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, 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
221 then the MANAGE mode is assumed.
222 Anything other than these will cause the
226 .SH Options that are not mode-specific are:
229 .BR \-h ", " \-\-help
230 Display general help message or, after one of the above options, a
231 mode-specific help message.
235 Display more detailed help about command line parsing and some commonly
239 .BR \-V ", " \-\-version
240 Print version information for mdadm.
243 .BR \-v ", " \-\-verbose
244 Be more verbose about what is happening. This can be used twice to be
246 The extra verbosity currently only affects
247 .B \-\-detail \-\-scan
249 .BR "\-\-examine \-\-scan" .
252 .BR \-q ", " \-\-quiet
253 Avoid printing purely informative messages. With this,
255 will be silent unless there is something really important to report.
258 .BR \-f ", " \-\-force
259 Be more forceful about certain operations. See the various modes for
260 the exact meaning of this option in different contexts.
263 .BR \-c ", " \-\-config=
264 Specify the config file. Default is to use
265 .BR /etc/mdadm.conf ,
266 or if that is missing then
267 .BR /etc/mdadm/mdadm.conf .
268 If the config file given is
270 then nothing will be read, but
272 will act as though the config file contained exactly
273 .B "DEVICE partitions containers"
276 to find a list of devices to scan, and
278 to find a list of containers to examine.
281 is given for the config file, then
283 will act as though the config file were empty.
286 .BR \-s ", " \-\-scan
289 for missing information.
290 In general, this option gives
292 permission to get any missing information (like component devices,
293 array devices, array identities, and alert destination) from the
294 configuration file (see previous option);
295 one exception is MISC mode when using
301 says to get a list of array devices from
305 .BR \-e ", " \-\-metadata=
306 Declare the style of RAID metadata (superblock) to be used. The
307 default is {DEFAULT_METADATA} for
309 and to guess for other operations.
310 The default can be overridden by setting the
319 .ie '{DEFAULT_METADATA}'0.90'
320 .IP "0, 0.90, default"
324 Use the original 0.90 format superblock. This format limits arrays to
325 28 component devices and limits component devices of levels 1 and
326 greater to 2 terabytes. It is also possible for there to be confusion
327 about whether the superblock applies to a whole device or just the
328 last partition, if that partition starts on a 64K boundary.
329 .ie '{DEFAULT_METADATA}'0.90'
330 .IP "1, 1.0, 1.1, 1.2"
332 .IP "1, 1.0, 1.1, 1.2 default"
334 Use the new version-1 format superblock. This has fewer restrictions.
335 It can easily be moved between hosts with different endian-ness, and a
336 recovery operation can be checkpointed and restarted. The different
337 sub-versions store the superblock at different locations on the
338 device, either at the end (for 1.0), at the start (for 1.1) or 4K from
339 the start (for 1.2). "1" is equivalent to "1.2" (the commonly
340 preferred 1.x format).
341 'if '{DEFAULT_METADATA}'1.2' "default" is equivalent to "1.2".
343 Use the "Industry Standard" DDF (Disk Data Format) format defined by
345 When creating a DDF array a
347 will be created, and normal arrays can be created in that container.
349 Use the Intel(R) Matrix Storage Manager metadata format. This creates a
351 which is managed in a similar manner to DDF, and is supported by an
352 option-rom on some platforms:
354 .B http://www.intel.com/design/chipsets/matrixstorage_sb.htm
360 This will override any
362 setting in the config file and provides the identity of the host which
363 should be considered the home for any arrays.
365 When creating an array, the
367 will be recorded in the metadata. For version-1 superblocks, it will
368 be prefixed to the array name. For version-0.90 superblocks, part of
369 the SHA1 hash of the hostname will be stored in the later half of the
372 When reporting information about an array, any array which is tagged
373 for the given homehost will be reported as such.
375 When using Auto-Assemble, only arrays tagged for the given homehost
376 will be allowed to use 'local' names (i.e. not ending in '_' followed
377 by a digit string). See below under
378 .BR "Auto Assembly" .
380 .SH For create, build, or grow:
383 .BR \-n ", " \-\-raid\-devices=
384 Specify the number of active devices in the array. This, plus the
385 number of spare devices (see below) must equal the number of
387 (including "\fBmissing\fP" devices)
388 that are listed on the command line for
390 Setting a value of 1 is probably
391 a mistake and so requires that
393 be specified first. A value of 1 will then be allowed for linear,
394 multipath, RAID0 and RAID1. It is never allowed for RAID4, RAID5 or RAID6.
396 This number can only be changed using
398 for RAID1, RAID4, RAID5 and RAID6 arrays, and only on kernels which provide
399 the necessary support.
402 .BR \-x ", " \-\-spare\-devices=
403 Specify the number of spare (eXtra) devices in the initial array.
404 Spares can also be added
405 and removed later. The number of component devices listed
406 on the command line must equal the number of RAID devices plus the
407 number of spare devices.
410 .BR \-z ", " \-\-size=
411 Amount (in Kibibytes) of space to use from each drive in RAID levels 1/4/5/6.
412 This must be a multiple of the chunk size, and must leave about 128Kb
413 of space at the end of the drive for the RAID superblock.
414 If this is not specified
415 (as it normally is not) the smallest drive (or partition) sets the
416 size, though if there is a variance among the drives of greater than 1%, a warning is
419 A suffix of 'M' or 'G' can be given to indicate Megabytes or
420 Gigabytes respectively.
422 Sometimes a replacement drive can be a little smaller than the
423 original drives though this should be minimised by IDEMA standards.
424 Such a replacement drive will be rejected by
426 To guard against this it can be useful to set the initial size
427 slightly smaller than the smaller device with the aim that it will
428 still be larger than any replacement.
430 This value can be set with
432 for RAID level 1/4/5/6 though
434 based arrays such as those with IMSM metadata may not be able to
436 If the array was created with a size smaller than the currently
437 active drives, the extra space can be accessed using
439 The size can be given as
441 which means to choose the largest size that fits on all current drives.
443 Before reducing the size of the array (with
444 .BR "\-\-grow \-\-size=" )
445 you should make sure that space isn't needed. If the device holds a
446 filesystem, you would need to resize the filesystem to use less space.
448 After reducing the array size you should check that the data stored in
449 the device is still available. If the device holds a filesystem, then
450 an 'fsck' of the filesystem is a minimum requirement. If there are
451 problems the array can be made bigger again with no loss with another
452 .B "\-\-grow \-\-size="
455 This value cannot be used when creating a
457 such as with DDF and IMSM metadata, though it perfectly valid when
458 creating an array inside a container.
461 .BR \-Z ", " \-\-array\-size=
462 This is only meaningful with
464 and its effect is not persistent: when the array is stopped and
465 restarted the default array size will be restored.
467 Setting the array-size causes the array to appear smaller to programs
468 that access the data. This is particularly needed before reshaping an
469 array so that it will be smaller. As the reshape is not reversible,
470 but setting the size with
472 is, it is required that the array size is reduced as appropriate
473 before the number of devices in the array is reduced.
475 Before reducing the size of the array you should make sure that space
476 isn't needed. If the device holds a filesystem, you would need to
477 resize the filesystem to use less space.
479 After reducing the array size you should check that the data stored in
480 the device is still available. If the device holds a filesystem, then
481 an 'fsck' of the filesystem is a minimum requirement. If there are
482 problems the array can be made bigger again with no loss with another
483 .B "\-\-grow \-\-array\-size="
486 A suffix of 'M' or 'G' can be given to indicate Megabytes or
487 Gigabytes respectively.
490 restores the apparent size of the array to be whatever the real
491 amount of available space is.
494 .BR \-c ", " \-\-chunk=
495 Specify chunk size of kibibytes. The default when creating an
496 array is 512KB. To ensure compatibility with earlier versions, the
497 default when Building and array with no persistent metadata is 64KB.
498 This is only meaningful for RAID0, RAID4, RAID5, RAID6, and RAID10.
500 RAID4, RAID5, RAID6, and RAID10 require the chunk size to be a power
501 of 2. In any case it must be a multiple of 4KB.
503 A suffix of 'M' or 'G' can be given to indicate Megabytes or
504 Gigabytes respectively.
508 Specify rounding factor for a Linear array. The size of each
509 component will be rounded down to a multiple of this size.
