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.
699 To help catch typing errors, the filename must contain at least one
700 slash ('/') if it is a real file (not 'internal' or 'none').
702 Note: external bitmaps are only known to work on ext2 and ext3.
703 Storing bitmap files on other filesystems may result in serious problems.
705 When creating an array on devices which are 100G or larger,
707 automatically adds an internal bitmap as it will usually be
708 beneficial. This can be suppressed with
709 .B "\-\-bitmap=none".
712 .BR \-\-bitmap\-chunk=
713 Set the chunksize of the bitmap. Each bit corresponds to that many
714 Kilobytes of storage.
715 When using a file based bitmap, the default is to use the smallest
716 size that is at-least 4 and requires no more than 2^21 chunks.
719 bitmap, the chunksize defaults to 64Meg, or larger if necessary to
720 fit the bitmap into the available space.
722 A suffix of 'M' or 'G' can be given to indicate Megabytes or
723 Gigabytes respectively.
726 .BR \-W ", " \-\-write\-mostly
727 subsequent devices listed in a
732 command will be flagged as 'write-mostly'. This is valid for RAID1
733 only and means that the 'md' driver will avoid reading from these
734 devices if at all possible. This can be useful if mirroring over a
738 .BR \-\-write\-behind=
739 Specify that write-behind mode should be enabled (valid for RAID1
740 only). If an argument is specified, it will set the maximum number
741 of outstanding writes allowed. The default value is 256.
742 A write-intent bitmap is required in order to use write-behind
743 mode, and write-behind is only attempted on drives marked as
747 .BR \-\-assume\-clean
750 that the array pre-existed and is known to be clean. It can be useful
751 when trying to recover from a major failure as you can be sure that no
752 data will be affected unless you actually write to the array. It can
753 also be used when creating a RAID1 or RAID10 if you want to avoid the
754 initial resync, however this practice \(em while normally safe \(em is not
755 recommended. Use this only if you really know what you are doing.
757 When the devices that will be part of a new array were filled
758 with zeros before creation the operator knows the array is
759 actually clean. If that is the case, such as after running
760 badblocks, this argument can be used to tell mdadm the
761 facts the operator knows.
763 When an array is resized to a larger size with
764 .B "\-\-grow \-\-size="
765 the new space is normally resynced in that same way that the whole
766 array is resynced at creation. From Linux version 3.0,
768 can be used with that command to avoid the automatic resync.
771 .BR \-\-backup\-file=
774 is used to increase the number of raid-devices in a RAID5 or RAID6 if
775 there are no spare devices available, or to shrink, change RAID level
776 or layout. See the GROW MODE section below on RAID\-DEVICES CHANGES.
777 The file must be stored on a separate device, not on the RAID array
782 Arrays with 1.x metadata can leave a gap between the start of the
783 device and the start of array data. This gap can be used for various
784 metadata. The start of data is known as the
786 Normally an appropriate data offset is computed automatically.
787 However it can be useful to set it explicitly such as when re-creating
788 an array which was originally created using a different version of
790 which computed a different offset.
792 Setting the offset explicitly over-rides the default. The value given
793 is in Kilobytes unless an 'M' or 'G' suffix is given.
797 can also be used with
799 for some RAID levels (initially on RAID10). This allows the
800 data\-offset to be changed as part of the reshape process. When the
801 data offset is changed, no backup file is required as the difference
802 in offsets is used to provide the same functionality.
804 When the new offset is earlier than the old offset, the number of
805 devices in the array cannot shrink. When it is after the old offset,
806 the number of devices in the array cannot increase.
808 When creating an array,
812 In the case each member device is expected to have a offset appended
813 to the name, separated by a colon. This makes it possible to recreate
814 exactly an array which has varying data offsets (as can happen when
815 different versions of
817 are used to add different devices).
821 This option is complementary to the
822 .B \-\-freeze-reshape
823 option for assembly. It is needed when
825 operation is interrupted and it is not restarted automatically due to
826 .B \-\-freeze-reshape
827 usage during array assembly. This option is used together with
831 ) command and device for a pending reshape to be continued.
832 All parameters required for reshape continuation will be read from array metadata.
836 .BR \-\-backup\-file=
837 option to be set, continuation option will require to have exactly the same
838 backup file given as well.
840 Any other parameter passed together with
842 option will be ignored.
845 .BR \-N ", " \-\-name=
848 for the array. This is currently only effective when creating an
849 array with a version-1 superblock, or an array in a DDF container.
850 The name is a simple textual string that can be used to identify array
851 components when assembling. If name is needed but not specified, it
852 is taken from the basename of the device that is being created.
864 run the array, even if some of the components
865 appear to be active in another array or filesystem. Normally
867 will ask for confirmation before including such components in an
868 array. This option causes that question to be suppressed.
871 .BR \-f ", " \-\-force
874 accept the geometry and layout specified without question. Normally
876 will not allow creation of an array with only one device, and will try
877 to create a RAID5 array with one missing drive (as this makes the
878 initial resync work faster). With
881 will not try to be so clever.
884 .BR \-o ", " \-\-readonly
887 rather than read-write as normal. No writes will be allowed to the
888 array, and no resync, recovery, or reshape will be started.
891 .BR \-a ", " "\-\-auto{=yes,md,mdp,part,p}{NN}"
892 Instruct mdadm how to create the device file if needed, possibly allocating
893 an unused minor number. "md" causes a non-partitionable array
894 to be used (though since Linux 2.6.28, these array devices are in fact
895 partitionable). "mdp", "part" or "p" causes a partitionable array (2.6 and
896 later) to be used. "yes" requires the named md device to have
897 a 'standard' format, and the type and minor number will be determined
898 from this. With mdadm 3.0, device creation is normally left up to
900 so this option is unlikely to be needed.
901 See DEVICE NAMES below.
903 The argument can also come immediately after
908 is not given on the command line or in the config file, then
914 is also given, then any
916 entries in the config file will override the
918 instruction given on the command line.
920 For partitionable arrays,
922 will create the device file for the whole array and for the first 4
923 partitions. A different number of partitions can be specified at the
924 end of this option (e.g.
926 If the device name ends with a digit, the partition names add a 'p',
928 .IR /dev/md/home1p3 .
929 If there is no trailing digit, then the partition names just have a
931 .IR /dev/md/scratch3 .
933 If the md device name is in a 'standard' format as described in DEVICE
934 NAMES, then it will be created, if necessary, with the appropriate
935 device number based on that name. If the device name is not in one of these
936 formats, then a unused device number will be allocated. The device
937 number will be considered unused if there is no active array for that
938 number, and there is no entry in /dev for that number and with a
939 non-standard name. Names that are not in 'standard' format are only
940 allowed in "/dev/md/".
942 This is meaningful with
948 .BR \-a ", " "\-\-add"
949 This option can be used in Grow mode in two cases.
951 If the target array is a Linear array, then
953 can be used to add one or more devices to the array. They
954 are simply catenated on to the end of the array. Once added, the
955 devices cannot be removed.
959 option is being used to increase the number of devices in an array,
962 can be used to add some extra devices to be included in the array.
963 In most cases this is not needed as the extra devices can be added as
964 spares first, and then the number of raid-disks can be changed.
965 However for RAID0, it is not possible to add spares. So to increase
966 the number of devices in a RAID0, it is necessary to set the new
967 number of devices, and to add the new devices, in the same command.
