RAID level 1 or
1169 greater) on a 2.6 (or later) kernel.
1173 option will change the uuid of the array. If a UUID is given with the
1175 option that UUID will be used as a new UUID and will
1177 be used to help identify the devices in the array.
1180 is given, a random UUID is chosen.
1184 option will change the
1186 of the array as stored in the superblock. This is only supported for
1187 version-1 superblocks.
1191 option will change the
1193 of the array as stored in the bitmap superblock. This option only
1194 works for a clustered environment.
1198 option will change the
1200 as recorded in the superblock. For version-0 superblocks, this is the
1201 same as updating the UUID.
1202 For version-1 superblocks, this involves updating the name.
1206 option will change the cluster name as recorded in the superblock and
1207 bitmap. This option only works for clustered environment.
1211 option will cause the array to be marked
1213 meaning that any redundancy in the array (e.g. parity for RAID5,
1214 copies for RAID1) may be incorrect. This will cause the RAID system
1215 to perform a "resync" pass to make sure that all redundant information
1220 option allows arrays to be moved between machines with different
1222 When assembling such an array for the first time after a move, giving
1223 .B "\-\-update=byteorder"
1226 to expect superblocks to have their byteorder reversed, and will
1227 correct that order before assembling the array. This is only valid
1228 with original (Version 0.90) superblocks.
1232 option will correct the summaries in the superblock. That is the
1233 counts of total, working, active, failed, and spare devices.
1237 option will rarely be of use. It applies to version 1.1 and 1.2 metadata
1238 only (where the metadata is at the start of the device) and is only
1239 useful when the component device has changed size (typically become
1240 larger). The version 1 metadata records the amount of the device that
1241 can be used to store data, so if a device in a version 1.1 or 1.2
1242 array becomes larger, the metadata will still be visible, but the
1243 extra space will not. In this case it might be useful to assemble the
1245 .BR \-\-update=devicesize .
1248 to determine the maximum usable amount of space on each device and
1249 update the relevant field in the metadata.
1253 option only works on v0.90 metadata arrays and will convert them to
1254 v1.0 metadata. The array must not be dirty (i.e. it must not need a
1255 sync) and it must not have a write-intent bitmap.
1257 The old metadata will remain on the devices, but will appear older
1258 than the new metadata and so will usually be ignored. The old metadata
1259 (or indeed the new metadata) can be removed by giving the appropriate
1262 .BR \-\-zero\-superblock .
1266 option can be used when an array has an internal bitmap which is
1267 corrupt in some way so that assembling the array normally fails. It
1268 will cause any internal bitmap to be ignored.
1272 option will reserve space in each device for a bad block list. This
1273 will be 4K in size and positioned near the end of any free space
1274 between the superblock and the data.
1278 option will cause any reservation of space for a bad block list to be
1279 removed. If the bad block list contains entries, this will fail, as
1280 removing the list could cause data corruption.
1283 .BR \-\-freeze\-reshape
1284 Option is intended to be used in start-up scripts during initrd boot phase.
1285 When array under reshape is assembled during initrd phase, this option
1286 stops reshape after reshape critical section is being restored. This happens
1287 before file system pivot operation and avoids loss of file system context.
1288 Losing file system context would cause reshape to be broken.
1290 Reshape can be continued later using the
1292 option for the grow command.
1294 .SH For Manage mode:
1297 .BR \-t ", " \-\-test
1298 Unless a more serious error occurred,
1300 will exit with a status of 2 if no changes were made to the array and
1301 0 if at least one change was made.
1302 This can be useful when an indirect specifier such as
1307 is used in requesting an operation on the array.
1309 will report failure if these specifiers didn't find any match.
1312 .BR \-a ", " \-\-add
1313 hot-add listed devices.
1314 If a device appears to have recently been part of the array
1315 (possibly it failed or was removed) the device is re\-added as described
1317 If that fails or the device was never part of the array, the device is
1318 added as a hot-spare.
1319 If the array is degraded, it will immediately start to rebuild data
1322 Note that this and the following options are only meaningful on array
1323 with redundancy. They don't apply to RAID0 or Linear.
1327 re\-add a device that was previously removed from an array.
1328 If the metadata on the device reports that it is a member of the
1329 array, and the slot that it used is still vacant, then the device will
1330 be added back to the array in the same position. This will normally
1331 cause the data for that device to be recovered. However based on the
1332 event count on the device, the recovery may only require sections that
1333 are flagged a write-intent bitmap to be recovered or may not require
1334 any recovery at all.
1336 When used on an array that has no metadata (i.e. it was built with
1338 it will be assumed that bitmap-based recovery is enough to make the
1339 device fully consistent with the array.
1341 When used with v1.x metadata,
1343 can be accompanied by
1344 .BR \-\-update=devicesize ,
1345 .BR \-\-update=bbl ", or"
1346 .BR \-\-update=no\-bbl .
1347 See the description of these option when used in Assemble mode for an
1348 explanation of their use.
1350 If the device name given is
1354 will try to find any device that looks like it should be
1355 part of the array but isn't and will try to re\-add all such devices.
1357 If the device name given is
1361 will find all devices in the array that are marked
1363 remove them and attempt to immediately re\-add them. This can be
1364 useful if you are certain that the reason for failure has been
1369 Add a device as a spare. This is similar to
1371 except that it does not attempt
1373 first. The device will be added as a spare even if it looks like it
1374 could be an recent member of the array.
1377 .BR \-r ", " \-\-remove
1378 remove listed devices. They must not be active. i.e. they should
1379 be failed or spare devices.
1381 As well as the name of a device file
1391 The first causes all failed device to be removed. The second causes
1392 any device which is no longer connected to the system (i.e an 'open'
1396 The third will remove a set as describe below under
1400 .BR \-f ", " \-\-fail
1401 Mark listed devices as faulty.
1402 As well as the name of a device file, the word
1406 can be given. The former will cause any device that has been detached from
1407 the system to be marked as failed. It can then be removed.
1409 For RAID10 arrays where the number of copies evenly divides the number
1410 of devices, the devices can be conceptually divided into sets where
1411 each set contains a single complete copy of the data on the array.
1412 Sometimes a RAID10 array will be configured so that these sets are on
1413 separate controllers. In this case all the devices in one set can be
1414 failed by giving a name like
1420 The appropriate set names are reported by
1430 Mark listed devices as requiring replacement. As soon as a spare is
1431 available, it will be rebuilt and will replace the marked device.