510 This is a synonym for
512 but highlights the different meaning for Linear as compared to other
513 RAID levels. The default is 64K if a kernel earlier than 2.6.16 is in
514 use, and is 0K (i.e. no rounding) in later kernels.
517 .BR \-l ", " \-\-level=
518 Set RAID level. When used with
520 options are: linear, raid0, 0, stripe, raid1, 1, mirror, raid4, 4,
521 raid5, 5, raid6, 6, raid10, 10, multipath, mp, faulty, container.
522 Obviously some of these are synonymous.
526 metadata type is requested, only the
528 level is permitted, and it does not need to be explicitly given.
532 only linear, stripe, raid0, 0, raid1, multipath, mp, and faulty are valid.
536 to change the RAID level in some cases. See LEVEL CHANGES below.
539 .BR \-p ", " \-\-layout=
540 This option configures the fine details of data layout for RAID5, RAID6,
541 and RAID10 arrays, and controls the failure modes for
544 The layout of the RAID5 parity block can be one of
545 .BR left\-asymmetric ,
546 .BR left\-symmetric ,
547 .BR right\-asymmetric ,
548 .BR right\-symmetric ,
549 .BR la ", " ra ", " ls ", " rs .
551 .BR left\-symmetric .
553 It is also possible to cause RAID5 to use a RAID4-like layout by
559 Finally for RAID5 there are DDF\-compatible layouts,
560 .BR ddf\-zero\-restart ,
561 .BR ddf\-N\-restart ,
563 .BR ddf\-N\-continue .
565 These same layouts are available for RAID6. There are also 4 layouts
566 that will provide an intermediate stage for converting between RAID5
567 and RAID6. These provide a layout which is identical to the
568 corresponding RAID5 layout on the first N\-1 devices, and has the 'Q'
569 syndrome (the second 'parity' block used by RAID6) on the last device.
571 .BR left\-symmetric\-6 ,
572 .BR right\-symmetric\-6 ,
573 .BR left\-asymmetric\-6 ,
574 .BR right\-asymmetric\-6 ,
576 .BR parity\-first\-6 .
578 When setting the failure mode for level
581 .BR write\-transient ", " wt ,
582 .BR read\-transient ", " rt ,
583 .BR write\-persistent ", " wp ,
584 .BR read\-persistent ", " rp ,
586 .BR read\-fixable ", " rf ,
587 .BR clear ", " flush ", " none .
589 Each failure mode can be followed by a number, which is used as a period
590 between fault generation. Without a number, the fault is generated
591 once on the first relevant request. With a number, the fault will be
592 generated after that many requests, and will continue to be generated
593 every time the period elapses.
595 Multiple failure modes can be current simultaneously by using the
597 option to set subsequent failure modes.
599 "clear" or "none" will remove any pending or periodic failure modes,
600 and "flush" will clear any persistent faults.
602 Finally, the layout options for RAID10 are one of 'n', 'o' or 'f' followed
603 by a small number. The default is 'n2'. The supported options are:
606 signals 'near' copies. Multiple copies of one data block are at
607 similar offsets in different devices.
610 signals 'offset' copies. Rather than the chunks being duplicated
611 within a stripe, whole stripes are duplicated but are rotated by one
612 device so duplicate blocks are on different devices. Thus subsequent
613 copies of a block are in the next drive, and are one chunk further
618 (multiple copies have very different offsets).
619 See md(4) for more detail about 'near', 'offset', and 'far'.
621 The number is the number of copies of each datablock. 2 is normal, 3
622 can be useful. This number can be at most equal to the number of
623 devices in the array. It does not need to divide evenly into that
624 number (e.g. it is perfectly legal to have an 'n2' layout for an array
625 with an odd number of devices).
627 When an array is converted between RAID5 and RAID6 an intermediate
628 RAID6 layout is used in which the second parity block (Q) is always on
629 the last device. To convert a RAID5 to RAID6 and leave it in this new
630 layout (which does not require re-striping) use
631 .BR \-\-layout=preserve .
632 This will try to avoid any restriping.
634 The converse of this is
635 .B \-\-layout=normalise
636 which will change a non-standard RAID6 layout into a more standard
643 (thus explaining the p of
647 .BR \-b ", " \-\-bitmap=
648 Specify a file to store a write-intent bitmap in. The file should not
651 is also given. The same file should be provided
652 when assembling the array. If the word
654 is given, then the bitmap is stored with the metadata on the array,
655 and so is replicated on all devices. If the word
659 mode, then any bitmap that is present is removed.
661 To help catch typing errors, the filename must contain at least one
662 slash ('/') if it is a real file (not 'internal' or 'none').
664 Note: external bitmaps are only known to work on ext2 and ext3.
665 Storing bitmap files on other filesystems may result in serious problems.
668 .BR \-\-bitmap\-chunk=
669 Set the chunksize of the bitmap. Each bit corresponds to that many
670 Kilobytes of storage.
671 When using a file based bitmap, the default is to use the smallest
672 size that is at-least 4 and requires no more than 2^21 chunks.
675 bitmap, the chunksize defaults to 64Meg, or larger if necessary to
676 fit the bitmap into the available space.
678 A suffix of 'M' or 'G' can be given to indicate Megabytes or
679 Gigabytes respectively.
682 .BR \-W ", " \-\-write\-mostly
683 subsequent devices listed in a
688 command will be flagged as 'write-mostly'. This is valid for RAID1
689 only and means that the 'md' driver will avoid reading from these
690 devices if at all possible. This can be useful if mirroring over a
694 .BR \-\-write\-behind=
695 Specify that write-behind mode should be enabled (valid for RAID1
696 only). If an argument is specified, it will set the maximum number
697 of outstanding writes allowed. The default value is 256.
698 A write-intent bitmap is required in order to use write-behind
699 mode, and write-behind is only attempted on drives marked as
703 .BR \-\-assume\-clean
706 that the array pre-existed and is known to be clean. It can be useful
707 when trying to recover from a major failure as you can be sure that no
708 data will be affected unless you actually write to the array. It can
709 also be used when creating a RAID1 or RAID10 if you want to avoid the
710 initial resync, however this practice \(em while normally safe \(em is not
711 recommended. Use this only if you really know what you are doing.
713 When the devices that will be part of a new array were filled
714 with zeros before creation the operator knows the array is
715 actually clean. If that is the case, such as after running
716 badblocks, this argument can be used to tell mdadm the
717 facts the operator knows.
719 When an array is resized to a larger size with
720 .B "\-\-grow \-\-size="
721 the new space is normally resynced in that same way that the whole
722 array is resynced at creation. From Linux version 3.0,
724 can be used with that command to avoid the automatic resync.
727 .BR \-\-backup\-file=
730 is used to increase the number of raid-devices in a RAID5 or RAID6 if
731 there are no spare devices available, or to shrink, change RAID level
732 or layout. See the GROW MODE section below on RAID\-DEVICES CHANGES.
733 The file must be stored on a separate device, not on the RAID array
737 .BR \-N ", " \-\-name=
740 for the array. This is currently only effective when creating an
741 array with a version-1 superblock, or an array in a DDF container.
742 The name is a simple textual string that can be used to identify array
743 components when assembling. If name is needed but not specified, it
744 is taken from the basename of the device that is being created.
756 run the array, even if some of the components
757 appear to be active in another array or filesystem. Normally
759 will ask for confirmation before including such components in an
760 array. This option causes that question to be suppressed.
763 .BR \-f ", " \-\-force
766 accept the geometry and layout specified without question. Normally
768 will not allow creation of an array with only one device, and will try
769 to create a RAID5 array with one missing drive (as this makes the
770 initial resync work faster). With
773 will not try to be so clever.
776 .BR \-a ", " "\-\-auto{=yes,md,mdp,part,p}{NN}"
777 Instruct mdadm how to create the device file if needed, possibly allocating
778 an unused minor number. "md" causes a non-partitionable array
779 to be used (though since Linux 2.6.28, these array devices are in fact
780 partitionable). "mdp", "part" or "p" causes a partitionable array (2.6 and
781 later) to be used. "yes" requires the named md device to have
782 a 'standard' format, and the type and minor number will be determined
783 from this. With mdadm 3.0, device creation is normally left up to
785 so this option is unlikely to be needed.
