2 .\" Copyright Neil Brown and others.
3 .\" This program is free software; you can redistribute it and/or modify
4 .\" it under the terms of the GNU General Public License as published by
5 .\" the Free Software Foundation; either version 2 of the License, or
6 .\" (at your option) any later version.
7 .\" See file COPYING in distribution for details.
10 mdadm \- manage MD devices
16 .BI mdadm " [mode] <raiddevice> [options] <component-devices>"
19 RAID devices are virtual devices created from two or more
20 real block devices. This allows multiple devices (typically disk
21 drives or partitions thereof) to be combined into a single device to
22 hold (for example) a single filesystem.
23 Some RAID levels include redundancy and so can survive some degree of
26 Linux Software RAID devices are implemented through the md (Multiple
27 Devices) device driver.
29 Currently, Linux supports
46 is not a Software RAID mechanism, but does involve
48 each device is a path to one common physical storage device.
49 New installations should not use md/multipath as it is not well
50 supported and has no ongoing development. Use the Device Mapper based
51 multipath-tools instead.
54 is also not true RAID, and it only involves one device. It
55 provides a layer over a true device that can be used to inject faults.
60 is a collection of devices that are
61 managed as a set. This is similar to the set of devices connected to
62 a hardware RAID controller. The set of devices may contain a number
63 of different RAID arrays each utilising some (or all) of the blocks from a
64 number of the devices in the set. For example, two devices in a 5-device set
65 might form a RAID1 using the whole devices. The remaining three might
66 have a RAID5 over the first half of each device, and a RAID0 over the
71 there is one set of metadata that describes all of
72 the arrays in the container. So when
76 device, the device just represents the metadata. Other normal arrays (RAID1
77 etc) can be created inside the container.
80 mdadm has several major modes of operation:
83 Assemble the components of a previously created
84 array into an active array. Components can be explicitly given
85 or can be searched for.
87 checks that the components
88 do form a bona fide array, and can, on request, fiddle superblock
89 information so as to assemble a faulty array.
93 Build an array that doesn't have per-device metadata (superblocks). For these
96 cannot differentiate between initial creation and subsequent assembly
97 of an array. It also cannot perform any checks that appropriate
98 components have been requested. Because of this, the
100 mode should only be used together with a complete understanding of
105 Create a new array with per-device metadata (superblocks).
106 Appropriate metadata is written to each device, and then the array
107 comprising those devices is activated. A 'resync' process is started
108 to make sure that the array is consistent (e.g. both sides of a mirror
109 contain the same data) but the content of the device is left otherwise
111 The array can be used as soon as it has been created. There is no
112 need to wait for the initial resync to finish.
115 .B "Follow or Monitor"
116 Monitor one or more md devices and act on any state changes. This is
117 only meaningful for RAID1, 4, 5, 6, 10 or multipath arrays, as
118 only these have interesting state. RAID0 or Linear never have
119 missing, spare, or failed drives, so there is nothing to monitor.
123 Grow (or shrink) an array, or otherwise reshape it in some way.
124 Currently supported growth options including changing the active size
125 of component devices and changing the number of active devices in
126 Linear and RAID levels 0/1/4/5/6,
127 changing the RAID level between 0, 1, 5, and 6, and between 0 and 10,
128 changing the chunk size and layout for RAID 0,4,5,6,10 as well as adding or
129 removing a write-intent bitmap.
132 .B "Incremental Assembly"
133 Add a single device to an appropriate array. If the addition of the
134 device makes the array runnable, the array will be started.
135 This provides a convenient interface to a
137 system. As each device is detected,
139 has a chance to include it in some array as appropriate.
142 flag is passed in we will remove the device from any active array
143 instead of adding it.
149 in this mode, then any arrays within that container will be assembled
154 This is for doing things to specific components of an array such as
155 adding new spares and removing faulty devices.
159 This is an 'everything else' mode that supports operations on active
160 arrays, operations on component devices such as erasing old superblocks, and
161 information gathering operations.
162 .\"This mode allows operations on independent devices such as examine MD
163 .\"superblocks, erasing old superblocks and stopping active arrays.
167 This mode does not act on a specific device or array, but rather it
168 requests the Linux Kernel to activate any auto-detected arrays.
171 .SH Options for selecting a mode are:
174 .BR \-A ", " \-\-assemble
175 Assemble a pre-existing array.
178 .BR \-B ", " \-\-build
179 Build a legacy array without superblocks.
182 .BR \-C ", " \-\-create
186 .BR \-F ", " \-\-follow ", " \-\-monitor
192 .BR \-G ", " \-\-grow
193 Change the size or shape of an active array.
196 .BR \-I ", " \-\-incremental
197 Add/remove a single device to/from an appropriate array, and possibly start the array.
201 Request that the kernel starts any auto-detected arrays. This can only
204 is compiled into the kernel \(em not if it is a module.
205 Arrays can be auto-detected by the kernel if all the components are in
206 primary MS-DOS partitions with partition type
208 and all use v0.90 metadata.
209 In-kernel autodetect is not recommended for new installations. Using
211 to detect and assemble arrays \(em possibly in an
213 \(em is substantially more flexible and should be preferred.
216 If a device is given before any options, or if the first option is
225 then the MANAGE mode is assumed.
226 Anything other than these will cause the
230 .SH Options that are not mode-specific are:
233 .BR \-h ", " \-\-help
234 Display general help message or, after one of the above options, a
235 mode-specific help message.
239 Display more detailed help about command line parsing and some commonly
243 .BR \-V ", " \-\-version
244 Print version information for mdadm.
247 .BR \-v ", " \-\-verbose
248 Be more verbose about what is happening. This can be used twice to be
250 The extra verbosity currently only affects
251 .B \-\-detail \-\-scan
253 .BR "\-\-examine \-\-scan" .
256 .BR \-q ", " \-\-quiet
257 Avoid printing purely informative messages. With this,
259 will be silent unless there is something really important to report.
263 .BR \-f ", " \-\-force
264 Be more forceful about certain operations. See the various modes for
265 the exact meaning of this option in different contexts.
268 .BR \-c ", " \-\-config=
269 Specify the config file or directory. Default is to use
272 .BR /etc/mdadm.conf.d ,
273 or if those are missing then
274 .B /etc/mdadm/mdadm.conf
276 .BR /etc/mdadm/mdadm.conf.d .
277 If the config file given is
279 then nothing will be read, but
281 will act as though the config file contained exactly
283 .B " DEVICE partitions containers"
287 to find a list of devices to scan, and
289 to find a list of containers to examine.
292 is given for the config file, then
294 will act as though the config file were empty.
296 If the name given is of a directory, then
298 will collect all the files contained in the directory with a name ending
301 sort them lexically, and process all of those files as config files.
304 .BR \-s ", " \-\-scan
307 for missing information.
308 In general, this option gives
310 permission to get any missing information (like component devices,
311 array devices, array identities, and alert destination) from the
312 configuration file (see previous option);
313 one exception is MISC mode when using
319 says to get a list of array devices from
323 .BR \-e ", " \-\-metadata=
324 Declare the style of RAID metadata (superblock) to be used. The
325 default is {DEFAULT_METADATA} for
327 and to guess for other operations.
328 The default can be overridden by setting the
337 .ie '{DEFAULT_METADATA}'0.90'
338 .IP "0, 0.90, default"
341 Use the original 0.90 format superblock. This format limits arrays to
342 28 component devices and limits component devices of levels 1 and
343 greater to 2 terabytes. It is also possible for there to be confusion
344 about whether the superblock applies to a whole device or just the
345 last partition, if that partition starts on a 64K boundary.
346 .ie '{DEFAULT_METADATA}'0.90'
347 .IP "1, 1.0, 1.1, 1.2"
349 .IP "1, 1.0, 1.1, 1.2 default"
350 Use the new version-1 format superblock. This has fewer restrictions.
351 It can easily be moved between hosts with different endian-ness, and a
352 recovery operation can be checkpointed and restarted. The different
353 sub-versions store the superblock at different locations on the
354 device, either at the end (for 1.0), at the start (for 1.1) or 4K from
355 the start (for 1.2). "1" is equivalent to "1.2" (the commonly
356 preferred 1.x format).
357 'if '{DEFAULT_METADATA}'1.2' "default" is equivalent to "1.2".
359 Use the "Industry Standard" DDF (Disk Data Format) format defined by
361 When creating a DDF array a
363 will be created, and normal arrays can be created in that container.
365 Use the Intel(R) Matrix Storage Manager metadata format. This creates a
367 which is managed in a similar manner to DDF, and is supported by an
368 option-rom on some platforms:
370 .B http://www.intel.com/design/chipsets/matrixstorage_sb.htm
376 This will override any
378 setting in the config file and provides the identity of the host which
379 should be considered the home for any arrays.
381 When creating an array, the
383 will be recorded in the metadata. For version-1 superblocks, it will
384 be prefixed to the array name. For version-0.90 superblocks, part of
385 the SHA1 hash of the hostname will be stored in the later half of the
388 When reporting information about an array, any array which is tagged
389 for the given homehost will be reported as such.
391 When using Auto-Assemble, only arrays tagged for the given homehost
392 will be allowed to use 'local' names (i.e. not ending in '_' followed
393 by a digit string). See below under
394 .BR "Auto Assembly" .
396 The special name "\fBany\fP" can be used as a wild card. If an array
399 then the name "\fBany\fP" will be stored in the array and it can be
400 assembled in the same way on any host. If an array is assembled with
401 this option, then the homehost recorded on the array will be ignored.
407 needs to print the name for a device it normally finds the name in
409 which refers to the device and is shortest. When a path component is
413 will prefer a longer name if it contains that component. For example
414 .B \-\-prefer=by-uuid
415 will prefer a name in a subdirectory of
420 This functionality is currently only provided by
426 .B \-\-home\-cluster=
427 specifies the cluster name for the md device. The md device can be assembled
428 only on the cluster which matches the name specified. If this option is not
429 provided, mdadm tries to detect the cluster name automatically.
