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 RAID
126 levels 1/4/5/6, changing the RAID level between 1, 5, and 6, changing
127 the chunk size and layout for RAID5 and RAID5, as well as adding or
128 removing a write-intent bitmap.
131 .B "Incremental Assembly"
132 Add a single device to an appropriate array. If the addition of the
133 device makes the array runnable, the array will be started.
134 This provides a convenient interface to a
136 system. As each device is detected,
138 has a chance to include it in some array as appropriate.
141 flag is passed in we will remove the device from any active array
142 instead of adding it.
148 in this mode, then any arrays within that container will be assembled
153 This is for doing things to specific components of an array such as
154 adding new spares and removing faulty devices.
158 This is an 'everything else' mode that supports operations on active
159 arrays, operations on component devices such as erasing old superblocks, and
160 information gathering operations.
161 .\"This mode allows operations on independent devices such as examine MD
162 .\"superblocks, erasing old superblocks and stopping active arrays.
166 This mode does not act on a specific device or array, but rather it
167 requests the Linux Kernel to activate any auto-detected arrays.
170 .SH Options for selecting a mode are:
173 .BR \-A ", " \-\-assemble
174 Assemble a pre-existing array.
177 .BR \-B ", " \-\-build
178 Build a legacy array without superblocks.
181 .BR \-C ", " \-\-create
185 .BR \-F ", " \-\-follow ", " \-\-monitor
191 .BR \-G ", " \-\-grow
192 Change the size or shape of an active array.
195 .BR \-I ", " \-\-incremental
196 Add/remove a single device to/from an appropriate array, and possibly start the array.
200 Request that the kernel starts any auto-detected arrays. This can only
203 is compiled into the kernel \(em not if it is a module.
204 Arrays can be auto-detected by the kernel if all the components are in
205 primary MS-DOS partitions with partition type
207 and all use v0.90 metadata.
208 In-kernel autodetect is not recommended for new installations. Using
210 to detect and assemble arrays \(em possibly in an
212 \(em is substantially more flexible and should be preferred.
215 If a device is given before any options, or if the first option is
220 then the MANAGE mode is assumed.
221 Anything other than these will cause the
225 .SH Options that are not mode-specific are:
228 .BR \-h ", " \-\-help
229 Display general help message or, after one of the above options, a
230 mode-specific help message.
234 Display more detailed help about command line parsing and some commonly
238 .BR \-V ", " \-\-version
239 Print version information for mdadm.
242 .BR \-v ", " \-\-verbose
243 Be more verbose about what is happening. This can be used twice to be
245 The extra verbosity currently only affects
246 .B \-\-detail \-\-scan
248 .BR "\-\-examine \-\-scan" .
251 .BR \-q ", " \-\-quiet
252 Avoid printing purely informative messages. With this,
254 will be silent unless there is something really important to report.
257 .BR \-f ", " \-\-force
258 Be more forceful about certain operations. See the various modes for
259 the exact meaning of this option in different contexts.
262 .BR \-c ", " \-\-config=
263 Specify the config file. Default is to use
264 .BR /etc/mdadm.conf ,
265 or if that is missing then
266 .BR /etc/mdadm/mdadm.conf .
267 If the config file given is
269 then nothing will be read, but
271 will act as though the config file contained exactly
272 .B "DEVICE partitions containers"
275 to find a list of devices to scan, and
277 to find a list of containers to examine.
280 is given for the config file, then
282 will act as though the config file were empty.
285 .BR \-s ", " \-\-scan
288 for missing information.
289 In general, this option gives
291 permission to get any missing information (like component devices,
292 array devices, array identities, and alert destination) from the
293 configuration file (see previous option);
294 one exception is MISC mode when using
300 says to get a list of array devices from
304 .BR \-e ", " \-\-metadata=
305 Declare the style of RAID metadata (superblock) to be used. The
306 default is {DEFAULT_METADATA} for
308 and to guess for other operations.
309 The default can be overridden by setting the
318 .ie '{DEFAULT_METADATA}'0.90'
319 .IP "0, 0.90, default"
323 Use the original 0.90 format superblock. This format limits arrays to
324 28 component devices and limits component devices of levels 1 and
325 greater to 2 terabytes. It is also possible for there to be confusion
326 about whether the superblock applies to a whole device or just the
327 last partition, if that partition starts on a 64K boundary.
328 .ie '{DEFAULT_METADATA}'0.90'
329 .IP "1, 1.0, 1.1, 1.2"
331 .IP "1, 1.0, 1.1, 1.2 default"
333 Use the new version-1 format superblock. This has fewer restrictions.
334 It can easily be moved between hosts with different endian-ness, and a
335 recovery operation can be checkpointed and restarted. The different
336 sub-versions store the superblock at different locations on the
337 device, either at the end (for 1.0), at the start (for 1.1) or 4K from
338 the start (for 1.2). "1" is equivalent to "1.0".
339 'if '{DEFAULT_METADATA}'1.2' "default" is equivalent to "1.2".
341 Use the "Industry Standard" DDF (Disk Data Format) format defined by
343 When creating a DDF array a
345 will be created, and normal arrays can be created in that container.