1432 This is similar to marking a device as faulty, but the device remains
1433 in service during the recovery process to increase resilience against
1434 multiple failures. When the replacement process finishes, the
1435 replaced device will be marked as faulty.
1439 This can follow a list of
1441 devices. The devices listed after
1443 will be preferentially used to replace the devices listed after
1445 These device must already be spare devices in the array.
1448 .BR \-\-write\-mostly
1449 Subsequent devices that are added or re\-added will have the 'write-mostly'
1450 flag set. This is only valid for RAID1 and means that the 'md' driver
1451 will avoid reading from these devices if possible.
1454 Subsequent devices that are added or re\-added will have the 'write-mostly'
1457 .BR \-\-cluster\-confirm
1458 Confirm the existence of the device. This is issued in response to an \-\-add
1459 request by a node in a cluster. When a node adds a device it sends a message
1460 to all nodes in the cluster to look for a device with a UUID. This translates
1461 to a udev notification with the UUID of the device to be added and the slot
1462 number. The receiving node must acknowledge this message
1463 with \-\-cluster\-confirm. Valid arguments are <slot>:<devicename> in case
1464 the device is found or <slot>:missing in case the device is not found.
1468 Recreate journal for RAID-4/5/6 array that lost a journal device. In the
1469 current implementation, this command cannot add a journal to an array
1470 that had a failed journal. To avoid interrupting on-going write opertions,
1472 only works for array in Read-Only state.
1476 Subsequent devices that are added or re\-added will have
1477 the 'failfast' flag set. This is only valid for RAID1 and RAID10 and
1478 means that the 'md' driver will avoid long timeouts on error handling
1482 Subsequent devices that are re\-added will be re\-added without
1483 the 'failfast' flag set.
1486 Each of these options requires that the first device listed is the array
1487 to be acted upon, and the remainder are component devices to be added,
1488 removed, marked as faulty, etc. Several different operations can be
1489 specified for different devices, e.g.
1491 mdadm /dev/md0 \-\-add /dev/sda1 \-\-fail /dev/sdb1 \-\-remove /dev/sdb1
1493 Each operation applies to all devices listed until the next
1496 If an array is using a write-intent bitmap, then devices which have
1497 been removed can be re\-added in a way that avoids a full
1498 reconstruction but instead just updates the blocks that have changed
1499 since the device was removed. For arrays with persistent metadata
1500 (superblocks) this is done automatically. For arrays created with
1502 mdadm needs to be told that this device we removed recently with
1505 Devices can only be removed from an array if they are not in active
1506 use, i.e. that must be spares or failed devices. To remove an active
1507 device, it must first be marked as
1513 .BR \-Q ", " \-\-query
1514 Examine a device to see
1515 (1) if it is an md device and (2) if it is a component of an md
1517 Information about what is discovered is presented.
1520 .BR \-D ", " \-\-detail
1521 Print details of one or more md devices.
1524 .BR \-\-detail\-platform
1525 Print details of the platform's RAID capabilities (firmware / hardware
1526 topology) for a given metadata format. If used without argument, mdadm
1527 will scan all controllers looking for their capabilities. Otherwise, mdadm
1528 will only look at the controller specified by the argument in form of an
1529 absolute filepath or a link, e.g.
1530 .IR /sys/devices/pci0000:00/0000:00:1f.2 .
1533 .BR \-Y ", " \-\-export
1536 .BR \-\-detail-platform ,
1540 output will be formatted as
1542 pairs for easy import into the environment.
1548 indicates whether an array was started
1550 or not, which may include a reason
1551 .RB ( unsafe ", " nothing ", " no ).
1554 indicates if the array is expected on this host
1556 or seems to be from elsewhere
1560 .BR \-E ", " \-\-examine
1561 Print contents of the metadata stored on the named device(s).
1562 Note the contrast between
1567 applies to devices which are components of an array, while
1569 applies to a whole array which is currently active.
1572 If an array was created on a SPARC machine with a 2.2 Linux kernel
1573 patched with RAID support, the superblock will have been created
1574 incorrectly, or at least incompatibly with 2.4 and later kernels.
1579 will fix the superblock before displaying it. If this appears to do
1580 the right thing, then the array can be successfully assembled using
1581 .BR "\-\-assemble \-\-update=sparc2.2" .
1584 .BR \-X ", " \-\-examine\-bitmap
1585 Report information about a bitmap file.
1586 The argument is either an external bitmap file or an array component
1587 in case of an internal bitmap. Note that running this on an array
1590 does not report the bitmap for that array.
1593 .B \-\-examine\-badblocks
1594 List the bad-blocks recorded for the device, if a bad-blocks list has
1595 been configured. Currently only
1597 metadata supports bad-blocks lists.
1600 .BI \-\-dump= directory
1602 .BI \-\-restore= directory
1603 Save metadata from lists devices, or restore metadata to listed devices.
1606 .BR \-R ", " \-\-run
1607 start a partially assembled array. If
1609 did not find enough devices to fully start the array, it might leaving
1610 it partially assembled. If you wish, you can then use
1612 to start the array in degraded mode.
1615 .BR \-S ", " \-\-stop
1616 deactivate array, releasing all resources.
1619 .BR \-o ", " \-\-readonly
1620 mark array as readonly.
1623 .BR \-w ", " \-\-readwrite
1624 mark array as readwrite.
1627 .B \-\-zero\-superblock
1628 If the device contains a valid md superblock, the block is
1629 overwritten with zeros. With
1631 the block where the superblock would be is overwritten even if it
1632 doesn't appear to be valid.
1635 .B \-\-kill\-subarray=
1636 If the device is a container and the argument to \-\-kill\-subarray
1637 specifies an inactive subarray in the container, then the subarray is
1638 deleted. Deleting all subarrays will leave an 'empty-container' or
1639 spare superblock on the drives. See
1640 .B \-\-zero\-superblock
1642 removing a superblock. Note that some formats depend on the subarray
1643 index for generating a UUID, this command will fail if it would change
1644 the UUID of an active subarray.
1647 .B \-\-update\-subarray=
1648 If the device is a container and the argument to \-\-update\-subarray
1649 specifies a subarray in the container, then attempt to update the given
1650 superblock field in the subarray. See below in
1655 .BR \-t ", " \-\-test
1660 is set to reflect the status of the device. See below in
1665 .BR \-W ", " \-\-wait
1666 For each md device given, wait for any resync, recovery, or reshape
1667 activity to finish before returning.
1669 will return with success if it actually waited for every device
1670 listed, otherwise it will return failure.