786 See DEVICE NAMES below.
788 The argument can also come immediately after
793 is not given on the command line or in the config file, then
799 is also given, then any
801 entries in the config file will override the
803 instruction given on the command line.
805 For partitionable arrays,
807 will create the device file for the whole array and for the first 4
808 partitions. A different number of partitions can be specified at the
809 end of this option (e.g.
811 If the device name ends with a digit, the partition names add a 'p',
813 .IR /dev/md/home1p3 .
814 If there is no trailing digit, then the partition names just have a
816 .IR /dev/md/scratch3 .
818 If the md device name is in a 'standard' format as described in DEVICE
819 NAMES, then it will be created, if necessary, with the appropriate
820 device number based on that name. If the device name is not in one of these
821 formats, then a unused device number will be allocated. The device
822 number will be considered unused if there is no active array for that
823 number, and there is no entry in /dev for that number and with a
824 non-standard name. Names that are not in 'standard' format are only
825 allowed in "/dev/md/".
827 This is meaningful with
834 .\".BR \-\-symlink = no
839 .\"to create devices in
841 .\"it will also create symlinks from
843 .\"with names starting with
849 .\"to suppress this, or
850 .\".B \-\-symlink=yes
851 .\"to enforce this even if it is suppressing
857 .BR \-a ", " "\-\-add"
858 This option can be used in Grow mode in two cases.
860 If the target array is a Linear array, then
862 can be used to add one or more devices to the array. They
863 are simply catenated on to the end of the array. Once added, the
864 devices cannot be removed.
868 option is being used to increase the number of devices in an array,
871 can be used to add some extra devices to be included in the array.
872 In most cases this is not needed as the extra devices can be added as
873 spares first, and then the number of raid-disks can be changed.
874 However for RAID0, it is not possible to add spares. So to increase
875 the number of devices in a RAID0, it is necessary to set the new
876 number of devices, and to add the new devices, in the same command.
881 .BR \-u ", " \-\-uuid=
882 uuid of array to assemble. Devices which don't have this uuid are
886 .BR \-m ", " \-\-super\-minor=
887 Minor number of device that array was created for. Devices which
888 don't have this minor number are excluded. If you create an array as
889 /dev/md1, then all superblocks will contain the minor number 1, even if
890 the array is later assembled as /dev/md2.
892 Giving the literal word "dev" for
896 to use the minor number of the md device that is being assembled.
899 .B \-\-super\-minor=dev
900 will look for super blocks with a minor number of 0.
903 is only relevant for v0.90 metadata, and should not normally be used.
909 .BR \-N ", " \-\-name=
910 Specify the name of the array to assemble. This must be the name
911 that was specified when creating the array. It must either match
912 the name stored in the superblock exactly, or it must match
915 prefixed to the start of the given name.
918 .BR \-f ", " \-\-force
919 Assemble the array even if the metadata on some devices appears to be
922 cannot find enough working devices to start the array, but can find
923 some devices that are recorded as having failed, then it will mark
924 those devices as working so that the array can be started.
925 An array which requires
927 to be started may contain data corruption. Use it carefully.
931 Attempt to start the array even if fewer drives were given than were
932 present last time the array was active. Normally if not all the
933 expected drives are found and
935 is not used, then the array will be assembled but not started.
938 an attempt will be made to start it anyway.
942 This is the reverse of
944 in that it inhibits the startup of array unless all expected drives
945 are present. This is only needed with
947 and can be used if the physical connections to devices are
948 not as reliable as you would like.
951 .BR \-a ", " "\-\-auto{=no,yes,md,mdp,part}"
952 See this option under Create and Build options.
955 .BR \-b ", " \-\-bitmap=
956 Specify the bitmap file that was given when the array was created. If
959 bitmap, there is no need to specify this when assembling the array.
962 .BR \-\-backup\-file=
965 was used while reshaping an array (e.g. changing number of devices or
966 chunk size) and the system crashed during the critical section, then the same
970 to allow possibly corrupted data to be restored, and the reshape
974 .BR \-\-invalid\-backup
975 If the file needed for the above option is not available for any
976 reason an empty file can be given together with this option to
977 indicate that the backup file is invalid. In this case the data that
978 was being rearranged at the time of the crash could be irrecoverably
979 lost, but the rest of the array may still be recoverable. This option
980 should only be used as a last resort if there is no way to recover the
985 .BR \-U ", " \-\-update=
986 Update the superblock on each device while assembling the array. The
987 argument given to this flag can be one of
1002 option will adjust the superblock of an array what was created on a Sparc
1003 machine running a patched 2.2 Linux kernel. This kernel got the
1004 alignment of part of the superblock wrong. You can use the
1005 .B "\-\-examine \-\-sparc2.2"
1008 to see what effect this would have.
1012 option will update the
1013 .B "preferred minor"
1014 field on each superblock to match the minor number of the array being
1016 This can be useful if
1018 reports a different "Preferred Minor" to
1020 In some cases this update will be performed automatically
1021 by the kernel driver. In particular the update happens automatically
1022 at the first write to an array with redundancy (RAID level 1 or
1023 greater) on a 2.6 (or later) kernel.
1027 option will change the uuid of the array. If a UUID is given with the
1029 option that UUID will be used as a new UUID and will
1031 be used to help identify the devices in the array.
1034 is given, a random UUID is chosen.
1038 option will change the
1040 of the array as stored in the superblock. This is only supported for
1041 version-1 superblocks.
1045 option will change the
1047 as recorded in the superblock. For version-0 superblocks, this is the
1048 same as updating the UUID.
1049 For version-1 superblocks, this involves updating the name.
1053 option will cause the array to be marked
1055 meaning that any redundancy in the array (e.g. parity for RAID5,
1056 copies for RAID1) may be incorrect. This will cause the RAID system
1057 to perform a "resync" pass to make sure that all redundant information
1062 option allows arrays to be moved between machines with different
1064 When assembling such an array for the first time after a move, giving
1065 .B "\-\-update=byteorder"
1068 to expect superblocks to have their byteorder reversed, and will
1069 correct that order before assembling the array. This is only valid
1070 with original (Version 0.90) superblocks.
1074 option will correct the summaries in the superblock. That is the
1075 counts of total, working, active, failed, and spare devices.
1079 option will rarely be of use. It applies to version 1.1 and 1.2 metadata
1080 only (where the metadata is at the start of the device) and is only
1081 useful when the component device has changed size (typically become
1082 larger). The version 1 metadata records the amount of the device that
1083 can be used to store data, so if a device in a version 1.1 or 1.2
1084 array becomes larger, the metadata will still be visible, but the
1085 extra space will not. In this case it might be useful to assemble the
1087 .BR \-\-update=devicesize .
1090 to determine the maximum usable amount of space on each device and
1091 update the relevant field in the metadata.
1095 option can be used when an array has an internal bitmap which is
1096 corrupt in some way so that assembling the array normally fails. It
1097 will cause any internal bitmap to be ignored.
1099 .SH For Manage mode:
1102 .BR \-t ", " \-\-test
1103 Unless a more serious error occurred,
1105 will exit with a status of 2 if no changes were made to the array and
1106 0 if at least one change was made.
1107 This can be useful when an indirect specifier such as
1112 is used in requesting an operation on the array.
1114 will report failure if these specifiers didn't find any match.
1117 .BR \-a ", " \-\-add
1118 hot-add listed devices.
1119 If a device appears to have recently been part of the array
1120 (possibly it failed or was removed) the device is re\-added as describe
1122 If that fails or the device was never part of the array, the device is
1123 added as a hot-spare.
1124 If the array is degraded, it will immediately start to rebuild data
1127 Note that this and the following options are only meaningful on array
1128 with redundancy. They don't apply to RAID0 or Linear.
1132 re\-add a device that was previous removed from an array.
1133 If the metadata on the device reports that it is a member of the
1134 array, and the slot that it used is still vacant, then the device will
1135 be added back to the array in the same position. This will normally
1136 cause the data for that device to be recovered. However based on the
1137 event count on the device, the recovery may only require sections that
1138 are flagged a write-intent bitmap to be recovered or may not require
1139 any recovery at all.