972 .BR \-u ", " \-\-uuid=
973 uuid of array to assemble. Devices which don't have this uuid are
977 .BR \-m ", " \-\-super\-minor=
978 Minor number of device that array was created for. Devices which
979 don't have this minor number are excluded. If you create an array as
980 /dev/md1, then all superblocks will contain the minor number 1, even if
981 the array is later assembled as /dev/md2.
983 Giving the literal word "dev" for
987 to use the minor number of the md device that is being assembled.
990 .B \-\-super\-minor=dev
991 will look for super blocks with a minor number of 0.
994 is only relevant for v0.90 metadata, and should not normally be used.
1000 .BR \-N ", " \-\-name=
1001 Specify the name of the array to assemble. This must be the name
1002 that was specified when creating the array. It must either match
1003 the name stored in the superblock exactly, or it must match
1006 prefixed to the start of the given name.
1009 .BR \-f ", " \-\-force
1010 Assemble the array even if the metadata on some devices appears to be
1013 cannot find enough working devices to start the array, but can find
1014 some devices that are recorded as having failed, then it will mark
1015 those devices as working so that the array can be started.
1016 An array which requires
1018 to be started may contain data corruption. Use it carefully.
1021 .BR \-R ", " \-\-run
1022 Attempt to start the array even if fewer drives were given than were
1023 present last time the array was active. Normally if not all the
1024 expected drives are found and
1026 is not used, then the array will be assembled but not started.
1029 an attempt will be made to start it anyway.
1033 This is the reverse of
1035 in that it inhibits the startup of array unless all expected drives
1036 are present. This is only needed with
1038 and can be used if the physical connections to devices are
1039 not as reliable as you would like.
1042 .BR \-a ", " "\-\-auto{=no,yes,md,mdp,part}"
1043 See this option under Create and Build options.
1046 .BR \-b ", " \-\-bitmap=
1047 Specify the bitmap file that was given when the array was created. If
1050 bitmap, there is no need to specify this when assembling the array.
1053 .BR \-\-backup\-file=
1056 was used while reshaping an array (e.g. changing number of devices or
1057 chunk size) and the system crashed during the critical section, then the same
1059 must be presented to
1061 to allow possibly corrupted data to be restored, and the reshape
1065 .BR \-\-invalid\-backup
1066 If the file needed for the above option is not available for any
1067 reason an empty file can be given together with this option to
1068 indicate that the backup file is invalid. In this case the data that
1069 was being rearranged at the time of the crash could be irrecoverably
1070 lost, but the rest of the array may still be recoverable. This option
1071 should only be used as a last resort if there is no way to recover the
1076 .BR \-U ", " \-\-update=
1077 Update the superblock on each device while assembling the array. The
1078 argument given to this flag can be one of
1096 option will adjust the superblock of an array what was created on a Sparc
1097 machine running a patched 2.2 Linux kernel. This kernel got the
1098 alignment of part of the superblock wrong. You can use the
1099 .B "\-\-examine \-\-sparc2.2"
1102 to see what effect this would have.
1106 option will update the
1107 .B "preferred minor"
1108 field on each superblock to match the minor number of the array being
1110 This can be useful if
1112 reports a different "Preferred Minor" to
1114 In some cases this update will be performed automatically
1115 by the kernel driver. In particular the update happens automatically
1116 at the first write to an array with redundancy (RAID level 1 or
1117 greater) on a 2.6 (or later) kernel.
1121 option will change the uuid of the array. If a UUID is given with the
1123 option that UUID will be used as a new UUID and will
1125 be used to help identify the devices in the array.
1128 is given, a random UUID is chosen.
1132 option will change the
1134 of the array as stored in the superblock. This is only supported for
1135 version-1 superblocks.
1139 option will change the
1141 as recorded in the superblock. For version-0 superblocks, this is the
1142 same as updating the UUID.
1143 For version-1 superblocks, this involves updating the name.
1147 option will cause the array to be marked
1149 meaning that any redundancy in the array (e.g. parity for RAID5,
1150 copies for RAID1) may be incorrect. This will cause the RAID system
1151 to perform a "resync" pass to make sure that all redundant information
1156 option allows arrays to be moved between machines with different
1158 When assembling such an array for the first time after a move, giving
1159 .B "\-\-update=byteorder"
1162 to expect superblocks to have their byteorder reversed, and will
1163 correct that order before assembling the array. This is only valid
1164 with original (Version 0.90) superblocks.
1168 option will correct the summaries in the superblock. That is the
1169 counts of total, working, active, failed, and spare devices.
1173 option will rarely be of use. It applies to version 1.1 and 1.2 metadata
1174 only (where the metadata is at the start of the device) and is only
1175 useful when the component device has changed size (typically become
1176 larger). The version 1 metadata records the amount of the device that
1177 can be used to store data, so if a device in a version 1.1 or 1.2
1178 array becomes larger, the metadata will still be visible, but the
1179 extra space will not. In this case it might be useful to assemble the
1181 .BR \-\-update=devicesize .
1184 to determine the maximum usable amount of space on each device and
1185 update the relevant field in the metadata.
1189 option only works on v0.90 metadata arrays and will convert them to
1190 v1.0 metadata. The array must not be dirty (i.e. it must not need a
1191 sync) and it must not have a write-intent bitmap.
1193 The old metadata will remain on the devices, but will appear older
1194 than the new metadata and so will usually be ignored. The old metadata
1195 (or indeed the new metadata) can be removed by giving the appropriate
1198 .BR \-\-zero\-superblock .
1202 option can be used when an array has an internal bitmap which is
1203 corrupt in some way so that assembling the array normally fails. It
1204 will cause any internal bitmap to be ignored.
1208 option will reserve space in each device for a bad block list. This
1209 will be 4K in size and positioned near the end of any free space
1210 between the superblock and the data.
1214 option will cause any reservation of space for a bad block list to be
1215 removed. If the bad block list contains entries, this will fail, as
1216 removing the list could cause data corruption.
1219 .BR \-\-freeze\-reshape
1220 Option is intended to be used in start-up scripts during initrd boot phase.
1221 When array under reshape is assembled during initrd phase, this option
1222 stops reshape after reshape critical section is being restored. This happens
1223 before file system pivot operation and avoids loss of file system context.
1224 Losing file system context would cause reshape to be broken.
1226 Reshape can be continued later using the
1228 option for the grow command.
1230 .SH For Manage mode:
1233 .BR \-t ", " \-\-test
1234 Unless a more serious error occurred,
1236 will exit with a status of 2 if no changes were made to the array and
1237 0 if at least one change was made.
1238 This can be useful when an indirect specifier such as
1243 is used in requesting an operation on the array.
1245 will report failure if these specifiers didn't find any match.
1248 .BR \-a ", " \-\-add
1249 hot-add listed devices.
1250 If a device appears to have recently been part of the array
1251 (possibly it failed or was removed) the device is re\-added as described
1253 If that fails or the device was never part of the array, the device is
1254 added as a hot-spare.
1255 If the array is degraded, it will immediately start to rebuild data
1258 Note that this and the following options are only meaningful on array
1259 with redundancy. They don't apply to RAID0 or Linear.
1263 re\-add a device that was previously removed from an array.
1264 If the metadata on the device reports that it is a member of the
1265 array, and the slot that it used is still vacant, then the device will
1266 be added back to the array in the same position. This will normally
1267 cause the data for that device to be recovered. However based on the
1268 event count on the device, the recovery may only require sections that
1269 are flagged a write-intent bitmap to be recovered or may not require
1270 any recovery at all.
1272 When used on an array that has no metadata (i.e. it was built with
1274 it will be assumed that bitmap-based recovery is enough to make the
1275 device fully consistent with the array.