431 .SH For create, build, or grow:
434 .BR \-n ", " \-\-raid\-devices=
435 Specify the number of active devices in the array. This, plus the
436 number of spare devices (see below) must equal the number of
438 (including "\fBmissing\fP" devices)
439 that are listed on the command line for
441 Setting a value of 1 is probably
442 a mistake and so requires that
444 be specified first. A value of 1 will then be allowed for linear,
445 multipath, RAID0 and RAID1. It is never allowed for RAID4, RAID5 or RAID6.
447 This number can only be changed using
449 for RAID1, RAID4, RAID5 and RAID6 arrays, and only on kernels which provide
450 the necessary support.
453 .BR \-x ", " \-\-spare\-devices=
454 Specify the number of spare (eXtra) devices in the initial array.
455 Spares can also be added
456 and removed later. The number of component devices listed
457 on the command line must equal the number of RAID devices plus the
458 number of spare devices.
461 .BR \-z ", " \-\-size=
462 Amount (in Kibibytes) of space to use from each drive in RAID levels 1/4/5/6.
463 This must be a multiple of the chunk size, and must leave about 128Kb
464 of space at the end of the drive for the RAID superblock.
465 If this is not specified
466 (as it normally is not) the smallest drive (or partition) sets the
467 size, though if there is a variance among the drives of greater than 1%, a warning is
470 A suffix of 'M' or 'G' can be given to indicate Megabytes or
471 Gigabytes respectively.
473 Sometimes a replacement drive can be a little smaller than the
474 original drives though this should be minimised by IDEMA standards.
475 Such a replacement drive will be rejected by
477 To guard against this it can be useful to set the initial size
478 slightly smaller than the smaller device with the aim that it will
479 still be larger than any replacement.
481 This value can be set with
483 for RAID level 1/4/5/6 though
485 based arrays such as those with IMSM metadata may not be able to
487 If the array was created with a size smaller than the currently
488 active drives, the extra space can be accessed using
490 The size can be given as
492 which means to choose the largest size that fits on all current drives.
494 Before reducing the size of the array (with
495 .BR "\-\-grow \-\-size=" )
496 you should make sure that space isn't needed. If the device holds a
497 filesystem, you would need to resize the filesystem to use less space.
499 After reducing the array size you should check that the data stored in
500 the device is still available. If the device holds a filesystem, then
501 an 'fsck' of the filesystem is a minimum requirement. If there are
502 problems the array can be made bigger again with no loss with another
503 .B "\-\-grow \-\-size="
506 This value cannot be used when creating a
508 such as with DDF and IMSM metadata, though it perfectly valid when
509 creating an array inside a container.
512 .BR \-Z ", " \-\-array\-size=
513 This is only meaningful with
515 and its effect is not persistent: when the array is stopped and
516 restarted the default array size will be restored.
518 Setting the array-size causes the array to appear smaller to programs
519 that access the data. This is particularly needed before reshaping an
520 array so that it will be smaller. As the reshape is not reversible,
521 but setting the size with
523 is, it is required that the array size is reduced as appropriate
524 before the number of devices in the array is reduced.
526 Before reducing the size of the array you should make sure that space
527 isn't needed. If the device holds a filesystem, you would need to
528 resize the filesystem to use less space.
530 After reducing the array size you should check that the data stored in
531 the device is still available. If the device holds a filesystem, then
532 an 'fsck' of the filesystem is a minimum requirement. If there are
533 problems the array can be made bigger again with no loss with another
534 .B "\-\-grow \-\-array\-size="
537 A suffix of 'M' or 'G' can be given to indicate Megabytes or
538 Gigabytes respectively.
541 restores the apparent size of the array to be whatever the real
542 amount of available space is.
545 .BR \-c ", " \-\-chunk=
546 Specify chunk size of kibibytes. The default when creating an
547 array is 512KB. To ensure compatibility with earlier versions, the
548 default when building an array with no persistent metadata is 64KB.
549 This is only meaningful for RAID0, RAID4, RAID5, RAID6, and RAID10.
551 RAID4, RAID5, RAID6, and RAID10 require the chunk size to be a power
552 of 2. In any case it must be a multiple of 4KB.
554 A suffix of 'M' or 'G' can be given to indicate Megabytes or
555 Gigabytes respectively.
559 Specify rounding factor for a Linear array. The size of each
560 component will be rounded down to a multiple of this size.
561 This is a synonym for
563 but highlights the different meaning for Linear as compared to other
564 RAID levels. The default is 64K if a kernel earlier than 2.6.16 is in
565 use, and is 0K (i.e. no rounding) in later kernels.
568 .BR \-l ", " \-\-level=
569 Set RAID level. When used with
571 options are: linear, raid0, 0, stripe, raid1, 1, mirror, raid4, 4,
572 raid5, 5, raid6, 6, raid10, 10, multipath, mp, faulty, container.
573 Obviously some of these are synonymous.
577 metadata type is requested, only the
579 level is permitted, and it does not need to be explicitly given.
583 only linear, stripe, raid0, 0, raid1, multipath, mp, and faulty are valid.
587 to change the RAID level in some cases. See LEVEL CHANGES below.
590 .BR \-p ", " \-\-layout=
591 This option configures the fine details of data layout for RAID5, RAID6,
592 and RAID10 arrays, and controls the failure modes for
595 The layout of the RAID5 parity block can be one of
596 .BR left\-asymmetric ,
597 .BR left\-symmetric ,
598 .BR right\-asymmetric ,
599 .BR right\-symmetric ,
600 .BR la ", " ra ", " ls ", " rs .
602 .BR left\-symmetric .
604 It is also possible to cause RAID5 to use a RAID4-like layout by
610 Finally for RAID5 there are DDF\-compatible layouts,
611 .BR ddf\-zero\-restart ,
612 .BR ddf\-N\-restart ,
614 .BR ddf\-N\-continue .
616 These same layouts are available for RAID6. There are also 4 layouts
617 that will provide an intermediate stage for converting between RAID5
618 and RAID6. These provide a layout which is identical to the
619 corresponding RAID5 layout on the first N\-1 devices, and has the 'Q'
620 syndrome (the second 'parity' block used by RAID6) on the last device.
622 .BR left\-symmetric\-6 ,
623 .BR right\-symmetric\-6 ,
624 .BR left\-asymmetric\-6 ,
625 .BR right\-asymmetric\-6 ,
627 .BR parity\-first\-6 .
629 When setting the failure mode for level
632 .BR write\-transient ", " wt ,
633 .BR read\-transient ", " rt ,
634 .BR write\-persistent ", " wp ,
635 .BR read\-persistent ", " rp ,
637 .BR read\-fixable ", " rf ,
638 .BR clear ", " flush ", " none .
640 Each failure mode can be followed by a number, which is used as a period
641 between fault generation. Without a number, the fault is generated
642 once on the first relevant request. With a number, the fault will be
643 generated after that many requests, and will continue to be generated
644 every time the period elapses.
646 Multiple failure modes can be current simultaneously by using the
648 option to set subsequent failure modes.
650 "clear" or "none" will remove any pending or periodic failure modes,
651 and "flush" will clear any persistent faults.
653 Finally, the layout options for RAID10 are one of 'n', 'o' or 'f' followed
654 by a small number. The default is 'n2'. The supported options are:
657 signals 'near' copies. Multiple copies of one data block are at
658 similar offsets in different devices.
661 signals 'offset' copies. Rather than the chunks being duplicated
662 within a stripe, whole stripes are duplicated but are rotated by one
663 device so duplicate blocks are on different devices. Thus subsequent
664 copies of a block are in the next drive, and are one chunk further
669 (multiple copies have very different offsets).
670 See md(4) for more detail about 'near', 'offset', and 'far'.
672 The number is the number of copies of each datablock. 2 is normal, 3
673 can be useful. This number can be at most equal to the number of
674 devices in the array. It does not need to divide evenly into that
675 number (e.g. it is perfectly legal to have an 'n2' layout for an array
676 with an odd number of devices).
678 When an array is converted between RAID5 and RAID6 an intermediate
679 RAID6 layout is used in which the second parity block (Q) is always on
680 the last device. To convert a RAID5 to RAID6 and leave it in this new
681 layout (which does not require re-striping) use
682 .BR \-\-layout=preserve .
683 This will try to avoid any restriping.
685 The converse of this is
686 .B \-\-layout=normalise
687 which will change a non-standard RAID6 layout into a more standard
694 (thus explaining the p of
698 .BR \-b ", " \-\-bitmap=
699 Specify a file to store a write-intent bitmap in. The file should not
702 is also given. The same file should be provided
703 when assembling the array. If the word
705 is given, then the bitmap is stored with the metadata on the array,
706 and so is replicated on all devices. If the word
710 mode, then any bitmap that is present is removed. If the word
712 is given, the array is created for a clustered environment. One bitmap
713 is created for each node as defined by the
715 parameter and are stored internally.
717 To help catch typing errors, the filename must contain at least one
718 slash ('/') if it is a real file (not 'internal' or 'none').
720 Note: external bitmaps are only known to work on ext2 and ext3.
721 Storing bitmap files on other filesystems may result in serious problems.
723 When creating an array on devices which are 100G or larger,
725 automatically adds an internal bitmap as it will usually be
726 beneficial. This can be suppressed with
727 .B "\-\-bitmap=none".
730 .BR \-\-bitmap\-chunk=
731 Set the chunksize of the bitmap. Each bit corresponds to that many
732 Kilobytes of storage.
733 When using a file based bitmap, the default is to use the smallest
734 size that is at-least 4 and requires no more than 2^21 chunks.
737 bitmap, the chunksize defaults to 64Meg, or larger if necessary to
738 fit the bitmap into the available space.
740 A suffix of 'M' or 'G' can be given to indicate Megabytes or
741 Gigabytes respectively.
744 .BR \-W ", " \-\-write\-mostly
745 subsequent devices listed in a
750 command will be flagged as 'write-mostly'. This is valid for RAID1
751 only and means that the 'md' driver will avoid reading from these
752 devices if at all possible. This can be useful if mirroring over a
756 .BR \-\-write\-behind=
757 Specify that write-behind mode should be enabled (valid for RAID1
758 only). If an argument is specified, it will set the maximum number
759 of outstanding writes allowed. The default value is 256.
