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" .
400 needs to print the name for a device it normally finds the name in
402 which refers to the device and is shortest. When a path component is
406 will prefer a longer name if it contains that component. For example
407 .B \-\-prefer=by-uuid
408 will prefer a name in a subdirectory of
413 This functionality is currently only provided by
418 .SH For create, build, or grow:
421 .BR \-n ", " \-\-raid\-devices=
422 Specify the number of active devices in the array. This, plus the
423 number of spare devices (see below) must equal the number of
425 (including "\fBmissing\fP" devices)
426 that are listed on the command line for
428 Setting a value of 1 is probably
429 a mistake and so requires that
431 be specified first. A value of 1 will then be allowed for linear,
432 multipath, RAID0 and RAID1. It is never allowed for RAID4, RAID5 or RAID6.
434 This number can only be changed using
436 for RAID1, RAID4, RAID5 and RAID6 arrays, and only on kernels which provide
437 the necessary support.
440 .BR \-x ", " \-\-spare\-devices=
441 Specify the number of spare (eXtra) devices in the initial array.
442 Spares can also be added
443 and removed later. The number of component devices listed
444 on the command line must equal the number of RAID devices plus the
445 number of spare devices.
448 .BR \-z ", " \-\-size=
449 Amount (in Kibibytes) of space to use from each drive in RAID levels 1/4/5/6.
450 This must be a multiple of the chunk size, and must leave about 128Kb
451 of space at the end of the drive for the RAID superblock.
452 If this is not specified
453 (as it normally is not) the smallest drive (or partition) sets the
454 size, though if there is a variance among the drives of greater than 1%, a warning is
457 A suffix of 'M' or 'G' can be given to indicate Megabytes or
458 Gigabytes respectively.
460 Sometimes a replacement drive can be a little smaller than the
461 original drives though this should be minimised by IDEMA standards.
462 Such a replacement drive will be rejected by
464 To guard against this it can be useful to set the initial size
465 slightly smaller than the smaller device with the aim that it will
466 still be larger than any replacement.
468 This value can be set with
470 for RAID level 1/4/5/6 though
472 based arrays such as those with IMSM metadata may not be able to
474 If the array was created with a size smaller than the currently
475 active drives, the extra space can be accessed using
477 The size can be given as
479 which means to choose the largest size that fits on all current drives.
481 Before reducing the size of the array (with
482 .BR "\-\-grow \-\-size=" )
483 you should make sure that space isn't needed. If the device holds a
484 filesystem, you would need to resize the filesystem to use less space.
486 After reducing the array size you should check that the data stored in
487 the device is still available. If the device holds a filesystem, then
488 an 'fsck' of the filesystem is a minimum requirement. If there are
489 problems the array can be made bigger again with no loss with another
490 .B "\-\-grow \-\-size="
493 This value cannot be used when creating a
495 such as with DDF and IMSM metadata, though it perfectly valid when
496 creating an array inside a container.
499 .BR \-Z ", " \-\-array\-size=
500 This is only meaningful with
502 and its effect is not persistent: when the array is stopped and
503 restarted the default array size will be restored.
505 Setting the array-size causes the array to appear smaller to programs
506 that access the data. This is particularly needed before reshaping an
507 array so that it will be smaller. As the reshape is not reversible,
508 but setting the size with
510 is, it is required that the array size is reduced as appropriate
511 before the number of devices in the array is reduced.
513 Before reducing the size of the array you should make sure that space
514 isn't needed. If the device holds a filesystem, you would need to
515 resize the filesystem to use less space.
517 After reducing the array size you should check that the data stored in
518 the device is still available. If the device holds a filesystem, then
519 an 'fsck' of the filesystem is a minimum requirement. If there are
520 problems the array can be made bigger again with no loss with another
521 .B "\-\-grow \-\-array\-size="
524 A suffix of 'M' or 'G' can be given to indicate Megabytes or
525 Gigabytes respectively.
528 restores the apparent size of the array to be whatever the real
529 amount of available space is.
532 .BR \-c ", " \-\-chunk=
533 Specify chunk size of kibibytes. The default when creating an
534 array is 512KB. To ensure compatibility with earlier versions, the
535 default when building an array with no persistent metadata is 64KB.
536 This is only meaningful for RAID0, RAID4, RAID5, RAID6, and RAID10.
538 RAID4, RAID5, RAID6, and RAID10 require the chunk size to be a power
539 of 2. In any case it must be a multiple of 4KB.
541 A suffix of 'M' or 'G' can be given to indicate Megabytes or
542 Gigabytes respectively.
546 Specify rounding factor for a Linear array. The size of each
547 component will be rounded down to a multiple of this size.
548 This is a synonym for
550 but highlights the different meaning for Linear as compared to other
551 RAID levels. The default is 64K if a kernel earlier than 2.6.16 is in
552 use, and is 0K (i.e. no rounding) in later kernels.
555 .BR \-l ", " \-\-level=
556 Set RAID level. When used with
558 options are: linear, raid0, 0, stripe, raid1, 1, mirror, raid4, 4,
559 raid5, 5, raid6, 6, raid10, 10, multipath, mp, faulty, container.
560 Obviously some of these are synonymous.
564 metadata type is requested, only the
566 level is permitted, and it does not need to be explicitly given.
570 only linear, stripe, raid0, 0, raid1, multipath, mp, and faulty are valid.
574 to change the RAID level in some cases. See LEVEL CHANGES below.
577 .BR \-p ", " \-\-layout=
578 This option configures the fine details of data layout for RAID5, RAID6,
579 and RAID10 arrays, and controls the failure modes for
582 The layout of the RAID5 parity block can be one of
583 .BR left\-asymmetric ,
584 .BR left\-symmetric ,
585 .BR right\-asymmetric ,
586 .BR right\-symmetric ,
587 .BR la ", " ra ", " ls ", " rs .
589 .BR left\-symmetric .
591 It is also possible to cause RAID5 to use a RAID4-like layout by
597 Finally for RAID5 there are DDF\-compatible layouts,
598 .BR ddf\-zero\-restart ,
599 .BR ddf\-N\-restart ,
601 .BR ddf\-N\-continue .
603 These same layouts are available for RAID6. There are also 4 layouts
604 that will provide an intermediate stage for converting between RAID5
605 and RAID6. These provide a layout which is identical to the
606 corresponding RAID5 layout on the first N\-1 devices, and has the 'Q'
607 syndrome (the second 'parity' block used by RAID6) on the last device.
609 .BR left\-symmetric\-6 ,
610 .BR right\-symmetric\-6 ,
611 .BR left\-asymmetric\-6 ,
612 .BR right\-asymmetric\-6 ,
614 .BR parity\-first\-6 .
616 When setting the failure mode for level
619 .BR write\-transient ", " wt ,
620 .BR read\-transient ", " rt ,
621 .BR write\-persistent ", " wp ,
622 .BR read\-persistent ", " rp ,
624 .BR read\-fixable ", " rf ,
625 .BR clear ", " flush ", " none .
627 Each failure mode can be followed by a number, which is used as a period
628 between fault generation. Without a number, the fault is generated
629 once on the first relevant request. With a number, the fault will be
630 generated after that many requests, and will continue to be generated
631 every time the period elapses.
633 Multiple failure modes can be current simultaneously by using the
635 option to set subsequent failure modes.
637 "clear" or "none" will remove any pending or periodic failure modes,
638 and "flush" will clear any persistent faults.
640 Finally, the layout options for RAID10 are one of 'n', 'o' or 'f' followed
641 by a small number. The default is 'n2'. The supported options are:
644 signals 'near' copies. Multiple copies of one data block are at
645 similar offsets in different devices.
648 signals 'offset' copies. Rather than the chunks being duplicated
649 within a stripe, whole stripes are duplicated but are rotated by one
650 device so duplicate blocks are on different devices. Thus subsequent
651 copies of a block are in the next drive, and are one chunk further
656 (multiple copies have very different offsets).
657 See md(4) for more detail about 'near', 'offset', and 'far'.
659 The number is the number of copies of each datablock. 2 is normal, 3
660 can be useful. This number can be at most equal to the number of
661 devices in the array. It does not need to divide evenly into that
662 number (e.g. it is perfectly legal to have an 'n2' layout for an array
663 with an odd number of devices).
665 When an array is converted between RAID5 and RAID6 an intermediate
666 RAID6 layout is used in which the second parity block (Q) is always on
667 the last device. To convert a RAID5 to RAID6 and leave it in this new
668 layout (which does not require re-striping) use
669 .BR \-\-layout=preserve .
