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.
977 .BR \-u ", " \-\-uuid=
978 uuid of array to assemble. Devices which don't have this uuid are
982 .BR \-m ", " \-\-super\-minor=
983 Minor number of device that array was created for. Devices which
984 don't have this minor number are excluded. If you create an array as
985 /dev/md1, then all superblocks will contain the minor number 1, even if
986 the array is later assembled as /dev/md2.
988 Giving the literal word "dev" for
992 to use the minor number of the md device that is being assembled.
995 .B \-\-super\-minor=dev
996 will look for super blocks with a minor number of 0.
999 is only relevant for v0.90 metadata, and should not normally be used.
1005 .BR \-N ", " \-\-name=
1006 Specify the name of the array to assemble. This must be the name
1007 that was specified when creating the array. It must either match
1008 the name stored in the superblock exactly, or it must match
1011 prefixed to the start of the given name.
1014 .BR \-f ", " \-\-force
1015 Assemble the array even if the metadata on some devices appears to be
1018 cannot find enough working devices to start the array, but can find
1019 some devices that are recorded as having failed, then it will mark
1020 those devices as working so that the array can be started.
1021 An array which requires
1023 to be started may contain data corruption. Use it carefully.
1026 .BR \-R ", " \-\-run
1027 Attempt to start the array even if fewer drives were given than were
1028 present last time the array was active. Normally if not all the
1029 expected drives are found and
1031 is not used, then the array will be assembled but not started.
1034 an attempt will be made to start it anyway.
1038 This is the reverse of
1040 in that it inhibits the startup of array unless all expected drives
1041 are present. This is only needed with
1043 and can be used if the physical connections to devices are
1044 not as reliable as you would like.
1047 .BR \-a ", " "\-\-auto{=no,yes,md,mdp,part}"
1048 See this option under Create and Build options.
1051 .BR \-b ", " \-\-bitmap=
1052 Specify the bitmap file that was given when the array was created. If
1055 bitmap, there is no need to specify this when assembling the array.
1058 .BR \-\-backup\-file=
1061 was used while reshaping an array (e.g. changing number of devices or
1062 chunk size) and the system crashed during the critical section, then the same
1064 must be presented to
1066 to allow possibly corrupted data to be restored, and the reshape
1070 .BR \-\-invalid\-backup
1071 If the file needed for the above option is not available for any
1072 reason an empty file can be given together with this option to
1073 indicate that the backup file is invalid. In this case the data that
1074 was being rearranged at the time of the crash could be irrecoverably
1075 lost, but the rest of the array may still be recoverable. This option
1076 should only be used as a last resort if there is no way to recover the
1081 .BR \-U ", " \-\-update=
1082 Update the superblock on each device while assembling the array. The
1083 argument given to this flag can be one of
1101 option will adjust the superblock of an array what was created on a Sparc
1102 machine running a patched 2.2 Linux kernel. This kernel got the
1103 alignment of part of the superblock wrong. You can use the
1104 .B "\-\-examine \-\-sparc2.2"
1107 to see what effect this would have.
1111 option will update the
1112 .B "preferred minor"
1113 field on each superblock to match the minor number of the array being
1115 This can be useful if
1117 reports a different "Preferred Minor" to
1119 In some cases this update will be performed automatically
1120 by the kernel driver. In particular the update happens automatically
1121 at the first write to an array with redundancy (RAID level 1 or
1122 greater) on a 2.6 (or later) kernel.
1126 option will change the uuid of the array. If a UUID is given with the
1128 option that UUID will be used as a new UUID and will
1130 be used to help identify the devices in the array.
1133 is given, a random UUID is chosen.
1137 option will change the
1139 of the array as stored in the superblock. This is only supported for
1140 version-1 superblocks.
1144 option will change the
1146 as recorded in the superblock. For version-0 superblocks, this is the
1147 same as updating the UUID.
1148 For version-1 superblocks, this involves updating the name.
1152 option will cause the array to be marked
1154 meaning that any redundancy in the array (e.g. parity for RAID5,
1155 copies for RAID1) may be incorrect. This will cause the RAID system
1156 to perform a "resync" pass to make sure that all redundant information
1161 option allows arrays to be moved between machines with different
1163 When assembling such an array for the first time after a move, giving
1164 .B "\-\-update=byteorder"
1167 to expect superblocks to have their byteorder reversed, and will
1168 correct that order before assembling the array. This is only valid
1169 with original (Version 0.90) superblocks.
1173 option will correct the summaries in the superblock. That is the
1174 counts of total, working, active, failed, and spare devices.
1178 option will rarely be of use. It applies to version 1.1 and 1.2 metadata
1179 only (where the metadata is at the start of the device) and is only
1180 useful when the component device has changed size (typically become
1181 larger). The version 1 metadata records the amount of the device that
1182 can be used to store data, so if a device in a version 1.1 or 1.2
1183 array becomes larger, the metadata will still be visible, but the
1184 extra space will not. In this case it might be useful to assemble the
1186 .BR \-\-update=devicesize .
1189 to determine the maximum usable amount of space on each device and
1190 update the relevant field in the metadata.
1194 option only works on v0.90 metadata arrays and will convert them to
1195 v1.0 metadata. The array must not be dirty (i.e. it must not need a
1196 sync) and it must not have a write-intent bitmap.
1198 The old metadata will remain on the devices, but will appear older
1199 than the new metadata and so will usually be ignored. The old metadata
1200 (or indeed the new metadata) can be removed by giving the appropriate
1203 .BR \-\-zero\-superblock .
1207 option can be used when an array has an internal bitmap which is
1208 corrupt in some way so that assembling the array normally fails. It
1209 will cause any internal bitmap to be ignored.
1213 option will reserve space in each device for a bad block list. This
1214 will be 4K in size and positioned near the end of any free space
1215 between the superblock and the data.
1219 option will cause any reservation of space for a bad block list to be
1220 removed. If the bad block list contains entries, this will fail, as
1221 removing the list could cause data corruption.
1224 .BR \-\-freeze\-reshape
1225 Option is intended to be used in start-up scripts during initrd boot phase.
1226 When array under reshape is assembled during initrd phase, this option
1227 stops reshape after reshape critical section is being restored. This happens
1228 before file system pivot operation and avoids loss of file system context.
1229 Losing file system context would cause reshape to be broken.
1231 Reshape can be continued later using the
1233 option for the grow command.
1235 .SH For Manage mode:
1238 .BR \-t ", " \-\-test
1239 Unless a more serious error occurred,
1241 will exit with a status of 2 if no changes were made to the array and
1242 0 if at least one change was made.
1243 This can be useful when an indirect specifier such as
1248 is used in requesting an operation on the array.
1250 will report failure if these specifiers didn't find any match.