1674 For each md device given, or each device in /proc/mdstat if
1676 is given, arrange for the array to be marked clean as soon as possible.
1678 will return with success if the array uses external metadata and we
1679 successfully waited. For native arrays this returns immediately as the
1680 kernel handles dirty-clean transitions at shutdown. No action is taken
1681 if safe-mode handling is disabled.
1685 Set the "sync_action" for all md devices given to one of
1692 will abort any currently running action though some actions will
1693 automatically restart.
1696 will abort any current action and ensure no other action starts
1706 .BR "SCRUBBING AND MISMATCHES" .
1708 .SH For Incremental Assembly mode:
1710 .BR \-\-rebuild\-map ", " \-r
1711 Rebuild the map file
1715 uses to help track which arrays are currently being assembled.
1718 .BR \-\-run ", " \-R
1719 Run any array assembled as soon as a minimal number of devices are
1720 available, rather than waiting until all expected devices are present.
1723 .BR \-\-scan ", " \-s
1724 Only meaningful with
1728 file for arrays that are being incrementally assembled and will try to
1729 start any that are not already started. If any such array is listed
1732 as requiring an external bitmap, that bitmap will be attached first.
1735 .BR \-\-fail ", " \-f
1736 This allows the hot-plug system to remove devices that have fully disappeared
1737 from the kernel. It will first fail and then remove the device from any
1738 array it belongs to.
1739 The device name given should be a kernel device name such as "sda",
1745 Only used with \-\-fail. The 'path' given will be recorded so that if
1746 a new device appears at the same location it can be automatically
1747 added to the same array. This allows the failed device to be
1748 automatically replaced by a new device without metadata if it appears
1749 at specified path. This option is normally only set by a
1753 .SH For Monitor mode:
1755 .BR \-m ", " \-\-mail
1756 Give a mail address to send alerts to.
1759 .BR \-p ", " \-\-program ", " \-\-alert
1760 Give a program to be run whenever an event is detected.
1763 .BR \-y ", " \-\-syslog
1764 Cause all events to be reported through 'syslog'. The messages have
1765 facility of 'daemon' and varying priorities.
1768 .BR \-d ", " \-\-delay
1769 Give a delay in seconds.
1771 polls the md arrays and then waits this many seconds before polling
1772 again. The default is 60 seconds. Since 2.6.16, there is no need to
1773 reduce this as the kernel alerts
1775 immediately when there is any change.
1778 .BR \-r ", " \-\-increment
1779 Give a percentage increment.
1781 will generate RebuildNN events with the given percentage increment.
1784 .BR \-f ", " \-\-daemonise
1787 to run as a background daemon if it decides to monitor anything. This
1788 causes it to fork and run in the child, and to disconnect from the
1789 terminal. The process id of the child is written to stdout.
1792 which will only continue monitoring if a mail address or alert program
1793 is found in the config file.
1796 .BR \-i ", " \-\-pid\-file
1799 is running in daemon mode, write the pid of the daemon process to
1800 the specified file, instead of printing it on standard output.
1803 .BR \-1 ", " \-\-oneshot
1804 Check arrays only once. This will generate
1806 events and more significantly
1812 .B " mdadm \-\-monitor \-\-scan \-1"
1814 from a cron script will ensure regular notification of any degraded arrays.
1817 .BR \-t ", " \-\-test
1820 alert for every array found at startup. This alert gets mailed and
1821 passed to the alert program. This can be used for testing that alert
1822 message do get through successfully.
1826 This inhibits the functionality for moving spares between arrays.
1827 Only one monitoring process started with
1829 but without this flag is allowed, otherwise the two could interfere
1836 .B mdadm \-\-assemble
1837 .I md-device options-and-component-devices...
1840 .B mdadm \-\-assemble \-\-scan
1841 .I md-devices-and-options...
1844 .B mdadm \-\-assemble \-\-scan
1848 This usage assembles one or more RAID arrays from pre-existing components.
1849 For each array, mdadm needs to know the md device, the identity of the
1850 array, and a number of component-devices. These can be found in a number of ways.
1852 In the first usage example (without the
1854 the first device given is the md device.
1855 In the second usage example, all devices listed are treated as md
1856 devices and assembly is attempted.
1857 In the third (where no devices are listed) all md devices that are
1858 listed in the configuration file are assembled. If no arrays are
1859 described by the configuration file, then any arrays that
1860 can be found on unused devices will be assembled.
1862 If precisely one device is listed, but
1868 was given and identity information is extracted from the configuration file.
1870 The identity can be given with the
1876 option, will be taken from the md-device record in the config file, or
1877 will be taken from the super block of the first component-device
1878 listed on the command line.
1880 Devices can be given on the
1882 command line or in the config file. Only devices which have an md
1883 superblock which contains the right identity will be considered for
1886 The config file is only used if explicitly named with
1888 or requested with (a possibly implicit)
1893 .B /etc/mdadm/mdadm.conf
1898 is not given, then the config file will only be used to find the
1899 identity of md arrays.
1901 Normally the array will be started after it is assembled. However if
1903 is not given and not all expected drives were listed, then the array
1904 is not started (to guard against usage errors). To insist that the
1905 array be started in this case (as may work for RAID1, 4, 5, 6, or 10),
1914 does not create any entries in
1918 It does record information in
1922 to choose the correct name.
1926 detects that udev is not configured, it will create the devices in
1930 In Linux kernels prior to version 2.6.28 there were two distinctly
1931 different types of md devices that could be created: one that could be
1932 partitioned using standard partitioning tools and one that could not.
1933 Since 2.6.28 that distinction is no longer relevant as both type of
1934 devices can be partitioned.
1936 will normally create the type that originally could not be partitioned
1937 as it has a well defined major number (9).
1939 Prior to 2.6.28, it is important that mdadm chooses the correct type
1940 of array device to use. This can be controlled with the
1942 option. In particular, a value of "mdp" or "part" or "p" tells mdadm
1943 to use a partitionable device rather than the default.
1945 In the no-udev case, the value given to
1947 can be suffixed by a number. This tells
1949 to create that number of partition devices rather than the default of 4.
1953 can also be given in the configuration file as a word starting
1955 on the ARRAY line for the relevant array.
1962 and no devices are listed,
1964 will first attempt to assemble all the arrays listed in the config
1967 If no arrays are listed in the config (other than those marked
1969 it will look through the available devices for possible arrays and
1970 will try to assemble anything that it finds. Arrays which are tagged
1971 as belonging to the given homehost will be assembled and started
1972 normally. Arrays which do not obviously belong to this host are given
1973 names that are expected not to conflict with anything local, and are
1974 started "read-auto" so that nothing is written to any device until the
1975 array is written to. i.e. automatic resync etc is delayed.