760 A write-intent bitmap is required in order to use write-behind
761 mode, and write-behind is only attempted on drives marked as
765 .BR \-\-assume\-clean
768 that the array pre-existed and is known to be clean. It can be useful
769 when trying to recover from a major failure as you can be sure that no
770 data will be affected unless you actually write to the array. It can
771 also be used when creating a RAID1 or RAID10 if you want to avoid the
772 initial resync, however this practice \(em while normally safe \(em is not
773 recommended. Use this only if you really know what you are doing.
775 When the devices that will be part of a new array were filled
776 with zeros before creation the operator knows the array is
777 actually clean. If that is the case, such as after running
778 badblocks, this argument can be used to tell mdadm the
779 facts the operator knows.
781 When an array is resized to a larger size with
782 .B "\-\-grow \-\-size="
783 the new space is normally resynced in that same way that the whole
784 array is resynced at creation. From Linux version 3.0,
786 can be used with that command to avoid the automatic resync.
789 .BR \-\-backup\-file=
792 is used to increase the number of raid-devices in a RAID5 or RAID6 if
793 there are no spare devices available, or to shrink, change RAID level
794 or layout. See the GROW MODE section below on RAID\-DEVICES CHANGES.
795 The file must be stored on a separate device, not on the RAID array
800 Arrays with 1.x metadata can leave a gap between the start of the
801 device and the start of array data. This gap can be used for various
802 metadata. The start of data is known as the
804 Normally an appropriate data offset is computed automatically.
805 However it can be useful to set it explicitly such as when re-creating
806 an array which was originally created using a different version of
808 which computed a different offset.
810 Setting the offset explicitly over-rides the default. The value given
811 is in Kilobytes unless an 'M' or 'G' suffix is given.
815 can also be used with
817 for some RAID levels (initially on RAID10). This allows the
818 data\-offset to be changed as part of the reshape process. When the
819 data offset is changed, no backup file is required as the difference
820 in offsets is used to provide the same functionality.
822 When the new offset is earlier than the old offset, the number of
823 devices in the array cannot shrink. When it is after the old offset,
824 the number of devices in the array cannot increase.
826 When creating an array,
830 In the case each member device is expected to have a offset appended
831 to the name, separated by a colon. This makes it possible to recreate
832 exactly an array which has varying data offsets (as can happen when
833 different versions of
835 are used to add different devices).
839 This option is complementary to the
840 .B \-\-freeze-reshape
841 option for assembly. It is needed when
843 operation is interrupted and it is not restarted automatically due to
844 .B \-\-freeze-reshape
845 usage during array assembly. This option is used together with
849 ) command and device for a pending reshape to be continued.
850 All parameters required for reshape continuation will be read from array metadata.
854 .BR \-\-backup\-file=
855 option to be set, continuation option will require to have exactly the same
856 backup file given as well.
858 Any other parameter passed together with
860 option will be ignored.
863 .BR \-N ", " \-\-name=
866 for the array. This is currently only effective when creating an
867 array with a version-1 superblock, or an array in a DDF container.
868 The name is a simple textual string that can be used to identify array
869 components when assembling. If name is needed but not specified, it
870 is taken from the basename of the device that is being created.
882 run the array, even if some of the components
883 appear to be active in another array or filesystem. Normally
885 will ask for confirmation before including such components in an
886 array. This option causes that question to be suppressed.
889 .BR \-f ", " \-\-force
892 accept the geometry and layout specified without question. Normally
894 will not allow creation of an array with only one device, and will try
895 to create a RAID5 array with one missing drive (as this makes the
896 initial resync work faster). With
899 will not try to be so clever.
902 .BR \-o ", " \-\-readonly
905 rather than read-write as normal. No writes will be allowed to the
906 array, and no resync, recovery, or reshape will be started.
909 .BR \-a ", " "\-\-auto{=yes,md,mdp,part,p}{NN}"
910 Instruct mdadm how to create the device file if needed, possibly allocating
911 an unused minor number. "md" causes a non-partitionable array
912 to be used (though since Linux 2.6.28, these array devices are in fact
913 partitionable). "mdp", "part" or "p" causes a partitionable array (2.6 and
914 later) to be used. "yes" requires the named md device to have
915 a 'standard' format, and the type and minor number will be determined
916 from this. With mdadm 3.0, device creation is normally left up to
918 so this option is unlikely to be needed.
919 See DEVICE NAMES below.
921 The argument can also come immediately after
926 is not given on the command line or in the config file, then
932 is also given, then any
934 entries in the config file will override the
936 instruction given on the command line.
938 For partitionable arrays,
940 will create the device file for the whole array and for the first 4
941 partitions. A different number of partitions can be specified at the
942 end of this option (e.g.
944 If the device name ends with a digit, the partition names add a 'p',
946 .IR /dev/md/home1p3 .
947 If there is no trailing digit, then the partition names just have a
949 .IR /dev/md/scratch3 .
951 If the md device name is in a 'standard' format as described in DEVICE
952 NAMES, then it will be created, if necessary, with the appropriate
953 device number based on that name. If the device name is not in one of these
954 formats, then a unused device number will be allocated. The device
955 number will be considered unused if there is no active array for that
956 number, and there is no entry in /dev for that number and with a
957 non-standard name. Names that are not in 'standard' format are only
958 allowed in "/dev/md/".
960 This is meaningful with
966 .BR \-a ", " "\-\-add"
967 This option can be used in Grow mode in two cases.
969 If the target array is a Linear array, then
971 can be used to add one or more devices to the array. They
972 are simply catenated on to the end of the array. Once added, the
973 devices cannot be removed.
977 option is being used to increase the number of devices in an array,
980 can be used to add some extra devices to be included in the array.
981 In most cases this is not needed as the extra devices can be added as
982 spares first, and then the number of raid-disks can be changed.
983 However for RAID0, it is not possible to add spares. So to increase
984 the number of devices in a RAID0, it is necessary to set the new
985 number of devices, and to add the new devices, in the same command.
989 Only works when the array is for clustered environment. It specifies
990 the maximum number of nodes in the cluster that will use this device
991 simultaneously. If not specified, this defaults to 4.
996 .BR \-u ", " \-\-uuid=
997 uuid of array to assemble. Devices which don't have this uuid are
1001 .BR \-m ", " \-\-super\-minor=
1002 Minor number of device that array was created for. Devices which
1003 don't have this minor number are excluded. If you create an array as
1004 /dev/md1, then all superblocks will contain the minor number 1, even if
1005 the array is later assembled as /dev/md2.
1007 Giving the literal word "dev" for
1011 to use the minor number of the md device that is being assembled.
1012 e.g. when assembling
1014 .B \-\-super\-minor=dev
1015 will look for super blocks with a minor number of 0.
1018 is only relevant for v0.90 metadata, and should not normally be used.
1024 .BR \-N ", " \-\-name=
1025 Specify the name of the array to assemble. This must be the name
1026 that was specified when creating the array. It must either match
1027 the name stored in the superblock exactly, or it must match
1030 prefixed to the start of the given name.
1033 .BR \-f ", " \-\-force
1034 Assemble the array even if the metadata on some devices appears to be
1037 cannot find enough working devices to start the array, but can find
1038 some devices that are recorded as having failed, then it will mark
1039 those devices as working so that the array can be started.
1040 An array which requires
1042 to be started may contain data corruption. Use it carefully.
1045 .BR \-R ", " \-\-run
1046 Attempt to start the array even if fewer drives were given than were
1047 present last time the array was active. Normally if not all the
1048 expected drives are found and
1050 is not used, then the array will be assembled but not started.
1053 an attempt will be made to start it anyway.
1057 This is the reverse of
1059 in that it inhibits the startup of array unless all expected drives
1060 are present. This is only needed with
1062 and can be used if the physical connections to devices are
1063 not as reliable as you would like.
1066 .BR \-a ", " "\-\-auto{=no,yes,md,mdp,part}"
1067 See this option under Create and Build options.
1070 .BR \-b ", " \-\-bitmap=
1071 Specify the bitmap file that was given when the array was created. If
1074 bitmap, there is no need to specify this when assembling the array.
1077 .BR \-\-backup\-file=
1080 was used while reshaping an array (e.g. changing number of devices or
1081 chunk size) and the system crashed during the critical section, then the same
1083 must be presented to
1085 to allow possibly corrupted data to be restored, and the reshape
1089 .BR \-\-invalid\-backup
1090 If the file needed for the above option is not available for any
1091 reason an empty file can be given together with this option to
1092 indicate that the backup file is invalid. In this case the data that
1093 was being rearranged at the time of the crash could be irrecoverably
1094 lost, but the rest of the array may still be recoverable. This option
1095 should only be used as a last resort if there is no way to recover the
1100 .BR \-U ", " \-\-update=
1101 Update the superblock on each device while assembling the array. The
1102 argument given to this flag can be one of
1122 option will adjust the superblock of an array what was created on a Sparc
1123 machine running a patched 2.2 Linux kernel. This kernel got the
1124 alignment of part of the superblock wrong. You can use the
1125 .B "\-\-examine \-\-sparc2.2"
1128 to see what effect this would have.
1132 option will update the
1133 .B "preferred minor"
1134 field on each superblock to match the minor number of the array being
1136 This can be useful if
1138 reports a different "Preferred Minor" to
1140 In some cases this update will be performed automatically
1141 by the kernel driver. In particular the update happens automatically
1142 at the first write to an array with redundancy (RAID level 1 or
1143 greater) on a 2.6 (or later) kernel.
1147 option will change the uuid of the array. If a UUID is given with the
1149 option that UUID will be used as a new UUID and will
1151 be used to help identify the devices in the array.
1154 is given, a random UUID is chosen.
1158 option will change the
1160 of the array as stored in the superblock and bitmap. This option only
1161 works for clustered environment.
1165 option will change the
1167 of the array as stored in the superblock. This is only supported for
1168 version-1 superblocks.
1172 option will change the
1174 as recorded in the superblock. For version-0 superblocks, this is the
1175 same as updating the UUID.