1277 When used with v1.x metadata,
1279 can be accompanied by
1280 .BR \-\-update=devicesize ,
1281 .BR \-\-update=bbl ", or"
1282 .BR \-\-update=no\-bbl .
1283 See the description of these option when used in Assemble mode for an
1284 explanation of their use.
1286 If the device name given is
1290 will try to find any device that looks like it should be
1291 part of the array but isn't and will try to re\-add all such devices.
1293 If the device name given is
1297 will find all devices in the array that are marked
1299 remove them and attempt to immediately re\-add them. This can be
1300 useful if you are certain that the reason for failure has been
1305 Add a device as a spare. This is similar to
1307 except that it does not attempt
1309 first. The device will be added as a spare even if it looks like it
1310 could be an recent member of the array.
1313 .BR \-r ", " \-\-remove
1314 remove listed devices. They must not be active. i.e. they should
1315 be failed or spare devices.
1317 As well as the name of a device file
1327 The first causes all failed device to be removed. The second causes
1328 any device which is no longer connected to the system (i.e an 'open'
1332 The third will remove a set as describe below under
1336 .BR \-f ", " \-\-fail
1337 Mark listed devices as faulty.
1338 As well as the name of a device file, the word
1342 can be given. The former will cause any device that has been detached from
1343 the system to be marked as failed. It can then be removed.
1345 For RAID10 arrays where the number of copies evenly divides the number
1346 of devices, the devices can be conceptually divided into sets where
1347 each set contains a single complete copy of the data on the array.
1348 Sometimes a RAID10 array will be configured so that these sets are on
1349 separate controllers. In this case all the devices in one set can be
1350 failed by giving a name like
1356 The appropriate set names are reported by
1366 Mark listed devices as requiring replacement. As soon as a spare is
1367 available, it will be rebuilt and will replace the marked device.
1368 This is similar to marking a device as faulty, but the device remains
1369 in service during the recovery process to increase resilience against
1370 multiple failures. When the replacement process finishes, the
1371 replaced device will be marked as faulty.
1375 This can follow a list of
1377 devices. The devices listed after
1379 will be preferentially used to replace the devices listed after
1381 These device must already be spare devices in the array.
1384 .BR \-\-write\-mostly
1385 Subsequent devices that are added or re\-added will have the 'write-mostly'
1386 flag set. This is only valid for RAID1 and means that the 'md' driver
1387 will avoid reading from these devices if possible.
1390 Subsequent devices that are added or re\-added will have the 'write-mostly'
1394 Each of these options requires that the first device listed is the array
1395 to be acted upon, and the remainder are component devices to be added,
1396 removed, marked as faulty, etc. Several different operations can be
1397 specified for different devices, e.g.
1399 mdadm /dev/md0 \-\-add /dev/sda1 \-\-fail /dev/sdb1 \-\-remove /dev/sdb1
1401 Each operation applies to all devices listed until the next
1404 If an array is using a write-intent bitmap, then devices which have
1405 been removed can be re\-added in a way that avoids a full
1406 reconstruction but instead just updates the blocks that have changed
1407 since the device was removed. For arrays with persistent metadata
1408 (superblocks) this is done automatically. For arrays created with
1410 mdadm needs to be told that this device we removed recently with
1413 Devices can only be removed from an array if they are not in active
1414 use, i.e. that must be spares or failed devices. To remove an active
1415 device, it must first be marked as
1421 .BR \-Q ", " \-\-query
1422 Examine a device to see
1423 (1) if it is an md device and (2) if it is a component of an md
1425 Information about what is discovered is presented.
1428 .BR \-D ", " \-\-detail
1429 Print details of one or more md devices.
1432 .BR \-\-detail\-platform
1433 Print details of the platform's RAID capabilities (firmware / hardware
1434 topology) for a given metadata format. If used without argument, mdadm
1435 will scan all controllers looking for their capabilities. Otherwise, mdadm
1436 will only look at the controller specified by the argument in form of an
1437 absolute filepath or a link, e.g.
1438 .IR /sys/devices/pci0000:00/0000:00:1f.2 .
1441 .BR \-Y ", " \-\-export
1443 .B \-\-detail , \-\-detail-platform
1446 output will be formatted as
1448 pairs for easy import into the environment.
1451 .BR \-E ", " \-\-examine
1452 Print contents of the metadata stored on the named device(s).
1453 Note the contrast between
1458 applies to devices which are components of an array, while
1460 applies to a whole array which is currently active.
1463 If an array was created on a SPARC machine with a 2.2 Linux kernel
1464 patched with RAID support, the superblock will have been created
1465 incorrectly, or at least incompatibly with 2.4 and later kernels.
1470 will fix the superblock before displaying it. If this appears to do
1471 the right thing, then the array can be successfully assembled using
1472 .BR "\-\-assemble \-\-update=sparc2.2" .
1475 .BR \-X ", " \-\-examine\-bitmap
1476 Report information about a bitmap file.
1477 The argument is either an external bitmap file or an array component
1478 in case of an internal bitmap. Note that running this on an array
1481 does not report the bitmap for that array.
1484 .B \-\-examine\-badblocks
1485 List the bad-blocks recorded for the device, if a bad-blocks list has
1486 been configured. Currently only
1488 metadata supports bad-blocks lists.
1491 .BI \-\-dump= directory
1493 .BI \-\-restore= directory
1494 Save metadata from lists devices, or restore metadata to listed devices.
1497 .BR \-R ", " \-\-run
1498 start a partially assembled array. If
1500 did not find enough devices to fully start the array, it might leaving
1501 it partially assembled. If you wish, you can then use
1503 to start the array in degraded mode.
1506 .BR \-S ", " \-\-stop
1507 deactivate array, releasing all resources.
1510 .BR \-o ", " \-\-readonly
1511 mark array as readonly.
1514 .BR \-w ", " \-\-readwrite
1515 mark array as readwrite.
1518 .B \-\-zero\-superblock
1519 If the device contains a valid md superblock, the block is
1520 overwritten with zeros. With
1522 the block where the superblock would be is overwritten even if it
1523 doesn't appear to be valid.
1526 .B \-\-kill\-subarray=
1527 If the device is a container and the argument to \-\-kill\-subarray
1528 specifies an inactive subarray in the container, then the subarray is
1529 deleted. Deleting all subarrays will leave an 'empty-container' or
1530 spare superblock on the drives. See
1531 .B \-\-zero\-superblock
1533 removing a superblock. Note that some formats depend on the subarray
1534 index for generating a UUID, this command will fail if it would change
1535 the UUID of an active subarray.
1538 .B \-\-update\-subarray=
1539 If the device is a container and the argument to \-\-update\-subarray
1540 specifies a subarray in the container, then attempt to update the given
1541 superblock field in the subarray. See below in
1546 .BR \-t ", " \-\-test
1551 is set to reflect the status of the device. See below in
1556 .BR \-W ", " \-\-wait
1557 For each md device given, wait for any resync, recovery, or reshape
1558 activity to finish before returning.
1560 will return with success if it actually waited for every device
1561 listed, otherwise it will return failure.
1565 For each md device given, or each device in /proc/mdstat if
1567 is given, arrange for the array to be marked clean as soon as possible.
1569 will return with success if the array uses external metadata and we
1570 successfully waited. For native arrays this returns immediately as the
1571 kernel handles dirty-clean transitions at shutdown. No action is taken
1572 if safe-mode handling is disabled.