1979 finds a consistent set of devices that look like they should comprise
1980 an array, and if the superblock is tagged as belonging to the given
1981 home host, it will automatically choose a device name and try to
1982 assemble the array. If the array uses version-0.90 metadata, then the
1984 number as recorded in the superblock is used to create a name in
1988 If the array uses version-1 metadata, then the
1990 from the superblock is used to similarly create a name in
1992 (the name will have any 'host' prefix stripped first).
1994 This behaviour can be modified by the
1998 configuration file. This line can indicate that specific metadata
1999 type should, or should not, be automatically assembled. If an array
2000 is found which is not listed in
2002 and has a metadata format that is denied by the
2004 line, then it will not be assembled.
2007 line can also request that all arrays identified as being for this
2008 homehost should be assembled regardless of their metadata type.
2011 for further details.
2013 Note: Auto assembly cannot be used for assembling and activating some
2014 arrays which are undergoing reshape. In particular as the
2016 cannot be given, any reshape which requires a backup-file to continue
2017 cannot be started by auto assembly. An array which is growing to more
2018 devices and has passed the critical section can be assembled using
2029 .BI \-\-raid\-devices= Z
2033 This usage is similar to
2035 The difference is that it creates an array without a superblock. With
2036 these arrays there is no difference between initially creating the array and
2037 subsequently assembling the array, except that hopefully there is useful
2038 data there in the second case.
2040 The level may raid0, linear, raid1, raid10, multipath, or faulty, or
2041 one of their synonyms. All devices must be listed and the array will
2042 be started once complete. It will often be appropriate to use
2043 .B \-\-assume\-clean
2044 with levels raid1 or raid10.
2055 .BI \-\-raid\-devices= Z
2059 This usage will initialise a new md array, associate some devices with
2060 it, and activate the array.
2062 The named device will normally not exist when
2063 .I "mdadm \-\-create"
2064 is run, but will be created by
2066 once the array becomes active.
2068 As devices are added, they are checked to see if they contain RAID
2069 superblocks or filesystems. They are also checked to see if the variance in
2070 device size exceeds 1%.
2072 If any discrepancy is found, the array will not automatically be run, though
2075 can override this caution.
2077 To create a "degraded" array in which some devices are missing, simply
2078 give the word "\fBmissing\fP"
2079 in place of a device name. This will cause
2081 to leave the corresponding slot in the array empty.
2082 For a RAID4 or RAID5 array at most one slot can be
2083 "\fBmissing\fP"; for a RAID6 array at most two slots.
2084 For a RAID1 array, only one real device needs to be given. All of the
2088 When creating a RAID5 array,
2090 will automatically create a degraded array with an extra spare drive.
2091 This is because building the spare into a degraded array is in general
2092 faster than resyncing the parity on a non-degraded, but not clean,
2093 array. This feature can be overridden with the
2097 When creating an array with version-1 metadata a name for the array is
2099 If this is not given with the
2103 will choose a name based on the last component of the name of the
2104 device being created. So if
2106 is being created, then the name
2111 is being created, then the name
2115 When creating a partition based array, using
2117 with version-1.x metadata, the partition type should be set to
2119 (non fs-data). This type selection allows for greater precision since
2120 using any other [RAID auto-detect (0xFD) or a GNU/Linux partition (0x83)],
2121 might create problems in the event of array recovery through a live cdrom.
2123 A new array will normally get a randomly assigned 128bit UUID which is
2124 very likely to be unique. If you have a specific need, you can choose
2125 a UUID for the array by giving the
2127 option. Be warned that creating two arrays with the same UUID is a
2128 recipe for disaster. Also, using
2130 when creating a v0.90 array will silently override any
2135 .\"option is given, it is not necessary to list any component-devices in this command.
2136 .\"They can be added later, before a
2140 .\"is given, the apparent size of the smallest drive given is used.
2142 If the array type supports a write-intent bitmap, and if the devices
2143 in the array exceed 100G is size, an internal write-intent bitmap
2144 will automatically be added unless some other option is explicitly
2147 option. In any case space for a bitmap will be reserved so that one
2148 can be added layer with
2149 .BR "\-\-grow \-\-bitmap=internal" .
2151 If the metadata type supports it (currently only 1.x metadata), space
2152 will be allocated to store a bad block list. This allows a modest
2153 number of bad blocks to be recorded, allowing the drive to remain in
2154 service while only partially functional.
2156 When creating an array within a
2159 can be given either the list of devices to use, or simply the name of
2160 the container. The former case gives control over which devices in
2161 the container will be used for the array. The latter case allows
2163 to automatically choose which devices to use based on how much spare
2166 The General Management options that are valid with
2171 insist on running the array even if some devices look like they might
2176 start the array readonly \(em not supported yet.
2183 .I options... devices...
2186 This usage will allow individual devices in an array to be failed,
2187 removed or added. It is possible to perform multiple operations with
2188 on command. For example:
2190 .B " mdadm /dev/md0 \-f /dev/hda1 \-r /dev/hda1 \-a /dev/hda1"
2196 and will then remove it from the array and finally add it back
2197 in as a spare. However only one md array can be affected by a single
2200 When a device is added to an active array, mdadm checks to see if it
2201 has metadata on it which suggests that it was recently a member of the
2202 array. If it does, it tries to "re\-add" the device. If there have
2203 been no changes since the device was removed, or if the array has a
2204 write-intent bitmap which has recorded whatever changes there were,
2205 then the device will immediately become a full member of the array and
2206 those differences recorded in the bitmap will be resolved.
2216 MISC mode includes a number of distinct operations that
2217 operate on distinct devices. The operations are:
2220 The device is examined to see if it is
2221 (1) an active md array, or
2222 (2) a component of an md array.
2223 The information discovered is reported.
2227 The device should be an active md device.
2229 will display a detailed description of the array.