670 This will try to avoid any restriping.
672 The converse of this is
673 .B \-\-layout=normalise
674 which will change a non-standard RAID6 layout into a more standard
681 (thus explaining the p of
685 .BR \-b ", " \-\-bitmap=
686 Specify a file to store a write-intent bitmap in. The file should not
689 is also given. The same file should be provided
690 when assembling the array. If the word
692 is given, then the bitmap is stored with the metadata on the array,
693 and so is replicated on all devices. If the word
697 mode, then any bitmap that is present is removed. If the word
699 is given, the array is created for a clustered environment. One bitmap
700 is created for each node as defined by the
702 parameter and are stored internally.
704 To help catch typing errors, the filename must contain at least one
705 slash ('/') if it is a real file (not 'internal' or 'none').
707 Note: external bitmaps are only known to work on ext2 and ext3.
708 Storing bitmap files on other filesystems may result in serious problems.
710 When creating an array on devices which are 100G or larger,
712 automatically adds an internal bitmap as it will usually be
713 beneficial. This can be suppressed with
714 .B "\-\-bitmap=none".
717 .BR \-\-bitmap\-chunk=
718 Set the chunksize of the bitmap. Each bit corresponds to that many
719 Kilobytes of storage.
720 When using a file based bitmap, the default is to use the smallest
721 size that is at-least 4 and requires no more than 2^21 chunks.
724 bitmap, the chunksize defaults to 64Meg, or larger if necessary to
725 fit the bitmap into the available space.
727 A suffix of 'M' or 'G' can be given to indicate Megabytes or
728 Gigabytes respectively.
731 .BR \-W ", " \-\-write\-mostly
732 subsequent devices listed in a
737 command will be flagged as 'write-mostly'. This is valid for RAID1
738 only and means that the 'md' driver will avoid reading from these
739 devices if at all possible. This can be useful if mirroring over a
743 .BR \-\-write\-behind=
744 Specify that write-behind mode should be enabled (valid for RAID1
745 only). If an argument is specified, it will set the maximum number
746 of outstanding writes allowed. The default value is 256.
747 A write-intent bitmap is required in order to use write-behind
748 mode, and write-behind is only attempted on drives marked as
752 .BR \-\-assume\-clean
755 that the array pre-existed and is known to be clean. It can be useful
756 when trying to recover from a major failure as you can be sure that no
757 data will be affected unless you actually write to the array. It can
758 also be used when creating a RAID1 or RAID10 if you want to avoid the
759 initial resync, however this practice \(em while normally safe \(em is not
760 recommended. Use this only if you really know what you are doing.
762 When the devices that will be part of a new array were filled
763 with zeros before creation the operator knows the array is
764 actually clean. If that is the case, such as after running
765 badblocks, this argument can be used to tell mdadm the
766 facts the operator knows.
768 When an array is resized to a larger size with
769 .B "\-\-grow \-\-size="
770 the new space is normally resynced in that same way that the whole
771 array is resynced at creation. From Linux version 3.0,
773 can be used with that command to avoid the automatic resync.
776 .BR \-\-backup\-file=
779 is used to increase the number of raid-devices in a RAID5 or RAID6 if
780 there are no spare devices available, or to shrink, change RAID level
781 or layout. See the GROW MODE section below on RAID\-DEVICES CHANGES.
782 The file must be stored on a separate device, not on the RAID array
787 Arrays with 1.x metadata can leave a gap between the start of the
788 device and the start of array data. This gap can be used for various
789 metadata. The start of data is known as the
791 Normally an appropriate data offset is computed automatically.
792 However it can be useful to set it explicitly such as when re-creating
793 an array which was originally created using a different version of
795 which computed a different offset.
797 Setting the offset explicitly over-rides the default. The value given
798 is in Kilobytes unless an 'M' or 'G' suffix is given.
802 can also be used with
804 for some RAID levels (initially on RAID10). This allows the
805 data\-offset to be changed as part of the reshape process. When the
806 data offset is changed, no backup file is required as the difference
807 in offsets is used to provide the same functionality.
809 When the new offset is earlier than the old offset, the number of
810 devices in the array cannot shrink. When it is after the old offset,
811 the number of devices in the array cannot increase.
813 When creating an array,
817 In the case each member device is expected to have a offset appended
818 to the name, separated by a colon. This makes it possible to recreate
819 exactly an array which has varying data offsets (as can happen when
820 different versions of
822 are used to add different devices).
826 This option is complementary to the
827 .B \-\-freeze-reshape
828 option for assembly. It is needed when
830 operation is interrupted and it is not restarted automatically due to
831 .B \-\-freeze-reshape
832 usage during array assembly. This option is used together with
836 ) command and device for a pending reshape to be continued.
837 All parameters required for reshape continuation will be read from array metadata.
841 .BR \-\-backup\-file=
842 option to be set, continuation option will require to have exactly the same
843 backup file given as well.
845 Any other parameter passed together with
847 option will be ignored.
850 .BR \-N ", " \-\-name=
853 for the array. This is currently only effective when creating an
854 array with a version-1 superblock, or an array in a DDF container.
855 The name is a simple textual string that can be used to identify array
856 components when assembling. If name is needed but not specified, it
857 is taken from the basename of the device that is being created.
869 run the array, even if some of the components
870 appear to be active in another array or filesystem. Normally
872 will ask for confirmation before including such components in an
873 array. This option causes that question to be suppressed.
876 .BR \-f ", " \-\-force
879 accept the geometry and layout specified without question. Normally
881 will not allow creation of an array with only one device, and will try
882 to create a RAID5 array with one missing drive (as this makes the
883 initial resync work faster). With
886 will not try to be so clever.
889 .BR \-o ", " \-\-readonly
892 rather than read-write as normal. No writes will be allowed to the
893 array, and no resync, recovery, or reshape will be started.
896 .BR \-a ", " "\-\-auto{=yes,md,mdp,part,p}{NN}"
897 Instruct mdadm how to create the device file if needed, possibly allocating
898 an unused minor number. "md" causes a non-partitionable array
899 to be used (though since Linux 2.6.28, these array devices are in fact
900 partitionable). "mdp", "part" or "p" causes a partitionable array (2.6 and
901 later) to be used. "yes" requires the named md device to have
902 a 'standard' format, and the type and minor number will be determined
903 from this. With mdadm 3.0, device creation is normally left up to
905 so this option is unlikely to be needed.
906 See DEVICE NAMES below.
908 The argument can also come immediately after
913 is not given on the command line or in the config file, then
919 is also given, then any
921 entries in the config file will override the
923 instruction given on the command line.
925 For partitionable arrays,
927 will create the device file for the whole array and for the first 4
928 partitions. A different number of partitions can be specified at the
929 end of this option (e.g.
931 If the device name ends with a digit, the partition names add a 'p',
933 .IR /dev/md/home1p3 .
934 If there is no trailing digit, then the partition names just have a
936 .IR /dev/md/scratch3 .
938 If the md device name is in a 'standard' format as described in DEVICE
939 NAMES, then it will be created, if necessary, with the appropriate
940 device number based on that name. If the device name is not in one of these
941 formats, then a unused device number will be allocated. The device
942 number will be considered unused if there is no active array for that
943 number, and there is no entry in /dev for that number and with a
944 non-standard name. Names that are not in 'standard' format are only
945 allowed in "/dev/md/".
947 This is meaningful with
953 .BR \-a ", " "\-\-add"
954 This option can be used in Grow mode in two cases.
956 If the target array is a Linear array, then
958 can be used to add one or more devices to the array. They
959 are simply catenated on to the end of the array. Once added, the
960 devices cannot be removed.
964 option is being used to increase the number of devices in an array,
967 can be used to add some extra devices to be included in the array.
968 In most cases this is not needed as the extra devices can be added as
969 spares first, and then the number of raid-disks can be changed.
970 However for RAID0, it is not possible to add spares. So to increase
971 the number of devices in a RAID0, it is necessary to set the new
972 number of devices, and to add the new devices, in the same command.
976 Only works when the array is for clustered environment. It specifies
977 the maximum number of nodes in the cluster that will use this device
978 simultaneously. If not specified, this defaults to 4.
983 .BR \-u ", " \-\-uuid=
984 uuid of array to assemble. Devices which don't have this uuid are
988 .BR \-m ", " \-\-super\-minor=
989 Minor number of device that array was created for. Devices which
990 don't have this minor number are excluded. If you create an array as
991 /dev/md1, then all superblocks will contain the minor number 1, even if
992 the array is later assembled as /dev/md2.
994 Giving the literal word "dev" for
998 to use the minor number of the md device that is being assembled.
1001 .B \-\-super\-minor=dev
1002 will look for super blocks with a minor number of 0.
1005 is only relevant for v0.90 metadata, and should not normally be used.
1011 .BR \-N ", " \-\-name=
1012 Specify the name of the array to assemble. This must be the name
1013 that was specified when creating the array. It must either match
1014 the name stored in the superblock exactly, or it must match
1017 prefixed to the start of the given name.