1141 When used on an array that has no metadata (i.e. it was built with
1143 it will be assumed that bitmap-based recovery is enough to make the
1144 device fully consistent with the array.
1148 can be accompanied by
1149 .BR \-\-update=devicesize .
1150 See the description of this option when used in Assemble mode for an
1151 explanation of its use.
1153 If the device name given is
1155 then mdadm will try to find any device that looks like it should be
1156 part of the array but isn't and will try to re\-add all such devices.
1159 .BR \-r ", " \-\-remove
1160 remove listed devices. They must not be active. i.e. they should
1161 be failed or spare devices. As well as the name of a device file
1170 The first causes all failed device to be removed. The second causes
1171 any device which is no longer connected to the system (i.e an 'open'
1174 to be removed. This will only succeed for devices that are spares or
1175 have already been marked as failed.
1178 .BR \-f ", " \-\-fail
1179 mark listed devices as faulty.
1180 As well as the name of a device file, the word
1182 can be given. This will cause any device that has been detached from
1183 the system to be marked as failed. It can then be removed.
1191 .BR \-\-write\-mostly
1192 Subsequent devices that are added or re\-added will have the 'write-mostly'
1193 flag set. This is only valid for RAID1 and means that the 'md' driver
1194 will avoid reading from these devices if possible.
1197 Subsequent devices that are added or re\-added will have the 'write-mostly'
1201 Each of these options requires that the first device listed is the array
1202 to be acted upon, and the remainder are component devices to be added,
1203 removed, marked as faulty, etc. Several different operations can be
1204 specified for different devices, e.g.
1206 mdadm /dev/md0 \-\-add /dev/sda1 \-\-fail /dev/sdb1 \-\-remove /dev/sdb1
1208 Each operation applies to all devices listed until the next
1211 If an array is using a write-intent bitmap, then devices which have
1212 been removed can be re\-added in a way that avoids a full
1213 reconstruction but instead just updates the blocks that have changed
1214 since the device was removed. For arrays with persistent metadata
1215 (superblocks) this is done automatically. For arrays created with
1217 mdadm needs to be told that this device we removed recently with
1220 Devices can only be removed from an array if they are not in active
1221 use, i.e. that must be spares or failed devices. To remove an active
1222 device, it must first be marked as
1228 .BR \-Q ", " \-\-query
1229 Examine a device to see
1230 (1) if it is an md device and (2) if it is a component of an md
1232 Information about what is discovered is presented.
1235 .BR \-D ", " \-\-detail
1236 Print details of one or more md devices.
1239 .BR \-\-detail\-platform
1240 Print details of the platform's RAID capabilities (firmware / hardware
1241 topology) for a given metadata format.
1244 .BR \-Y ", " \-\-export
1249 output will be formatted as
1251 pairs for easy import into the environment.
1254 .BR \-E ", " \-\-examine
1255 Print contents of the metadata stored on the named device(s).
1256 Note the contrast between
1261 applies to devices which are components of an array, while
1263 applies to a whole array which is currently active.
1266 If an array was created on a SPARC machine with a 2.2 Linux kernel
1267 patched with RAID support, the superblock will have been created
1268 incorrectly, or at least incompatibly with 2.4 and later kernels.
1273 will fix the superblock before displaying it. If this appears to do
1274 the right thing, then the array can be successfully assembled using
1275 .BR "\-\-assemble \-\-update=sparc2.2" .
1278 .BR \-X ", " \-\-examine\-bitmap
1279 Report information about a bitmap file.
1280 The argument is either an external bitmap file or an array component
1281 in case of an internal bitmap. Note that running this on an array
1284 does not report the bitmap for that array.
1287 .BR \-R ", " \-\-run
1288 start a partially assembled array. If
1290 did not find enough devices to fully start the array, it might leaving
1291 it partially assembled. If you wish, you can then use
1293 to start the array in degraded mode.
1296 .BR \-S ", " \-\-stop
1297 deactivate array, releasing all resources.
1300 .BR \-o ", " \-\-readonly
1301 mark array as readonly.
1304 .BR \-w ", " \-\-readwrite
1305 mark array as readwrite.
1308 .B \-\-zero\-superblock
1309 If the device contains a valid md superblock, the block is
1310 overwritten with zeros. With
1312 the block where the superblock would be is overwritten even if it
1313 doesn't appear to be valid.
1316 .B \-\-kill\-subarray=
1317 If the device is a container and the argument to \-\-kill\-subarray
1318 specifies an inactive subarray in the container, then the subarray is
1319 deleted. Deleting all subarrays will leave an 'empty-container' or
1320 spare superblock on the drives. See \-\-zero\-superblock for completely
1321 removing a superblock. Note that some formats depend on the subarray
1322 index for generating a UUID, this command will fail if it would change
1323 the UUID of an active subarray.
1326 .B \-\-update\-subarray=
1327 If the device is a container and the argument to \-\-update\-subarray
1328 specifies a subarray in the container, then attempt to update the given
1329 superblock field in the subarray. See below in
1334 .BR \-t ", " \-\-test
1339 is set to reflect the status of the device. See below in
1344 .BR \-W ", " \-\-wait
1345 For each md device given, wait for any resync, recovery, or reshape
1346 activity to finish before returning.
1348 will return with success if it actually waited for every device
1349 listed, otherwise it will return failure.
1353 For each md device given, or each device in /proc/mdstat if
1355 is given, arrange for the array to be marked clean as soon as possible.
1357 will return with success if the array uses external metadata and we
1358 successfully waited. For native arrays this returns immediately as the
1359 kernel handles dirty-clean transitions at shutdown. No action is taken
1360 if safe-mode handling is disabled.
1362 .SH For Incremental Assembly mode:
1364 .BR \-\-rebuild\-map ", " \-r
1365 Rebuild the map file
1366 .RB ( /var/run/mdadm/map )
1369 uses to help track which arrays are currently being assembled.
1372 .BR \-\-run ", " \-R
1373 Run any array assembled as soon as a minimal number of devices are
1374 available, rather than waiting until all expected devices are present.
1377 .BR \-\-scan ", " \-s
1378 Only meaningful with
1382 file for arrays that are being incrementally assembled and will try to
1383 start any that are not already started. If any such array is listed
1386 as requiring an external bitmap, that bitmap will be attached first.
1389 .BR \-\-fail ", " \-f
1390 This allows the hot-plug system to remove devices that have fully disappeared
1391 from the kernel. It will first fail and then remove the device from any
1392 array it belongs to.
1393 The device name given should be a kernel device name such as "sda",
1399 Only used with \-\-fail. The 'path' given will be recorded so that if
1400 a new device appears at the same location it can be automatically
1401 added to the same array. This allows the failed device to be
1402 automatically replaced by a new device without metadata if it appears
1403 at specified path. This option is normally only set by a
1407 .SH For Monitor mode:
1409 .BR \-m ", " \-\-mail
1410 Give a mail address to send alerts to.
1413 .BR \-p ", " \-\-program ", " \-\-alert
1414 Give a program to be run whenever an event is detected.
1417 .BR \-y ", " \-\-syslog
1418 Cause all events to be reported through 'syslog'. The messages have
1419 facility of 'daemon' and varying priorities.
1422 .BR \-d ", " \-\-delay
1423 Give a delay in seconds.
1425 polls the md arrays and then waits this many seconds before polling
1426 again. The default is 60 seconds. Since 2.6.16, there is no need to
1427 reduce this as the kernel alerts
1429 immediately when there is any change.
1432 .BR \-r ", " \-\-increment
1433 Give a percentage increment.
1435 will generate RebuildNN events with the given percentage increment.
1438 .BR \-f ", " \-\-daemonise
1441 to run as a background daemon if it decides to monitor anything. This
1442 causes it to fork and run in the child, and to disconnect from the
1443 terminal. The process id of the child is written to stdout.
1446 which will only continue monitoring if a mail address or alert program
1447 is found in the config file.
1450 .BR \-i ", " \-\-pid\-file
1453 is running in daemon mode, write the pid of the daemon process to
1454 the specified file, instead of printing it on standard output.
1457 .BR \-1 ", " \-\-oneshot
1458 Check arrays only once. This will generate
1460 events and more significantly
1466 .B " mdadm \-\-monitor \-\-scan \-1"
1468 from a cron script will ensure regular notification of any degraded arrays.