2233 will cause the output to be less detailed and the format to be
2234 suitable for inclusion in
2238 will normally be 0 unless
2240 failed to get useful information about the device(s); however, if the
2242 option is given, then the exit status will be:
2246 The array is functioning normally.
2249 The array has at least one failed device.
2252 The array has multiple failed devices such that it is unusable.
2255 There was an error while trying to get information about the device.
2259 .B \-\-detail\-platform
2260 Print detail of the platform's RAID capabilities (firmware / hardware
2261 topology). If the metadata is specified with
2265 then the return status will be:
2269 metadata successfully enumerated its platform components on this system
2272 metadata is platform independent
2275 metadata failed to find its platform components on this system
2279 .B \-\-update\-subarray=
2280 If the device is a container and the argument to \-\-update\-subarray
2281 specifies a subarray in the container, then attempt to update the given
2282 superblock field in the subarray. Similar to updating an array in
2283 "assemble" mode, the field to update is selected by
2287 option. Currently only
2293 option updates the subarray name in the metadata, it may not affect the
2294 device node name or the device node symlink until the subarray is
2295 re\-assembled. If updating
2297 would change the UUID of an active subarray this operation is blocked,
2298 and the command will end in an error.
2302 The device should be a component of an md array.
2304 will read the md superblock of the device and display the contents.
2309 is given, then multiple devices that are components of the one array
2310 are grouped together and reported in a single entry suitable
2316 without listing any devices will cause all devices listed in the
2317 config file to be examined.
2320 .BI \-\-dump= directory
2321 If the device contains RAID metadata, a file will be created in the
2323 and the metadata will be written to it. The file will be the same
2324 size as the device and have the metadata written in the file at the
2325 same locate that it exists in the device. However the file will be "sparse" so
2326 that only those blocks containing metadata will be allocated. The
2327 total space used will be small.
2329 The file name used in the
2331 will be the base name of the device. Further if any links appear in
2333 which point to the device, then hard links to the file will be created
2340 Multiple devices can be listed and their metadata will all be stored
2341 in the one directory.
2344 .BI \-\-restore= directory
2345 This is the reverse of
2348 will locate a file in the directory that has a name appropriate for
2349 the given device and will restore metadata from it. Names that match
2351 names are preferred, however if two of those refer to different files,
2353 will not choose between them but will abort the operation.
2355 If a file name is given instead of a
2359 will restore from that file to a single device, always provided the
2360 size of the file matches that of the device, and the file contains
2364 The devices should be active md arrays which will be deactivated, as
2365 long as they are not currently in use.
2369 This will fully activate a partially assembled md array.
2373 This will mark an active array as read-only, providing that it is
2374 not currently being used.
2380 array back to being read/write.
2384 For all operations except
2387 will cause the operation to be applied to all arrays listed in
2392 causes all devices listed in the config file to be examined.
2395 .BR \-b ", " \-\-brief
2396 Be less verbose. This is used with
2404 gives an intermediate level of verbosity.
2410 .B mdadm \-\-monitor
2411 .I options... devices...
2416 to periodically poll a number of md arrays and to report on any events
2419 will never exit once it decides that there are arrays to be checked,
2420 so it should normally be run in the background.
2422 As well as reporting events,
2424 may move a spare drive from one array to another if they are in the
2429 and if the destination array has a failed drive but no spares.
2431 If any devices are listed on the command line,
2433 will only monitor those devices. Otherwise all arrays listed in the
2434 configuration file will be monitored. Further, if
2436 is given, then any other md devices that appear in
2438 will also be monitored.
2440 The result of monitoring the arrays is the generation of events.
2441 These events are passed to a separate program (if specified) and may
2442 be mailed to a given E-mail address.
2444 When passing events to a program, the program is run once for each event,
2445 and is given 2 or 3 command-line arguments: the first is the
2446 name of the event (see below), the second is the name of the
2447 md device which is affected, and the third is the name of a related
2448 device if relevant (such as a component device that has failed).
2452 is given, then a program or an E-mail address must be specified on the
2453 command line or in the config file. If neither are available, then
2455 will not monitor anything.
2459 will continue monitoring as long as something was found to monitor. If
2460 no program or email is given, then each event is reported to
2463 The different events are:
2467 .B DeviceDisappeared
2468 An md array which previously was configured appears to no longer be
2469 configured. (syslog priority: Critical)
2473 was told to monitor an array which is RAID0 or Linear, then it will
2475 .B DeviceDisappeared
2476 with the extra information
2478 This is because RAID0 and Linear do not support the device-failed,
2479 hot-spare and resync operations which are monitored.
2483 An md array started reconstruction (e.g. recovery, resync, reshape,
2484 check, repair). (syslog priority: Warning)
2490 is a two-digit number (ie. 05, 48). This indicates that rebuild
2491 has passed that many percent of the total. The events are generated
2492 with fixed increment since 0. Increment size may be specified with
2493 a commandline option (default is 20). (syslog priority: Warning)
2497 An md array that was rebuilding, isn't any more, either because it
2498 finished normally or was aborted. (syslog priority: Warning)
2502 An active component device of an array has been marked as
2503 faulty. (syslog priority: Critical)
2507 A spare component device which was being rebuilt to replace a faulty
2508 device has failed. (syslog priority: Critical)
2512 A spare component device which was being rebuilt to replace a faulty
2513 device has been successfully rebuilt and has been made active.
2514 (syslog priority: Info)
2518 A new md array has been detected in the
2520 file. (syslog priority: Info)
2524 A newly noticed array appears to be degraded. This message is not
2527 notices a drive failure which causes degradation, but only when
2529 notices that an array is degraded when it first sees the array.
2530 (syslog priority: Critical)
2534 A spare drive has been moved from one array in a
2538 to another to allow a failed drive to be replaced.
2539 (syslog priority: Info)
2545 has been told, via the config file, that an array should have a certain
2546 number of spare devices, and
2548 detects that it has fewer than this number when it first sees the
2549 array, it will report a
2552 (syslog priority: Warning)
2556 An array was found at startup, and the
2559 (syslog priority: Info)
2569 cause Email to be sent. All events cause the program to be run.
2570 The program is run with two or three arguments: the event
2571 name, the array device and possibly a second device.
2573 Each event has an associated array device (e.g.
2575 and possibly a second device. For
2580 the second device is the relevant component device.
2583 the second device is the array that the spare was moved from.
2587 to move spares from one array to another, the different arrays need to
2588 be labeled with the same
2590 or the spares must be allowed to migrate through matching POLICY domains
2591 in the configuration file. The
2593 name can be any string; it is only necessary that different spare
2594 groups use different names.
2598 detects that an array in a spare group has fewer active
2599 devices than necessary for the complete array, and has no spare
2600 devices, it will look for another array in the same spare group that
2601 has a full complement of working drive and a spare. It will then
2602 attempt to remove the spare from the second drive and add it to the
2604 If the removal succeeds but the adding fails, then it is added back to
2607 If the spare group for a degraded array is not defined,
2609 will look at the rules of spare migration specified by POLICY lines in
2611 and then follow similar steps as above if a matching spare is found.