1574 .SH For Incremental Assembly mode:
1576 .BR \-\-rebuild\-map ", " \-r
1577 Rebuild the map file
1581 uses to help track which arrays are currently being assembled.
1584 .BR \-\-run ", " \-R
1585 Run any array assembled as soon as a minimal number of devices are
1586 available, rather than waiting until all expected devices are present.
1589 .BR \-\-scan ", " \-s
1590 Only meaningful with
1594 file for arrays that are being incrementally assembled and will try to
1595 start any that are not already started. If any such array is listed
1598 as requiring an external bitmap, that bitmap will be attached first.
1601 .BR \-\-fail ", " \-f
1602 This allows the hot-plug system to remove devices that have fully disappeared
1603 from the kernel. It will first fail and then remove the device from any
1604 array it belongs to.
1605 The device name given should be a kernel device name such as "sda",
1611 Only used with \-\-fail. The 'path' given will be recorded so that if
1612 a new device appears at the same location it can be automatically
1613 added to the same array. This allows the failed device to be
1614 automatically replaced by a new device without metadata if it appears
1615 at specified path. This option is normally only set by a
1619 .SH For Monitor mode:
1621 .BR \-m ", " \-\-mail
1622 Give a mail address to send alerts to.
1625 .BR \-p ", " \-\-program ", " \-\-alert
1626 Give a program to be run whenever an event is detected.
1629 .BR \-y ", " \-\-syslog
1630 Cause all events to be reported through 'syslog'. The messages have
1631 facility of 'daemon' and varying priorities.
1634 .BR \-d ", " \-\-delay
1635 Give a delay in seconds.
1637 polls the md arrays and then waits this many seconds before polling
1638 again. The default is 60 seconds. Since 2.6.16, there is no need to
1639 reduce this as the kernel alerts
1641 immediately when there is any change.
1644 .BR \-r ", " \-\-increment
1645 Give a percentage increment.
1647 will generate RebuildNN events with the given percentage increment.
1650 .BR \-f ", " \-\-daemonise
1653 to run as a background daemon if it decides to monitor anything. This
1654 causes it to fork and run in the child, and to disconnect from the
1655 terminal. The process id of the child is written to stdout.
1658 which will only continue monitoring if a mail address or alert program
1659 is found in the config file.
1662 .BR \-i ", " \-\-pid\-file
1665 is running in daemon mode, write the pid of the daemon process to
1666 the specified file, instead of printing it on standard output.
1669 .BR \-1 ", " \-\-oneshot
1670 Check arrays only once. This will generate
1672 events and more significantly
1678 .B " mdadm \-\-monitor \-\-scan \-1"
1680 from a cron script will ensure regular notification of any degraded arrays.
1683 .BR \-t ", " \-\-test
1686 alert for every array found at startup. This alert gets mailed and
1687 passed to the alert program. This can be used for testing that alert
1688 message do get through successfully.
1692 This inhibits the functionality for moving spares between arrays.
1693 Only one monitoring process started with
1695 but without this flag is allowed, otherwise the two could interfere
1702 .B mdadm \-\-assemble
1703 .I md-device options-and-component-devices...
1706 .B mdadm \-\-assemble \-\-scan
1707 .I md-devices-and-options...
1710 .B mdadm \-\-assemble \-\-scan
1714 This usage assembles one or more RAID arrays from pre-existing components.
1715 For each array, mdadm needs to know the md device, the identity of the
1716 array, and a number of component-devices. These can be found in a number of ways.
1718 In the first usage example (without the
1720 the first device given is the md device.
1721 In the second usage example, all devices listed are treated as md
1722 devices and assembly is attempted.
1723 In the third (where no devices are listed) all md devices that are
1724 listed in the configuration file are assembled. If no arrays are
1725 described by the configuration file, then any arrays that
1726 can be found on unused devices will be assembled.
1728 If precisely one device is listed, but
1734 was given and identity information is extracted from the configuration file.
1736 The identity can be given with the
1742 option, will be taken from the md-device record in the config file, or
1743 will be taken from the super block of the first component-device
1744 listed on the command line.
1746 Devices can be given on the
1748 command line or in the config file. Only devices which have an md
1749 superblock which contains the right identity will be considered for
1752 The config file is only used if explicitly named with
1754 or requested with (a possibly implicit)
1759 .B /etc/mdadm/mdadm.conf
1764 is not given, then the config file will only be used to find the
1765 identity of md arrays.
1767 Normally the array will be started after it is assembled. However if
1769 is not given and not all expected drives were listed, then the array
1770 is not started (to guard against usage errors). To insist that the
1771 array be started in this case (as may work for RAID1, 4, 5, 6, or 10),
1780 does not create any entries in
1784 It does record information in
1788 to choose the correct name.
1792 detects that udev is not configured, it will create the devices in
1796 In Linux kernels prior to version 2.6.28 there were two distinctly
1797 different types of md devices that could be created: one that could be
1798 partitioned using standard partitioning tools and one that could not.
1799 Since 2.6.28 that distinction is no longer relevant as both type of
1800 devices can be partitioned.
1802 will normally create the type that originally could not be partitioned
1803 as it has a well defined major number (9).
1805 Prior to 2.6.28, it is important that mdadm chooses the correct type
1806 of array device to use. This can be controlled with the
1808 option. In particular, a value of "mdp" or "part" or "p" tells mdadm
1809 to use a partitionable device rather than the default.
1811 In the no-udev case, the value given to
1813 can be suffixed by a number. This tells
1815 to create that number of partition devices rather than the default of 4.
1819 can also be given in the configuration file as a word starting
1821 on the ARRAY line for the relevant array.
1828 and no devices are listed,
1830 will first attempt to assemble all the arrays listed in the config
1833 If no arrays are listed in the config (other than those marked
1835 it will look through the available devices for possible arrays and
1836 will try to assemble anything that it finds. Arrays which are tagged
1837 as belonging to the given homehost will be assembled and started
1838 normally. Arrays which do not obviously belong to this host are given
1839 names that are expected not to conflict with anything local, and are
1840 started "read-auto" so that nothing is written to any device until the
1841 array is written to. i.e. automatic resync etc is delayed.
1845 finds a consistent set of devices that look like they should comprise
1846 an array, and if the superblock is tagged as belonging to the given
1847 home host, it will automatically choose a device name and try to
1848 assemble the array. If the array uses version-0.90 metadata, then the
1850 number as recorded in the superblock is used to create a name in
1854 If the array uses version-1 metadata, then the
1856 from the superblock is used to similarly create a name in
1858 (the name will have any 'host' prefix stripped first).
1860 This behaviour can be modified by the
1864 configuration file. This line can indicate that specific metadata
1865 type should, or should not, be automatically assembled. If an array
1866 is found which is not listed in
1868 and has a metadata format that is denied by the
1870 line, then it will not be assembled.
1873 line can also request that all arrays identified as being for this
1874 homehost should be assembled regardless of their metadata type.
1877 for further details.
1879 Note: Auto assembly cannot be used for assembling and activating some
1880 arrays which are undergoing reshape. In particular as the
1882 cannot be given, any reshape which requires a backup-file to continue
1883 cannot be started by auto assembly. An array which is growing to more
1884 devices and has passed the critical section can be assembled using
1895 .BI \-\-raid\-devices= Z
1899 This usage is similar to
1901 The difference is that it creates an array without a superblock. With
1902 these arrays there is no difference between initially creating the array and
1903 subsequently assembling the array, except that hopefully there is useful
1904 data there in the second case.