1020 .BR \-f ", " \-\-force
1021 Assemble the array even if the metadata on some devices appears to be
1024 cannot find enough working devices to start the array, but can find
1025 some devices that are recorded as having failed, then it will mark
1026 those devices as working so that the array can be started.
1027 An array which requires
1029 to be started may contain data corruption. Use it carefully.
1032 .BR \-R ", " \-\-run
1033 Attempt to start the array even if fewer drives were given than were
1034 present last time the array was active. Normally if not all the
1035 expected drives are found and
1037 is not used, then the array will be assembled but not started.
1040 an attempt will be made to start it anyway.
1044 This is the reverse of
1046 in that it inhibits the startup of array unless all expected drives
1047 are present. This is only needed with
1049 and can be used if the physical connections to devices are
1050 not as reliable as you would like.
1053 .BR \-a ", " "\-\-auto{=no,yes,md,mdp,part}"
1054 See this option under Create and Build options.
1057 .BR \-b ", " \-\-bitmap=
1058 Specify the bitmap file that was given when the array was created. If
1061 bitmap, there is no need to specify this when assembling the array.
1064 .BR \-\-backup\-file=
1067 was used while reshaping an array (e.g. changing number of devices or
1068 chunk size) and the system crashed during the critical section, then the same
1070 must be presented to
1072 to allow possibly corrupted data to be restored, and the reshape
1076 .BR \-\-invalid\-backup
1077 If the file needed for the above option is not available for any
1078 reason an empty file can be given together with this option to
1079 indicate that the backup file is invalid. In this case the data that
1080 was being rearranged at the time of the crash could be irrecoverably
1081 lost, but the rest of the array may still be recoverable. This option
1082 should only be used as a last resort if there is no way to recover the
1087 .BR \-U ", " \-\-update=
1088 Update the superblock on each device while assembling the array. The
1089 argument given to this flag can be one of
1107 option will adjust the superblock of an array what was created on a Sparc
1108 machine running a patched 2.2 Linux kernel. This kernel got the
1109 alignment of part of the superblock wrong. You can use the
1110 .B "\-\-examine \-\-sparc2.2"
1113 to see what effect this would have.
1117 option will update the
1118 .B "preferred minor"
1119 field on each superblock to match the minor number of the array being
1121 This can be useful if
1123 reports a different "Preferred Minor" to
1125 In some cases this update will be performed automatically
1126 by the kernel driver. In particular the update happens automatically
1127 at the first write to an array with redundancy (RAID level 1 or
1128 greater) on a 2.6 (or later) kernel.
1132 option will change the uuid of the array. If a UUID is given with the
1134 option that UUID will be used as a new UUID and will
1136 be used to help identify the devices in the array.
1139 is given, a random UUID is chosen.
1143 option will change the
1145 of the array as stored in the superblock. This is only supported for
1146 version-1 superblocks.
1150 option will change the
1152 as recorded in the superblock. For version-0 superblocks, this is the
1153 same as updating the UUID.
1154 For version-1 superblocks, this involves updating the name.
1158 option will cause the array to be marked
1160 meaning that any redundancy in the array (e.g. parity for RAID5,
1161 copies for RAID1) may be incorrect. This will cause the RAID system
1162 to perform a "resync" pass to make sure that all redundant information
1167 option allows arrays to be moved between machines with different
1169 When assembling such an array for the first time after a move, giving
1170 .B "\-\-update=byteorder"
1173 to expect superblocks to have their byteorder reversed, and will
1174 correct that order before assembling the array. This is only valid
1175 with original (Version 0.90) superblocks.
1179 option will correct the summaries in the superblock. That is the
1180 counts of total, working, active, failed, and spare devices.
1184 option will rarely be of use. It applies to version 1.1 and 1.2 metadata
1185 only (where the metadata is at the start of the device) and is only
1186 useful when the component device has changed size (typically become
1187 larger). The version 1 metadata records the amount of the device that
1188 can be used to store data, so if a device in a version 1.1 or 1.2
1189 array becomes larger, the metadata will still be visible, but the
1190 extra space will not. In this case it might be useful to assemble the
1192 .BR \-\-update=devicesize .
1195 to determine the maximum usable amount of space on each device and
1196 update the relevant field in the metadata.
1200 option only works on v0.90 metadata arrays and will convert them to
1201 v1.0 metadata. The array must not be dirty (i.e. it must not need a
1202 sync) and it must not have a write-intent bitmap.
1204 The old metadata will remain on the devices, but will appear older
1205 than the new metadata and so will usually be ignored. The old metadata
1206 (or indeed the new metadata) can be removed by giving the appropriate
1209 .BR \-\-zero\-superblock .
1213 option can be used when an array has an internal bitmap which is
1214 corrupt in some way so that assembling the array normally fails. It
1215 will cause any internal bitmap to be ignored.
1219 option will reserve space in each device for a bad block list. This
1220 will be 4K in size and positioned near the end of any free space
1221 between the superblock and the data.
1225 option will cause any reservation of space for a bad block list to be
1226 removed. If the bad block list contains entries, this will fail, as
1227 removing the list could cause data corruption.
1230 .BR \-\-freeze\-reshape
1231 Option is intended to be used in start-up scripts during initrd boot phase.
1232 When array under reshape is assembled during initrd phase, this option
1233 stops reshape after reshape critical section is being restored. This happens
1234 before file system pivot operation and avoids loss of file system context.
1235 Losing file system context would cause reshape to be broken.
1237 Reshape can be continued later using the
1239 option for the grow command.
1241 .SH For Manage mode:
1244 .BR \-t ", " \-\-test
1245 Unless a more serious error occurred,
1247 will exit with a status of 2 if no changes were made to the array and
1248 0 if at least one change was made.
1249 This can be useful when an indirect specifier such as
1254 is used in requesting an operation on the array.
1256 will report failure if these specifiers didn't find any match.
1259 .BR \-a ", " \-\-add
1260 hot-add listed devices.
1261 If a device appears to have recently been part of the array
1262 (possibly it failed or was removed) the device is re\-added as described
1264 If that fails or the device was never part of the array, the device is
1265 added as a hot-spare.
1266 If the array is degraded, it will immediately start to rebuild data
1269 Note that this and the following options are only meaningful on array
1270 with redundancy. They don't apply to RAID0 or Linear.
1274 re\-add a device that was previously removed from an array.
1275 If the metadata on the device reports that it is a member of the
1276 array, and the slot that it used is still vacant, then the device will
1277 be added back to the array in the same position. This will normally
1278 cause the data for that device to be recovered. However based on the
1279 event count on the device, the recovery may only require sections that
1280 are flagged a write-intent bitmap to be recovered or may not require
1281 any recovery at all.
1283 When used on an array that has no metadata (i.e. it was built with
1285 it will be assumed that bitmap-based recovery is enough to make the
1286 device fully consistent with the array.
1288 When used with v1.x metadata,
1290 can be accompanied by
1291 .BR \-\-update=devicesize ,
1292 .BR \-\-update=bbl ", or"
1293 .BR \-\-update=no\-bbl .
1294 See the description of these option when used in Assemble mode for an
1295 explanation of their use.
1297 If the device name given is
1301 will try to find any device that looks like it should be
1302 part of the array but isn't and will try to re\-add all such devices.
1304 If the device name given is
1308 will find all devices in the array that are marked
1310 remove them and attempt to immediately re\-add them. This can be
1311 useful if you are certain that the reason for failure has been
1316 Add a device as a spare. This is similar to
1318 except that it does not attempt
1320 first. The device will be added as a spare even if it looks like it
1321 could be an recent member of the array.
1324 .BR \-r ", " \-\-remove
1325 remove listed devices. They must not be active. i.e. they should
1326 be failed or spare devices.
1328 As well as the name of a device file
1338 The first causes all failed device to be removed. The second causes
1339 any device which is no longer connected to the system (i.e an 'open'
1343 The third will remove a set as describe below under
1347 .BR \-f ", " \-\-fail
1348 Mark listed devices as faulty.
1349 As well as the name of a device file, the word
1353 can be given. The former will cause any device that has been detached from
1354 the system to be marked as failed. It can then be removed.
1356 For RAID10 arrays where the number of copies evenly divides the number
1357 of devices, the devices can be conceptually divided into sets where
1358 each set contains a single complete copy of the data on the array.
1359 Sometimes a RAID10 array will be configured so that these sets are on
1360 separate controllers. In this case all the devices in one set can be
1361 failed by giving a name like
1367 The appropriate set names are reported by
1377 Mark listed devices as requiring replacement. As soon as a spare is
1378 available, it will be rebuilt and will replace the marked device.
1379 This is similar to marking a device as faulty, but the device remains
1380 in service during the recovery process to increase resilience against
1381 multiple failures. When the replacement process finishes, the
1382 replaced device will be marked as faulty.