1253 .BR \-a ", " \-\-add
1254 hot-add listed devices.
1255 If a device appears to have recently been part of the array
1256 (possibly it failed or was removed) the device is re\-added as described
1258 If that fails or the device was never part of the array, the device is
1259 added as a hot-spare.
1260 If the array is degraded, it will immediately start to rebuild data
1263 Note that this and the following options are only meaningful on array
1264 with redundancy. They don't apply to RAID0 or Linear.
1268 re\-add a device that was previously removed from an array.
1269 If the metadata on the device reports that it is a member of the
1270 array, and the slot that it used is still vacant, then the device will
1271 be added back to the array in the same position. This will normally
1272 cause the data for that device to be recovered. However based on the
1273 event count on the device, the recovery may only require sections that
1274 are flagged a write-intent bitmap to be recovered or may not require
1275 any recovery at all.
1277 When used on an array that has no metadata (i.e. it was built with
1279 it will be assumed that bitmap-based recovery is enough to make the
1280 device fully consistent with the array.
1282 When used with v1.x metadata,
1284 can be accompanied by
1285 .BR \-\-update=devicesize ,
1286 .BR \-\-update=bbl ", or"
1287 .BR \-\-update=no\-bbl .
1288 See the description of these option when used in Assemble mode for an
1289 explanation of their use.
1291 If the device name given is
1295 will try to find any device that looks like it should be
1296 part of the array but isn't and will try to re\-add all such devices.
1298 If the device name given is
1302 will find all devices in the array that are marked
1304 remove them and attempt to immediately re\-add them. This can be
1305 useful if you are certain that the reason for failure has been
1310 Add a device as a spare. This is similar to
1312 except that it does not attempt
1314 first. The device will be added as a spare even if it looks like it
1315 could be an recent member of the array.
1318 .BR \-r ", " \-\-remove
1319 remove listed devices. They must not be active. i.e. they should
1320 be failed or spare devices.
1322 As well as the name of a device file
1332 The first causes all failed device to be removed. The second causes
1333 any device which is no longer connected to the system (i.e an 'open'
1337 The third will remove a set as describe below under
1341 .BR \-f ", " \-\-fail
1342 Mark listed devices as faulty.
1343 As well as the name of a device file, the word
1347 can be given. The former will cause any device that has been detached from
1348 the system to be marked as failed. It can then be removed.
1350 For RAID10 arrays where the number of copies evenly divides the number
1351 of devices, the devices can be conceptually divided into sets where
1352 each set contains a single complete copy of the data on the array.
1353 Sometimes a RAID10 array will be configured so that these sets are on
1354 separate controllers. In this case all the devices in one set can be
1355 failed by giving a name like
1361 The appropriate set names are reported by
1371 Mark listed devices as requiring replacement. As soon as a spare is
1372 available, it will be rebuilt and will replace the marked device.
1373 This is similar to marking a device as faulty, but the device remains
1374 in service during the recovery process to increase resilience against
1375 multiple failures. When the replacement process finishes, the
1376 replaced device will be marked as faulty.
1380 This can follow a list of
1382 devices. The devices listed after
1384 will be preferentially used to replace the devices listed after
1386 These device must already be spare devices in the array.
1389 .BR \-\-write\-mostly
1390 Subsequent devices that are added or re\-added will have the 'write-mostly'
1391 flag set. This is only valid for RAID1 and means that the 'md' driver
1392 will avoid reading from these devices if possible.
1395 Subsequent devices that are added or re\-added will have the 'write-mostly'
1399 Each of these options requires that the first device listed is the array
1400 to be acted upon, and the remainder are component devices to be added,
1401 removed, marked as faulty, etc. Several different operations can be
1402 specified for different devices, e.g.
1404 mdadm /dev/md0 \-\-add /dev/sda1 \-\-fail /dev/sdb1 \-\-remove /dev/sdb1
1406 Each operation applies to all devices listed until the next
1409 If an array is using a write-intent bitmap, then devices which have
1410 been removed can be re\-added in a way that avoids a full
1411 reconstruction but instead just updates the blocks that have changed
1412 since the device was removed. For arrays with persistent metadata
1413 (superblocks) this is done automatically. For arrays created with
1415 mdadm needs to be told that this device we removed recently with
1418 Devices can only be removed from an array if they are not in active
1419 use, i.e. that must be spares or failed devices. To remove an active
1420 device, it must first be marked as
1426 .BR \-Q ", " \-\-query
1427 Examine a device to see
1428 (1) if it is an md device and (2) if it is a component of an md
1430 Information about what is discovered is presented.
1433 .BR \-D ", " \-\-detail
1434 Print details of one or more md devices.
1437 .BR \-\-detail\-platform
1438 Print details of the platform's RAID capabilities (firmware / hardware
1439 topology) for a given metadata format. If used without argument, mdadm
1440 will scan all controllers looking for their capabilities. Otherwise, mdadm
1441 will only look at the controller specified by the argument in form of an
1442 absolute filepath or a link, e.g.
1443 .IR /sys/devices/pci0000:00/0000:00:1f.2 .
1446 .BR \-Y ", " \-\-export
1449 .BR \-\-detail-platform ,
1453 output will be formatted as
1455 pairs for easy import into the environment.
1461 indicates whether an array was started
1463 or not, which may include a reason
1464 .RB ( unsafe ", " nothing ", " no ).
1467 indicates if the array is expected on this host
1469 or seems to be from elsewhere
1473 .BR \-E ", " \-\-examine
1474 Print contents of the metadata stored on the named device(s).
1475 Note the contrast between
1480 applies to devices which are components of an array, while
1482 applies to a whole array which is currently active.
1485 If an array was created on a SPARC machine with a 2.2 Linux kernel
1486 patched with RAID support, the superblock will have been created
1487 incorrectly, or at least incompatibly with 2.4 and later kernels.
1492 will fix the superblock before displaying it. If this appears to do
1493 the right thing, then the array can be successfully assembled using
1494 .BR "\-\-assemble \-\-update=sparc2.2" .
1497 .BR \-X ", " \-\-examine\-bitmap
1498 Report information about a bitmap file.
1499 The argument is either an external bitmap file or an array component
1500 in case of an internal bitmap. Note that running this on an array
1503 does not report the bitmap for that array.
1506 .B \-\-examine\-badblocks
1507 List the bad-blocks recorded for the device, if a bad-blocks list has
1508 been configured. Currently only
1510 metadata supports bad-blocks lists.
1513 .BI \-\-dump= directory
1515 .BI \-\-restore= directory
1516 Save metadata from lists devices, or restore metadata to listed devices.
1519 .BR \-R ", " \-\-run
1520 start a partially assembled array. If
1522 did not find enough devices to fully start the array, it might leaving
1523 it partially assembled. If you wish, you can then use
1525 to start the array in degraded mode.