2614 The GROW mode is used for changing the size or shape of an active
2616 For this to work, the kernel must support the necessary change.
2617 Various types of growth are being added during 2.6 development.
2619 Currently the supported changes include
2621 change the "size" attribute for RAID1, RAID4, RAID5 and RAID6.
2623 increase or decrease the "raid\-devices" attribute of RAID0, RAID1, RAID4,
2626 change the chunk-size and layout of RAID0, RAID4, RAID5, RAID6 and RAID10.
2628 convert between RAID1 and RAID5, between RAID5 and RAID6, between
2629 RAID0, RAID4, and RAID5, and between RAID0 and RAID10 (in the near-2 mode).
2631 add a write-intent bitmap to any array which supports these bitmaps, or
2632 remove a write-intent bitmap from such an array.
2635 Using GROW on containers is currently supported only for Intel's IMSM
2636 container format. The number of devices in a container can be
2637 increased - which affects all arrays in the container - or an array
2638 in a container can be converted between levels where those levels are
2639 supported by the container, and the conversion is on of those listed
2640 above. Resizing arrays in an IMSM container with
2642 is not yet supported.
2644 Grow functionality (e.g. expand a number of raid devices) for Intel's
2645 IMSM container format has an experimental status. It is guarded by the
2646 .B MDADM_EXPERIMENTAL
2647 environment variable which must be set to '1' for a GROW command to
2649 This is for the following reasons:
2652 Intel's native IMSM check-pointing is not fully tested yet.
2653 This can causes IMSM incompatibility during the grow process: an array
2654 which is growing cannot roam between Microsoft Windows(R) and Linux
2658 Interrupting a grow operation is not recommended, because it
2659 has not been fully tested for Intel's IMSM container format yet.
2662 Note: Intel's native checkpointing doesn't use
2664 option and it is transparent for assembly feature.
2667 Normally when an array is built the "size" is taken from the smallest
2668 of the drives. If all the small drives in an arrays are, one at a
2669 time, removed and replaced with larger drives, then you could have an
2670 array of large drives with only a small amount used. In this
2671 situation, changing the "size" with "GROW" mode will allow the extra
2672 space to start being used. If the size is increased in this way, a
2673 "resync" process will start to make sure the new parts of the array
2676 Note that when an array changes size, any filesystem that may be
2677 stored in the array will not automatically grow or shrink to use or
2678 vacate the space. The
2679 filesystem will need to be explicitly told to use the extra space
2680 after growing, or to reduce its size
2682 to shrinking the array.
2684 Also the size of an array cannot be changed while it has an active
2685 bitmap. If an array has a bitmap, it must be removed before the size
2686 can be changed. Once the change is complete a new bitmap can be created.
2688 .SS RAID\-DEVICES CHANGES
2690 A RAID1 array can work with any number of devices from 1 upwards
2691 (though 1 is not very useful). There may be times which you want to
2692 increase or decrease the number of active devices. Note that this is
2693 different to hot-add or hot-remove which changes the number of
2696 When reducing the number of devices in a RAID1 array, the slots which
2697 are to be removed from the array must already be vacant. That is, the
2698 devices which were in those slots must be failed and removed.
2700 When the number of devices is increased, any hot spares that are
2701 present will be activated immediately.
2703 Changing the number of active devices in a RAID5 or RAID6 is much more
2704 effort. Every block in the array will need to be read and written
2705 back to a new location. From 2.6.17, the Linux Kernel is able to
2706 increase the number of devices in a RAID5 safely, including restarting
2707 an interrupted "reshape". From 2.6.31, the Linux Kernel is able to
2708 increase or decrease the number of devices in a RAID5 or RAID6.
2710 From 2.6.35, the Linux Kernel is able to convert a RAID0 in to a RAID4
2713 uses this functionality and the ability to add
2714 devices to a RAID4 to allow devices to be added to a RAID0. When
2715 requested to do this,
2717 will convert the RAID0 to a RAID4, add the necessary disks and make
2718 the reshape happen, and then convert the RAID4 back to RAID0.
2720 When decreasing the number of devices, the size of the array will also
2721 decrease. If there was data in the array, it could get destroyed and
2722 this is not reversible, so you should firstly shrink the filesystem on
2723 the array to fit within the new size. To help prevent accidents,
2725 requires that the size of the array be decreased first with
2726 .BR "mdadm --grow --array-size" .
2727 This is a reversible change which simply makes the end of the array
2728 inaccessible. The integrity of any data can then be checked before
2729 the non-reversible reduction in the number of devices is request.
2731 When relocating the first few stripes on a RAID5 or RAID6, it is not
2732 possible to keep the data on disk completely consistent and
2733 crash-proof. To provide the required safety, mdadm disables writes to
2734 the array while this "critical section" is reshaped, and takes a
2735 backup of the data that is in that section. For grows, this backup may be
2736 stored in any spare devices that the array has, however it can also be
2737 stored in a separate file specified with the
2739 option, and is required to be specified for shrinks, RAID level
2740 changes and layout changes. If this option is used, and the system
2741 does crash during the critical period, the same file must be passed to
2743 to restore the backup and reassemble the array. When shrinking rather
2744 than growing the array, the reshape is done from the end towards the
2745 beginning, so the "critical section" is at the end of the reshape.
2749 Changing the RAID level of any array happens instantaneously. However
2750 in the RAID5 to RAID6 case this requires a non-standard layout of the
2751 RAID6 data, and in the RAID6 to RAID5 case that non-standard layout is
2752 required before the change can be accomplished. So while the level
2753 change is instant, the accompanying layout change can take quite a
2756 is required. If the array is not simultaneously being grown or
2757 shrunk, so that the array size will remain the same - for example,
2758 reshaping a 3-drive RAID5 into a 4-drive RAID6 - the backup file will
2759 be used not just for a "cricital section" but throughout the reshape
2760 operation, as described below under LAYOUT CHANGES.
2762 .SS CHUNK-SIZE AND LAYOUT CHANGES
2764 Changing the chunk-size of layout without also changing the number of
2765 devices as the same time will involve re-writing all blocks in-place.
2766 To ensure against data loss in the case of a crash, a
2768 must be provided for these changes. Small sections of the array will
2769 be copied to the backup file while they are being rearranged. This
2770 means that all the data is copied twice, once to the backup and once
2771 to the new layout on the array, so this type of reshape will go very
2774 If the reshape is interrupted for any reason, this backup file must be
2776 .B "mdadm --assemble"
2777 so the array can be reassembled. Consequently the file cannot be
2778 stored on the device being reshaped.