1386 This can follow a list of
1388 devices. The devices listed after
1390 will be preferentially used to replace the devices listed after
1392 These device must already be spare devices in the array.
1395 .BR \-\-write\-mostly
1396 Subsequent devices that are added or re\-added will have the 'write-mostly'
1397 flag set. This is only valid for RAID1 and means that the 'md' driver
1398 will avoid reading from these devices if possible.
1401 Subsequent devices that are added or re\-added will have the 'write-mostly'
1405 Each of these options requires that the first device listed is the array
1406 to be acted upon, and the remainder are component devices to be added,
1407 removed, marked as faulty, etc. Several different operations can be
1408 specified for different devices, e.g.
1410 mdadm /dev/md0 \-\-add /dev/sda1 \-\-fail /dev/sdb1 \-\-remove /dev/sdb1
1412 Each operation applies to all devices listed until the next
1415 If an array is using a write-intent bitmap, then devices which have
1416 been removed can be re\-added in a way that avoids a full
1417 reconstruction but instead just updates the blocks that have changed
1418 since the device was removed. For arrays with persistent metadata
1419 (superblocks) this is done automatically. For arrays created with
1421 mdadm needs to be told that this device we removed recently with
1424 Devices can only be removed from an array if they are not in active
1425 use, i.e. that must be spares or failed devices. To remove an active
1426 device, it must first be marked as
1432 .BR \-Q ", " \-\-query
1433 Examine a device to see
1434 (1) if it is an md device and (2) if it is a component of an md
1436 Information about what is discovered is presented.
1439 .BR \-D ", " \-\-detail
1440 Print details of one or more md devices.
1443 .BR \-\-detail\-platform
1444 Print details of the platform's RAID capabilities (firmware / hardware
1445 topology) for a given metadata format. If used without argument, mdadm
1446 will scan all controllers looking for their capabilities. Otherwise, mdadm
1447 will only look at the controller specified by the argument in form of an
1448 absolute filepath or a link, e.g.
1449 .IR /sys/devices/pci0000:00/0000:00:1f.2 .
1452 .BR \-Y ", " \-\-export
1455 .BR \-\-detail-platform ,
1459 output will be formatted as
1461 pairs for easy import into the environment.
1467 indicates whether an array was started
1469 or not, which may include a reason
1470 .RB ( unsafe ", " nothing ", " no ).
1473 indicates if the array is expected on this host
1475 or seems to be from elsewhere
1479 .BR \-E ", " \-\-examine
1480 Print contents of the metadata stored on the named device(s).
1481 Note the contrast between
1486 applies to devices which are components of an array, while
1488 applies to a whole array which is currently active.
1491 If an array was created on a SPARC machine with a 2.2 Linux kernel
1492 patched with RAID support, the superblock will have been created
1493 incorrectly, or at least incompatibly with 2.4 and later kernels.
1498 will fix the superblock before displaying it. If this appears to do
1499 the right thing, then the array can be successfully assembled using
1500 .BR "\-\-assemble \-\-update=sparc2.2" .
1503 .BR \-X ", " \-\-examine\-bitmap
1504 Report information about a bitmap file.
1505 The argument is either an external bitmap file or an array component
1506 in case of an internal bitmap. Note that running this on an array
1509 does not report the bitmap for that array.
1512 .B \-\-examine\-badblocks
1513 List the bad-blocks recorded for the device, if a bad-blocks list has
1514 been configured. Currently only
1516 metadata supports bad-blocks lists.
1519 .BI \-\-dump= directory
1521 .BI \-\-restore= directory
1522 Save metadata from lists devices, or restore metadata to listed devices.
1525 .BR \-R ", " \-\-run
1526 start a partially assembled array. If
1528 did not find enough devices to fully start the array, it might leaving
1529 it partially assembled. If you wish, you can then use
1531 to start the array in degraded mode.
1534 .BR \-S ", " \-\-stop
1535 deactivate array, releasing all resources.
1538 .BR \-o ", " \-\-readonly
1539 mark array as readonly.
1542 .BR \-w ", " \-\-readwrite
1543 mark array as readwrite.
1546 .B \-\-zero\-superblock
1547 If the device contains a valid md superblock, the block is
1548 overwritten with zeros. With
1550 the block where the superblock would be is overwritten even if it
1551 doesn't appear to be valid.
1554 .B \-\-kill\-subarray=
1555 If the device is a container and the argument to \-\-kill\-subarray
1556 specifies an inactive subarray in the container, then the subarray is
1557 deleted. Deleting all subarrays will leave an 'empty-container' or
1558 spare superblock on the drives. See
1559 .B \-\-zero\-superblock
1561 removing a superblock. Note that some formats depend on the subarray
1562 index for generating a UUID, this command will fail if it would change
1563 the UUID of an active subarray.
1566 .B \-\-update\-subarray=
1567 If the device is a container and the argument to \-\-update\-subarray
1568 specifies a subarray in the container, then attempt to update the given
1569 superblock field in the subarray. See below in
1574 .BR \-t ", " \-\-test
1579 is set to reflect the status of the device. See below in
1584 .BR \-W ", " \-\-wait
1585 For each md device given, wait for any resync, recovery, or reshape
1586 activity to finish before returning.
1588 will return with success if it actually waited for every device
1589 listed, otherwise it will return failure.
1593 For each md device given, or each device in /proc/mdstat if
1595 is given, arrange for the array to be marked clean as soon as possible.
1597 will return with success if the array uses external metadata and we
1598 successfully waited. For native arrays this returns immediately as the
1599 kernel handles dirty-clean transitions at shutdown. No action is taken
1600 if safe-mode handling is disabled.
1604 Set the "sync_action" for all md devices given to one of
1611 will abort any currently running action though some actions will
1612 automatically restart.
1615 will abort any current action and ensure no other action starts
1625 .BR "SCRUBBING AND MISMATCHES" .
1627 .SH For Incremental Assembly mode:
1629 .BR \-\-rebuild\-map ", " \-r
1630 Rebuild the map file
1634 uses to help track which arrays are currently being assembled.
1637 .BR \-\-run ", " \-R
1638 Run any array assembled as soon as a minimal number of devices are
1639 available, rather than waiting until all expected devices are present.
1642 .BR \-\-scan ", " \-s
1643 Only meaningful with
1647 file for arrays that are being incrementally assembled and will try to
1648 start any that are not already started. If any such array is listed
1651 as requiring an external bitmap, that bitmap will be attached first.
1654 .BR \-\-fail ", " \-f
1655 This allows the hot-plug system to remove devices that have fully disappeared
1656 from the kernel. It will first fail and then remove the device from any
1657 array it belongs to.
1658 The device name given should be a kernel device name such as "sda",
1664 Only used with \-\-fail. The 'path' given will be recorded so that if
1665 a new device appears at the same location it can be automatically
1666 added to the same array. This allows the failed device to be
1667 automatically replaced by a new device without metadata if it appears
1668 at specified path. This option is normally only set by a
1672 .SH For Monitor mode:
1674 .BR \-m ", " \-\-mail
1675 Give a mail address to send alerts to.
1678 .BR \-p ", " \-\-program ", " \-\-alert
1679 Give a program to be run whenever an event is detected.
1682 .BR \-y ", " \-\-syslog
1683 Cause all events to be reported through 'syslog'. The messages have
1684 facility of 'daemon' and varying priorities.
1687 .BR \-d ", " \-\-delay
1688 Give a delay in seconds.
1690 polls the md arrays and then waits this many seconds before polling
1691 again. The default is 60 seconds. Since 2.6.16, there is no need to
1692 reduce this as the kernel alerts
1694 immediately when there is any change.
1697 .BR \-r ", " \-\-increment
1698 Give a percentage increment.
1700 will generate RebuildNN events with the given percentage increment.
1703 .BR \-f ", " \-\-daemonise
1706 to run as a background daemon if it decides to monitor anything. This
1707 causes it to fork and run in the child, and to disconnect from the
1708 terminal. The process id of the child is written to stdout.
1711 which will only continue monitoring if a mail address or alert program
1712 is found in the config file.
1715 .BR \-i ", " \-\-pid\-file
1718 is running in daemon mode, write the pid of the daemon process to
1719 the specified file, instead of printing it on standard output.
1722 .BR \-1 ", " \-\-oneshot
1723 Check arrays only once. This will generate
1725 events and more significantly
1731 .B " mdadm \-\-monitor \-\-scan \-1"
1733 from a cron script will ensure regular notification of any degraded arrays.
1736 .BR \-t ", " \-\-test
1739 alert for every array found at startup. This alert gets mailed and
1740 passed to the alert program. This can be used for testing that alert
1741 message do get through successfully.
1745 This inhibits the functionality for moving spares between arrays.
1746 Only one monitoring process started with
1748 but without this flag is allowed, otherwise the two could interfere
1755 .B mdadm \-\-assemble
1756 .I md-device options-and-component-devices...