1471 .BR \-t ", " \-\-test
1474 alert for every array found at startup. This alert gets mailed and
1475 passed to the alert program. This can be used for testing that alert
1476 message do get through successfully.
1480 This inhibits the functionality for moving spares between arrays.
1481 Only one monitoring process started with
1483 but without this flag is allowed, otherwise the two could interfere
1490 .B mdadm \-\-assemble
1491 .I md-device options-and-component-devices...
1494 .B mdadm \-\-assemble \-\-scan
1495 .I md-devices-and-options...
1498 .B mdadm \-\-assemble \-\-scan
1502 This usage assembles one or more RAID arrays from pre-existing components.
1503 For each array, mdadm needs to know the md device, the identity of the
1504 array, and a number of component-devices. These can be found in a number of ways.
1506 In the first usage example (without the
1508 the first device given is the md device.
1509 In the second usage example, all devices listed are treated as md
1510 devices and assembly is attempted.
1511 In the third (where no devices are listed) all md devices that are
1512 listed in the configuration file are assembled. If no arrays are
1513 described by the configuration file, then any arrays that
1514 can be found on unused devices will be assembled.
1516 If precisely one device is listed, but
1522 was given and identity information is extracted from the configuration file.
1524 The identity can be given with the
1530 option, will be taken from the md-device record in the config file, or
1531 will be taken from the super block of the first component-device
1532 listed on the command line.
1534 Devices can be given on the
1536 command line or in the config file. Only devices which have an md
1537 superblock which contains the right identity will be considered for
1540 The config file is only used if explicitly named with
1542 or requested with (a possibly implicit)
1547 .B /etc/mdadm/mdadm.conf
1552 is not given, then the config file will only be used to find the
1553 identity of md arrays.
1555 Normally the array will be started after it is assembled. However if
1557 is not given and not all expected drives were listed, then the array
1558 is not started (to guard against usage errors). To insist that the
1559 array be started in this case (as may work for RAID1, 4, 5, 6, or 10),
1568 does not create any entries in
1572 It does record information in
1573 .B /var/run/mdadm/map
1576 to choose the correct name.
1580 detects that udev is not configured, it will create the devices in
1584 In Linux kernels prior to version 2.6.28 there were two distinctly
1585 different types of md devices that could be created: one that could be
1586 partitioned using standard partitioning tools and one that could not.
1587 Since 2.6.28 that distinction is no longer relevant as both type of
1588 devices can be partitioned.
1590 will normally create the type that originally could not be partitioned
1591 as it has a well defined major number (9).
1593 Prior to 2.6.28, it is important that mdadm chooses the correct type
1594 of array device to use. This can be controlled with the
1596 option. In particular, a value of "mdp" or "part" or "p" tells mdadm
1597 to use a partitionable device rather than the default.
1599 In the no-udev case, the value given to
1601 can be suffixed by a number. This tells
1603 to create that number of partition devices rather than the default of 4.
1607 can also be given in the configuration file as a word starting
1609 on the ARRAY line for the relevant array.
1616 and no devices are listed,
1618 will first attempt to assemble all the arrays listed in the config
1621 If no arrays are listed in the config (other than those marked
1623 it will look through the available devices for possible arrays and
1624 will try to assemble anything that it finds. Arrays which are tagged
1625 as belonging to the given homehost will be assembled and started
1626 normally. Arrays which do not obviously belong to this host are given
1627 names that are expected not to conflict with anything local, and are
1628 started "read-auto" so that nothing is written to any device until the
1629 array is written to. i.e. automatic resync etc is delayed.
1633 finds a consistent set of devices that look like they should comprise
1634 an array, and if the superblock is tagged as belonging to the given
1635 home host, it will automatically choose a device name and try to
1636 assemble the array. If the array uses version-0.90 metadata, then the
1638 number as recorded in the superblock is used to create a name in
1642 If the array uses version-1 metadata, then the
1644 from the superblock is used to similarly create a name in
1646 (the name will have any 'host' prefix stripped first).
1648 This behaviour can be modified by the
1652 configuration file. This line can indicate that specific metadata
1653 type should, or should not, be automatically assembled. If an array
1654 is found which is not listed in
1656 and has a metadata format that is denied by the
1658 line, then it will not be assembled.
1661 line can also request that all arrays identified as being for this
1662 homehost should be assembled regardless of their metadata type.
1665 for further details.
1667 Note: Auto assembly cannot be used for assembling and activating some
1668 arrays which are undergoing reshape. In particular as the
1670 cannot be given, any reshape which requires a backup-file to continue
1671 cannot be started by auto assembly. An array which is growing to more
1672 devices and has passed the critical section can be assembled using
1683 .BI \-\-raid\-devices= Z
1687 This usage is similar to
1689 The difference is that it creates an array without a superblock. With
1690 these arrays there is no difference between initially creating the array and
1691 subsequently assembling the array, except that hopefully there is useful
1692 data there in the second case.
1694 The level may raid0, linear, raid1, raid10, multipath, or faulty, or
1695 one of their synonyms. All devices must be listed and the array will
1696 be started once complete. It will often be appropriate to use
1697 .B \-\-assume\-clean
1698 with levels raid1 or raid10.
1709 .BI \-\-raid\-devices= Z
1713 This usage will initialise a new md array, associate some devices with
1714 it, and activate the array.
1716 The named device will normally not exist when
1717 .I "mdadm \-\-create"
1718 is run, but will be created by
1720 once the array becomes active.
1722 As devices are added, they are checked to see if they contain RAID
1723 superblocks or filesystems. They are also checked to see if the variance in
1724 device size exceeds 1%.
1726 If any discrepancy is found, the array will not automatically be run, though
1729 can override this caution.
1731 To create a "degraded" array in which some devices are missing, simply
1732 give the word "\fBmissing\fP"
1733 in place of a device name. This will cause
1735 to leave the corresponding slot in the array empty.
1736 For a RAID4 or RAID5 array at most one slot can be
1737 "\fBmissing\fP"; for a RAID6 array at most two slots.
1738 For a RAID1 array, only one real device needs to be given. All of the
1742 When creating a RAID5 array,
1744 will automatically create a degraded array with an extra spare drive.
1745 This is because building the spare into a degraded array is in general
1746 faster than resyncing the parity on a non-degraded, but not clean,
1747 array. This feature can be overridden with the
1751 When creating an array with version-1 metadata a name for the array is
1753 If this is not given with the
1757 will choose a name based on the last component of the name of the
1758 device being created. So if
1760 is being created, then the name
1765 is being created, then the name
1769 When creating a partition based array, using
1771 with version-1.x metadata, the partition type should be set to
1773 (non fs-data). This type selection allows for greater precision since
1774 using any other [RAID auto-detect (0xFD) or a GNU/Linux partition (0x83)],
1775 might create problems in the event of array recovery through a live cdrom.
1777 A new array will normally get a randomly assigned 128bit UUID which is
1778 very likely to be unique. If you have a specific need, you can choose
1779 a UUID for the array by giving the
1781 option. Be warned that creating two arrays with the same UUID is a
1782 recipe for disaster. Also, using
1784 when creating a v0.90 array will silently override any
1789 .\"option is given, it is not necessary to list any component-devices in this command.
1790 .\"They can be added later, before a
1794 .\"is given, the apparent size of the smallest drive given is used.
1796 When creating an array within a
1799 can be given either the list of devices to use, or simply the name of
1800 the container. The former case gives control over which devices in
1801 the container will be used for the array. The latter case allows
1803 to automatically choose which devices to use based on how much spare
1806 The General Management options that are valid with
1811 insist on running the array even if some devices look like they might
1816 start the array readonly \(em not supported yet.
1823 .I options... devices...
1826 This usage will allow individual devices in an array to be failed,
1827 removed or added. It is possible to perform multiple operations with
1828 on command. For example:
1830 .B " mdadm /dev/md0 \-f /dev/hda1 \-r /dev/hda1 \-a /dev/hda1"
1836 and will then remove it from the array and finally add it back
1837 in as a spare. However only one md array can be affected by a single
1840 When a device is added to an active array, mdadm checks to see if it
1841 has metadata on it which suggests that it was recently a member of the
1842 array. If it does, it tries to "re\-add" the device. If there have
1843 been no changes since the device was removed, or if the array has a
1844 write-intent bitmap which has recorded whatever changes there were,
1845 then the device will immediately become a full member of the array and
1846 those differences recorded in the bitmap will be resolved.