1528 .BR \-S ", " \-\-stop
1529 deactivate array, releasing all resources.
1532 .BR \-o ", " \-\-readonly
1533 mark array as readonly.
1536 .BR \-w ", " \-\-readwrite
1537 mark array as readwrite.
1540 .B \-\-zero\-superblock
1541 If the device contains a valid md superblock, the block is
1542 overwritten with zeros. With
1544 the block where the superblock would be is overwritten even if it
1545 doesn't appear to be valid.
1548 .B \-\-kill\-subarray=
1549 If the device is a container and the argument to \-\-kill\-subarray
1550 specifies an inactive subarray in the container, then the subarray is
1551 deleted. Deleting all subarrays will leave an 'empty-container' or
1552 spare superblock on the drives. See
1553 .B \-\-zero\-superblock
1555 removing a superblock. Note that some formats depend on the subarray
1556 index for generating a UUID, this command will fail if it would change
1557 the UUID of an active subarray.
1560 .B \-\-update\-subarray=
1561 If the device is a container and the argument to \-\-update\-subarray
1562 specifies a subarray in the container, then attempt to update the given
1563 superblock field in the subarray. See below in
1568 .BR \-t ", " \-\-test
1573 is set to reflect the status of the device. See below in
1578 .BR \-W ", " \-\-wait
1579 For each md device given, wait for any resync, recovery, or reshape
1580 activity to finish before returning.
1582 will return with success if it actually waited for every device
1583 listed, otherwise it will return failure.
1587 For each md device given, or each device in /proc/mdstat if
1589 is given, arrange for the array to be marked clean as soon as possible.
1591 will return with success if the array uses external metadata and we
1592 successfully waited. For native arrays this returns immediately as the
1593 kernel handles dirty-clean transitions at shutdown. No action is taken
1594 if safe-mode handling is disabled.
1598 Set the "sync_action" for all md devices given to one of
1605 will abort any currently running action though some actions will
1606 automatically restart.
1609 will abort any current action and ensure no other action starts
1619 .BR "SCRUBBING AND MISMATCHES" .
1621 .SH For Incremental Assembly mode:
1623 .BR \-\-rebuild\-map ", " \-r
1624 Rebuild the map file
1628 uses to help track which arrays are currently being assembled.
1631 .BR \-\-run ", " \-R
1632 Run any array assembled as soon as a minimal number of devices are
1633 available, rather than waiting until all expected devices are present.
1636 .BR \-\-scan ", " \-s
1637 Only meaningful with
1641 file for arrays that are being incrementally assembled and will try to
1642 start any that are not already started. If any such array is listed
1645 as requiring an external bitmap, that bitmap will be attached first.
1648 .BR \-\-fail ", " \-f
1649 This allows the hot-plug system to remove devices that have fully disappeared
1650 from the kernel. It will first fail and then remove the device from any
1651 array it belongs to.
1652 The device name given should be a kernel device name such as "sda",
1658 Only used with \-\-fail. The 'path' given will be recorded so that if
1659 a new device appears at the same location it can be automatically
1660 added to the same array. This allows the failed device to be
1661 automatically replaced by a new device without metadata if it appears
1662 at specified path. This option is normally only set by a
1666 .SH For Monitor mode:
1668 .BR \-m ", " \-\-mail
1669 Give a mail address to send alerts to.
1672 .BR \-p ", " \-\-program ", " \-\-alert
1673 Give a program to be run whenever an event is detected.
1676 .BR \-y ", " \-\-syslog
1677 Cause all events to be reported through 'syslog'. The messages have
1678 facility of 'daemon' and varying priorities.
1681 .BR \-d ", " \-\-delay
1682 Give a delay in seconds.
1684 polls the md arrays and then waits this many seconds before polling
1685 again. The default is 60 seconds. Since 2.6.16, there is no need to
1686 reduce this as the kernel alerts
1688 immediately when there is any change.
1691 .BR \-r ", " \-\-increment
1692 Give a percentage increment.
1694 will generate RebuildNN events with the given percentage increment.
1697 .BR \-f ", " \-\-daemonise
1700 to run as a background daemon if it decides to monitor anything. This
1701 causes it to fork and run in the child, and to disconnect from the
1702 terminal. The process id of the child is written to stdout.
1705 which will only continue monitoring if a mail address or alert program
1706 is found in the config file.
1709 .BR \-i ", " \-\-pid\-file
1712 is running in daemon mode, write the pid of the daemon process to
1713 the specified file, instead of printing it on standard output.
1716 .BR \-1 ", " \-\-oneshot
1717 Check arrays only once. This will generate
1719 events and more significantly
1725 .B " mdadm \-\-monitor \-\-scan \-1"
1727 from a cron script will ensure regular notification of any degraded arrays.
1730 .BR \-t ", " \-\-test
1733 alert for every array found at startup. This alert gets mailed and
1734 passed to the alert program. This can be used for testing that alert
1735 message do get through successfully.
1739 This inhibits the functionality for moving spares between arrays.
1740 Only one monitoring process started with
1742 but without this flag is allowed, otherwise the two could interfere
1749 .B mdadm \-\-assemble
1750 .I md-device options-and-component-devices...
1753 .B mdadm \-\-assemble \-\-scan
1754 .I md-devices-and-options...
1757 .B mdadm \-\-assemble \-\-scan
1761 This usage assembles one or more RAID arrays from pre-existing components.
1762 For each array, mdadm needs to know the md device, the identity of the
1763 array, and a number of component-devices. These can be found in a number of ways.
1765 In the first usage example (without the
1767 the first device given is the md device.
1768 In the second usage example, all devices listed are treated as md
1769 devices and assembly is attempted.
1770 In the third (where no devices are listed) all md devices that are
1771 listed in the configuration file are assembled. If no arrays are
1772 described by the configuration file, then any arrays that
1773 can be found on unused devices will be assembled.
1775 If precisely one device is listed, but
1781 was given and identity information is extracted from the configuration file.
1783 The identity can be given with the
1789 option, will be taken from the md-device record in the config file, or
1790 will be taken from the super block of the first component-device
1791 listed on the command line.
1793 Devices can be given on the
1795 command line or in the config file. Only devices which have an md
1796 superblock which contains the right identity will be considered for
1799 The config file is only used if explicitly named with
1801 or requested with (a possibly implicit)
1806 .B /etc/mdadm/mdadm.conf
1811 is not given, then the config file will only be used to find the
1812 identity of md arrays.
1814 Normally the array will be started after it is assembled. However if
1816 is not given and not all expected drives were listed, then the array
1817 is not started (to guard against usage errors). To insist that the
1818 array be started in this case (as may work for RAID1, 4, 5, 6, or 10),
1827 does not create any entries in
1831 It does record information in
1835 to choose the correct name.