1906 The level may raid0, linear, raid1, raid10, multipath, or faulty, or
1907 one of their synonyms. All devices must be listed and the array will
1908 be started once complete. It will often be appropriate to use
1909 .B \-\-assume\-clean
1910 with levels raid1 or raid10.
1921 .BI \-\-raid\-devices= Z
1925 This usage will initialise a new md array, associate some devices with
1926 it, and activate the array.
1928 The named device will normally not exist when
1929 .I "mdadm \-\-create"
1930 is run, but will be created by
1932 once the array becomes active.
1934 As devices are added, they are checked to see if they contain RAID
1935 superblocks or filesystems. They are also checked to see if the variance in
1936 device size exceeds 1%.
1938 If any discrepancy is found, the array will not automatically be run, though
1941 can override this caution.
1943 To create a "degraded" array in which some devices are missing, simply
1944 give the word "\fBmissing\fP"
1945 in place of a device name. This will cause
1947 to leave the corresponding slot in the array empty.
1948 For a RAID4 or RAID5 array at most one slot can be
1949 "\fBmissing\fP"; for a RAID6 array at most two slots.
1950 For a RAID1 array, only one real device needs to be given. All of the
1954 When creating a RAID5 array,
1956 will automatically create a degraded array with an extra spare drive.
1957 This is because building the spare into a degraded array is in general
1958 faster than resyncing the parity on a non-degraded, but not clean,
1959 array. This feature can be overridden with the
1963 When creating an array with version-1 metadata a name for the array is
1965 If this is not given with the
1969 will choose a name based on the last component of the name of the
1970 device being created. So if
1972 is being created, then the name
1977 is being created, then the name
1981 When creating a partition based array, using
1983 with version-1.x metadata, the partition type should be set to
1985 (non fs-data). This type selection allows for greater precision since
1986 using any other [RAID auto-detect (0xFD) or a GNU/Linux partition (0x83)],
1987 might create problems in the event of array recovery through a live cdrom.
1989 A new array will normally get a randomly assigned 128bit UUID which is
1990 very likely to be unique. If you have a specific need, you can choose
1991 a UUID for the array by giving the
1993 option. Be warned that creating two arrays with the same UUID is a
1994 recipe for disaster. Also, using
1996 when creating a v0.90 array will silently override any
2001 .\"option is given, it is not necessary to list any component-devices in this command.
2002 .\"They can be added later, before a
2006 .\"is given, the apparent size of the smallest drive given is used.
2008 If the array type supports a write-intent bitmap, and if the devices
2009 in the array exceed 100G is size, an internal write-intent bitmap
2010 will automatically be added unless some other option is explicitly
2013 option. In any case space for a bitmap will be reserved so that one
2014 can be added layer with
2015 .BR "\-\-grow \-\-bitmap=internal" .
2017 If the metadata type supports it (currently only 1.x metadata), space
2018 will be allocated to store a bad block list. This allows a modest
2019 number of bad blocks to be recorded, allowing the drive to remain in
2020 service while only partially functional.
2022 When creating an array within a
2025 can be given either the list of devices to use, or simply the name of
2026 the container. The former case gives control over which devices in
2027 the container will be used for the array. The latter case allows
2029 to automatically choose which devices to use based on how much spare
2032 The General Management options that are valid with
2037 insist on running the array even if some devices look like they might
2042 start the array readonly \(em not supported yet.
2049 .I options... devices...
2052 This usage will allow individual devices in an array to be failed,
2053 removed or added. It is possible to perform multiple operations with
2054 on command. For example:
2056 .B " mdadm /dev/md0 \-f /dev/hda1 \-r /dev/hda1 \-a /dev/hda1"
2062 and will then remove it from the array and finally add it back
2063 in as a spare. However only one md array can be affected by a single
2066 When a device is added to an active array, mdadm checks to see if it
2067 has metadata on it which suggests that it was recently a member of the
2068 array. If it does, it tries to "re\-add" the device. If there have
2069 been no changes since the device was removed, or if the array has a
2070 write-intent bitmap which has recorded whatever changes there were,
2071 then the device will immediately become a full member of the array and
2072 those differences recorded in the bitmap will be resolved.
2082 MISC mode includes a number of distinct operations that
2083 operate on distinct devices. The operations are:
2086 The device is examined to see if it is
2087 (1) an active md array, or
2088 (2) a component of an md array.
2089 The information discovered is reported.
2093 The device should be an active md device.
2095 will display a detailed description of the array.
2099 will cause the output to be less detailed and the format to be
2100 suitable for inclusion in
2104 will normally be 0 unless
2106 failed to get useful information about the device(s); however, if the
2108 option is given, then the exit status will be:
2112 The array is functioning normally.
2115 The array has at least one failed device.
2118 The array has multiple failed devices such that it is unusable.
2121 There was an error while trying to get information about the device.
2125 .B \-\-detail\-platform
2126 Print detail of the platform's RAID capabilities (firmware / hardware
2127 topology). If the metadata is specified with
2131 then the return status will be:
2135 metadata successfully enumerated its platform components on this system
2138 metadata is platform independent
2141 metadata failed to find its platform components on this system
2145 .B \-\-update\-subarray=
2146 If the device is a container and the argument to \-\-update\-subarray
2147 specifies a subarray in the container, then attempt to update the given
2148 superblock field in the subarray. Similar to updating an array in
2149 "assemble" mode, the field to update is selected by
2153 option. Currently only
2159 option updates the subarray name in the metadata, it may not affect the
2160 device node name or the device node symlink until the subarray is
2161 re\-assembled. If updating
2163 would change the UUID of an active subarray this operation is blocked,
2164 and the command will end in an error.
2168 The device should be a component of an md array.
2170 will read the md superblock of the device and display the contents.
2175 is given, then multiple devices that are components of the one array
2176 are grouped together and reported in a single entry suitable
2182 without listing any devices will cause all devices listed in the
2183 config file to be examined.
2186 .BI \-\-dump= directory
2187 If the device contains RAID metadata, a file will be created in the
2189 and the metadata will be written to it. The file will be the same
2190 size as the device and have the metadata written in the file at the
2191 same locate that it exists in the device. However the file will be "sparse" so
2192 that only those blocks containing metadata will be allocated. The
2193 total space used will be small.
2195 The file name used in the
2197 will be the base name of the device. Further if any links appear in
2199 which point to the device, then hard links to the file will be created
2206 Multiple devices can be listed and their metadata will all be stored
2207 in the one directory.
2210 .BI \-\-restore= directory
2211 This is the reverse of
2214 will locate a file in the directory that has a name appropriate for
2215 the given device and will restore metadata from it. Names that match
2217 names are preferred, however if two of those refer to different files,
2219 will not choose between them but will abort the operation.
2221 If a file name is given instead of a
2225 will restore from that file to a single device, always provided the
2226 size of the file matches that of the device, and the file contains
2230 The devices should be active md arrays which will be deactivated, as
2231 long as they are not currently in use.
2235 This will fully activate a partially assembled md array.
2239 This will mark an active array as read-only, providing that it is
2240 not currently being used.
2246 array back to being read/write.
2250 For all operations except
2253 will cause the operation to be applied to all arrays listed in
2258 causes all devices listed in the config file to be examined.
2261 .BR \-b ", " \-\-brief
2262 Be less verbose. This is used with
2270 gives an intermediate level of verbosity.
2276 .B mdadm \-\-monitor
2277 .I options... devices...
2282 to periodically poll a number of md arrays and to report on any events
2285 will never exit once it decides that there are arrays to be checked,
2286 so it should normally be run in the background.