1856 MISC mode includes a number of distinct operations that
1857 operate on distinct devices. The operations are:
1860 The device is examined to see if it is
1861 (1) an active md array, or
1862 (2) a component of an md array.
1863 The information discovered is reported.
1867 The device should be an active md device.
1869 will display a detailed description of the array.
1873 will cause the output to be less detailed and the format to be
1874 suitable for inclusion in
1878 will normally be 0 unless
1880 failed to get useful information about the device(s); however, if the
1882 option is given, then the exit status will be:
1886 The array is functioning normally.
1889 The array has at least one failed device.
1892 The array has multiple failed devices such that it is unusable.
1895 There was an error while trying to get information about the device.
1899 .B \-\-detail\-platform
1900 Print detail of the platform's RAID capabilities (firmware / hardware
1901 topology). If the metadata is specified with
1905 then the return status will be:
1909 metadata successfully enumerated its platform components on this system
1912 metadata is platform independent
1915 metadata failed to find its platform components on this system
1919 .B \-\-update\-subarray=
1920 If the device is a container and the argument to \-\-update\-subarray
1921 specifies a subarray in the container, then attempt to update the given
1922 superblock field in the subarray. Similar to updating an array in
1923 "assemble" mode, the field to update is selected by
1927 option. Currently only
1933 option updates the subarray name in the metadata, it may not affect the
1934 device node name or the device node symlink until the subarray is
1935 re\-assembled. If updating
1937 would change the UUID of an active subarray this operation is blocked,
1938 and the command will end in an error.
1942 The device should be a component of an md array.
1944 will read the md superblock of the device and display the contents.
1949 is given, then multiple devices that are components of the one array
1950 are grouped together and reported in a single entry suitable
1956 without listing any devices will cause all devices listed in the
1957 config file to be examined.
1961 The devices should be active md arrays which will be deactivated, as
1962 long as they are not currently in use.
1966 This will fully activate a partially assembled md array.
1970 This will mark an active array as read-only, providing that it is
1971 not currently being used.
1977 array back to being read/write.
1981 For all operations except
1984 will cause the operation to be applied to all arrays listed in
1989 causes all devices listed in the config file to be examined.
1992 .BR \-b ", " \-\-brief
1993 Be less verbose. This is used with
2001 gives an intermediate level of verbosity.
2007 .B mdadm \-\-monitor
2008 .I options... devices...
2013 to periodically poll a number of md arrays and to report on any events
2016 will never exit once it decides that there are arrays to be checked,
2017 so it should normally be run in the background.
2019 As well as reporting events,
2021 may move a spare drive from one array to another if they are in the
2026 and if the destination array has a failed drive but no spares.
2028 If any devices are listed on the command line,
2030 will only monitor those devices. Otherwise all arrays listed in the
2031 configuration file will be monitored. Further, if
2033 is given, then any other md devices that appear in
2035 will also be monitored.
2037 The result of monitoring the arrays is the generation of events.
2038 These events are passed to a separate program (if specified) and may
2039 be mailed to a given E-mail address.
2041 When passing events to a program, the program is run once for each event,
2042 and is given 2 or 3 command-line arguments: the first is the
2043 name of the event (see below), the second is the name of the
2044 md device which is affected, and the third is the name of a related
2045 device if relevant (such as a component device that has failed).
2049 is given, then a program or an E-mail address must be specified on the
2050 command line or in the config file. If neither are available, then
2052 will not monitor anything.
2056 will continue monitoring as long as something was found to monitor. If
2057 no program or email is given, then each event is reported to
2060 The different events are:
2064 .B DeviceDisappeared
2065 An md array which previously was configured appears to no longer be
2066 configured. (syslog priority: Critical)
2070 was told to monitor an array which is RAID0 or Linear, then it will
2072 .B DeviceDisappeared
2073 with the extra information
2075 This is because RAID0 and Linear do not support the device-failed,
2076 hot-spare and resync operations which are monitored.
2080 An md array started reconstruction. (syslog priority: Warning)
2086 is a two-digit number (ie. 05, 48). This indicates that rebuild
2087 has passed that many percent of the total. The events are generated
2088 with fixed increment since 0. Increment size may be specified with
2089 a commandline option (default is 20). (syslog priority: Warning)
2093 An md array that was rebuilding, isn't any more, either because it
2094 finished normally or was aborted. (syslog priority: Warning)
2098 An active component device of an array has been marked as
2099 faulty. (syslog priority: Critical)
2103 A spare component device which was being rebuilt to replace a faulty
2104 device has failed. (syslog priority: Critical)
2108 A spare component device which was being rebuilt to replace a faulty
2109 device has been successfully rebuilt and has been made active.
2110 (syslog priority: Info)
2114 A new md array has been detected in the
2116 file. (syslog priority: Info)
2120 A newly noticed array appears to be degraded. This message is not
2123 notices a drive failure which causes degradation, but only when
2125 notices that an array is degraded when it first sees the array.
2126 (syslog priority: Critical)
2130 A spare drive has been moved from one array in a
2134 to another to allow a failed drive to be replaced.
2135 (syslog priority: Info)
2141 has been told, via the config file, that an array should have a certain
2142 number of spare devices, and
2144 detects that it has fewer than this number when it first sees the
2145 array, it will report a
2148 (syslog priority: Warning)
2152 An array was found at startup, and the
2155 (syslog priority: Info)
2165 cause Email to be sent. All events cause the program to be run.
2166 The program is run with two or three arguments: the event
2167 name, the array device and possibly a second device.
2169 Each event has an associated array device (e.g.
2171 and possibly a second device. For
2176 the second device is the relevant component device.
2179 the second device is the array that the spare was moved from.
2183 to move spares from one array to another, the different arrays need to
2184 be labeled with the same
2186 or the spares must be allowed to migrate through matching POLICY domains
2187 in the configuration file. The
2189 name can be any string; it is only necessary that different spare
2190 groups use different names.
2194 detects that an array in a spare group has fewer active
2195 devices than necessary for the complete array, and has no spare
2196 devices, it will look for another array in the same spare group that
2197 has a full complement of working drive and a spare. It will then
2198 attempt to remove the spare from the second drive and add it to the
2200 If the removal succeeds but the adding fails, then it is added back to
2203 If the spare group for a degraded array is not defined,
2205 will look at the rules of spare migration specified by POLICY lines in
2207 and then follow similar steps as above if a matching spare is found.
2210 The GROW mode is used for changing the size or shape of an active
2212 For this to work, the kernel must support the necessary change.
2213 Various types of growth are being added during 2.6 development.
2215 Currently the supported changes include
2217 change the "size" attribute for RAID1, RAID4, RAID5 and RAID6.
2219 increase or decrease the "raid\-devices" attribute of RAID0, RAID1, RAID4,
2222 change the chunk-size and layout of RAID0, RAID4, RAID5 and RAID6.
2224 convert between RAID1 and RAID5, between RAID5 and RAID6, between
2225 RAID0, RAID4, and RAID5, and between RAID0 and RAID10 (in the near-2 mode).
2227 add a write-intent bitmap to any array which supports these bitmaps, or
2228 remove a write-intent bitmap from such an array.
2231 Using GROW on containers is currently supported only for Intel's IMSM
2232 container format. The number of devices in a container can be
2233 increased - which affects all arrays in the container - or an array
2234 in a container can be converted between levels where those levels are
2235 supported by the container, and the conversion is on of those listed
2236 above. Resizing arrays in an IMSM container with
2238 is not yet supported.
2240 Grow functionality (e.g. expand a number of raid devices) for Intel's
2241 IMSM container format has an experimental status. It is guarded by the
2242 .B MDADM_EXPERIMENTAL
2243 environment variable which must be set to '1' for a GROW command to
2245 This is for the following reasons:
2248 Intel's native IMSM check-pointing is not fully tested yet.
2249 This can causes IMSM incompatibility during the grow process: an array
2250 which is growing cannot roam between Microsoft Windows(R) and Linux
2254 Interrupting a grow operation is not recommended, because it
2255 has not been fully tested for Intel's IMSM container format yet.