2783 A write-intent bitmap can be added to, or removed from, an active
2784 array. Either internal bitmaps, or bitmaps stored in a separate file,
2785 can be added. Note that if you add a bitmap stored in a file which is
2786 in a filesystem that is on the RAID array being affected, the system
2787 will deadlock. The bitmap must be on a separate filesystem.
2789 .SH INCREMENTAL MODE
2793 .B mdadm \-\-incremental
2797 .RI [ optional-aliases-for-device ]
2800 .B mdadm \-\-incremental \-\-fail
2804 .B mdadm \-\-incremental \-\-rebuild\-map
2807 .B mdadm \-\-incremental \-\-run \-\-scan
2810 This mode is designed to be used in conjunction with a device
2811 discovery system. As devices are found in a system, they can be
2813 .B "mdadm \-\-incremental"
2814 to be conditionally added to an appropriate array.
2816 Conversely, it can also be used with the
2818 flag to do just the opposite and find whatever array a particular device
2819 is part of and remove the device from that array.
2821 If the device passed is a
2823 device created by a previous call to
2825 then rather than trying to add that device to an array, all the arrays
2826 described by the metadata of the container will be started.
2829 performs a number of tests to determine if the device is part of an
2830 array, and which array it should be part of. If an appropriate array
2831 is found, or can be created,
2833 adds the device to the array and conditionally starts the array.
2837 will normally only add devices to an array which were previously working
2838 (active or spare) parts of that array. The support for automatic
2839 inclusion of a new drive as a spare in some array requires
2840 a configuration through POLICY in config file.
2844 makes are as follow:
2846 Is the device permitted by
2848 That is, is it listed in a
2850 line in that file. If
2852 is absent then the default it to allow any device. Similarly if
2854 contains the special word
2856 then any device is allowed. Otherwise the device name given to
2858 or one of the aliases given, or an alias found in the filesystem,
2859 must match one of the names or patterns in a
2863 This is the only context where the aliases are used. They are
2864 usually provided by a
2870 Does the device have a valid md superblock? If a specific metadata
2871 version is requested with
2875 then only that style of metadata is accepted, otherwise
2877 finds any known version of metadata. If no
2879 metadata is found, the device may be still added to an array
2880 as a spare if POLICY allows.
2884 Does the metadata match an expected array?
2885 The metadata can match in two ways. Either there is an array listed
2888 which identifies the array (either by UUID, by name, by device list,
2889 or by minor-number), or the array was created with a
2895 or on the command line.
2898 is not able to positively identify the array as belonging to the
2899 current host, the device will be rejected.
2904 keeps a list of arrays that it has partially assembled in
2906 If no array exists which matches
2907 the metadata on the new device,
2909 must choose a device name and unit number. It does this based on any
2912 or any name information stored in the metadata. If this name
2913 suggests a unit number, that number will be used, otherwise a free
2914 unit number will be chosen. Normally
2916 will prefer to create a partitionable array, however if the
2920 suggests that a non-partitionable array is preferred, that will be
2923 If the array is not found in the config file and its metadata does not
2924 identify it as belonging to the "homehost", then
2926 will choose a name for the array which is certain not to conflict with
2927 any array which does belong to this host. It does this be adding an
2928 underscore and a small number to the name preferred by the metadata.
2930 Once an appropriate array is found or created and the device is added,
2932 must decide if the array is ready to be started. It will
2933 normally compare the number of available (non-spare) devices to the
2934 number of devices that the metadata suggests need to be active. If
2935 there are at least that many, the array will be started. This means
2936 that if any devices are missing the array will not be restarted.
2942 in which case the array will be run as soon as there are enough
2943 devices present for the data to be accessible. For a RAID1, that
2944 means one device will start the array. For a clean RAID5, the array
2945 will be started as soon as all but one drive is present.
2947 Note that neither of these approaches is really ideal. If it can
2948 be known that all device discovery has completed, then
2952 can be run which will try to start all arrays that are being
2953 incrementally assembled. They are started in "read-auto" mode in
2954 which they are read-only until the first write request. This means
2955 that no metadata updates are made and no attempt at resync or recovery
2956 happens. Further devices that are found before the first write can
2957 still be added safely.
2960 This section describes environment variables that affect how mdadm
2965 Setting this value to 1 will prevent mdadm from automatically launching
2966 mdmon. This variable is intended primarily for debugging mdadm/mdmon.
2972 does not create any device nodes in /dev, but leaves that task to
2976 appears not to be configured, or if this environment variable is set
2979 will create and devices that are needed.
2982 .B MDADM_NO_SYSTEMCTL
2987 is in use it will normally request
2989 to start various background tasks (particularly
2991 rather than forking and running them in the background. This can be
2992 suppressed by setting
2993 .BR MDADM_NO_SYSTEMCTL=1 .
2997 A key value of IMSM metadata is that it allows interoperability with
2998 boot ROMs on Intel platforms, and with other major operating systems.
3001 will only allow an IMSM array to be created or modified if detects
3002 that it is running on an Intel platform which supports IMSM, and
3003 supports the particular configuration of IMSM that is being requested
3004 (some functionality requires newer OROM support).
3006 These checks can be suppressed by setting IMSM_NO_PLATFORM=1 in the
3007 environment. This can be useful for testing or for disaster
3008 recovery. You should be aware that interoperability may be
3009 compromised by setting this value.
3012 .B MDADM_GROW_ALLOW_OLD
3013 If an array is stopped while it is performing a reshape and that
3014 reshape was making use of a backup file, then when the array is
3017 will sometimes complain that the backup file is too old. If this
3018 happens and you are certain it is the right backup file, you can
3019 over-ride this check by setting
3020 .B MDADM_GROW_ALLOW_OLD=1
3025 Any string given in this variable is added to the start of the
3027 line in the config file, or treated as the whole
3029 line if none is given. It can be used to disable certain metadata
3032 is called from a boot script. For example
3034 .B " export MDADM_CONF_AUTO='-ddf -imsm'
3038 does not automatically assemble any DDF or
3039 IMSM arrays that are found. This can be useful on systems configured
3040 to manage such arrays with
3046 .B " mdadm \-\-query /dev/name-of-device"
3048 This will find out if a given device is a RAID array, or is part of
3049 one, and will provide brief information about the device.
3051 .B " mdadm \-\-assemble \-\-scan"
3053 This will assemble and start all arrays listed in the standard config
3054 file. This command will typically go in a system startup file.