1176 For version-1 superblocks, this involves updating the name.
1180 option will change the cluster name as recorded in the superblock and
1181 bitmap. This option only works for clustered environment.
1185 option will cause the array to be marked
1187 meaning that any redundancy in the array (e.g. parity for RAID5,
1188 copies for RAID1) may be incorrect. This will cause the RAID system
1189 to perform a "resync" pass to make sure that all redundant information
1194 option allows arrays to be moved between machines with different
1196 When assembling such an array for the first time after a move, giving
1197 .B "\-\-update=byteorder"
1200 to expect superblocks to have their byteorder reversed, and will
1201 correct that order before assembling the array. This is only valid
1202 with original (Version 0.90) superblocks.
1206 option will correct the summaries in the superblock. That is the
1207 counts of total, working, active, failed, and spare devices.
1211 option will rarely be of use. It applies to version 1.1 and 1.2 metadata
1212 only (where the metadata is at the start of the device) and is only
1213 useful when the component device has changed size (typically become
1214 larger). The version 1 metadata records the amount of the device that
1215 can be used to store data, so if a device in a version 1.1 or 1.2
1216 array becomes larger, the metadata will still be visible, but the
1217 extra space will not. In this case it might be useful to assemble the
1219 .BR \-\-update=devicesize .
1222 to determine the maximum usable amount of space on each device and
1223 update the relevant field in the metadata.
1227 option only works on v0.90 metadata arrays and will convert them to
1228 v1.0 metadata. The array must not be dirty (i.e. it must not need a
1229 sync) and it must not have a write-intent bitmap.
1231 The old metadata will remain on the devices, but will appear older
1232 than the new metadata and so will usually be ignored. The old metadata
1233 (or indeed the new metadata) can be removed by giving the appropriate
1236 .BR \-\-zero\-superblock .
1240 option can be used when an array has an internal bitmap which is
1241 corrupt in some way so that assembling the array normally fails. It
1242 will cause any internal bitmap to be ignored.
1246 option will reserve space in each device for a bad block list. This
1247 will be 4K in size and positioned near the end of any free space
1248 between the superblock and the data.
1252 option will cause any reservation of space for a bad block list to be
1253 removed. If the bad block list contains entries, this will fail, as
1254 removing the list could cause data corruption.
1257 .BR \-\-freeze\-reshape
1258 Option is intended to be used in start-up scripts during initrd boot phase.
1259 When array under reshape is assembled during initrd phase, this option
1260 stops reshape after reshape critical section is being restored. This happens
1261 before file system pivot operation and avoids loss of file system context.
1262 Losing file system context would cause reshape to be broken.
1264 Reshape can be continued later using the
1266 option for the grow command.
1268 .SH For Manage mode:
1271 .BR \-t ", " \-\-test
1272 Unless a more serious error occurred,
1274 will exit with a status of 2 if no changes were made to the array and
1275 0 if at least one change was made.
1276 This can be useful when an indirect specifier such as
1281 is used in requesting an operation on the array.
1283 will report failure if these specifiers didn't find any match.
1286 .BR \-a ", " \-\-add
1287 hot-add listed devices.
1288 If a device appears to have recently been part of the array
1289 (possibly it failed or was removed) the device is re\-added as described
1291 If that fails or the device was never part of the array, the device is
1292 added as a hot-spare.
1293 If the array is degraded, it will immediately start to rebuild data
1296 Note that this and the following options are only meaningful on array
1297 with redundancy. They don't apply to RAID0 or Linear.
1301 re\-add a device that was previously removed from an array.
1302 If the metadata on the device reports that it is a member of the
1303 array, and the slot that it used is still vacant, then the device will
1304 be added back to the array in the same position. This will normally
1305 cause the data for that device to be recovered. However based on the
1306 event count on the device, the recovery may only require sections that
1307 are flagged a write-intent bitmap to be recovered or may not require
1308 any recovery at all.
1310 When used on an array that has no metadata (i.e. it was built with
1312 it will be assumed that bitmap-based recovery is enough to make the
1313 device fully consistent with the array.
1315 When used with v1.x metadata,
1317 can be accompanied by
1318 .BR \-\-update=devicesize ,
1319 .BR \-\-update=bbl ", or"
1320 .BR \-\-update=no\-bbl .
1321 See the description of these option when used in Assemble mode for an
1322 explanation of their use.
1324 If the device name given is
1328 will try to find any device that looks like it should be
1329 part of the array but isn't and will try to re\-add all such devices.
1331 If the device name given is
1335 will find all devices in the array that are marked
1337 remove them and attempt to immediately re\-add them. This can be
1338 useful if you are certain that the reason for failure has been
1343 Add a device as a spare. This is similar to
1345 except that it does not attempt
1347 first. The device will be added as a spare even if it looks like it
1348 could be an recent member of the array.
1351 .BR \-r ", " \-\-remove
1352 remove listed devices. They must not be active. i.e. they should
1353 be failed or spare devices.
1355 As well as the name of a device file
1365 The first causes all failed device to be removed. The second causes
1366 any device which is no longer connected to the system (i.e an 'open'
1370 The third will remove a set as describe below under
1374 .BR \-f ", " \-\-fail
1375 Mark listed devices as faulty.
1376 As well as the name of a device file, the word
1380 can be given. The former will cause any device that has been detached from
1381 the system to be marked as failed. It can then be removed.
1383 For RAID10 arrays where the number of copies evenly divides the number
1384 of devices, the devices can be conceptually divided into sets where
1385 each set contains a single complete copy of the data on the array.
1386 Sometimes a RAID10 array will be configured so that these sets are on
1387 separate controllers. In this case all the devices in one set can be
1388 failed by giving a name like
1394 The appropriate set names are reported by
1404 Mark listed devices as requiring replacement. As soon as a spare is
1405 available, it will be rebuilt and will replace the marked device.
1406 This is similar to marking a device as faulty, but the device remains
1407 in service during the recovery process to increase resilience against
1408 multiple failures. When the replacement process finishes, the
1409 replaced device will be marked as faulty.
1413 This can follow a list of
1415 devices. The devices listed after
1417 will be preferentially used to replace the devices listed after
1419 These device must already be spare devices in the array.
1422 .BR \-\-write\-mostly
1423 Subsequent devices that are added or re\-added will have the 'write-mostly'
1424 flag set. This is only valid for RAID1 and means that the 'md' driver
1425 will avoid reading from these devices if possible.
1428 Subsequent devices that are added or re\-added will have the 'write-mostly'
1431 .BR \-\-cluster\-confirm
1432 Confirm the existence of the device. This is issued in response to an \-\-add
1433 request by a node in a cluster. When a node adds a device it sends a message
1434 to all nodes in the cluster to look for a device with a UUID. This translates
1435 to a udev notification with the UUID of the device to be added and the slot
1436 number. The receiving node must acknowledge this message
1437 with \-\-cluster\-confirm. Valid arguments are <slot>:<devicename> in case
1438 the device is found or <slot>:missing in case the device is not found.
1441 Each of these options requires that the first device listed is the array
1442 to be acted upon, and the remainder are component devices to be added,
1443 removed, marked as faulty, etc. Several different operations can be
1444 specified for different devices, e.g.
1446 mdadm /dev/md0 \-\-add /dev/sda1 \-\-fail /dev/sdb1 \-\-remove /dev/sdb1
1448 Each operation applies to all devices listed until the next
1451 If an array is using a write-intent bitmap, then devices which have
1452 been removed can be re\-added in a way that avoids a full
1453 reconstruction but instead just updates the blocks that have changed
1454 since the device was removed. For arrays with persistent metadata
1455 (superblocks) this is done automatically. For arrays created with
1457 mdadm needs to be told that this device we removed recently with
1460 Devices can only be removed from an array if they are not in active
1461 use, i.e. that must be spares or failed devices. To remove an active
1462 device, it must first be marked as
1468 .BR \-Q ", " \-\-query
1469 Examine a device to see
1470 (1) if it is an md device and (2) if it is a component of an md
1472 Information about what is discovered is presented.
1475 .BR \-D ", " \-\-detail
1476 Print details of one or more md devices.
1479 .BR \-\-detail\-platform
1480 Print details of the platform's RAID capabilities (firmware / hardware
1481 topology) for a given metadata format. If used without argument, mdadm
1482 will scan all controllers looking for their capabilities. Otherwise, mdadm
1483 will only look at the controller specified by the argument in form of an
1484 absolute filepath or a link, e.g.
1485 .IR /sys/devices/pci0000:00/0000:00:1f.2 .
1488 .BR \-Y ", " \-\-export
1491 .BR \-\-detail-platform ,
1495 output will be formatted as
1497 pairs for easy import into the environment.
1503 indicates whether an array was started
1505 or not, which may include a reason
1506 .RB ( unsafe ", " nothing ", " no ).
1509 indicates if the array is expected on this host
1511 or seems to be from elsewhere
1515 .BR \-E ", " \-\-examine
1516 Print contents of the metadata stored on the named device(s).
1517 Note the contrast between
1522 applies to devices which are components of an array, while
1524 applies to a whole array which is currently active.
1527 If an array was created on a SPARC machine with a 2.2 Linux kernel
1528 patched with RAID support, the superblock will have been created
1529 incorrectly, or at least incompatibly with 2.4 and later kernels.
1534 will fix the superblock before displaying it. If this appears to do
1535 the right thing, then the array can be successfully assembled using
1536 .BR "\-\-assemble \-\-update=sparc2.2" .
1539 .BR \-X ", " \-\-examine\-bitmap
1540 Report information about a bitmap file.
1541 The argument is either an external bitmap file or an array component
1542 in case of an internal bitmap. Note that running this on an array
1545 does not report the bitmap for that array.
1548 .B \-\-examine\-badblocks
1549 List the bad-blocks recorded for the device, if a bad-blocks list has
1550 been configured. Currently only
1552 metadata supports bad-blocks lists.
1555 .BI \-\-dump= directory
1557 .BI \-\-restore= directory
1558 Save metadata from lists devices, or restore metadata to listed devices.
1561 .BR \-R ", " \-\-run
1562 start a partially assembled array. If
1564 did not find enough devices to fully start the array, it might leaving
1565 it partially assembled. If you wish, you can then use
1567 to start the array in degraded mode.