1759 .B mdadm \-\-assemble \-\-scan
1760 .I md-devices-and-options...
1763 .B mdadm \-\-assemble \-\-scan
1767 This usage assembles one or more RAID arrays from pre-existing components.
1768 For each array, mdadm needs to know the md device, the identity of the
1769 array, and a number of component-devices. These can be found in a number of ways.
1771 In the first usage example (without the
1773 the first device given is the md device.
1774 In the second usage example, all devices listed are treated as md
1775 devices and assembly is attempted.
1776 In the third (where no devices are listed) all md devices that are
1777 listed in the configuration file are assembled. If no arrays are
1778 described by the configuration file, then any arrays that
1779 can be found on unused devices will be assembled.
1781 If precisely one device is listed, but
1787 was given and identity information is extracted from the configuration file.
1789 The identity can be given with the
1795 option, will be taken from the md-device record in the config file, or
1796 will be taken from the super block of the first component-device
1797 listed on the command line.
1799 Devices can be given on the
1801 command line or in the config file. Only devices which have an md
1802 superblock which contains the right identity will be considered for
1805 The config file is only used if explicitly named with
1807 or requested with (a possibly implicit)
1812 .B /etc/mdadm/mdadm.conf
1817 is not given, then the config file will only be used to find the
1818 identity of md arrays.
1820 Normally the array will be started after it is assembled. However if
1822 is not given and not all expected drives were listed, then the array
1823 is not started (to guard against usage errors). To insist that the
1824 array be started in this case (as may work for RAID1, 4, 5, 6, or 10),
1833 does not create any entries in
1837 It does record information in
1841 to choose the correct name.
1845 detects that udev is not configured, it will create the devices in
1849 In Linux kernels prior to version 2.6.28 there were two distinctly
1850 different types of md devices that could be created: one that could be
1851 partitioned using standard partitioning tools and one that could not.
1852 Since 2.6.28 that distinction is no longer relevant as both type of
1853 devices can be partitioned.
1855 will normally create the type that originally could not be partitioned
1856 as it has a well defined major number (9).
1858 Prior to 2.6.28, it is important that mdadm chooses the correct type
1859 of array device to use. This can be controlled with the
1861 option. In particular, a value of "mdp" or "part" or "p" tells mdadm
1862 to use a partitionable device rather than the default.
1864 In the no-udev case, the value given to
1866 can be suffixed by a number. This tells
1868 to create that number of partition devices rather than the default of 4.
1872 can also be given in the configuration file as a word starting
1874 on the ARRAY line for the relevant array.
1881 and no devices are listed,
1883 will first attempt to assemble all the arrays listed in the config
1886 If no arrays are listed in the config (other than those marked
1888 it will look through the available devices for possible arrays and
1889 will try to assemble anything that it finds. Arrays which are tagged
1890 as belonging to the given homehost will be assembled and started
1891 normally. Arrays which do not obviously belong to this host are given
1892 names that are expected not to conflict with anything local, and are
1893 started "read-auto" so that nothing is written to any device until the
1894 array is written to. i.e. automatic resync etc is delayed.
1898 finds a consistent set of devices that look like they should comprise
1899 an array, and if the superblock is tagged as belonging to the given
1900 home host, it will automatically choose a device name and try to
1901 assemble the array. If the array uses version-0.90 metadata, then the
1903 number as recorded in the superblock is used to create a name in
1907 If the array uses version-1 metadata, then the
1909 from the superblock is used to similarly create a name in
1911 (the name will have any 'host' prefix stripped first).
1913 This behaviour can be modified by the
1917 configuration file. This line can indicate that specific metadata
1918 type should, or should not, be automatically assembled. If an array
1919 is found which is not listed in
1921 and has a metadata format that is denied by the
1923 line, then it will not be assembled.
1926 line can also request that all arrays identified as being for this
1927 homehost should be assembled regardless of their metadata type.
1930 for further details.
1932 Note: Auto assembly cannot be used for assembling and activating some
1933 arrays which are undergoing reshape. In particular as the
1935 cannot be given, any reshape which requires a backup-file to continue
1936 cannot be started by auto assembly. An array which is growing to more
1937 devices and has passed the critical section can be assembled using
1948 .BI \-\-raid\-devices= Z
1952 This usage is similar to
1954 The difference is that it creates an array without a superblock. With
1955 these arrays there is no difference between initially creating the array and
1956 subsequently assembling the array, except that hopefully there is useful
1957 data there in the second case.
1959 The level may raid0, linear, raid1, raid10, multipath, or faulty, or
1960 one of their synonyms. All devices must be listed and the array will
1961 be started once complete. It will often be appropriate to use
1962 .B \-\-assume\-clean
1963 with levels raid1 or raid10.
1974 .BI \-\-raid\-devices= Z
1978 This usage will initialise a new md array, associate some devices with
1979 it, and activate the array.
1981 The named device will normally not exist when
1982 .I "mdadm \-\-create"
1983 is run, but will be created by
1985 once the array becomes active.
1987 As devices are added, they are checked to see if they contain RAID
1988 superblocks or filesystems. They are also checked to see if the variance in
1989 device size exceeds 1%.
1991 If any discrepancy is found, the array will not automatically be run, though
1994 can override this caution.
1996 To create a "degraded" array in which some devices are missing, simply
1997 give the word "\fBmissing\fP"
1998 in place of a device name. This will cause
2000 to leave the corresponding slot in the array empty.
2001 For a RAID4 or RAID5 array at most one slot can be
2002 "\fBmissing\fP"; for a RAID6 array at most two slots.
2003 For a RAID1 array, only one real device needs to be given. All of the
2007 When creating a RAID5 array,
2009 will automatically create a degraded array with an extra spare drive.
2010 This is because building the spare into a degraded array is in general
2011 faster than resyncing the parity on a non-degraded, but not clean,
2012 array. This feature can be overridden with the
2016 When creating an array with version-1 metadata a name for the array is
2018 If this is not given with the
2022 will choose a name based on the last component of the name of the
2023 device being created. So if
2025 is being created, then the name
2030 is being created, then the name
2034 When creating a partition based array, using
2036 with version-1.x metadata, the partition type should be set to
2038 (non fs-data). This type selection allows for greater precision since
2039 using any other [RAID auto-detect (0xFD) or a GNU/Linux partition (0x83)],
2040 might create problems in the event of array recovery through a live cdrom.
2042 A new array will normally get a randomly assigned 128bit UUID which is
2043 very likely to be unique. If you have a specific need, you can choose
2044 a UUID for the array by giving the
2046 option. Be warned that creating two arrays with the same UUID is a
2047 recipe for disaster. Also, using
2049 when creating a v0.90 array will silently override any
2054 .\"option is given, it is not necessary to list any component-devices in this command.
2055 .\"They can be added later, before a
2059 .\"is given, the apparent size of the smallest drive given is used.
2061 If the array type supports a write-intent bitmap, and if the devices
2062 in the array exceed 100G is size, an internal write-intent bitmap
2063 will automatically be added unless some other option is explicitly
2066 option. In any case space for a bitmap will be reserved so that one
2067 can be added layer with
2068 .BR "\-\-grow \-\-bitmap=internal" .
2070 If the metadata type supports it (currently only 1.x metadata), space
2071 will be allocated to store a bad block list. This allows a modest
2072 number of bad blocks to be recorded, allowing the drive to remain in
2073 service while only partially functional.
2075 When creating an array within a
2078 can be given either the list of devices to use, or simply the name of
2079 the container. The former case gives control over which devices in
2080 the container will be used for the array. The latter case allows
2082 to automatically choose which devices to use based on how much spare
2085 The General Management options that are valid with
2090 insist on running the array even if some devices look like they might
2095 start the array readonly \(em not supported yet.
2102 .I options... devices...
2105 This usage will allow individual devices in an array to be failed,
2106 removed or added. It is possible to perform multiple operations with
2107 on command. For example:
2109 .B " mdadm /dev/md0 \-f /dev/hda1 \-r /dev/hda1 \-a /dev/hda1"
2115 and will then remove it from the array and finally add it back
2116 in as a spare. However only one md array can be affected by a single
2119 When a device is added to an active array, mdadm checks to see if it
2120 has metadata on it which suggests that it was recently a member of the
2121 array. If it does, it tries to "re\-add" the device. If there have
2122 been no changes since the device was removed, or if the array has a
2123 write-intent bitmap which has recorded whatever changes there were,
2124 then the device will immediately become a full member of the array and
2125 those differences recorded in the bitmap will be resolved.
2135 MISC mode includes a number of distinct operations that
2136 operate on distinct devices. The operations are:
2139 The device is examined to see if it is
2140 (1) an active md array, or
2141 (2) a component of an md array.
2142 The information discovered is reported.
2146 The device should be an active md device.
2148 will display a detailed description of the array.