3056 .B " mdadm \-\-stop \-\-scan"
3058 This will shut down all arrays that can be shut down (i.e. are not
3059 currently in use). This will typically go in a system shutdown script.
3061 .B " mdadm \-\-follow \-\-scan \-\-delay=120"
3063 If (and only if) there is an Email address or program given in the
3064 standard config file, then
3065 monitor the status of all arrays listed in that file by
3066 polling them ever 2 minutes.
3068 .B " mdadm \-\-create /dev/md0 \-\-level=1 \-\-raid\-devices=2 /dev/hd[ac]1"
3070 Create /dev/md0 as a RAID1 array consisting of /dev/hda1 and /dev/hdc1.
3073 .B " echo 'DEVICE /dev/hd*[0\-9] /dev/sd*[0\-9]' > mdadm.conf"
3075 .B " mdadm \-\-detail \-\-scan >> mdadm.conf"
3077 This will create a prototype config file that describes currently
3078 active arrays that are known to be made from partitions of IDE or SCSI drives.
3079 This file should be reviewed before being used as it may
3080 contain unwanted detail.
3082 .B " echo 'DEVICE /dev/hd[a\-z] /dev/sd*[a\-z]' > mdadm.conf"
3084 .B " mdadm \-\-examine \-\-scan \-\-config=mdadm.conf >> mdadm.conf"
3086 This will find arrays which could be assembled from existing IDE and
3087 SCSI whole drives (not partitions), and store the information in the
3088 format of a config file.
3089 This file is very likely to contain unwanted detail, particularly
3092 entries. It should be reviewed and edited before being used as an
3095 .B " mdadm \-\-examine \-\-brief \-\-scan \-\-config=partitions"
3097 .B " mdadm \-Ebsc partitions"
3099 Create a list of devices by reading
3100 .BR /proc/partitions ,
3101 scan these for RAID superblocks, and printout a brief listing of all
3104 .B " mdadm \-Ac partitions \-m 0 /dev/md0"
3106 Scan all partitions and devices listed in
3107 .BR /proc/partitions
3110 out of all such devices with a RAID superblock with a minor number of 0.
3112 .B " mdadm \-\-monitor \-\-scan \-\-daemonise > /run/mdadm/mon.pid"
3114 If config file contains a mail address or alert program, run mdadm in
3115 the background in monitor mode monitoring all md devices. Also write
3116 pid of mdadm daemon to
3117 .BR /run/mdadm/mon.pid .
3119 .B " mdadm \-Iq /dev/somedevice"
3121 Try to incorporate newly discovered device into some array as
3124 .B " mdadm \-\-incremental \-\-rebuild\-map \-\-run \-\-scan"
3126 Rebuild the array map from any current arrays, and then start any that
3129 .B " mdadm /dev/md4 --fail detached --remove detached"
3131 Any devices which are components of /dev/md4 will be marked as faulty
3132 and then remove from the array.
3134 .B " mdadm --grow /dev/md4 --level=6 --backup-file=/root/backup-md4"
3138 which is currently a RAID5 array will be converted to RAID6. There
3139 should normally already be a spare drive attached to the array as a
3140 RAID6 needs one more drive than a matching RAID5.
3142 .B " mdadm --create /dev/md/ddf --metadata=ddf --raid-disks 6 /dev/sd[a-f]"
3144 Create a DDF array over 6 devices.
3146 .B " mdadm --create /dev/md/home -n3 -l5 -z 30000000 /dev/md/ddf"
3148 Create a RAID5 array over any 3 devices in the given DDF set. Use
3149 only 30 gigabytes of each device.
3151 .B " mdadm -A /dev/md/ddf1 /dev/sd[a-f]"
3153 Assemble a pre-exist ddf array.
3155 .B " mdadm -I /dev/md/ddf1"
3157 Assemble all arrays contained in the ddf array, assigning names as
3160 .B " mdadm \-\-create \-\-help"
3162 Provide help about the Create mode.
3164 .B " mdadm \-\-config \-\-help"
3166 Provide help about the format of the config file.
3168 .B " mdadm \-\-help"
3170 Provide general help.
3180 lists all active md devices with information about them.
3182 uses this to find arrays when
3184 is given in Misc mode, and to monitor array reconstruction
3189 The config file lists which devices may be scanned to see if
3190 they contain MD super block, and gives identifying information
3191 (e.g. UUID) about known MD arrays. See
3195 .SS /etc/mdadm.conf.d
3197 A directory containing configuration files which are read in lexical
3203 mode is used, this file gets a list of arrays currently being created.
3208 understand two sorts of names for array devices.
3210 The first is the so-called 'standard' format name, which matches the
3211 names used by the kernel and which appear in
3214 The second sort can be freely chosen, but must reside in
3216 When giving a device name to
3218 to create or assemble an array, either full path name such as
3222 can be given, or just the suffix of the second sort of name, such as
3228 chooses device names during auto-assembly or incremental assembly, it
3229 will sometimes add a small sequence number to the end of the name to
3230 avoid conflicted between multiple arrays that have the same name. If
3232 can reasonably determine that the array really is meant for this host,
3233 either by a hostname in the metadata, or by the presence of the array
3236 then it will leave off the suffix if possible.
3237 Also if the homehost is specified as
3240 will only use a suffix if a different array of the same name already
3241 exists or is listed in the config file.
3243 The standard names for non-partitioned arrays (the only sort of md
3244 array available in 2.4 and earlier) are of the form
3248 where NN is a number.
3249 The standard names for partitionable arrays (as available from 2.6
3250 onwards) are of the form:
3254 Partition numbers should be indicated by adding "pMM" to these, thus "/dev/md/d1p2".
3256 From kernel version 2.6.28 the "non-partitioned array" can actually
3257 be partitioned. So the "md_d\fBNN\fP"
3258 names are no longer needed, and
3259 partitions such as "/dev/md\fBNN\fPp\fBXX\fP"
3262 From kernel version 2.6.29 standard names can be non-numeric following
3269 is any string. These names are supported by
3271 since version 3.3 provided they are enabled in
3276 was previously known as
3280 For further information on mdadm usage, MD and the various levels of
3283 .B http://raid.wiki.kernel.org/
3285 (based upon Jakob \(/Ostergaard's Software\-RAID.HOWTO)
3287 The latest version of
3289 should always be available from
3291 .B http://www.kernel.org/pub/linux/utils/raid/mdadm/
projects / thirdparty / mdadm.git / blob