2288 As well as reporting events,
2290 may move a spare drive from one array to another if they are in the
2295 and if the destination array has a failed drive but no spares.
2297 If any devices are listed on the command line,
2299 will only monitor those devices. Otherwise all arrays listed in the
2300 configuration file will be monitored. Further, if
2302 is given, then any other md devices that appear in
2304 will also be monitored.
2306 The result of monitoring the arrays is the generation of events.
2307 These events are passed to a separate program (if specified) and may
2308 be mailed to a given E-mail address.
2310 When passing events to a program, the program is run once for each event,
2311 and is given 2 or 3 command-line arguments: the first is the
2312 name of the event (see below), the second is the name of the
2313 md device which is affected, and the third is the name of a related
2314 device if relevant (such as a component device that has failed).
2318 is given, then a program or an E-mail address must be specified on the
2319 command line or in the config file. If neither are available, then
2321 will not monitor anything.
2325 will continue monitoring as long as something was found to monitor. If
2326 no program or email is given, then each event is reported to
2329 The different events are:
2333 .B DeviceDisappeared
2334 An md array which previously was configured appears to no longer be
2335 configured. (syslog priority: Critical)
2339 was told to monitor an array which is RAID0 or Linear, then it will
2341 .B DeviceDisappeared
2342 with the extra information
2344 This is because RAID0 and Linear do not support the device-failed,
2345 hot-spare and resync operations which are monitored.
2349 An md array started reconstruction. (syslog priority: Warning)
2355 is a two-digit number (ie. 05, 48). This indicates that rebuild
2356 has passed that many percent of the total. The events are generated
2357 with fixed increment since 0. Increment size may be specified with
2358 a commandline option (default is 20). (syslog priority: Warning)
2362 An md array that was rebuilding, isn't any more, either because it
2363 finished normally or was aborted. (syslog priority: Warning)
2367 An active component device of an array has been marked as
2368 faulty. (syslog priority: Critical)
2372 A spare component device which was being rebuilt to replace a faulty
2373 device has failed. (syslog priority: Critical)
2377 A spare component device which was being rebuilt to replace a faulty
2378 device has been successfully rebuilt and has been made active.
2379 (syslog priority: Info)
2383 A new md array has been detected in the
2385 file. (syslog priority: Info)
2389 A newly noticed array appears to be degraded. This message is not
2392 notices a drive failure which causes degradation, but only when
2394 notices that an array is degraded when it first sees the array.
2395 (syslog priority: Critical)
2399 A spare drive has been moved from one array in a
2403 to another to allow a failed drive to be replaced.
2404 (syslog priority: Info)
2410 has been told, via the config file, that an array should have a certain
2411 number of spare devices, and
2413 detects that it has fewer than this number when it first sees the
2414 array, it will report a
2417 (syslog priority: Warning)
2421 An array was found at startup, and the
2424 (syslog priority: Info)
2434 cause Email to be sent. All events cause the program to be run.
2435 The program is run with two or three arguments: the event
2436 name, the array device and possibly a second device.
2438 Each event has an associated array device (e.g.
2440 and possibly a second device. For
2445 the second device is the relevant component device.
2448 the second device is the array that the spare was moved from.
2452 to move spares from one array to another, the different arrays need to
2453 be labeled with the same
2455 or the spares must be allowed to migrate through matching POLICY domains
2456 in the configuration file. The
2458 name can be any string; it is only necessary that different spare
2459 groups use different names.
2463 detects that an array in a spare group has fewer active
2464 devices than necessary for the complete array, and has no spare
2465 devices, it will look for another array in the same spare group that
2466 has a full complement of working drive and a spare. It will then
2467 attempt to remove the spare from the second drive and add it to the
2469 If the removal succeeds but the adding fails, then it is added back to
2472 If the spare group for a degraded array is not defined,
2474 will look at the rules of spare migration specified by POLICY lines in
2476 and then follow similar steps as above if a matching spare is found.
2479 The GROW mode is used for changing the size or shape of an active
2481 For this to work, the kernel must support the necessary change.
2482 Various types of growth are being added during 2.6 development.
2484 Currently the supported changes include
2486 change the "size" attribute for RAID1, RAID4, RAID5 and RAID6.
2488 increase or decrease the "raid\-devices" attribute of RAID0, RAID1, RAID4,
2491 change the chunk-size and layout of RAID0, RAID4, RAID5, RAID6 and RAID10.
2493 convert between RAID1 and RAID5, between RAID5 and RAID6, between
2494 RAID0, RAID4, and RAID5, and between RAID0 and RAID10 (in the near-2 mode).
2496 add a write-intent bitmap to any array which supports these bitmaps, or
2497 remove a write-intent bitmap from such an array.
2500 Using GROW on containers is currently supported only for Intel's IMSM
2501 container format. The number of devices in a container can be
2502 increased - which affects all arrays in the container - or an array
2503 in a container can be converted between levels where those levels are
2504 supported by the container, and the conversion is on of those listed
2505 above. Resizing arrays in an IMSM container with
2507 is not yet supported.
2509 Grow functionality (e.g. expand a number of raid devices) for Intel's
2510 IMSM container format has an experimental status. It is guarded by the
2511 .B MDADM_EXPERIMENTAL
2512 environment variable which must be set to '1' for a GROW command to
2514 This is for the following reasons:
2517 Intel's native IMSM check-pointing is not fully tested yet.
2518 This can causes IMSM incompatibility during the grow process: an array
2519 which is growing cannot roam between Microsoft Windows(R) and Linux
2523 Interrupting a grow operation is not recommended, because it
2524 has not been fully tested for Intel's IMSM container format yet.
2527 Note: Intel's native checkpointing doesn't use
2529 option and it is transparent for assembly feature.
2532 Normally when an array is built the "size" is taken from the smallest
2533 of the drives. If all the small drives in an arrays are, one at a
2534 time, removed and replaced with larger drives, then you could have an
2535 array of large drives with only a small amount used. In this
2536 situation, changing the "size" with "GROW" mode will allow the extra
2537 space to start being used. If the size is increased in this way, a
2538 "resync" process will start to make sure the new parts of the array
2541 Note that when an array changes size, any filesystem that may be
2542 stored in the array will not automatically grow or shrink to use or
2543 vacate the space. The
2544 filesystem will need to be explicitly told to use the extra space
2545 after growing, or to reduce its size
2547 to shrinking the array.
2549 Also the size of an array cannot be changed while it has an active
2550 bitmap. If an array has a bitmap, it must be removed before the size
2551 can be changed. Once the change is complete a new bitmap can be created.
2553 .SS RAID\-DEVICES CHANGES
2555 A RAID1 array can work with any number of devices from 1 upwards
2556 (though 1 is not very useful). There may be times which you want to
2557 increase or decrease the number of active devices. Note that this is
2558 different to hot-add or hot-remove which changes the number of
2561 When reducing the number of devices in a RAID1 array, the slots which
2562 are to be removed from the array must already be vacant. That is, the
2563 devices which were in those slots must be failed and removed.
2565 When the number of devices is increased, any hot spares that are
2566 present will be activated immediately.
2568 Changing the number of active devices in a RAID5 or RAID6 is much more
2569 effort. Every block in the array will need to be read and written
2570 back to a new location. From 2.6.17, the Linux Kernel is able to
2571 increase the number of devices in a RAID5 safely, including restarting
2572 an interrupted "reshape". From 2.6.31, the Linux Kernel is able to
2573 increase or decrease the number of devices in a RAID5 or RAID6.