2152 will cause the output to be less detailed and the format to be
2153 suitable for inclusion in
2157 will normally be 0 unless
2159 failed to get useful information about the device(s); however, if the
2161 option is given, then the exit status will be:
2165 The array is functioning normally.
2168 The array has at least one failed device.
2171 The array has multiple failed devices such that it is unusable.
2174 There was an error while trying to get information about the device.
2178 .B \-\-detail\-platform
2179 Print detail of the platform's RAID capabilities (firmware / hardware
2180 topology). If the metadata is specified with
2184 then the return status will be:
2188 metadata successfully enumerated its platform components on this system
2191 metadata is platform independent
2194 metadata failed to find its platform components on this system
2198 .B \-\-update\-subarray=
2199 If the device is a container and the argument to \-\-update\-subarray
2200 specifies a subarray in the container, then attempt to update the given
2201 superblock field in the subarray. Similar to updating an array in
2202 "assemble" mode, the field to update is selected by
2206 option. Currently only
2212 option updates the subarray name in the metadata, it may not affect the
2213 device node name or the device node symlink until the subarray is
2214 re\-assembled. If updating
2216 would change the UUID of an active subarray this operation is blocked,
2217 and the command will end in an error.
2221 The device should be a component of an md array.
2223 will read the md superblock of the device and display the contents.
2228 is given, then multiple devices that are components of the one array
2229 are grouped together and reported in a single entry suitable
2235 without listing any devices will cause all devices listed in the
2236 config file to be examined.
2239 .BI \-\-dump= directory
2240 If the device contains RAID metadata, a file will be created in the
2242 and the metadata will be written to it. The file will be the same
2243 size as the device and have the metadata written in the file at the
2244 same locate that it exists in the device. However the file will be "sparse" so
2245 that only those blocks containing metadata will be allocated. The
2246 total space used will be small.
2248 The file name used in the
2250 will be the base name of the device. Further if any links appear in
2252 which point to the device, then hard links to the file will be created
2259 Multiple devices can be listed and their metadata will all be stored
2260 in the one directory.
2263 .BI \-\-restore= directory
2264 This is the reverse of
2267 will locate a file in the directory that has a name appropriate for
2268 the given device and will restore metadata from it. Names that match
2270 names are preferred, however if two of those refer to different files,
2272 will not choose between them but will abort the operation.
2274 If a file name is given instead of a
2278 will restore from that file to a single device, always provided the
2279 size of the file matches that of the device, and the file contains
2283 The devices should be active md arrays which will be deactivated, as
2284 long as they are not currently in use.
2288 This will fully activate a partially assembled md array.
2292 This will mark an active array as read-only, providing that it is
2293 not currently being used.
2299 array back to being read/write.
2303 For all operations except
2306 will cause the operation to be applied to all arrays listed in
2311 causes all devices listed in the config file to be examined.
2314 .BR \-b ", " \-\-brief
2315 Be less verbose. This is used with
2323 gives an intermediate level of verbosity.
2329 .B mdadm \-\-monitor
2330 .I options... devices...
2335 to periodically poll a number of md arrays and to report on any events
2338 will never exit once it decides that there are arrays to be checked,
2339 so it should normally be run in the background.
2341 As well as reporting events,
2343 may move a spare drive from one array to another if they are in the
2348 and if the destination array has a failed drive but no spares.
2350 If any devices are listed on the command line,
2352 will only monitor those devices. Otherwise all arrays listed in the
2353 configuration file will be monitored. Further, if
2355 is given, then any other md devices that appear in
2357 will also be monitored.
2359 The result of monitoring the arrays is the generation of events.
2360 These events are passed to a separate program (if specified) and may
2361 be mailed to a given E-mail address.
2363 When passing events to a program, the program is run once for each event,
2364 and is given 2 or 3 command-line arguments: the first is the
2365 name of the event (see below), the second is the name of the
2366 md device which is affected, and the third is the name of a related
2367 device if relevant (such as a component device that has failed).
2371 is given, then a program or an E-mail address must be specified on the
2372 command line or in the config file. If neither are available, then
2374 will not monitor anything.
2378 will continue monitoring as long as something was found to monitor. If
2379 no program or email is given, then each event is reported to
2382 The different events are:
2386 .B DeviceDisappeared
2387 An md array which previously was configured appears to no longer be
2388 configured. (syslog priority: Critical)
2392 was told to monitor an array which is RAID0 or Linear, then it will
2394 .B DeviceDisappeared
2395 with the extra information
2397 This is because RAID0 and Linear do not support the device-failed,
2398 hot-spare and resync operations which are monitored.
2402 An md array started reconstruction (e.g. recovery, resync, reshape,
2403 check, repair). (syslog priority: Warning)
2409 is a two-digit number (ie. 05, 48). This indicates that rebuild
2410 has passed that many percent of the total. The events are generated
2411 with fixed increment since 0. Increment size may be specified with
2412 a commandline option (default is 20). (syslog priority: Warning)
2416 An md array that was rebuilding, isn't any more, either because it
2417 finished normally or was aborted. (syslog priority: Warning)
2421 An active component device of an array has been marked as
2422 faulty. (syslog priority: Critical)
2426 A spare component device which was being rebuilt to replace a faulty
2427 device has failed. (syslog priority: Critical)
2431 A spare component device which was being rebuilt to replace a faulty
2432 device has been successfully rebuilt and has been made active.
2433 (syslog priority: Info)
2437 A new md array has been detected in the
2439 file. (syslog priority: Info)
2443 A newly noticed array appears to be degraded. This message is not
2446 notices a drive failure which causes degradation, but only when
2448 notices that an array is degraded when it first sees the array.
2449 (syslog priority: Critical)
2453 A spare drive has been moved from one array in a
2457 to another to allow a failed drive to be replaced.
2458 (syslog priority: Info)
2464 has been told, via the config file, that an array should have a certain
2465 number of spare devices, and
2467 detects that it has fewer than this number when it first sees the
2468 array, it will report a
2471 (syslog priority: Warning)
2475 An array was found at startup, and the
2478 (syslog priority: Info)
2488 cause Email to be sent. All events cause the program to be run.
2489 The program is run with two or three arguments: the event
2490 name, the array device and possibly a second device.
2492 Each event has an associated array device (e.g.
2494 and possibly a second device. For
2499 the second device is the relevant component device.
2502 the second device is the array that the spare was moved from.
2506 to move spares from one array to another, the different arrays need to
2507 be labeled with the same
2509 or the spares must be allowed to migrate through matching POLICY domains
2510 in the configuration file. The
2512 name can be any string; it is only necessary that different spare
2513 groups use different names.
2517 detects that an array in a spare group has fewer active
2518 devices than necessary for the complete array, and has no spare
2519 devices, it will look for another array in the same spare group that
2520 has a full complement of working drive and a spare. It will then
2521 attempt to remove the spare from the second drive and add it to the
2523 If the removal succeeds but the adding fails, then it is added back to
2526 If the spare group for a degraded array is not defined,
2528 will look at the rules of spare migration specified by POLICY lines in
2530 and then follow similar steps as above if a matching spare is found.
2533 The GROW mode is used for changing the size or shape of an active
2535 For this to work, the kernel must support the necessary change.
2536 Various types of growth are being added during 2.6 development.
2538 Currently the supported changes include
2540 change the "size" attribute for RAID1, RAID4, RAID5 and RAID6.
2542 increase or decrease the "raid\-devices" attribute of RAID0, RAID1, RAID4,
2545 change the chunk-size and layout of RAID0, RAID4, RAID5, RAID6 and RAID10.
2547 convert between RAID1 and RAID5, between RAID5 and RAID6, between
2548 RAID0, RAID4, and RAID5, and between RAID0 and RAID10 (in the near-2 mode).
2550 add a write-intent bitmap to any array which supports these bitmaps, or
2551 remove a write-intent bitmap from such an array.
2554 Using GROW on containers is currently supported only for Intel's IMSM
2555 container format. The number of devices in a container can be
2556 increased - which affects all arrays in the container - or an array
2557 in a container can be converted between levels where those levels are
2558 supported by the container, and the conversion is on of those listed
2559 above. Resizing arrays in an IMSM container with
2561 is not yet supported.
2563 Grow functionality (e.g. expand a number of raid devices) for Intel's
2564 IMSM container format has an experimental status. It is guarded by the
2565 .B MDADM_EXPERIMENTAL
2566 environment variable which must be set to '1' for a GROW command to
2568 This is for the following reasons:
2571 Intel's native IMSM check-pointing is not fully tested yet.
2572 This can causes IMSM incompatibility during the grow process: an array
2573 which is growing cannot roam between Microsoft Windows(R) and Linux
2577 Interrupting a grow operation is not recommended, because it
2578 has not been fully tested for Intel's IMSM container format yet.