1570 .BR \-S ", " \-\-stop
1571 deactivate array, releasing all resources.
1574 .BR \-o ", " \-\-readonly
1575 mark array as readonly.
1578 .BR \-w ", " \-\-readwrite
1579 mark array as readwrite.
1582 .B \-\-zero\-superblock
1583 If the device contains a valid md superblock, the block is
1584 overwritten with zeros. With
1586 the block where the superblock would be is overwritten even if it
1587 doesn't appear to be valid.
1590 .B \-\-kill\-subarray=
1591 If the device is a container and the argument to \-\-kill\-subarray
1592 specifies an inactive subarray in the container, then the subarray is
1593 deleted. Deleting all subarrays will leave an 'empty-container' or
1594 spare superblock on the drives. See
1595 .B \-\-zero\-superblock
1597 removing a superblock. Note that some formats depend on the subarray
1598 index for generating a UUID, this command will fail if it would change
1599 the UUID of an active subarray.
1602 .B \-\-update\-subarray=
1603 If the device is a container and the argument to \-\-update\-subarray
1604 specifies a subarray in the container, then attempt to update the given
1605 superblock field in the subarray. See below in
1610 .BR \-t ", " \-\-test
1615 is set to reflect the status of the device. See below in
1620 .BR \-W ", " \-\-wait
1621 For each md device given, wait for any resync, recovery, or reshape
1622 activity to finish before returning.
1624 will return with success if it actually waited for every device
1625 listed, otherwise it will return failure.
1629 For each md device given, or each device in /proc/mdstat if
1631 is given, arrange for the array to be marked clean as soon as possible.
1633 will return with success if the array uses external metadata and we
1634 successfully waited. For native arrays this returns immediately as the
1635 kernel handles dirty-clean transitions at shutdown. No action is taken
1636 if safe-mode handling is disabled.
1640 Set the "sync_action" for all md devices given to one of
1647 will abort any currently running action though some actions will
1648 automatically restart.
1651 will abort any current action and ensure no other action starts
1661 .BR "SCRUBBING AND MISMATCHES" .
1663 .SH For Incremental Assembly mode:
1665 .BR \-\-rebuild\-map ", " \-r
1666 Rebuild the map file
1670 uses to help track which arrays are currently being assembled.
1673 .BR \-\-run ", " \-R
1674 Run any array assembled as soon as a minimal number of devices are
1675 available, rather than waiting until all expected devices are present.
1678 .BR \-\-scan ", " \-s
1679 Only meaningful with
1683 file for arrays that are being incrementally assembled and will try to
1684 start any that are not already started. If any such array is listed
1687 as requiring an external bitmap, that bitmap will be attached first.
1690 .BR \-\-fail ", " \-f
1691 This allows the hot-plug system to remove devices that have fully disappeared
1692 from the kernel. It will first fail and then remove the device from any
1693 array it belongs to.
1694 The device name given should be a kernel device name such as "sda",
1700 Only used with \-\-fail. The 'path' given will be recorded so that if
1701 a new device appears at the same location it can be automatically
1702 added to the same array. This allows the failed device to be
1703 automatically replaced by a new device without metadata if it appears
1704 at specified path. This option is normally only set by a
1708 .SH For Monitor mode:
1710 .BR \-m ", " \-\-mail
1711 Give a mail address to send alerts to.
1714 .BR \-p ", " \-\-program ", " \-\-alert
1715 Give a program to be run whenever an event is detected.
1718 .BR \-y ", " \-\-syslog
1719 Cause all events to be reported through 'syslog'. The messages have
1720 facility of 'daemon' and varying priorities.
1723 .BR \-d ", " \-\-delay
1724 Give a delay in seconds.
1726 polls the md arrays and then waits this many seconds before polling
1727 again. The default is 60 seconds. Since 2.6.16, there is no need to
1728 reduce this as the kernel alerts
1730 immediately when there is any change.
1733 .BR \-r ", " \-\-increment
1734 Give a percentage increment.
1736 will generate RebuildNN events with the given percentage increment.
1739 .BR \-f ", " \-\-daemonise
1742 to run as a background daemon if it decides to monitor anything. This
1743 causes it to fork and run in the child, and to disconnect from the
1744 terminal. The process id of the child is written to stdout.
1747 which will only continue monitoring if a mail address or alert program
1748 is found in the config file.
1751 .BR \-i ", " \-\-pid\-file
1754 is running in daemon mode, write the pid of the daemon process to
1755 the specified file, instead of printing it on standard output.
1758 .BR \-1 ", " \-\-oneshot
1759 Check arrays only once. This will generate
1761 events and more significantly
1767 .B " mdadm \-\-monitor \-\-scan \-1"
1769 from a cron script will ensure regular notification of any degraded arrays.
1772 .BR \-t ", " \-\-test
1775 alert for every array found at startup. This alert gets mailed and
1776 passed to the alert program. This can be used for testing that alert
1777 message do get through successfully.
1781 This inhibits the functionality for moving spares between arrays.
1782 Only one monitoring process started with
1784 but without this flag is allowed, otherwise the two could interfere
1791 .B mdadm \-\-assemble
1792 .I md-device options-and-component-devices...
1795 .B mdadm \-\-assemble \-\-scan
1796 .I md-devices-and-options...
1799 .B mdadm \-\-assemble \-\-scan
1803 This usage assembles one or more RAID arrays from pre-existing components.
1804 For each array, mdadm needs to know the md device, the identity of the
1805 array, and a number of component-devices. These can be found in a number of ways.
1807 In the first usage example (without the
1809 the first device given is the md device.
1810 In the second usage example, all devices listed are treated as md
1811 devices and assembly is attempted.
1812 In the third (where no devices are listed) all md devices that are
1813 listed in the configuration file are assembled. If no arrays are
1814 described by the configuration file, then any arrays that
1815 can be found on unused devices will be assembled.
1817 If precisely one device is listed, but
1823 was given and identity information is extracted from the configuration file.
1825 The identity can be given with the
1831 option, will be taken from the md-device record in the config file, or
1832 will be taken from the super block of the first component-device
1833 listed on the command line.
1835 Devices can be given on the
1837 command line or in the config file. Only devices which have an md
1838 superblock which contains the right identity will be considered for
1841 The config file is only used if explicitly named with
1843 or requested with (a possibly implicit)
1848 .B /etc/mdadm/mdadm.conf
1853 is not given, then the config file will only be used to find the
1854 identity of md arrays.
1856 Normally the array will be started after it is assembled. However if
1858 is not given and not all expected drives were listed, then the array
1859 is not started (to guard against usage errors). To insist that the
1860 array be started in this case (as may work for RAID1, 4, 5, 6, or 10),
1869 does not create any entries in
1873 It does record information in
1877 to choose the correct name.
1881 detects that udev is not configured, it will create the devices in
1885 In Linux kernels prior to version 2.6.28 there were two distinctly
1886 different types of md devices that could be created: one that could be
1887 partitioned using standard partitioning tools and one that could not.
1888 Since 2.6.28 that distinction is no longer relevant as both type of
1889 devices can be partitioned.
1891 will normally create the type that originally could not be partitioned
1892 as it has a well defined major number (9).
1894 Prior to 2.6.28, it is important that mdadm chooses the correct type
1895 of array device to use. This can be controlled with the
1897 option. In particular, a value of "mdp" or "part" or "p" tells mdadm
1898 to use a partitionable device rather than the default.
1900 In the no-udev case, the value given to
1902 can be suffixed by a number. This tells
1904 to create that number of partition devices rather than the default of 4.
1908 can also be given in the configuration file as a word starting
1910 on the ARRAY line for the relevant array.
1917 and no devices are listed,
1919 will first attempt to assemble all the arrays listed in the config
1922 If no arrays are listed in the config (other than those marked
1924 it will look through the available devices for possible arrays and
1925 will try to assemble anything that it finds. Arrays which are tagged
1926 as belonging to the given homehost will be assembled and started
1927 normally. Arrays which do not obviously belong to this host are given
1928 names that are expected not to conflict with anything local, and are
1929 started "read-auto" so that nothing is written to any device until the
1930 array is written to. i.e. automatic resync etc is delayed.
1934 finds a consistent set of devices that look like they should comprise
1935 an array, and if the superblock is tagged as belonging to the given
1936 home host, it will automatically choose a device name and try to
1937 assemble the array. If the array uses version-0.90 metadata, then the
1939 number as recorded in the superblock is used to create a name in
1943 If the array uses version-1 metadata, then the
1945 from the superblock is used to similarly create a name in
1947 (the name will have any 'host' prefix stripped first).
1949 This behaviour can be modified by the
1953 configuration file. This line can indicate that specific metadata
1954 type should, or should not, be automatically assembled. If an array
1955 is found which is not listed in
1957 and has a metadata format that is denied by the
1959 line, then it will not be assembled.
1962 line can also request that all arrays identified as being for this
1963 homehost should be assembled regardless of their metadata type.
1966 for further details.
1968 Note: Auto assembly cannot be used for assembling and activating some
1969 arrays which are undergoing reshape. In particular as the
1971 cannot be given, any reshape which requires a backup-file to continue
1972 cannot be started by auto assembly. An array which is growing to more
1973 devices and has passed the critical section can be assembled using
1984 .BI \-\-raid\-devices= Z
1988 This usage is similar to
1990 The difference is that it creates an array without a superblock. With
1991 these arrays there is no difference between initially creating the array and
1992 subsequently assembling the array, except that hopefully there is useful
1993 data there in the second case.
1995 The level may raid0, linear, raid1, raid10, multipath, or faulty, or
1996 one of their synonyms. All devices must be listed and the array will
1997 be started once complete. It will often be appropriate to use
1998 .B \-\-assume\-clean
1999 with levels raid1 or raid10.
2010 .BI \-\-raid\-devices= Z
2014 This usage will initialise a new md array, associate some devices with
2015 it, and activate the array.