2575 From 2.6.35, the Linux Kernel is able to convert a RAID0 in to a RAID4
2578 uses this functionality and the ability to add
2579 devices to a RAID4 to allow devices to be added to a RAID0. When
2580 requested to do this,
2582 will convert the RAID0 to a RAID4, add the necessary disks and make
2583 the reshape happen, and then convert the RAID4 back to RAID0.
2585 When decreasing the number of devices, the size of the array will also
2586 decrease. If there was data in the array, it could get destroyed and
2587 this is not reversible, so you should firstly shrink the filesystem on
2588 the array to fit within the new size. To help prevent accidents,
2590 requires that the size of the array be decreased first with
2591 .BR "mdadm --grow --array-size" .
2592 This is a reversible change which simply makes the end of the array
2593 inaccessible. The integrity of any data can then be checked before
2594 the non-reversible reduction in the number of devices is request.
2596 When relocating the first few stripes on a RAID5 or RAID6, it is not
2597 possible to keep the data on disk completely consistent and
2598 crash-proof. To provide the required safety, mdadm disables writes to
2599 the array while this "critical section" is reshaped, and takes a
2600 backup of the data that is in that section. For grows, this backup may be
2601 stored in any spare devices that the array has, however it can also be
2602 stored in a separate file specified with the
2604 option, and is required to be specified for shrinks, RAID level
2605 changes and layout changes. If this option is used, and the system
2606 does crash during the critical period, the same file must be passed to
2608 to restore the backup and reassemble the array. When shrinking rather
2609 than growing the array, the reshape is done from the end towards the
2610 beginning, so the "critical section" is at the end of the reshape.
2614 Changing the RAID level of any array happens instantaneously. However
2615 in the RAID5 to RAID6 case this requires a non-standard layout of the
2616 RAID6 data, and in the RAID6 to RAID5 case that non-standard layout is
2617 required before the change can be accomplished. So while the level
2618 change is instant, the accompanying layout change can take quite a
2621 is required. If the array is not simultaneously being grown or
2622 shrunk, so that the array size will remain the same - for example,
2623 reshaping a 3-drive RAID5 into a 4-drive RAID6 - the backup file will
2624 be used not just for a "cricital section" but throughout the reshape
2625 operation, as described below under LAYOUT CHANGES.
2627 .SS CHUNK-SIZE AND LAYOUT CHANGES
2629 Changing the chunk-size of layout without also changing the number of
2630 devices as the same time will involve re-writing all blocks in-place.
2631 To ensure against data loss in the case of a crash, a
2633 must be provided for these changes. Small sections of the array will
2634 be copied to the backup file while they are being rearranged. This
2635 means that all the data is copied twice, once to the backup and once
2636 to the new layout on the array, so this type of reshape will go very
2639 If the reshape is interrupted for any reason, this backup file must be
2641 .B "mdadm --assemble"
2642 so the array can be reassembled. Consequently the file cannot be
2643 stored on the device being reshaped.
2648 A write-intent bitmap can be added to, or removed from, an active
2649 array. Either internal bitmaps, or bitmaps stored in a separate file,
2650 can be added. Note that if you add a bitmap stored in a file which is
2651 in a filesystem that is on the RAID array being affected, the system
2652 will deadlock. The bitmap must be on a separate filesystem.
2654 .SH INCREMENTAL MODE
2658 .B mdadm \-\-incremental
2664 .B mdadm \-\-incremental \-\-fail
2668 .B mdadm \-\-incremental \-\-rebuild\-map
2671 .B mdadm \-\-incremental \-\-run \-\-scan
2674 This mode is designed to be used in conjunction with a device
2675 discovery system. As devices are found in a system, they can be
2677 .B "mdadm \-\-incremental"
2678 to be conditionally added to an appropriate array.
2680 Conversely, it can also be used with the
2682 flag to do just the opposite and find whatever array a particular device
2683 is part of and remove the device from that array.
2685 If the device passed is a
2687 device created by a previous call to
2689 then rather than trying to add that device to an array, all the arrays
2690 described by the metadata of the container will be started.
2693 performs a number of tests to determine if the device is part of an
2694 array, and which array it should be part of. If an appropriate array
2695 is found, or can be created,
2697 adds the device to the array and conditionally starts the array.
2701 will normally only add devices to an array which were previously working
2702 (active or spare) parts of that array. The support for automatic
2703 inclusion of a new drive as a spare in some array requires
2704 a configuration through POLICY in config file.
2708 makes are as follow:
2710 Is the device permitted by
2712 That is, is it listed in a
2714 line in that file. If
2716 is absent then the default it to allow any device. Similar if
2718 contains the special word
2720 then any device is allowed. Otherwise the device name given to
2722 must match one of the names or patterns in a
2727 Does the device have a valid md superblock? If a specific metadata
2728 version is requested with
2732 then only that style of metadata is accepted, otherwise
2734 finds any known version of metadata. If no
2736 metadata is found, the device may be still added to an array
2737 as a spare if POLICY allows.
2741 Does the metadata match an expected array?
2742 The metadata can match in two ways. Either there is an array listed
2745 which identifies the array (either by UUID, by name, by device list,
2746 or by minor-number), or the array was created with a
2752 or on the command line.
2755 is not able to positively identify the array as belonging to the
2756 current host, the device will be rejected.
2761 keeps a list of arrays that it has partially assembled in
2763 If no array exists which matches
2764 the metadata on the new device,
2766 must choose a device name and unit number. It does this based on any
2769 or any name information stored in the metadata. If this name
2770 suggests a unit number, that number will be used, otherwise a free
2771 unit number will be chosen. Normally
2773 will prefer to create a partitionable array, however if the
2777 suggests that a non-partitionable array is preferred, that will be
2780 If the array is not found in the config file and its metadata does not
2781 identify it as belonging to the "homehost", then
2783 will choose a name for the array which is certain not to conflict with
2784 any array which does belong to this host. It does this be adding an
2785 underscore and a small number to the name preferred by the metadata.
2787 Once an appropriate array is found or created and the device is added,
2789 must decide if the array is ready to be started. It will
2790 normally compare the number of available (non-spare) devices to the
2791 number of devices that the metadata suggests need to be active. If
2792 there are at least that many, the array will be started. This means
2793 that if any devices are missing the array will not be restarted.
2799 in which case the array will be run as soon as there are enough
2800 devices present for the data to be accessible. For a RAID1, that
2801 means one device will start the array. For a clean RAID5, the array
2802 will be started as soon as all but one drive is present.
2804 Note that neither of these approaches is really ideal. If it can
2805 be known that all device discovery has completed, then
2809 can be run which will try to start all arrays that are being
2810 incrementally assembled. They are started in "read-auto" mode in
2811 which they are read-only until the first write request. This means
2812 that no metadata updates are made and no attempt at resync or recovery
2813 happens. Further devices that are found before the first write can
2814 still be added safely.
2817 This section describes environment variables that affect how mdadm
2822 Setting this value to 1 will prevent mdadm from automatically launching
2823 mdmon. This variable is intended primarily for debugging mdadm/mdmon.
2829 does not create any device nodes in /dev, but leaves that task to
2833 appears not to be configured, or if this environment variable is set
2836 will create and devices that are needed.
2840 A key value of IMSM metadata is that it allows interoperability with
2841 boot ROMs on Intel platforms, and with other major operating systems.