2258 Note: Intel's native checkpointing doesn't use
2260 option and it is transparent for assembly feature.
2263 Normally when an array is built the "size" is taken from the smallest
2264 of the drives. If all the small drives in an arrays are, one at a
2265 time, removed and replaced with larger drives, then you could have an
2266 array of large drives with only a small amount used. In this
2267 situation, changing the "size" with "GROW" mode will allow the extra
2268 space to start being used. If the size is increased in this way, a
2269 "resync" process will start to make sure the new parts of the array
2272 Note that when an array changes size, any filesystem that may be
2273 stored in the array will not automatically grow or shrink to use or
2274 vacate the space. The
2275 filesystem will need to be explicitly told to use the extra space
2276 after growing, or to reduce its size
2278 to shrinking the array.
2280 Also the size of an array cannot be changed while it has an active
2281 bitmap. If an array has a bitmap, it must be removed before the size
2282 can be changed. Once the change is complete a new bitmap can be created.
2284 .SS RAID\-DEVICES CHANGES
2286 A RAID1 array can work with any number of devices from 1 upwards
2287 (though 1 is not very useful). There may be times which you want to
2288 increase or decrease the number of active devices. Note that this is
2289 different to hot-add or hot-remove which changes the number of
2292 When reducing the number of devices in a RAID1 array, the slots which
2293 are to be removed from the array must already be vacant. That is, the
2294 devices which were in those slots must be failed and removed.
2296 When the number of devices is increased, any hot spares that are
2297 present will be activated immediately.
2299 Changing the number of active devices in a RAID5 or RAID6 is much more
2300 effort. Every block in the array will need to be read and written
2301 back to a new location. From 2.6.17, the Linux Kernel is able to
2302 increase the number of devices in a RAID5 safely, including restarting
2303 an interrupted "reshape". From 2.6.31, the Linux Kernel is able to
2304 increase or decrease the number of devices in a RAID5 or RAID6.
2306 From 2.6.35, the Linux Kernel is able to convert a RAID0 in to a RAID4
2309 uses this functionality and the ability to add
2310 devices to a RAID4 to allow devices to be added to a RAID0. When
2311 requested to do this,
2313 will convert the RAID0 to a RAID4, add the necessary disks and make
2314 the reshape happen, and then convert the RAID4 back to RAID0.
2316 When decreasing the number of devices, the size of the array will also
2317 decrease. If there was data in the array, it could get destroyed and
2318 this is not reversible, so you should firstly shrink the filesystem on
2319 the array to fit within the new size. To help prevent accidents,
2321 requires that the size of the array be decreased first with
2322 .BR "mdadm --grow --array-size" .
2323 This is a reversible change which simply makes the end of the array
2324 inaccessible. The integrity of any data can then be checked before
2325 the non-reversible reduction in the number of devices is request.
2327 When relocating the first few stripes on a RAID5 or RAID6, it is not
2328 possible to keep the data on disk completely consistent and
2329 crash-proof. To provide the required safety, mdadm disables writes to
2330 the array while this "critical section" is reshaped, and takes a
2331 backup of the data that is in that section. For grows, this backup may be
2332 stored in any spare devices that the array has, however it can also be
2333 stored in a separate file specified with the
2335 option, and is required to be specified for shrinks, RAID level
2336 changes and layout changes. If this option is used, and the system
2337 does crash during the critical period, the same file must be passed to
2339 to restore the backup and reassemble the array. When shrinking rather
2340 than growing the array, the reshape is done from the end towards the
2341 beginning, so the "critical section" is at the end of the reshape.
2345 Changing the RAID level of any array happens instantaneously. However
2346 in the RAID5 to RAID6 case this requires a non-standard layout of the
2347 RAID6 data, and in the RAID6 to RAID5 case that non-standard layout is
2348 required before the change can be accomplished. So while the level
2349 change is instant, the accompanying layout change can take quite a
2352 is required. If the array is not simultaneously being grown or
2353 shrunk, so that the array size will remain the same - for example,
2354 reshaping a 3-drive RAID5 into a 4-drive RAID6 - the backup file will
2355 be used not just for a "cricital section" but throughout the reshape
2356 operation, as described below under LAYOUT CHANGES.
2358 .SS CHUNK-SIZE AND LAYOUT CHANGES
2360 Changing the chunk-size of layout without also changing the number of
2361 devices as the same time will involve re-writing all blocks in-place.
2362 To ensure against data loss in the case of a crash, a
2364 must be provided for these changes. Small sections of the array will
2365 be copied to the backup file while they are being rearranged. This
2366 means that all the data is copied twice, once to the backup and once
2367 to the new layout on the array, so this type of reshape will go very
2370 If the reshape is interrupted for any reason, this backup file must be
2372 .B "mdadm --assemble"
2373 so the array can be reassembled. Consequently the file cannot be
2374 stored on the device being reshaped.
2379 A write-intent bitmap can be added to, or removed from, an active
2380 array. Either internal bitmaps, or bitmaps stored in a separate file,
2381 can be added. Note that if you add a bitmap stored in a file which is
2382 in a filesystem that is on the RAID array being affected, the system
2383 will deadlock. The bitmap must be on a separate filesystem.
2385 .SH INCREMENTAL MODE
2389 .B mdadm \-\-incremental
2395 .B mdadm \-\-incremental \-\-fail
2399 .B mdadm \-\-incremental \-\-rebuild\-map
2402 .B mdadm \-\-incremental \-\-run \-\-scan
2405 This mode is designed to be used in conjunction with a device
2406 discovery system. As devices are found in a system, they can be
2408 .B "mdadm \-\-incremental"
2409 to be conditionally added to an appropriate array.
2411 Conversely, it can also be used with the
2413 flag to do just the opposite and find whatever array a particular device
2414 is part of and remove the device from that array.
2416 If the device passed is a
2418 device created by a previous call to
2420 then rather than trying to add that device to an array, all the arrays
2421 described by the metadata of the container will be started.
2424 performs a number of tests to determine if the device is part of an
2425 array, and which array it should be part of. If an appropriate array
2426 is found, or can be created,
2428 adds the device to the array and conditionally starts the array.
2432 will normally only add devices to an array which were previously working
2433 (active or spare) parts of that array. The support for automatic
2434 inclusion of a new drive as a spare in some array requires
2435 a configuration through POLICY in config file.
2439 makes are as follow:
2441 Is the device permitted by
2443 That is, is it listed in a
2445 line in that file. If
2447 is absent then the default it to allow any device. Similar if
2449 contains the special word
2451 then any device is allowed. Otherwise the device name given to
2453 must match one of the names or patterns in a
2458 Does the device have a valid md superblock? If a specific metadata
2459 version is requested with
2463 then only that style of metadata is accepted, otherwise
2465 finds any known version of metadata. If no
2467 metadata is found, the device may be still added to an array
2468 as a spare if POLICY allows.
2472 Does the metadata match an expected array?
2473 The metadata can match in two ways. Either there is an array listed
2476 which identifies the array (either by UUID, by name, by device list,
2477 or by minor-number), or the array was created with a
2483 or on the command line.
2486 is not able to positively identify the array as belonging to the
2487 current host, the device will be rejected.
2492 keeps a list of arrays that it has partially assembled in
2493 .B /var/run/mdadm/map
2495 .B /var/run/mdadm.map
2496 if the directory doesn't exist. Or maybe even
2497 .BR /dev/.mdadm.map ).
2498 If no array exists which matches
2499 the metadata on the new device,
2501 must choose a device name and unit number. It does this based on any
2504 or any name information stored in the metadata. If this name
2505 suggests a unit number, that number will be used, otherwise a free
2506 unit number will be chosen. Normally
2508 will prefer to create a partitionable array, however if the
2512 suggests that a non-partitionable array is preferred, that will be
2515 If the array is not found in the config file and its metadata does not
2516 identify it as belonging to the "homehost", then
2518 will choose a name for the array which is certain not to conflict with
2519 any array which does belong to this host. It does this be adding an
2520 underscore and a small number to the name preferred by the metadata.
2522 Once an appropriate array is found or created and the device is added,
2524 must decide if the array is ready to be started. It will
2525 normally compare the number of available (non-spare) devices to the
2526 number of devices that the metadata suggests need to be active. If
2527 there are at least that many, the array will be started. This means
2528 that if any devices are missing the array will not be restarted.