1839 detects that udev is not configured, it will create the devices in
1843 In Linux kernels prior to version 2.6.28 there were two distinctly
1844 different types of md devices that could be created: one that could be
1845 partitioned using standard partitioning tools and one that could not.
1846 Since 2.6.28 that distinction is no longer relevant as both type of
1847 devices can be partitioned.
1849 will normally create the type that originally could not be partitioned
1850 as it has a well defined major number (9).
1852 Prior to 2.6.28, it is important that mdadm chooses the correct type
1853 of array device to use. This can be controlled with the
1855 option. In particular, a value of "mdp" or "part" or "p" tells mdadm
1856 to use a partitionable device rather than the default.
1858 In the no-udev case, the value given to
1860 can be suffixed by a number. This tells
1862 to create that number of partition devices rather than the default of 4.
1866 can also be given in the configuration file as a word starting
1868 on the ARRAY line for the relevant array.
1875 and no devices are listed,
1877 will first attempt to assemble all the arrays listed in the config
1880 If no arrays are listed in the config (other than those marked
1882 it will look through the available devices for possible arrays and
1883 will try to assemble anything that it finds. Arrays which are tagged
1884 as belonging to the given homehost will be assembled and started
1885 normally. Arrays which do not obviously belong to this host are given
1886 names that are expected not to conflict with anything local, and are
1887 started "read-auto" so that nothing is written to any device until the
1888 array is written to. i.e. automatic resync etc is delayed.
1892 finds a consistent set of devices that look like they should comprise
1893 an array, and if the superblock is tagged as belonging to the given
1894 home host, it will automatically choose a device name and try to
1895 assemble the array. If the array uses version-0.90 metadata, then the
1897 number as recorded in the superblock is used to create a name in
1901 If the array uses version-1 metadata, then the
1903 from the superblock is used to similarly create a name in
1905 (the name will have any 'host' prefix stripped first).
1907 This behaviour can be modified by the
1911 configuration file. This line can indicate that specific metadata
1912 type should, or should not, be automatically assembled. If an array
1913 is found which is not listed in
1915 and has a metadata format that is denied by the
1917 line, then it will not be assembled.
1920 line can also request that all arrays identified as being for this
1921 homehost should be assembled regardless of their metadata type.
1924 for further details.
1926 Note: Auto assembly cannot be used for assembling and activating some
1927 arrays which are undergoing reshape. In particular as the
1929 cannot be given, any reshape which requires a backup-file to continue
1930 cannot be started by auto assembly. An array which is growing to more
1931 devices and has passed the critical section can be assembled using
1942 .BI \-\-raid\-devices= Z
1946 This usage is similar to
1948 The difference is that it creates an array without a superblock. With
1949 these arrays there is no difference between initially creating the array and
1950 subsequently assembling the array, except that hopefully there is useful
1951 data there in the second case.
1953 The level may raid0, linear, raid1, raid10, multipath, or faulty, or
1954 one of their synonyms. All devices must be listed and the array will
1955 be started once complete. It will often be appropriate to use
1956 .B \-\-assume\-clean
1957 with levels raid1 or raid10.
1968 .BI \-\-raid\-devices= Z
1972 This usage will initialise a new md array, associate some devices with
1973 it, and activate the array.
1975 The named device will normally not exist when
1976 .I "mdadm \-\-create"
1977 is run, but will be created by
1979 once the array becomes active.
1981 As devices are added, they are checked to see if they contain RAID
1982 superblocks or filesystems. They are also checked to see if the variance in
1983 device size exceeds 1%.
1985 If any discrepancy is found, the array will not automatically be run, though
1988 can override this caution.
1990 To create a "degraded" array in which some devices are missing, simply
1991 give the word "\fBmissing\fP"
1992 in place of a device name. This will cause
1994 to leave the corresponding slot in the array empty.
1995 For a RAID4 or RAID5 array at most one slot can be
1996 "\fBmissing\fP"; for a RAID6 array at most two slots.
1997 For a RAID1 array, only one real device needs to be given. All of the
2001 When creating a RAID5 array,
2003 will automatically create a degraded array with an extra spare drive.
2004 This is because building the spare into a degraded array is in general
2005 faster than resyncing the parity on a non-degraded, but not clean,
2006 array. This feature can be overridden with the
2010 When creating an array with version-1 metadata a name for the array is
2012 If this is not given with the
2016 will choose a name based on the last component of the name of the
2017 device being created. So if
2019 is being created, then the name
2024 is being created, then the name
2028 When creating a partition based array, using
2030 with version-1.x metadata, the partition type should be set to
2032 (non fs-data). This type selection allows for greater precision since
2033 using any other [RAID auto-detect (0xFD) or a GNU/Linux partition (0x83)],
2034 might create problems in the event of array recovery through a live cdrom.
2036 A new array will normally get a randomly assigned 128bit UUID which is
2037 very likely to be unique. If you have a specific need, you can choose
2038 a UUID for the array by giving the
2040 option. Be warned that creating two arrays with the same UUID is a
2041 recipe for disaster. Also, using
2043 when creating a v0.90 array will silently override any
2048 .\"option is given, it is not necessary to list any component-devices in this command.
2049 .\"They can be added later, before a
2053 .\"is given, the apparent size of the smallest drive given is used.
2055 If the array type supports a write-intent bitmap, and if the devices
2056 in the array exceed 100G is size, an internal write-intent bitmap
2057 will automatically be added unless some other option is explicitly
2060 option. In any case space for a bitmap will be reserved so that one
2061 can be added layer with
2062 .BR "\-\-grow \-\-bitmap=internal" .
2064 If the metadata type supports it (currently only 1.x metadata), space
2065 will be allocated to store a bad block list. This allows a modest
2066 number of bad blocks to be recorded, allowing the drive to remain in
2067 service while only partially functional.
2069 When creating an array within a
2072 can be given either the list of devices to use, or simply the name of
2073 the container. The former case gives control over which devices in
2074 the container will be used for the array. The latter case allows
2076 to automatically choose which devices to use based on how much spare
2079 The General Management options that are valid with
2084 insist on running the array even if some devices look like they might
2089 start the array readonly \(em not supported yet.
2096 .I options... devices...
2099 This usage will allow individual devices in an array to be failed,
2100 removed or added. It is possible to perform multiple operations with
2101 on command. For example:
2103 .B " mdadm /dev/md0 \-f /dev/hda1 \-r /dev/hda1 \-a /dev/hda1"
2109 and will then remove it from the array and finally add it back
2110 in as a spare. However only one md array can be affected by a single
2113 When a device is added to an active array, mdadm checks to see if it
2114 has metadata on it which suggests that it was recently a member of the
2115 array. If it does, it tries to "re\-add" the device. If there have
2116 been no changes since the device was removed, or if the array has a
2117 write-intent bitmap which has recorded whatever changes there were,
2118 then the device will immediately become a full member of the array and
2119 those differences recorded in the bitmap will be resolved.