2844 will only allow an IMSM array to be created or modified if detects
2845 that it is running on an Intel platform which supports IMSM, and
2846 supports the particular configuration of IMSM that is being requested
2847 (some functionality requires newer OROM support).
2849 These checks can be suppressed by setting IMSM_NO_PLATFORM=1 in the
2850 environment. This can be useful for testing or for disaster
2851 recovery. You should be aware that interoperability may be
2852 compromised by setting this value.
2856 Any string given in this variable is added to the start of the
2858 line in the config file, or treated as the whole
2860 line if none is given. It can be used to disable certain metadata
2863 is called from a boot script. For example
2865 .B " export MDADM_CONF_AUTO='-ddf -imsm'
2869 does not automatically assemble any DDF or
2870 IMSM arrays that are found. This can be useful on systems configured
2871 to manage such arrays with
2877 .B " mdadm \-\-query /dev/name-of-device"
2879 This will find out if a given device is a RAID array, or is part of
2880 one, and will provide brief information about the device.
2882 .B " mdadm \-\-assemble \-\-scan"
2884 This will assemble and start all arrays listed in the standard config
2885 file. This command will typically go in a system startup file.
2887 .B " mdadm \-\-stop \-\-scan"
2889 This will shut down all arrays that can be shut down (i.e. are not
2890 currently in use). This will typically go in a system shutdown script.
2892 .B " mdadm \-\-follow \-\-scan \-\-delay=120"
2894 If (and only if) there is an Email address or program given in the
2895 standard config file, then
2896 monitor the status of all arrays listed in that file by
2897 polling them ever 2 minutes.
2899 .B " mdadm \-\-create /dev/md0 \-\-level=1 \-\-raid\-devices=2 /dev/hd[ac]1"
2901 Create /dev/md0 as a RAID1 array consisting of /dev/hda1 and /dev/hdc1.
2904 .B " echo 'DEVICE /dev/hd*[0\-9] /dev/sd*[0\-9]' > mdadm.conf"
2906 .B " mdadm \-\-detail \-\-scan >> mdadm.conf"
2908 This will create a prototype config file that describes currently
2909 active arrays that are known to be made from partitions of IDE or SCSI drives.
2910 This file should be reviewed before being used as it may
2911 contain unwanted detail.
2913 .B " echo 'DEVICE /dev/hd[a\-z] /dev/sd*[a\-z]' > mdadm.conf"
2915 .B " mdadm \-\-examine \-\-scan \-\-config=mdadm.conf >> mdadm.conf"
2917 This will find arrays which could be assembled from existing IDE and
2918 SCSI whole drives (not partitions), and store the information in the
2919 format of a config file.
2920 This file is very likely to contain unwanted detail, particularly
2923 entries. It should be reviewed and edited before being used as an
2926 .B " mdadm \-\-examine \-\-brief \-\-scan \-\-config=partitions"
2928 .B " mdadm \-Ebsc partitions"
2930 Create a list of devices by reading
2931 .BR /proc/partitions ,
2932 scan these for RAID superblocks, and printout a brief listing of all
2935 .B " mdadm \-Ac partitions \-m 0 /dev/md0"
2937 Scan all partitions and devices listed in
2938 .BR /proc/partitions
2941 out of all such devices with a RAID superblock with a minor number of 0.
2943 .B " mdadm \-\-monitor \-\-scan \-\-daemonise > /run/mdadm/mon.pid"
2945 If config file contains a mail address or alert program, run mdadm in
2946 the background in monitor mode monitoring all md devices. Also write
2947 pid of mdadm daemon to
2948 .BR /run/mdadm/mon.pid .
2950 .B " mdadm \-Iq /dev/somedevice"
2952 Try to incorporate newly discovered device into some array as
2955 .B " mdadm \-\-incremental \-\-rebuild\-map \-\-run \-\-scan"
2957 Rebuild the array map from any current arrays, and then start any that
2960 .B " mdadm /dev/md4 --fail detached --remove detached"
2962 Any devices which are components of /dev/md4 will be marked as faulty
2963 and then remove from the array.
2965 .B " mdadm --grow /dev/md4 --level=6 --backup-file=/root/backup-md4"
2969 which is currently a RAID5 array will be converted to RAID6. There
2970 should normally already be a spare drive attached to the array as a
2971 RAID6 needs one more drive than a matching RAID5.
2973 .B " mdadm --create /dev/md/ddf --metadata=ddf --raid-disks 6 /dev/sd[a-f]"
2975 Create a DDF array over 6 devices.
2977 .B " mdadm --create /dev/md/home -n3 -l5 -z 30000000 /dev/md/ddf"
2979 Create a RAID5 array over any 3 devices in the given DDF set. Use
2980 only 30 gigabytes of each device.
2982 .B " mdadm -A /dev/md/ddf1 /dev/sd[a-f]"
2984 Assemble a pre-exist ddf array.
2986 .B " mdadm -I /dev/md/ddf1"
2988 Assemble all arrays contained in the ddf array, assigning names as
2991 .B " mdadm \-\-create \-\-help"
2993 Provide help about the Create mode.
2995 .B " mdadm \-\-config \-\-help"
2997 Provide help about the format of the config file.
2999 .B " mdadm \-\-help"
3001 Provide general help.
3011 lists all active md devices with information about them.
3013 uses this to find arrays when
3015 is given in Misc mode, and to monitor array reconstruction
3020 The config file lists which devices may be scanned to see if
3021 they contain MD super block, and gives identifying information
3022 (e.g. UUID) about known MD arrays. See
3026 .SS /etc/mdadm.conf.d
3028 A directory containing configuration files which are read in lexical
3034 mode is used, this file gets a list of arrays currently being created.
3039 understand two sorts of names for array devices.
3041 The first is the so-called 'standard' format name, which matches the
3042 names used by the kernel and which appear in
3045 The second sort can be freely chosen, but must reside in
3047 When giving a device name to
3049 to create or assemble an array, either full path name such as
3053 can be given, or just the suffix of the second sort of name, such as
3059 chooses device names during auto-assembly or incremental assembly, it
3060 will sometimes add a small sequence number to the end of the name to
3061 avoid conflicted between multiple arrays that have the same name. If
3063 can reasonably determine that the array really is meant for this host,
3064 either by a hostname in the metadata, or by the presence of the array
3067 then it will leave off the suffix if possible.
3068 Also if the homehost is specified as
3071 will only use a suffix if a different array of the same name already
3072 exists or is listed in the config file.
3074 The standard names for non-partitioned arrays (the only sort of md
3075 array available in 2.4 and earlier) are of the form
3079 where NN is a number.
3080 The standard names for partitionable arrays (as available from 2.6
3081 onwards) are of the form:
3085 Partition numbers should be indicated by adding "pMM" to these, thus "/dev/md/d1p2".
3087 From kernel version 2.6.28 the "non-partitioned array" can actually
3088 be partitioned. So the "md_d\fBNN\fP"
3089 names are no longer needed, and
3090 partitions such as "/dev/md\fBNN\fPp\fBXX\fp"
3093 From kernel version 2.6.29 standard names can be non-numeric following
3100 is any string. These names are supported by
3102 since version 3.3 provided they are enabled in
3107 was previously known as
3111 For further information on mdadm usage, MD and the various levels of
3114 .B http://raid.wiki.kernel.org/
3116 (based upon Jakob \(/Ostergaard's Software\-RAID.HOWTO)
3118 The latest version of
3120 should always be available from
3122 .B http://www.kernel.org/pub/linux/utils/raid/mdadm/
projects / thirdparty / mdadm.git / blob