2581 Note: Intel's native checkpointing doesn't use
2583 option and it is transparent for assembly feature.
2586 Normally when an array is built the "size" is taken from the smallest
2587 of the drives. If all the small drives in an arrays are, one at a
2588 time, removed and replaced with larger drives, then you could have an
2589 array of large drives with only a small amount used. In this
2590 situation, changing the "size" with "GROW" mode will allow the extra
2591 space to start being used. If the size is increased in this way, a
2592 "resync" process will start to make sure the new parts of the array
2595 Note that when an array changes size, any filesystem that may be
2596 stored in the array will not automatically grow or shrink to use or
2597 vacate the space. The
2598 filesystem will need to be explicitly told to use the extra space
2599 after growing, or to reduce its size
2601 to shrinking the array.
2603 Also the size of an array cannot be changed while it has an active
2604 bitmap. If an array has a bitmap, it must be removed before the size
2605 can be changed. Once the change is complete a new bitmap can be created.
2607 .SS RAID\-DEVICES CHANGES
2609 A RAID1 array can work with any number of devices from 1 upwards
2610 (though 1 is not very useful). There may be times which you want to
2611 increase or decrease the number of active devices. Note that this is
2612 different to hot-add or hot-remove which changes the number of
2615 When reducing the number of devices in a RAID1 array, the slots which
2616 are to be removed from the array must already be vacant. That is, the
2617 devices which were in those slots must be failed and removed.
2619 When the number of devices is increased, any hot spares that are
2620 present will be activated immediately.
2622 Changing the number of active devices in a RAID5 or RAID6 is much more
2623 effort. Every block in the array will need to be read and written
2624 back to a new location. From 2.6.17, the Linux Kernel is able to
2625 increase the number of devices in a RAID5 safely, including restarting
2626 an interrupted "reshape". From 2.6.31, the Linux Kernel is able to
2627 increase or decrease the number of devices in a RAID5 or RAID6.
2629 From 2.6.35, the Linux Kernel is able to convert a RAID0 in to a RAID4
2632 uses this functionality and the ability to add
2633 devices to a RAID4 to allow devices to be added to a RAID0. When
2634 requested to do this,
2636 will convert the RAID0 to a RAID4, add the necessary disks and make
2637 the reshape happen, and then convert the RAID4 back to RAID0.
2639 When decreasing the number of devices, the size of the array will also
2640 decrease. If there was data in the array, it could get destroyed and
2641 this is not reversible, so you should firstly shrink the filesystem on
2642 the array to fit within the new size. To help prevent accidents,
2644 requires that the size of the array be decreased first with
2645 .BR "mdadm --grow --array-size" .
2646 This is a reversible change which simply makes the end of the array
2647 inaccessible. The integrity of any data can then be checked before
2648 the non-reversible reduction in the number of devices is request.
2650 When relocating the first few stripes on a RAID5 or RAID6, it is not
2651 possible to keep the data on disk completely consistent and
2652 crash-proof. To provide the required safety, mdadm disables writes to
2653 the array while this "critical section" is reshaped, and takes a
2654 backup of the data that is in that section. For grows, this backup may be
2655 stored in any spare devices that the array has, however it can also be
2656 stored in a separate file specified with the
2658 option, and is required to be specified for shrinks, RAID level
2659 changes and layout changes. If this option is used, and the system
2660 does crash during the critical period, the same file must be passed to
2662 to restore the backup and reassemble the array. When shrinking rather
2663 than growing the array, the reshape is done from the end towards the
2664 beginning, so the "critical section" is at the end of the reshape.
2668 Changing the RAID level of any array happens instantaneously. However
2669 in the RAID5 to RAID6 case this requires a non-standard layout of the
2670 RAID6 data, and in the RAID6 to RAID5 case that non-standard layout is
2671 required before the change can be accomplished. So while the level
2672 change is instant, the accompanying layout change can take quite a
2675 is required. If the array is not simultaneously being grown or
2676 shrunk, so that the array size will remain the same - for example,
2677 reshaping a 3-drive RAID5 into a 4-drive RAID6 - the backup file will
2678 be used not just for a "cricital section" but throughout the reshape
2679 operation, as described below under LAYOUT CHANGES.
2681 .SS CHUNK-SIZE AND LAYOUT CHANGES
2683 Changing the chunk-size of layout without also changing the number of
2684 devices as the same time will involve re-writing all blocks in-place.
2685 To ensure against data loss in the case of a crash, a
2687 must be provided for these changes. Small sections of the array will
2688 be copied to the backup file while they are being rearranged. This
2689 means that all the data is copied twice, once to the backup and once
2690 to the new layout on the array, so this type of reshape will go very
2693 If the reshape is interrupted for any reason, this backup file must be
2695 .B "mdadm --assemble"
2696 so the array can be reassembled. Consequently the file cannot be
2697 stored on the device being reshaped.
2702 A write-intent bitmap can be added to, or removed from, an active
2703 array. Either internal bitmaps, or bitmaps stored in a separate file,
2704 can be added. Note that if you add a bitmap stored in a file which is
2705 in a filesystem that is on the RAID array being affected, the system
2706 will deadlock. The bitmap must be on a separate filesystem.
2708 .SH INCREMENTAL MODE
2712 .B mdadm \-\-incremental
2716 .RI [ optional-aliases-for-device ]
2719 .B mdadm \-\-incremental \-\-fail
2723 .B mdadm \-\-incremental \-\-rebuild\-map
2726 .B mdadm \-\-incremental \-\-run \-\-scan
2729 This mode is designed to be used in conjunction with a device
2730 discovery system. As devices are found in a system, they can be
2732 .B "mdadm \-\-incremental"
2733 to be conditionally added to an appropriate array.
2735 Conversely, it can also be used with the
2737 flag to do just the opposite and find whatever array a particular device
2738 is part of and remove the device from that array.
2740 If the device passed is a
2742 device created by a previous call to
2744 then rather than trying to add that device to an array, all the arrays
2745 described by the metadata of the container will be started.
2748 performs a number of tests to determine if the device is part of an
2749 array, and which array it should be part of. If an appropriate array
2750 is found, or can be created,
2752 adds the device to the array and conditionally starts the array.
2756 will normally only add devices to an array which were previously working
2757 (active or spare) parts of that array. The support for automatic
2758 inclusion of a new drive as a spare in some array requires
2759 a configuration through POLICY in config file.
2763 makes are as follow:
2765 Is the device permitted by
2767 That is, is it listed in a
2769 line in that file. If
2771 is absent then the default it to allow any device. Similarly if
2773 contains the special word
2775 then any device is allowed. Otherwise the device name given to
2777 or one of the aliases given, or an alias found in the filesystem,
2778 must match one of the names or patterns in a
2782 This is the only context where the aliases are used. They are
2783 usually provided by a
2789 Does the device have a valid md superblock? If a specific metadata
2790 version is requested with
2794 then only that style of metadata is accepted, otherwise
2796 finds any known version of metadata. If no
2798 metadata is found, the device may be still added to an array
2799 as a spare if POLICY allows.
2803 Does the metadata match an expected array?
2804 The metadata can match in two ways. Either there is an array listed
2807 which identifies the array (either by UUID, by name, by device list,
2808 or by minor-number), or the array was created with a
2814 or on the command line.
2817 is not able to positively identify the array as belonging to the
2818 current host, the device will be rejected.
2823 keeps a list of arrays that it has partially assembled in
2825 If no array exists which matches
2826 the metadata on the new device,
2828 must choose a device name and unit number. It does this based on any
2831 or any name information stored in the metadata. If this name
2832 suggests a unit number, that number will be used, otherwise a free
2833 unit number will be chosen. Normally
2835 will prefer to create a partitionable array, however if the
2839 suggests that a non-partitionable array is preferred, that will be
2842 If the array is not found in the config file and its metadata does not
2843 identify it as belonging to the "homehost", then
2845 will choose a name for the array which is certain not to conflict with
2846 any array which does belong to this host. It does this be adding an
2847 underscore and a small number to the name preferred by the metadata.
2849 Once an appropriate array is found or created and the device is added,
2851 must decide if the array is ready to be started. It will
2852 normally compare the number of available (non-spare) devices to the
2853 number of devices that the metadata suggests need to be active. If
2854 there are at least that many, the array will be started. This means
2855 that if any devices are missing the array will not be restarted.
2861 in which case the array will be run as soon as there are enough
2862 devices present for the data to be accessible. For a RAID1, that
2863 means one device will start the array. For a clean RAID5, the array
2864 will be started as soon as all but one drive is present.
2866 Note that neither of these approaches is really ideal. If it can
2867 be known that all device discovery has completed, then
2871 can be run which will try to start all arrays that are being
2872 incrementally assembled. They are started in "read-auto" mode in
2873 which they are read-only until the first write request. This means
2874 that no metadata updates are made and no attempt at resync or recovery
2875 happens. Further devices that are found before the first write can
2876 still be added safely.