2017 The named device will normally not exist when
2018 .I "mdadm \-\-create"
2019 is run, but will be created by
2021 once the array becomes active.
2023 As devices are added, they are checked to see if they contain RAID
2024 superblocks or filesystems. They are also checked to see if the variance in
2025 device size exceeds 1%.
2027 If any discrepancy is found, the array will not automatically be run, though
2030 can override this caution.
2032 To create a "degraded" array in which some devices are missing, simply
2033 give the word "\fBmissing\fP"
2034 in place of a device name. This will cause
2036 to leave the corresponding slot in the array empty.
2037 For a RAID4 or RAID5 array at most one slot can be
2038 "\fBmissing\fP"; for a RAID6 array at most two slots.
2039 For a RAID1 array, only one real device needs to be given. All of the
2043 When creating a RAID5 array,
2045 will automatically create a degraded array with an extra spare drive.
2046 This is because building the spare into a degraded array is in general
2047 faster than resyncing the parity on a non-degraded, but not clean,
2048 array. This feature can be overridden with the
2052 When creating an array with version-1 metadata a name for the array is
2054 If this is not given with the
2058 will choose a name based on the last component of the name of the
2059 device being created. So if
2061 is being created, then the name
2066 is being created, then the name
2070 When creating a partition based array, using
2072 with version-1.x metadata, the partition type should be set to
2074 (non fs-data). This type selection allows for greater precision since
2075 using any other [RAID auto-detect (0xFD) or a GNU/Linux partition (0x83)],
2076 might create problems in the event of array recovery through a live cdrom.
2078 A new array will normally get a randomly assigned 128bit UUID which is
2079 very likely to be unique. If you have a specific need, you can choose
2080 a UUID for the array by giving the
2082 option. Be warned that creating two arrays with the same UUID is a
2083 recipe for disaster. Also, using
2085 when creating a v0.90 array will silently override any
2090 .\"option is given, it is not necessary to list any component-devices in this command.
2091 .\"They can be added later, before a
2095 .\"is given, the apparent size of the smallest drive given is used.
2097 If the array type supports a write-intent bitmap, and if the devices
2098 in the array exceed 100G is size, an internal write-intent bitmap
2099 will automatically be added unless some other option is explicitly
2102 option. In any case space for a bitmap will be reserved so that one
2103 can be added layer with
2104 .BR "\-\-grow \-\-bitmap=internal" .
2106 If the metadata type supports it (currently only 1.x metadata), space
2107 will be allocated to store a bad block list. This allows a modest
2108 number of bad blocks to be recorded, allowing the drive to remain in
2109 service while only partially functional.
2111 When creating an array within a
2114 can be given either the list of devices to use, or simply the name of
2115 the container. The former case gives control over which devices in
2116 the container will be used for the array. The latter case allows
2118 to automatically choose which devices to use based on how much spare
2121 The General Management options that are valid with
2126 insist on running the array even if some devices look like they might
2131 start the array readonly \(em not supported yet.
2138 .I options... devices...
2141 This usage will allow individual devices in an array to be failed,
2142 removed or added. It is possible to perform multiple operations with
2143 on command. For example:
2145 .B " mdadm /dev/md0 \-f /dev/hda1 \-r /dev/hda1 \-a /dev/hda1"
2151 and will then remove it from the array and finally add it back
2152 in as a spare. However only one md array can be affected by a single
2155 When a device is added to an active array, mdadm checks to see if it
2156 has metadata on it which suggests that it was recently a member of the
2157 array. If it does, it tries to "re\-add" the device. If there have
2158 been no changes since the device was removed, or if the array has a
2159 write-intent bitmap which has recorded whatever changes there were,
2160 then the device will immediately become a full member of the array and
2161 those differences recorded in the bitmap will be resolved.
2171 MISC mode includes a number of distinct operations that
2172 operate on distinct devices. The operations are:
2175 The device is examined to see if it is
2176 (1) an active md array, or
2177 (2) a component of an md array.
2178 The information discovered is reported.
2182 The device should be an active md device.
2184 will display a detailed description of the array.
2188 will cause the output to be less detailed and the format to be
2189 suitable for inclusion in
2193 will normally be 0 unless
2195 failed to get useful information about the device(s); however, if the
2197 option is given, then the exit status will be:
2201 The array is functioning normally.
2204 The array has at least one failed device.
2207 The array has multiple failed devices such that it is unusable.
2210 There was an error while trying to get information about the device.
2214 .B \-\-detail\-platform
2215 Print detail of the platform's RAID capabilities (firmware / hardware
2216 topology). If the metadata is specified with
2220 then the return status will be:
2224 metadata successfully enumerated its platform components on this system
2227 metadata is platform independent
2230 metadata failed to find its platform components on this system
2234 .B \-\-update\-subarray=
2235 If the device is a container and the argument to \-\-update\-subarray
2236 specifies a subarray in the container, then attempt to update the given
2237 superblock field in the subarray. Similar to updating an array in
2238 "assemble" mode, the field to update is selected by
2242 option. Currently only
2248 option updates the subarray name in the metadata, it may not affect the
2249 device node name or the device node symlink until the subarray is
2250 re\-assembled. If updating
2252 would change the UUID of an active subarray this operation is blocked,
2253 and the command will end in an error.
2257 The device should be a component of an md array.
2259 will read the md superblock of the device and display the contents.
2264 is given, then multiple devices that are components of the one array
2265 are grouped together and reported in a single entry suitable
2271 without listing any devices will cause all devices listed in the
2272 config file to be examined.
2275 .BI \-\-dump= directory
2276 If the device contains RAID metadata, a file will be created in the
2278 and the metadata will be written to it. The file will be the same
2279 size as the device and have the metadata written in the file at the
2280 same locate that it exists in the device. However the file will be "sparse" so
2281 that only those blocks containing metadata will be allocated. The
2282 total space used will be small.
2284 The file name used in the
2286 will be the base name of the device. Further if any links appear in
2288 which point to the device, then hard links to the file will be created
2295 Multiple devices can be listed and their metadata will all be stored
2296 in the one directory.
2299 .BI \-\-restore= directory
2300 This is the reverse of
2303 will locate a file in the directory that has a name appropriate for
2304 the given device and will restore metadata from it. Names that match
2306 names are preferred, however if two of those refer to different files,
2308 will not choose between them but will abort the operation.
2310 If a file name is given instead of a
2314 will restore from that file to a single device, always provided the
2315 size of the file matches that of the device, and the file contains
2319 The devices should be active md arrays which will be deactivated, as
2320 long as they are not currently in use.
2324 This will fully activate a partially assembled md array.
2328 This will mark an active array as read-only, providing that it is
2329 not currently being used.
2335 array back to being read/write.
2339 For all operations except
2342 will cause the operation to be applied to all arrays listed in
2347 causes all devices listed in the config file to be examined.
2350 .BR \-b ", " \-\-brief
2351 Be less verbose. This is used with
2359 gives an intermediate level of verbosity.
2365 .B mdadm \-\-monitor
2366 .I options... devices...
2371 to periodically poll a number of md arrays and to report on any events
2374 will never exit once it decides that there are arrays to be checked,
2375 so it should normally be run in the background.
2377 As well as reporting events,
2379 may move a spare drive from one array to another if they are in the
2384 and if the destination array has a failed drive but no spares.
2386 If any devices are listed on the command line,
2388 will only monitor those devices. Otherwise all arrays listed in the
2389 configuration file will be monitored. Further, if
2391 is given, then any other md devices that appear in
2393 will also be monitored.
2395 The result of monitoring the arrays is the generation of events.
2396 These events are passed to a separate program (if specified) and may
2397 be mailed to a given E-mail address.
2399 When passing events to a program, the program is run once for each event,
2400 and is given 2 or 3 command-line arguments: the first is the
2401 name of the event (see below), the second is the name of the
2402 md device which is affected, and the third is the name of a related
2403 device if relevant (such as a component device that has failed).
2407 is given, then a program or an E-mail address must be specified on the
2408 command line or in the config file. If neither are available, then
2410 will not monitor anything.
2414 will continue monitoring as long as something was found to monitor. If
2415 no program or email is given, then each event is reported to
2418 The different events are:
2422 .B DeviceDisappeared
2423 An md array which previously was configured appears to no longer be
2424 configured. (syslog priority: Critical)
2428 was told to monitor an array which is RAID0 or Linear, then it will
2430 .B DeviceDisappeared
2431 with the extra information
2433 This is because RAID0 and Linear do not support the device-failed,
2434 hot-spare and resync operations which are monitored.
2438 An md array started reconstruction (e.g. recovery, resync, reshape,
2439 check, repair). (syslog priority: Warning)
2445 is a two-digit number (ie. 05, 48). This indicates that rebuild
2446 has passed that many percent of the total. The events are generated
2447 with fixed increment since 0. Increment size may be specified with
2448 a commandline option (default is 20). (syslog priority: Warning)
2452 An md array that was rebuilding, isn't any more, either because it
2453 finished normally or was aborted. (syslog priority: Warning)
2457 An active component device of an array has been marked as
2458 faulty. (syslog priority: Critical)
2462 A spare component device which was being rebuilt to replace a faulty
2463 device has failed. (syslog priority: Critical)
2467 A spare component device which was being rebuilt to replace a faulty
2468 device has been successfully rebuilt and has been made active.
2469 (syslog priority: Info)
2473 A new md array has been detected in the
2475 file. (syslog priority: Info)
2479 A newly noticed array appears to be degraded. This message is not
2482 notices a drive failure which causes degradation, but only when
2484 notices that an array is degraded when it first sees the array.
2485 (syslog priority: Critical)
2489 A spare drive has been moved from one array in a
2493 to another to allow a failed drive to be replaced.
2494 (syslog priority: Info)
2500 has been told, via the config file, that an array should have a certain
2501 number of spare devices, and
2503 detects that it has fewer than this number when it first sees the
2504 array, it will report a
2507 (syslog priority: Warning)
2511 An array was found at startup, and the
2514 (syslog priority: Info)
2524 cause Email to be sent. All events cause the program to be run.
2525 The program is run with two or three arguments: the event
2526 name, the array device and possibly a second device.