2129 MISC mode includes a number of distinct operations that
2130 operate on distinct devices. The operations are:
2133 The device is examined to see if it is
2134 (1) an active md array, or
2135 (2) a component of an md array.
2136 The information discovered is reported.
2140 The device should be an active md device.
2142 will display a detailed description of the array.
2146 will cause the output to be less detailed and the format to be
2147 suitable for inclusion in
2151 will normally be 0 unless
2153 failed to get useful information about the device(s); however, if the
2155 option is given, then the exit status will be:
2159 The array is functioning normally.
2162 The array has at least one failed device.
2165 The array has multiple failed devices such that it is unusable.
2168 There was an error while trying to get information about the device.
2172 .B \-\-detail\-platform
2173 Print detail of the platform's RAID capabilities (firmware / hardware
2174 topology). If the metadata is specified with
2178 then the return status will be:
2182 metadata successfully enumerated its platform components on this system
2185 metadata is platform independent
2188 metadata failed to find its platform components on this system
2192 .B \-\-update\-subarray=
2193 If the device is a container and the argument to \-\-update\-subarray
2194 specifies a subarray in the container, then attempt to update the given
2195 superblock field in the subarray. Similar to updating an array in
2196 "assemble" mode, the field to update is selected by
2200 option. Currently only
2206 option updates the subarray name in the metadata, it may not affect the
2207 device node name or the device node symlink until the subarray is
2208 re\-assembled. If updating
2210 would change the UUID of an active subarray this operation is blocked,
2211 and the command will end in an error.
2215 The device should be a component of an md array.
2217 will read the md superblock of the device and display the contents.
2222 is given, then multiple devices that are components of the one array
2223 are grouped together and reported in a single entry suitable
2229 without listing any devices will cause all devices listed in the
2230 config file to be examined.
2233 .BI \-\-dump= directory
2234 If the device contains RAID metadata, a file will be created in the
2236 and the metadata will be written to it. The file will be the same
2237 size as the device and have the metadata written in the file at the
2238 same locate that it exists in the device. However the file will be "sparse" so
2239 that only those blocks containing metadata will be allocated. The
2240 total space used will be small.
2242 The file name used in the
2244 will be the base name of the device. Further if any links appear in
2246 which point to the device, then hard links to the file will be created
2253 Multiple devices can be listed and their metadata will all be stored
2254 in the one directory.
2257 .BI \-\-restore= directory
2258 This is the reverse of
2261 will locate a file in the directory that has a name appropriate for
2262 the given device and will restore metadata from it. Names that match
2264 names are preferred, however if two of those refer to different files,
2266 will not choose between them but will abort the operation.
2268 If a file name is given instead of a
2272 will restore from that file to a single device, always provided the
2273 size of the file matches that of the device, and the file contains
2277 The devices should be active md arrays which will be deactivated, as
2278 long as they are not currently in use.
2282 This will fully activate a partially assembled md array.
2286 This will mark an active array as read-only, providing that it is
2287 not currently being used.
2293 array back to being read/write.
2297 For all operations except
2300 will cause the operation to be applied to all arrays listed in
2305 causes all devices listed in the config file to be examined.
2308 .BR \-b ", " \-\-brief
2309 Be less verbose. This is used with
2317 gives an intermediate level of verbosity.
2323 .B mdadm \-\-monitor
2324 .I options... devices...
2329 to periodically poll a number of md arrays and to report on any events
2332 will never exit once it decides that there are arrays to be checked,
2333 so it should normally be run in the background.
2335 As well as reporting events,
2337 may move a spare drive from one array to another if they are in the
2342 and if the destination array has a failed drive but no spares.
2344 If any devices are listed on the command line,
2346 will only monitor those devices. Otherwise all arrays listed in the
2347 configuration file will be monitored. Further, if
2349 is given, then any other md devices that appear in
2351 will also be monitored.
2353 The result of monitoring the arrays is the generation of events.
2354 These events are passed to a separate program (if specified) and may
2355 be mailed to a given E-mail address.
2357 When passing events to a program, the program is run once for each event,
2358 and is given 2 or 3 command-line arguments: the first is the
2359 name of the event (see below), the second is the name of the
2360 md device which is affected, and the third is the name of a related
2361 device if relevant (such as a component device that has failed).
2365 is given, then a program or an E-mail address must be specified on the
2366 command line or in the config file. If neither are available, then
2368 will not monitor anything.
2372 will continue monitoring as long as something was found to monitor. If
2373 no program or email is given, then each event is reported to
2376 The different events are:
2380 .B DeviceDisappeared
2381 An md array which previously was configured appears to no longer be
2382 configured. (syslog priority: Critical)
2386 was told to monitor an array which is RAID0 or Linear, then it will
2388 .B DeviceDisappeared
2389 with the extra information
2391 This is because RAID0 and Linear do not support the device-failed,
2392 hot-spare and resync operations which are monitored.
2396 An md array started reconstruction (e.g. recovery, resync, reshape,
2397 check, repair). (syslog priority: Warning)
2403 is a two-digit number (ie. 05, 48). This indicates that rebuild
2404 has passed that many percent of the total. The events are generated
2405 with fixed increment since 0. Increment size may be specified with
2406 a commandline option (default is 20). (syslog priority: Warning)
2410 An md array that was rebuilding, isn't any more, either because it
2411 finished normally or was aborted. (syslog priority: Warning)
2415 An active component device of an array has been marked as
2416 faulty. (syslog priority: Critical)
2420 A spare component device which was being rebuilt to replace a faulty
2421 device has failed. (syslog priority: Critical)
2425 A spare component device which was being rebuilt to replace a faulty
2426 device has been successfully rebuilt and has been made active.
2427 (syslog priority: Info)
2431 A new md array has been detected in the
2433 file. (syslog priority: Info)
2437 A newly noticed array appears to be degraded. This message is not
2440 notices a drive failure which causes degradation, but only when
2442 notices that an array is degraded when it first sees the array.
2443 (syslog priority: Critical)
2447 A spare drive has been moved from one array in a
2451 to another to allow a failed drive to be replaced.
2452 (syslog priority: Info)
2458 has been told, via the config file, that an array should have a certain
2459 number of spare devices, and
2461 detects that it has fewer than this number when it first sees the
2462 array, it will report a
2465 (syslog priority: Warning)
2469 An array was found at startup, and the
2472 (syslog priority: Info)
2482 cause Email to be sent. All events cause the program to be run.
2483 The program is run with two or three arguments: the event
2484 name, the array device and possibly a second device.