2879 This section describes environment variables that affect how mdadm
2884 Setting this value to 1 will prevent mdadm from automatically launching
2885 mdmon. This variable is intended primarily for debugging mdadm/mdmon.
2891 does not create any device nodes in /dev, but leaves that task to
2895 appears not to be configured, or if this environment variable is set
2898 will create and devices that are needed.
2901 .B MDADM_NO_SYSTEMCTL
2906 is in use it will normally request
2908 to start various background tasks (particularly
2910 rather than forking and running them in the background. This can be
2911 suppressed by setting
2912 .BR MDADM_NO_SYSTEMCTL=1 .
2916 A key value of IMSM metadata is that it allows interoperability with
2917 boot ROMs on Intel platforms, and with other major operating systems.
2920 will only allow an IMSM array to be created or modified if detects
2921 that it is running on an Intel platform which supports IMSM, and
2922 supports the particular configuration of IMSM that is being requested
2923 (some functionality requires newer OROM support).
2925 These checks can be suppressed by setting IMSM_NO_PLATFORM=1 in the
2926 environment. This can be useful for testing or for disaster
2927 recovery. You should be aware that interoperability may be
2928 compromised by setting this value.
2931 .B MDADM_GROW_ALLOW_OLD
2932 If an array is stopped while it is performing a reshape and that
2933 reshape was making use of a backup file, then when the array is
2936 will sometimes complain that the backup file is too old. If this
2937 happens and you are certain it is the right backup file, you can
2938 over-ride this check by setting
2939 .B MDADM_GROW_ALLOW_OLD=1
2944 Any string given in this variable is added to the start of the
2946 line in the config file, or treated as the whole
2948 line if none is given. It can be used to disable certain metadata
2951 is called from a boot script. For example
2953 .B " export MDADM_CONF_AUTO='-ddf -imsm'
2957 does not automatically assemble any DDF or
2958 IMSM arrays that are found. This can be useful on systems configured
2959 to manage such arrays with
2965 .B " mdadm \-\-query /dev/name-of-device"
2967 This will find out if a given device is a RAID array, or is part of
2968 one, and will provide brief information about the device.
2970 .B " mdadm \-\-assemble \-\-scan"
2972 This will assemble and start all arrays listed in the standard config
2973 file. This command will typically go in a system startup file.
2975 .B " mdadm \-\-stop \-\-scan"
2977 This will shut down all arrays that can be shut down (i.e. are not
2978 currently in use). This will typically go in a system shutdown script.
2980 .B " mdadm \-\-follow \-\-scan \-\-delay=120"
2982 If (and only if) there is an Email address or program given in the
2983 standard config file, then
2984 monitor the status of all arrays listed in that file by
2985 polling them ever 2 minutes.
2987 .B " mdadm \-\-create /dev/md0 \-\-level=1 \-\-raid\-devices=2 /dev/hd[ac]1"
2989 Create /dev/md0 as a RAID1 array consisting of /dev/hda1 and /dev/hdc1.
2992 .B " echo 'DEVICE /dev/hd*[0\-9] /dev/sd*[0\-9]' > mdadm.conf"
2994 .B " mdadm \-\-detail \-\-scan >> mdadm.conf"
2996 This will create a prototype config file that describes currently
2997 active arrays that are known to be made from partitions of IDE or SCSI drives.
2998 This file should be reviewed before being used as it may
2999 contain unwanted detail.
3001 .B " echo 'DEVICE /dev/hd[a\-z] /dev/sd*[a\-z]' > mdadm.conf"
3003 .B " mdadm \-\-examine \-\-scan \-\-config=mdadm.conf >> mdadm.conf"
3005 This will find arrays which could be assembled from existing IDE and
3006 SCSI whole drives (not partitions), and store the information in the
3007 format of a config file.
3008 This file is very likely to contain unwanted detail, particularly
3011 entries. It should be reviewed and edited before being used as an
3014 .B " mdadm \-\-examine \-\-brief \-\-scan \-\-config=partitions"
3016 .B " mdadm \-Ebsc partitions"
3018 Create a list of devices by reading
3019 .BR /proc/partitions ,
3020 scan these for RAID superblocks, and printout a brief listing of all
3023 .B " mdadm \-Ac partitions \-m 0 /dev/md0"
3025 Scan all partitions and devices listed in
3026 .BR /proc/partitions
3029 out of all such devices with a RAID superblock with a minor number of 0.
3031 .B " mdadm \-\-monitor \-\-scan \-\-daemonise > /run/mdadm/mon.pid"
3033 If config file contains a mail address or alert program, run mdadm in
3034 the background in monitor mode monitoring all md devices. Also write
3035 pid of mdadm daemon to
3036 .BR /run/mdadm/mon.pid .
3038 .B " mdadm \-Iq /dev/somedevice"
3040 Try to incorporate newly discovered device into some array as
3043 .B " mdadm \-\-incremental \-\-rebuild\-map \-\-run \-\-scan"
3045 Rebuild the array map from any current arrays, and then start any that
3048 .B " mdadm /dev/md4 --fail detached --remove detached"
3050 Any devices which are components of /dev/md4 will be marked as faulty
3051 and then remove from the array.
3053 .B " mdadm --grow /dev/md4 --level=6 --backup-file=/root/backup-md4"
3057 which is currently a RAID5 array will be converted to RAID6. There
3058 should normally already be a spare drive attached to the array as a
3059 RAID6 needs one more drive than a matching RAID5.
3061 .B " mdadm --create /dev/md/ddf --metadata=ddf --raid-disks 6 /dev/sd[a-f]"
3063 Create a DDF array over 6 devices.
3065 .B " mdadm --create /dev/md/home -n3 -l5 -z 30000000 /dev/md/ddf"
3067 Create a RAID5 array over any 3 devices in the given DDF set. Use
3068 only 30 gigabytes of each device.
3070 .B " mdadm -A /dev/md/ddf1 /dev/sd[a-f]"
3072 Assemble a pre-exist ddf array.
3074 .B " mdadm -I /dev/md/ddf1"
3076 Assemble all arrays contained in the ddf array, assigning names as
3079 .B " mdadm \-\-create \-\-help"
3081 Provide help about the Create mode.
3083 .B " mdadm \-\-config \-\-help"
3085 Provide help about the format of the config file.
3087 .B " mdadm \-\-help"
3089 Provide general help.
3099 lists all active md devices with information about them.
3101 uses this to find arrays when
3103 is given in Misc mode, and to monitor array reconstruction
3108 The config file lists which devices may be scanned to see if
3109 they contain MD super block, and gives identifying information
3110 (e.g. UUID) about known MD arrays. See
3114 .SS /etc/mdadm.conf.d
3116 A directory containing configuration files which are read in lexical
3122 mode is used, this file gets a list of arrays currently being created.
3127 understand two sorts of names for array devices.
3129 The first is the so-called 'standard' format name, which matches the
3130 names used by the kernel and which appear in
3133 The second sort can be freely chosen, but must reside in
3135 When giving a device name to
3137 to create or assemble an array, either full path name such as
3141 can be given, or just the suffix of the second sort of name, such as
3147 chooses device names during auto-assembly or incremental assembly, it
3148 will sometimes add a small sequence number to the end of the name to
3149 avoid conflicted between multiple arrays that have the same name. If
3151 can reasonably determine that the array really is meant for this host,
3152 either by a hostname in the metadata, or by the presence of the array
3155 then it will leave off the suffix if possible.
3156 Also if the homehost is specified as
3159 will only use a suffix if a different array of the same name already
3160 exists or is listed in the config file.
3162 The standard names for non-partitioned arrays (the only sort of md
3163 array available in 2.4 and earlier) are of the form
3167 where NN is a number.
3168 The standard names for partitionable arrays (as available from 2.6
3169 onwards) are of the form:
3173 Partition numbers should be indicated by adding "pMM" to these, thus "/dev/md/d1p2".
3175 From kernel version 2.6.28 the "non-partitioned array" can actually
3176 be partitioned. So the "md_d\fBNN\fP"
3177 names are no longer needed, and
3178 partitions such as "/dev/md\fBNN\fPp\fBXX\fP"
3181 From kernel version 2.6.29 standard names can be non-numeric following
3188 is any string. These names are supported by
3190 since version 3.3 provided they are enabled in
3195 was previously known as
3199 For further information on mdadm usage, MD and the various levels of
3202 .B http://raid.wiki.kernel.org/
3204 (based upon Jakob \(/Ostergaard's Software\-RAID.HOWTO)
3206 The latest version of
3208 should always be available from
3210 .B http://www.kernel.org/pub/linux/utils/raid/mdadm/
projects / thirdparty / mdadm.git / blob