2534 in which case the array will be run as soon as there are enough
2535 devices present for the data to be accessible. For a RAID1, that
2536 means one device will start the array. For a clean RAID5, the array
2537 will be started as soon as all but one drive is present.
2539 Note that neither of these approaches is really ideal. If it can
2540 be known that all device discovery has completed, then
2544 can be run which will try to start all arrays that are being
2545 incrementally assembled. They are started in "read-auto" mode in
2546 which they are read-only until the first write request. This means
2547 that no metadata updates are made and no attempt at resync or recovery
2548 happens. Further devices that are found before the first write can
2549 still be added safely.
2552 This section describes environment variables that affect how mdadm
2557 Setting this value to 1 will prevent mdadm from automatically launching
2558 mdmon. This variable is intended primarily for debugging mdadm/mdmon.
2564 does not create any device nodes in /dev, but leaves that task to
2568 appears not to be configured, or if this environment variable is set
2571 will create and devices that are needed.
2575 .B " mdadm \-\-query /dev/name-of-device"
2577 This will find out if a given device is a RAID array, or is part of
2578 one, and will provide brief information about the device.
2580 .B " mdadm \-\-assemble \-\-scan"
2582 This will assemble and start all arrays listed in the standard config
2583 file. This command will typically go in a system startup file.
2585 .B " mdadm \-\-stop \-\-scan"
2587 This will shut down all arrays that can be shut down (i.e. are not
2588 currently in use). This will typically go in a system shutdown script.
2590 .B " mdadm \-\-follow \-\-scan \-\-delay=120"
2592 If (and only if) there is an Email address or program given in the
2593 standard config file, then
2594 monitor the status of all arrays listed in that file by
2595 polling them ever 2 minutes.
2597 .B " mdadm \-\-create /dev/md0 \-\-level=1 \-\-raid\-devices=2 /dev/hd[ac]1"
2599 Create /dev/md0 as a RAID1 array consisting of /dev/hda1 and /dev/hdc1.
2602 .B " echo 'DEVICE /dev/hd*[0\-9] /dev/sd*[0\-9]' > mdadm.conf"
2604 .B " mdadm \-\-detail \-\-scan >> mdadm.conf"
2606 This will create a prototype config file that describes currently
2607 active arrays that are known to be made from partitions of IDE or SCSI drives.
2608 This file should be reviewed before being used as it may
2609 contain unwanted detail.
2611 .B " echo 'DEVICE /dev/hd[a\-z] /dev/sd*[a\-z]' > mdadm.conf"
2613 .B " mdadm \-\-examine \-\-scan \-\-config=mdadm.conf >> mdadm.conf"
2615 This will find arrays which could be assembled from existing IDE and
2616 SCSI whole drives (not partitions), and store the information in the
2617 format of a config file.
2618 This file is very likely to contain unwanted detail, particularly
2621 entries. It should be reviewed and edited before being used as an
2624 .B " mdadm \-\-examine \-\-brief \-\-scan \-\-config=partitions"
2626 .B " mdadm \-Ebsc partitions"
2628 Create a list of devices by reading
2629 .BR /proc/partitions ,
2630 scan these for RAID superblocks, and printout a brief listing of all
2633 .B " mdadm \-Ac partitions \-m 0 /dev/md0"
2635 Scan all partitions and devices listed in
2636 .BR /proc/partitions
2639 out of all such devices with a RAID superblock with a minor number of 0.
2641 .B " mdadm \-\-monitor \-\-scan \-\-daemonise > /var/run/mdadm"
2643 If config file contains a mail address or alert program, run mdadm in
2644 the background in monitor mode monitoring all md devices. Also write
2645 pid of mdadm daemon to
2646 .BR /var/run/mdadm .
2648 .B " mdadm \-Iq /dev/somedevice"
2650 Try to incorporate newly discovered device into some array as
2653 .B " mdadm \-\-incremental \-\-rebuild\-map \-\-run \-\-scan"
2655 Rebuild the array map from any current arrays, and then start any that
2658 .B " mdadm /dev/md4 --fail detached --remove detached"
2660 Any devices which are components of /dev/md4 will be marked as faulty
2661 and then remove from the array.
2663 .B " mdadm --grow /dev/md4 --level=6 --backup-file=/root/backup-md4"
2667 which is currently a RAID5 array will be converted to RAID6. There
2668 should normally already be a spare drive attached to the array as a
2669 RAID6 needs one more drive than a matching RAID5.
2671 .B " mdadm --create /dev/md/ddf --metadata=ddf --raid-disks 6 /dev/sd[a-f]"
2673 Create a DDF array over 6 devices.
2675 .B " mdadm --create /dev/md/home -n3 -l5 -z 30000000 /dev/md/ddf"
2677 Create a RAID5 array over any 3 devices in the given DDF set. Use
2678 only 30 gigabytes of each device.
2680 .B " mdadm -A /dev/md/ddf1 /dev/sd[a-f]"
2682 Assemble a pre-exist ddf array.
2684 .B " mdadm -I /dev/md/ddf1"
2686 Assemble all arrays contained in the ddf array, assigning names as
2689 .B " mdadm \-\-create \-\-help"
2691 Provide help about the Create mode.
2693 .B " mdadm \-\-config \-\-help"
2695 Provide help about the format of the config file.
2697 .B " mdadm \-\-help"
2699 Provide general help.
2709 lists all active md devices with information about them.
2711 uses this to find arrays when
2713 is given in Misc mode, and to monitor array reconstruction
2718 The config file lists which devices may be scanned to see if
2719 they contain MD super block, and gives identifying information
2720 (e.g. UUID) about known MD arrays. See
2724 .SS /var/run/mdadm/map
2727 mode is used, this file gets a list of arrays currently being created.
2730 does not exist as a directory, then
2731 .B /var/run/mdadm.map
2734 is not available (as may be the case during early boot),
2736 is used on the basis that
2738 is usually available very early in boot.
2743 understand two sorts of names for array devices.
2745 The first is the so-called 'standard' format name, which matches the
2746 names used by the kernel and which appear in
2749 The second sort can be freely chosen, but must reside in
2751 When giving a device name to
2753 to create or assemble an array, either full path name such as
2757 can be given, or just the suffix of the second sort of name, such as
2763 chooses device names during auto-assembly or incremental assembly, it
2764 will sometimes add a small sequence number to the end of the name to
2765 avoid conflicted between multiple arrays that have the same name. If
2767 can reasonably determine that the array really is meant for this host,
2768 either by a hostname in the metadata, or by the presence of the array
2771 then it will leave off the suffix if possible.
2772 Also if the homehost is specified as
2775 will only use a suffix if a different array of the same name already
2776 exists or is listed in the config file.
2778 The standard names for non-partitioned arrays (the only sort of md
2779 array available in 2.4 and earlier) are of the form
2783 where NN is a number.
2784 The standard names for partitionable arrays (as available from 2.6
2785 onwards) are of the form
2789 Partition numbers should be indicated by added "pMM" to these, thus "/dev/md/d1p2".
2791 From kernel version, 2.6.28 the "non-partitioned array" can actually
2792 be partitioned. So the "md_dNN" names are no longer needed, and
2793 partitions such as "/dev/mdNNpXX" are possible.
2797 was previously known as
2801 is completely separate from the
2803 package, and does not use the
2805 configuration file at all.
2808 For further information on mdadm usage, MD and the various levels of
2811 .B http://raid.wiki.kernel.org/
2813 (based upon Jakob \(/Ostergaard's Software\-RAID.HOWTO)
2815 .\"for new releases of the RAID driver check out:
2818 .\".UR ftp://ftp.kernel.org/pub/linux/kernel/people/mingo/raid-patches
2819 .\"ftp://ftp.kernel.org/pub/linux/kernel/people/mingo/raid-patches
2824 .\".UR http://www.cse.unsw.edu.au/~neilb/patches/linux-stable/
2825 .\"http://www.cse.unsw.edu.au/~neilb/patches/linux-stable/
2828 The latest version of
2830 should always be available from
2832 .B http://www.kernel.org/pub/linux/utils/raid/mdadm/