2486 Each event has an associated array device (e.g.
2488 and possibly a second device. For
2493 the second device is the relevant component device.
2496 the second device is the array that the spare was moved from.
2500 to move spares from one array to another, the different arrays need to
2501 be labeled with the same
2503 or the spares must be allowed to migrate through matching POLICY domains
2504 in the configuration file. The
2506 name can be any string; it is only necessary that different spare
2507 groups use different names.
2511 detects that an array in a spare group has fewer active
2512 devices than necessary for the complete array, and has no spare
2513 devices, it will look for another array in the same spare group that
2514 has a full complement of working drive and a spare. It will then
2515 attempt to remove the spare from the second drive and add it to the
2517 If the removal succeeds but the adding fails, then it is added back to
2520 If the spare group for a degraded array is not defined,
2522 will look at the rules of spare migration specified by POLICY lines in
2524 and then follow similar steps as above if a matching spare is found.
2527 The GROW mode is used for changing the size or shape of an active
2529 For this to work, the kernel must support the necessary change.
2530 Various types of growth are being added during 2.6 development.
2532 Currently the supported changes include
2534 change the "size" attribute for RAID1, RAID4, RAID5 and RAID6.
2536 increase or decrease the "raid\-devices" attribute of RAID0, RAID1, RAID4,
2539 change the chunk-size and layout of RAID0, RAID4, RAID5, RAID6 and RAID10.
2541 convert between RAID1 and RAID5, between RAID5 and RAID6, between
2542 RAID0, RAID4, and RAID5, and between RAID0 and RAID10 (in the near-2 mode).
2544 add a write-intent bitmap to any array which supports these bitmaps, or
2545 remove a write-intent bitmap from such an array.
2548 Using GROW on containers is currently supported only for Intel's IMSM
2549 container format. The number of devices in a container can be
2550 increased - which affects all arrays in the container - or an array
2551 in a container can be converted between levels where those levels are
2552 supported by the container, and the conversion is on of those listed
2553 above. Resizing arrays in an IMSM container with
2555 is not yet supported.
2557 Grow functionality (e.g. expand a number of raid devices) for Intel's
2558 IMSM container format has an experimental status. It is guarded by the
2559 .B MDADM_EXPERIMENTAL
2560 environment variable which must be set to '1' for a GROW command to
2562 This is for the following reasons:
2565 Intel's native IMSM check-pointing is not fully tested yet.
2566 This can causes IMSM incompatibility during the grow process: an array
2567 which is growing cannot roam between Microsoft Windows(R) and Linux
2571 Interrupting a grow operation is not recommended, because it
2572 has not been fully tested for Intel's IMSM container format yet.
2575 Note: Intel's native checkpointing doesn't use
2577 option and it is transparent for assembly feature.
2580 Normally when an array is built the "size" is taken from the smallest
2581 of the drives. If all the small drives in an arrays are, one at a
2582 time, removed and replaced with larger drives, then you could have an
2583 array of large drives with only a small amount used. In this
2584 situation, changing the "size" with "GROW" mode will allow the extra
2585 space to start being used. If the size is increased in this way, a
2586 "resync" process will start to make sure the new parts of the array
2589 Note that when an array changes size, any filesystem that may be
2590 stored in the array will not automatically grow or shrink to use or
2591 vacate the space. The
2592 filesystem will need to be explicitly told to use the extra space
2593 after growing, or to reduce its size
2595 to shrinking the array.
2597 Also the size of an array cannot be changed while it has an active
2598 bitmap. If an array has a bitmap, it must be removed before the size
2599 can be changed. Once the change is complete a new bitmap can be created.
2601 .SS RAID\-DEVICES CHANGES
2603 A RAID1 array can work with any number of devices from 1 upwards
2604 (though 1 is not very useful). There may be times which you want to
2605 increase or decrease the number of active devices. Note that this is
2606 different to hot-add or hot-remove which changes the number of
2609 When reducing the number of devices in a RAID1 array, the slots which
2610 are to be removed from the array must already be vacant. That is, the
2611 devices which were in those slots must be failed and removed.
2613 When the number of devices is increased, any hot spares that are
2614 present will be activated immediately.
2616 Changing the number of active devices in a RAID5 or RAID6 is much more
2617 effort. Every block in the array will need to be read and written
2618 back to a new location. From 2.6.17, the Linux Kernel is able to
2619 increase the number of devices in a RAID5 safely, including restarting
2620 an interrupted "reshape". From 2.6.31, the Linux Kernel is able to
2621 increase or decrease the number of devices in a RAID5 or RAID6.
2623 From 2.6.35, the Linux Kernel is able to convert a RAID0 in to a RAID4
2626 uses this functionality and the ability to add
2627 devices to a RAID4 to allow devices to be added to a RAID0. When
2628 requested to do this,
2630 will convert the RAID0 to a RAID4, add the necessary disks and make
2631 the reshape happen, and then convert the RAID4 back to RAID0.
2633 When decreasing the number of devices, the size of the array will also
2634 decrease. If there was data in the array, it could get destroyed and
2635 this is not reversible, so you should firstly shrink the filesystem on
2636 the array to fit within the new size. To help prevent accidents,
2638 requires that the size of the array be decreased first with
2639 .BR "mdadm --grow --array-size" .
2640 This is a reversible change which simply makes the end of the array
2641 inaccessible. The integrity of any data can then be checked before
2642 the non-reversible reduction in the number of devices is request.
2644 When relocating the first few stripes on a RAID5 or RAID6, it is not
2645 possible to keep the data on disk completely consistent and
2646 crash-proof. To provide the required safety, mdadm disables writes to
2647 the array while this "critical section" is reshaped, and takes a
2648 backup of the data that is in that section. For grows, this backup may be
2649 stored in any spare devices that the array has, however it can also be
2650 stored in a separate file specified with the
2652 option, and is required to be specified for shrinks, RAID level
2653 changes and layout changes. If this option is used, and the system
2654 does crash during the critical period, the same file must be passed to
2656 to restore the backup and reassemble the array. When shrinking rather
2657 than growing the array, the reshape is done from the end towards the
2658 beginning, so the "critical section" is at the end of the reshape.
2662 Changing the RAID level of any array happens instantaneously. However
2663 in the RAID5 to RAID6 case this requires a non-standard layout of the
2664 RAID6 data, and in the RAID6 to RAID5 case that non-standard layout is
2665 required before the change can be accomplished. So while the level
2666 change is instant, the accompanying layout change can take quite a
2669 is required. If the array is not simultaneously being grown or
2670 shrunk, so that the array size will remain the same - for example,
2671 reshaping a 3-drive RAID5 into a 4-drive RAID6 - the backup file will
2672 be used not just for a "cricital section" but throughout the reshape
2673 operation, as described below under LAYOUT CHANGES.