2528 Each event has an associated array device (e.g.
2530 and possibly a second device. For
2535 the second device is the relevant component device.
2538 the second device is the array that the spare was moved from.
2542 to move spares from one array to another, the different arrays need to
2543 be labeled with the same
2545 or the spares must be allowed to migrate through matching POLICY domains
2546 in the configuration file. The
2548 name can be any string; it is only necessary that different spare
2549 groups use different names.
2553 detects that an array in a spare group has fewer active
2554 devices than necessary for the complete array, and has no spare
2555 devices, it will look for another array in the same spare group that
2556 has a full complement of working drive and a spare. It will then
2557 attempt to remove the spare from the second drive and add it to the
2559 If the removal succeeds but the adding fails, then it is added back to
2562 If the spare group for a degraded array is not defined,
2564 will look at the rules of spare migration specified by POLICY lines in
2566 and then follow similar steps as above if a matching spare is found.
2569 The GROW mode is used for changing the size or shape of an active
2571 For this to work, the kernel must support the necessary change.
2572 Various types of growth are being added during 2.6 development.
2574 Currently the supported changes include
2576 change the "size" attribute for RAID1, RAID4, RAID5 and RAID6.
2578 increase or decrease the "raid\-devices" attribute of RAID0, RAID1, RAID4,
2581 change the chunk-size and layout of RAID0, RAID4, RAID5, RAID6 and RAID10.
2583 convert between RAID1 and RAID5, between RAID5 and RAID6, between
2584 RAID0, RAID4, and RAID5, and between RAID0 and RAID10 (in the near-2 mode).
2586 add a write-intent bitmap to any array which supports these bitmaps, or
2587 remove a write-intent bitmap from such an array.
2590 Using GROW on containers is currently supported only for Intel's IMSM
2591 container format. The number of devices in a container can be
2592 increased - which affects all arrays in the container - or an array
2593 in a container can be converted between levels where those levels are
2594 supported by the container, and the conversion is on of those listed
2595 above. Resizing arrays in an IMSM container with
2597 is not yet supported.
2599 Grow functionality (e.g. expand a number of raid devices) for Intel's
2600 IMSM container format has an experimental status. It is guarded by the
2601 .B MDADM_EXPERIMENTAL
2602 environment variable which must be set to '1' for a GROW command to
2604 This is for the following reasons:
2607 Intel's native IMSM check-pointing is not fully tested yet.
2608 This can causes IMSM incompatibility during the grow process: an array
2609 which is growing cannot roam between Microsoft Windows(R) and Linux
2613 Interrupting a grow operation is not recommended, because it
2614 has not been fully tested for Intel's IMSM container format yet.
2617 Note: Intel's native checkpointing doesn't use
2619 option and it is transparent for assembly feature.
2622 Normally when an array is built the "size" is taken from the smallest
2623 of the drives. If all the small drives in an arrays are, one at a
2624 time, removed and replaced with larger drives, then you could have an
2625 array of large drives with only a small amount used. In this
2626 situation, changing the "size" with "GROW" mode will allow the extra
2627 space to start being used. If the size is increased in this way, a
2628 "resync" process will start to make sure the new parts of the array
2631 Note that when an array changes size, any filesystem that may be
2632 stored in the array will not automatically grow or shrink to use or
2633 vacate the space. The
2634 filesystem will need to be explicitly told to use the extra space
2635 after growing, or to reduce its size
2637 to shrinking the array.
2639 Also the size of an array cannot be changed while it has an active
2640 bitmap. If an array has a bitmap, it must be removed before the size
2641 can be changed. Once the change is complete a new bitmap can be created.
2643 .SS RAID\-DEVICES CHANGES
2645 A RAID1 array can work with any number of devices from 1 upwards
2646 (though 1 is not very useful). There may be times which you want to
2647 increase or decrease the number of active devices. Note that this is
2648 different to hot-add or hot-remove which changes the number of
2651 When reducing the number of devices in a RAID1 array, the slots which
2652 are to be removed from the array must already be vacant. That is, the
2653 devices which were in those slots must be failed and removed.
2655 When the number of devices is increased, any hot spares that are
2656 present will be activated immediately.
2658 Changing the number of active devices in a RAID5 or RAID6 is much more
2659 effort. Every block in the array will need to be read and written
2660 back to a new location. From 2.6.17, the Linux Kernel is able to
2661 increase the number of devices in a RAID5 safely, including restarting
2662 an interrupted "reshape". From 2.6.31, the Linux Kernel is able to
2663 increase or decrease the number of devices in a RAID5 or RAID6.
2665 From 2.6.35, the Linux Kernel is able to convert a RAID0 in to a RAID4
2668 uses this functionality and the ability to add
2669 devices to a RAID4 to allow devices to be added to a RAID0. When
2670 requested to do this,
2672 will convert the RAID0 to a RAID4, add the necessary disks and make
2673 the reshape happen, and then convert the RAID4 back to RAID0.
2675 When decreasing the number of devices, the size of the array will also
2676 decrease. If there was data in the array, it could get destroyed and
2677 this is not reversible, so you should firstly shrink the filesystem on
2678 the array to fit within the new size. To help prevent accidents,
2680 requires that the size of the array be decreased first with
2681 .BR "mdadm --grow --array-size" .
2682 This is a reversible change which simply makes the end of the array
2683 inaccessible. The integrity of any data can then be checked before
2684 the non-reversible reduction in the number of devices is request.
2686 When relocating the first few stripes on a RAID5 or RAID6, it is not
2687 possible to keep the data on disk completely consistent and
2688 crash-proof. To provide the required safety, mdadm disables writes to
2689 the array while this "critical section" is reshaped, and takes a
2690 backup of the data that is in that section. For grows, this backup may be
2691 stored in any spare devices that the array has, however it can also be
2692 stored in a separate file specified with the
2694 option, and is required to be specified for shrinks, RAID level
2695 changes and layout changes. If this option is used, and the system
2696 does crash during the critical period, the same file must be passed to
2698 to restore the backup and reassemble the array. When shrinking rather
2699 than growing the array, the reshape is done from the end towards the
2700 beginning, so the "critical section" is at the end of the reshape.
2704 Changing the RAID level of any array happens instantaneously. However
2705 in the RAID5 to RAID6 case this requires a non-standard layout of the
2706 RAID6 data, and in the RAID6 to RAID5 case that non-standard layout is
2707 required before the change can be accomplished. So while the level
2708 change is instant, the accompanying layout change can take quite a
2711 is required. If the array is not simultaneously being grown or
2712 shrunk, so that the array size will remain the same - for example,
2713 reshaping a 3-drive RAID5 into a 4-drive RAID6 - the backup file will
2714 be used not just for a "cricital section" but throughout the reshape
2715 operation, as described below under LAYOUT CHANGES.
2717 .SS CHUNK-SIZE AND LAYOUT CHANGES
2719 Changing the chunk-size of layout without also changing the number of
2720 devices as the same time will involve re-writing all blocks in-place.
2721 To ensure against data loss in the case of a crash, a
2723 must be provided for these changes. Small sections of the array will
2724 be copied to the backup file while they are being rearranged. This
2725 means that all the data is copied twice, once to the backup and once
2726 to the new layout on the array, so this type of reshape will go very
2729 If the reshape is interrupted for any reason, this backup file must be
2731 .B "mdadm --assemble"
2732 so the array can be reassembled. Consequently the file cannot be
2733 stored on the device being reshaped.
2738 A write-intent bitmap can be added to, or removed from, an active
2739 array. Either internal bitmaps, or bitmaps stored in a separate file,
2740 can be added. Note that if you add a bitmap stored in a file which is
2741 in a filesystem that is on the RAID array being affected, the system
2742 will deadlock. The bitmap must be on a separate filesystem.
2744 .SH INCREMENTAL MODE
2748 .B mdadm \-\-incremental
2752 .RI [ optional-aliases-for-device ]
2755 .B mdadm \-\-incremental \-\-fail
2759 .B mdadm \-\-incremental \-\-rebuild\-map
2762 .B mdadm \-\-incremental \-\-run \-\-scan
2765 This mode is designed to be used in conjunction with a device
2766 discovery system. As devices are found in a system, they can be
2768 .B "mdadm \-\-incremental"
2769 to be conditionally added to an appropriate array.
2771 Conversely, it can also be used with the
2773 flag to do just the opposite and find whatever array a particular device
2774 is part of and remove the device from that array.
2776 If the device passed is a
2778 device created by a previous call to
2780 then rather than trying to add that device to an array, all the arrays
2781 described by the metadata of the container will be started.
2784 performs a number of tests to determine if the device is part of an
2785 array, and which array it should be part of. If an appropriate array
2786 is found, or can be created,
2788 adds the device to the array and conditionally starts the array.
2792 will normally only add devices to an array which were previously working
2793 (active or spare) parts of that array. The support for automatic
2794 inclusion of a new drive as a spare in some array requires
2795 a configuration through POLICY in config file.
2799 makes are as follow:
2801 Is the device permitted by
2803 That is, is it listed in a
2805 line in that file. If
2807 is absent then the default it to allow any device. Similarly if
2809 contains the special word
2811 then any device is allowed. Otherwise the device name given to
2813 or one of the aliases given, or an alias found in the filesystem,
2814 must match one of the names or patterns in a
2818 This is the only context where the aliases are used. They are
2819 usually provided by a
2825 Does the device have a valid md superblock? If a specific metadata
2826 version is requested with
2830 then only that style of metadata is accepted, otherwise
2832 finds any known version of metadata. If no
2834 metadata is found, the device may be still added to an array
2835 as a spare if POLICY allows.
2839 Does the metadata match an expected array?
2840 The metadata can match in two ways. Either there is an array listed
2843 which identifies the array (either by UUID, by name, by device list,
2844 or by minor-number), or the array was created with a
2850 or on the command line.
2853 is not able to positively identify the array as belonging to the
2854 current host, the device will be rejected.