2675 .SS CHUNK-SIZE AND LAYOUT CHANGES
2677 Changing the chunk-size of layout without also changing the number of
2678 devices as the same time will involve re-writing all blocks in-place.
2679 To ensure against data loss in the case of a crash, a
2681 must be provided for these changes. Small sections of the array will
2682 be copied to the backup file while they are being rearranged. This
2683 means that all the data is copied twice, once to the backup and once
2684 to the new layout on the array, so this type of reshape will go very
2687 If the reshape is interrupted for any reason, this backup file must be
2689 .B "mdadm --assemble"
2690 so the array can be reassembled. Consequently the file cannot be
2691 stored on the device being reshaped.
2696 A write-intent bitmap can be added to, or removed from, an active
2697 array. Either internal bitmaps, or bitmaps stored in a separate file,
2698 can be added. Note that if you add a bitmap stored in a file which is
2699 in a filesystem that is on the RAID array being affected, the system
2700 will deadlock. The bitmap must be on a separate filesystem.
2702 .SH INCREMENTAL MODE
2706 .B mdadm \-\-incremental
2710 .RI [ optional-aliases-for-device ]
2713 .B mdadm \-\-incremental \-\-fail
2717 .B mdadm \-\-incremental \-\-rebuild\-map
2720 .B mdadm \-\-incremental \-\-run \-\-scan
2723 This mode is designed to be used in conjunction with a device
2724 discovery system. As devices are found in a system, they can be
2726 .B "mdadm \-\-incremental"
2727 to be conditionally added to an appropriate array.
2729 Conversely, it can also be used with the
2731 flag to do just the opposite and find whatever array a particular device
2732 is part of and remove the device from that array.
2734 If the device passed is a
2736 device created by a previous call to
2738 then rather than trying to add that device to an array, all the arrays
2739 described by the metadata of the container will be started.
2742 performs a number of tests to determine if the device is part of an
2743 array, and which array it should be part of. If an appropriate array
2744 is found, or can be created,
2746 adds the device to the array and conditionally starts the array.
2750 will normally only add devices to an array which were previously working
2751 (active or spare) parts of that array. The support for automatic
2752 inclusion of a new drive as a spare in some array requires
2753 a configuration through POLICY in config file.
2757 makes are as follow:
2759 Is the device permitted by
2761 That is, is it listed in a
2763 line in that file. If
2765 is absent then the default it to allow any device. Similarly if
2767 contains the special word
2769 then any device is allowed. Otherwise the device name given to
2771 or one of the aliases given, or an alias found in the filesystem,
2772 must match one of the names or patterns in a
2776 This is the only context where the aliases are used. They are
2777 usually provided by a
2783 Does the device have a valid md superblock? If a specific metadata
2784 version is requested with
2788 then only that style of metadata is accepted, otherwise
2790 finds any known version of metadata. If no
2792 metadata is found, the device may be still added to an array
2793 as a spare if POLICY allows.
2797 Does the metadata match an expected array?
2798 The metadata can match in two ways. Either there is an array listed
2801 which identifies the array (either by UUID, by name, by device list,
2802 or by minor-number), or the array was created with a
2808 or on the command line.
2811 is not able to positively identify the array as belonging to the
2812 current host, the device will be rejected.
2817 keeps a list of arrays that it has partially assembled in
2819 If no array exists which matches
2820 the metadata on the new device,
2822 must choose a device name and unit number. It does this based on any
2825 or any name information stored in the metadata. If this name
2826 suggests a unit number, that number will be used, otherwise a free
2827 unit number will be chosen. Normally
2829 will prefer to create a partitionable array, however if the
2833 suggests that a non-partitionable array is preferred, that will be
2836 If the array is not found in the config file and its metadata does not
2837 identify it as belonging to the "homehost", then
2839 will choose a name for the array which is certain not to conflict with
2840 any array which does belong to this host. It does this be adding an
2841 underscore and a small number to the name preferred by the metadata.
2843 Once an appropriate array is found or created and the device is added,
2845 must decide if the array is ready to be started. It will
2846 normally compare the number of available (non-spare) devices to the
2847 number of devices that the metadata suggests need to be active. If
2848 there are at least that many, the array will be started. This means
2849 that if any devices are missing the array will not be restarted.
2855 in which case the array will be run as soon as there are enough
2856 devices present for the data to be accessible. For a RAID1, that
2857 means one device will start the array. For a clean RAID5, the array
2858 will be started as soon as all but one drive is present.
2860 Note that neither of these approaches is really ideal. If it can
2861 be known that all device discovery has completed, then
2865 can be run which will try to start all arrays that are being
2866 incrementally assembled. They are started in "read-auto" mode in
2867 which they are read-only until the first write request. This means
2868 that no metadata updates are made and no attempt at resync or recovery
2869 happens. Further devices that are found before the first write can
2870 still be added safely.
2873 This section describes environment variables that affect how mdadm
2878 Setting this value to 1 will prevent mdadm from automatically launching
2879 mdmon. This variable is intended primarily for debugging mdadm/mdmon.
2885 does not create any device nodes in /dev, but leaves that task to
2889 appears not to be configured, or if this environment variable is set
2892 will create and devices that are needed.
2895 .B MDADM_NO_SYSTEMCTL
2900 is in use it will normally request
2902 to start various background tasks (particularly
2904 rather than forking and running them in the background. This can be
2905 suppressed by setting
2906 .BR MDADM_NO_SYSTEMCTL=1 .
2910 A key value of IMSM metadata is that it allows interoperability with
2911 boot ROMs on Intel platforms, and with other major operating systems.
2914 will only allow an IMSM array to be created or modified if detects
2915 that it is running on an Intel platform which supports IMSM, and
2916 supports the particular configuration of IMSM that is being requested
2917 (some functionality requires newer OROM support).
2919 These checks can be suppressed by setting IMSM_NO_PLATFORM=1 in the
2920 environment. This can be useful for testing or for disaster
2921 recovery. You should be aware that interoperability may be
2922 compromised by setting this value.
2925 .B MDADM_GROW_ALLOW_OLD
2926 If an array is stopped while it is performing a reshape and that
2927 reshape was making use of a backup file, then when the array is
2930 will sometimes complain that the backup file is too old. If this
2931 happens and you are certain it is the right backup file, you can
2932 over-ride this check by setting
2933 .B MDADM_GROW_ALLOW_OLD=1
2938 Any string given in this variable is added to the start of the
2940 line in the config file, or treated as the whole
2942 line if none is given. It can be used to disable certain metadata
2945 is called from a boot script. For example
2947 .B " export MDADM_CONF_AUTO='-ddf -imsm'
2951 does not automatically assemble any DDF or
2952 IMSM arrays that are found. This can be useful on systems configured
2953 to manage such arrays with
2959 .B " mdadm \-\-query /dev/name-of-device"
2961 This will find out if a given device is a RAID array, or is part of
2962 one, and will provide brief information about the device.
2964 .B " mdadm \-\-assemble \-\-scan"
2966 This will assemble and start all arrays listed in the standard config
2967 file. This command will typically go in a system startup file.
2969 .B " mdadm \-\-stop \-\-scan"
2971 This will shut down all arrays that can be shut down (i.e. are not
2972 currently in use). This will typically go in a system shutdown script.
2974 .B " mdadm \-\-follow \-\-scan \-\-delay=120"
2976 If (and only if) there is an Email address or program given in the
2977 standard config file, then
2978 monitor the status of all arrays listed in that file by
2979 polling them ever 2 minutes.
2981 .B " mdadm \-\-create /dev/md0 \-\-level=1 \-\-raid\-devices=2 /dev/hd[ac]1"
2983 Create /dev/md0 as a RAID1 array consisting of /dev/hda1 and /dev/hdc1.
2986 .B " echo 'DEVICE /dev/hd*[0\-9] /dev/sd*[0\-9]' > mdadm.conf"
2988 .B " mdadm \-\-detail \-\-scan >> mdadm.conf"
2990 This will create a prototype config file that describes currently
2991 active arrays that are known to be made from partitions of IDE or SCSI drives.
2992 This file should be reviewed before being used as it may
2993 contain unwanted detail.
2995 .B " echo 'DEVICE /dev/hd[a\-z] /dev/sd*[a\-z]' > mdadm.conf"
2997 .B " mdadm \-\-examine \-\-scan \-\-config=mdadm.conf >> mdadm.conf"
2999 This will find arrays which could be assembled from existing IDE and
3000 SCSI whole drives (not partitions), and store the information in the
3001 format of a config file.
3002 This file is very likely to contain unwanted detail, particularly
3005 entries. It should be reviewed and edited before being used as an
3008 .B " mdadm \-\-examine \-\-brief \-\-scan \-\-config=partitions"
3010 .B " mdadm \-Ebsc partitions"
3012 Create a list of devices by reading
3013 .BR /proc/partitions ,
3014 scan these for RAID superblocks, and printout a brief listing of all
3017 .B " mdadm \-Ac partitions \-m 0 /dev/md0"
3019 Scan all partitions and devices listed in
3020 .BR /proc/partitions
3023 out of all such devices with a RAID superblock with a minor number of 0.
3025 .B " mdadm \-\-monitor \-\-scan \-\-daemonise > /run/mdadm/mon.pid"
3027 If config file contains a mail address or alert program, run mdadm in
3028 the background in monitor mode monitoring all md devices. Also write
3029 pid of mdadm daemon to
3030 .BR /run/mdadm/mon.pid .
3032 .B " mdadm \-Iq /dev/somedevice"
3034 Try to incorporate newly discovered device into some array as
3037 .B " mdadm \-\-incremental \-\-rebuild\-map \-\-run \-\-scan"
3039 Rebuild the array map from any current arrays, and then start any that
3042 .B " mdadm /dev/md4 --fail detached --remove detached"
3044 Any devices which are components of /dev/md4 will be marked as faulty
3045 and then remove from the array.
3047 .B " mdadm --grow /dev/md4 --level=6 --backup-file=/root/backup-md4"
3051 which is currently a RAID5 array will be converted to RAID6. There
3052 should normally already be a spare drive attached to the array as a
3053 RAID6 needs one more drive than a matching RAID5.
3055 .B " mdadm --create /dev/md/ddf --metadata=ddf --raid-disks 6 /dev/sd[a-f]"
3057 Create a DDF array over 6 devices.
3059 .B " mdadm --create /dev/md/home -n3 -l5 -z 30000000 /dev/md/ddf"
3061 Create a RAID5 array over any 3 devices in the given DDF set. Use
3062 only 30 gigabytes of each device.
3064 .B " mdadm -A /dev/md/ddf1 /dev/sd[a-f]"
3066 Assemble a pre-exist ddf array.
3068 .B " mdadm -I /dev/md/ddf1"
3070 Assemble all arrays contained in the ddf array, assigning names as
3073 .B " mdadm \-\-create \-\-help"
3075 Provide help about the Create mode.
3077 .B " mdadm \-\-config \-\-help"
3079 Provide help about the format of the config file.
3081 .B " mdadm \-\-help"
3083 Provide general help.
3093 lists all active md devices with information about them.
3095 uses this to find arrays when
3097 is given in Misc mode, and to monitor array reconstruction
3102 The config file lists which devices may be scanned to see if
3103 they contain MD super block, and gives identifying information
3104 (e.g. UUID) about known MD arrays. See
3108 .SS /etc/mdadm.conf.d
3110 A directory containing configuration files which are read in lexical
3116 mode is used, this file gets a list of arrays currently being created.
3121 understand two sorts of names for array devices.
3123 The first is the so-called 'standard' format name, which matches the
3124 names used by the kernel and which appear in
3127 The second sort can be freely chosen, but must reside in
3129 When giving a device name to
3131 to create or assemble an array, either full path name such as
3135 can be given, or just the suffix of the second sort of name, such as
3141 chooses device names during auto-assembly or incremental assembly, it
3142 will sometimes add a small sequence number to the end of the name to
3143 avoid conflicted between multiple arrays that have the same name. If
3145 can reasonably determine that the array really is meant for this host,
3146 either by a hostname in the metadata, or by the presence of the array
3149 then it will leave off the suffix if possible.
3150 Also if the homehost is specified as
3153 will only use a suffix if a different array of the same name already
3154 exists or is listed in the config file.
3156 The standard names for non-partitioned arrays (the only sort of md
3157 array available in 2.4 and earlier) are of the form
3161 where NN is a number.
3162 The standard names for partitionable arrays (as available from 2.6
3163 onwards) are of the form:
3167 Partition numbers should be indicated by adding "pMM" to these, thus "/dev/md/d1p2".
3169 From kernel version 2.6.28 the "non-partitioned array" can actually
3170 be partitioned. So the "md_d\fBNN\fP"
3171 names are no longer needed, and
3172 partitions such as "/dev/md\fBNN\fPp\fBXX\fP"
3175 From kernel version 2.6.29 standard names can be non-numeric following
3182 is any string. These names are supported by
3184 since version 3.3 provided they are enabled in
3189 was previously known as
3193 For further information on mdadm usage, MD and the various levels of
3196 .B http://raid.wiki.kernel.org/
3198 (based upon Jakob \(/Ostergaard's Software\-RAID.HOWTO)
3200 The latest version of
3202 should always be available from
3204 .B http://www.kernel.org/pub/linux/utils/raid/mdadm/
projects / thirdparty / mdadm.git / blob