2859 keeps a list of arrays that it has partially assembled in
2861 If no array exists which matches
2862 the metadata on the new device,
2864 must choose a device name and unit number. It does this based on any
2867 or any name information stored in the metadata. If this name
2868 suggests a unit number, that number will be used, otherwise a free
2869 unit number will be chosen. Normally
2871 will prefer to create a partitionable array, however if the
2875 suggests that a non-partitionable array is preferred, that will be
2878 If the array is not found in the config file and its metadata does not
2879 identify it as belonging to the "homehost", then
2881 will choose a name for the array which is certain not to conflict with
2882 any array which does belong to this host. It does this be adding an
2883 underscore and a small number to the name preferred by the metadata.
2885 Once an appropriate array is found or created and the device is added,
2887 must decide if the array is ready to be started. It will
2888 normally compare the number of available (non-spare) devices to the
2889 number of devices that the metadata suggests need to be active. If
2890 there are at least that many, the array will be started. This means
2891 that if any devices are missing the array will not be restarted.
2897 in which case the array will be run as soon as there are enough
2898 devices present for the data to be accessible. For a RAID1, that
2899 means one device will start the array. For a clean RAID5, the array
2900 will be started as soon as all but one drive is present.
2902 Note that neither of these approaches is really ideal. If it can
2903 be known that all device discovery has completed, then
2907 can be run which will try to start all arrays that are being
2908 incrementally assembled. They are started in "read-auto" mode in
2909 which they are read-only until the first write request. This means
2910 that no metadata updates are made and no attempt at resync or recovery
2911 happens. Further devices that are found before the first write can
2912 still be added safely.
2915 This section describes environment variables that affect how mdadm
2920 Setting this value to 1 will prevent mdadm from automatically launching
2921 mdmon. This variable is intended primarily for debugging mdadm/mdmon.
2927 does not create any device nodes in /dev, but leaves that task to
2931 appears not to be configured, or if this environment variable is set
2934 will create and devices that are needed.
2937 .B MDADM_NO_SYSTEMCTL
2942 is in use it will normally request
2944 to start various background tasks (particularly
2946 rather than forking and running them in the background. This can be
2947 suppressed by setting
2948 .BR MDADM_NO_SYSTEMCTL=1 .
2952 A key value of IMSM metadata is that it allows interoperability with
2953 boot ROMs on Intel platforms, and with other major operating systems.
2956 will only allow an IMSM array to be created or modified if detects
2957 that it is running on an Intel platform which supports IMSM, and
2958 supports the particular configuration of IMSM that is being requested
2959 (some functionality requires newer OROM support).
2961 These checks can be suppressed by setting IMSM_NO_PLATFORM=1 in the
2962 environment. This can be useful for testing or for disaster
2963 recovery. You should be aware that interoperability may be
2964 compromised by setting this value.
2967 .B MDADM_GROW_ALLOW_OLD
2968 If an array is stopped while it is performing a reshape and that
2969 reshape was making use of a backup file, then when the array is
2972 will sometimes complain that the backup file is too old. If this
2973 happens and you are certain it is the right backup file, you can
2974 over-ride this check by setting
2975 .B MDADM_GROW_ALLOW_OLD=1
2980 Any string given in this variable is added to the start of the
2982 line in the config file, or treated as the whole
2984 line if none is given. It can be used to disable certain metadata
2987 is called from a boot script. For example
2989 .B " export MDADM_CONF_AUTO='-ddf -imsm'
2993 does not automatically assemble any DDF or
2994 IMSM arrays that are found. This can be useful on systems configured
2995 to manage such arrays with
3001 .B " mdadm \-\-query /dev/name-of-device"
3003 This will find out if a given device is a RAID array, or is part of
3004 one, and will provide brief information about the device.
3006 .B " mdadm \-\-assemble \-\-scan"
3008 This will assemble and start all arrays listed in the standard config
3009 file. This command will typically go in a system startup file.
3011 .B " mdadm \-\-stop \-\-scan"
3013 This will shut down all arrays that can be shut down (i.e. are not
3014 currently in use). This will typically go in a system shutdown script.
3016 .B " mdadm \-\-follow \-\-scan \-\-delay=120"
3018 If (and only if) there is an Email address or program given in the
3019 standard config file, then
3020 monitor the status of all arrays listed in that file by
3021 polling them ever 2 minutes.
3023 .B " mdadm \-\-create /dev/md0 \-\-level=1 \-\-raid\-devices=2 /dev/hd[ac]1"
3025 Create /dev/md0 as a RAID1 array consisting of /dev/hda1 and /dev/hdc1.
3028 .B " echo 'DEVICE /dev/hd*[0\-9] /dev/sd*[0\-9]' > mdadm.conf"
3030 .B " mdadm \-\-detail \-\-scan >> mdadm.conf"
3032 This will create a prototype config file that describes currently
3033 active arrays that are known to be made from partitions of IDE or SCSI drives.
3034 This file should be reviewed before being used as it may
3035 contain unwanted detail.
3037 .B " echo 'DEVICE /dev/hd[a\-z] /dev/sd*[a\-z]' > mdadm.conf"
3039 .B " mdadm \-\-examine \-\-scan \-\-config=mdadm.conf >> mdadm.conf"
3041 This will find arrays which could be assembled from existing IDE and
3042 SCSI whole drives (not partitions), and store the information in the
3043 format of a config file.
3044 This file is very likely to contain unwanted detail, particularly
3047 entries. It should be reviewed and edited before being used as an
3050 .B " mdadm \-\-examine \-\-brief \-\-scan \-\-config=partitions"
3052 .B " mdadm \-Ebsc partitions"
3054 Create a list of devices by reading
3055 .BR /proc/partitions ,
3056 scan these for RAID superblocks, and printout a brief listing of all
3059 .B " mdadm \-Ac partitions \-m 0 /dev/md0"
3061 Scan all partitions and devices listed in
3062 .BR /proc/partitions
3065 out of all such devices with a RAID superblock with a minor number of 0.
3067 .B " mdadm \-\-monitor \-\-scan \-\-daemonise > /run/mdadm/mon.pid"
3069 If config file contains a mail address or alert program, run mdadm in
3070 the background in monitor mode monitoring all md devices. Also write
3071 pid of mdadm daemon to
3072 .BR /run/mdadm/mon.pid .
3074 .B " mdadm \-Iq /dev/somedevice"
3076 Try to incorporate newly discovered device into some array as
3079 .B " mdadm \-\-incremental \-\-rebuild\-map \-\-run \-\-scan"
3081 Rebuild the array map from any current arrays, and then start any that
3084 .B " mdadm /dev/md4 --fail detached --remove detached"
3086 Any devices which are components of /dev/md4 will be marked as faulty
3087 and then remove from the array.
3089 .B " mdadm --grow /dev/md4 --level=6 --backup-file=/root/backup-md4"
3093 which is currently a RAID5 array will be converted to RAID6. There
3094 should normally already be a spare drive attached to the array as a
3095 RAID6 needs one more drive than a matching RAID5.
3097 .B " mdadm --create /dev/md/ddf --metadata=ddf --raid-disks 6 /dev/sd[a-f]"
3099 Create a DDF array over 6 devices.
3101 .B " mdadm --create /dev/md/home -n3 -l5 -z 30000000 /dev/md/ddf"
3103 Create a RAID5 array over any 3 devices in the given DDF set. Use
3104 only 30 gigabytes of each device.
3106 .B " mdadm -A /dev/md/ddf1 /dev/sd[a-f]"
3108 Assemble a pre-exist ddf array.
3110 .B " mdadm -I /dev/md/ddf1"
3112 Assemble all arrays contained in the ddf array, assigning names as
3115 .B " mdadm \-\-create \-\-help"
3117 Provide help about the Create mode.
3119 .B " mdadm \-\-config \-\-help"
3121 Provide help about the format of the config file.
3123 .B " mdadm \-\-help"
3125 Provide general help.
3135 lists all active md devices with information about them.
3137 uses this to find arrays when
3139 is given in Misc mode, and to monitor array reconstruction
3144 The config file lists which devices may be scanned to see if
3145 they contain MD super block, and gives identifying information
3146 (e.g. UUID) about known MD arrays. See
3150 .SS /etc/mdadm.conf.d
3152 A directory containing configuration files which are read in lexical
3158 mode is used, this file gets a list of arrays currently being created.
3163 understand two sorts of names for array devices.
3165 The first is the so-called 'standard' format name, which matches the
3166 names used by the kernel and which appear in
3169 The second sort can be freely chosen, but must reside in
3171 When giving a device name to
3173 to create or assemble an array, either full path name such as
3177 can be given, or just the suffix of the second sort of name, such as
3183 chooses device names during auto-assembly or incremental assembly, it
3184 will sometimes add a small sequence number to the end of the name to
3185 avoid conflicted between multiple arrays that have the same name. If
3187 can reasonably determine that the array really is meant for this host,
3188 either by a hostname in the metadata, or by the presence of the array
3191 then it will leave off the suffix if possible.
3192 Also if the homehost is specified as
3195 will only use a suffix if a different array of the same name already
3196 exists or is listed in the config file.
3198 The standard names for non-partitioned arrays (the only sort of md
3199 array available in 2.4 and earlier) are of the form
3203 where NN is a number.
3204 The standard names for partitionable arrays (as available from 2.6
3205 onwards) are of the form:
3209 Partition numbers should be indicated by adding "pMM" to these, thus "/dev/md/d1p2".
3211 From kernel version 2.6.28 the "non-partitioned array" can actually
3212 be partitioned. So the "md_d\fBNN\fP"
3213 names are no longer needed, and
3214 partitions such as "/dev/md\fBNN\fPp\fBXX\fP"
3217 From kernel version 2.6.29 standard names can be non-numeric following
3224 is any string. These names are supported by
3226 since version 3.3 provided they are enabled in
3231 was previously known as
3235 For further information on mdadm usage, MD and the various levels of
3238 .B http://raid.wiki.kernel.org/
3240 (based upon Jakob \(/Ostergaard's Software\-RAID.HOWTO)
3242 The latest version of
3244 should always be available from
3246 .B http://www.kernel.org/pub/linux/utils/raid/mdadm/
projects / thirdparty / mdadm.git / blob