347 Use the Intel(R) Matrix Storage Manager metadata format. This creates a
349 which is managed in a similar manner to DDF, and is supported by an
350 option-rom on some platforms:
352 .B http://www.intel.com/design/chipsets/matrixstorage_sb.htm
358 This will override any
360 setting in the config file and provides the identity of the host which
361 should be considered the home for any arrays.
363 When creating an array, the
365 will be recorded in the metadata. For version-1 superblocks, it will
366 be prefixed to the array name. For version-0.90 superblocks, part of
367 the SHA1 hash of the hostname will be stored in the later half of the
370 When reporting information about an array, any array which is tagged
371 for the given homehost will be reported as such.
373 When using Auto-Assemble, only arrays tagged for the given homehost
374 will be allowed to use 'local' names (i.e. not ending in '_' followed
375 by a digit string). See below under
376 .BR "Auto Assembly" .
378 .SH For create, build, or grow:
381 .BR \-n ", " \-\-raid\-devices=
382 Specify the number of active devices in the array. This, plus the
383 number of spare devices (see below) must equal the number of
385 (including "\fBmissing\fP" devices)
386 that are listed on the command line for
388 Setting a value of 1 is probably
389 a mistake and so requires that
391 be specified first. A value of 1 will then be allowed for linear,
392 multipath, RAID0 and RAID1. It is never allowed for RAID4, RAID5 or RAID6.
394 This number can only be changed using
396 for RAID1, RAID4, RAID5 and RAID6 arrays, and only on kernels which provide
397 the necessary support.
400 .BR \-x ", " \-\-spare\-devices=
401 Specify the number of spare (eXtra) devices in the initial array.
402 Spares can also be added
403 and removed later. The number of component devices listed
404 on the command line must equal the number of RAID devices plus the
405 number of spare devices.
408 .BR \-z ", " \-\-size=
409 Amount (in Kibibytes) of space to use from each drive in RAID levels 1/4/5/6.
410 This must be a multiple of the chunk size, and must leave about 128Kb
411 of space at the end of the drive for the RAID superblock.
412 If this is not specified
413 (as it normally is not) the smallest drive (or partition) sets the
414 size, though if there is a variance among the drives of greater than 1%, a warning is
417 A suffix of 'M' or 'G' can be given to indicate Megabytes or
418 Gigabytes respectively.
420 This value can be set with
422 for RAID level 1/4/5/6. If the array was created with a size smaller
423 than the currently active drives, the extra space can be accessed
426 The size can be given as
428 which means to choose the largest size that fits on all current drives.
430 This value can not be used with
432 metadata such as DDF and IMSM.
435 .BR \-Z ", " \-\-array-size=
436 This is only meaningful with
438 and its effect is not persistent: when the array is stopped and
439 restarted the default array size will be restored.
441 Setting the array-size causes the array to appear smaller to programs
442 that access the data. This is particularly needed before reshaping an
443 array so that it will be smaller. As the reshape is not reversible,
444 but setting the size with
446 is, it is required that the array size is reduced as appropriate
447 before the number of devices in the array is reduced.
449 A suffix of 'M' or 'G' can be given to indicate Megabytes or
450 Gigabytes respectively.
453 restores the apparent size of the array to be whatever the real
454 amount of available space is.
457 .BR \-c ", " \-\-chunk=
458 Specify chunk size of kibibytes. The default when creating an
459 array is 512KB. To ensure compatibility with earlier versions, the
460 default when Building and array with no persistent metadata is 64KB.
461 This is only meaningful for RAID0, RAID4, RAID5, RAID6, and RAID10.
463 A suffix of 'M' or 'G' can be given to indicate Megabytes or
464 Gigabytes respectively.
468 Specify rounding factor for a Linear array. The size of each
469 component will be rounded down to a multiple of this size.
470 This is a synonym for
472 but highlights the different meaning for Linear as compared to other
473 RAID levels. The default is 64K if a kernel earlier than 2.6.16 is in
474 use, and is 0K (i.e. no rounding) in later kernels.
477 .BR \-l ", " \-\-level=
478 Set RAID level. When used with
480 options are: linear, raid0, 0, stripe, raid1, 1, mirror, raid4, 4,
481 raid5, 5, raid6, 6, raid10, 10, multipath, mp, faulty, container.
482 Obviously some of these are synonymous.
486 metadata type is requested, only the
488 level is permitted, and it does not need to be explicitly given.
492 only linear, stripe, raid0, 0, raid1, multipath, mp, and faulty are valid.
496 to change the RAID level in some cases. See LEVEL CHANGES below.
499 .BR \-p ", " \-\-layout=
500 This option configures the fine details of data layout for RAID5, RAID6,
501 and RAID10 arrays, and controls the failure modes for
504 The layout of the RAID5 parity block can be one of
505 .BR left\-asymmetric ,
506 .BR left\-symmetric ,
507 .BR right\-asymmetric ,
508 .BR right\-symmetric ,
509 .BR la ", " ra ", " ls ", " rs .
511 .BR left\-symmetric .
513 It is also possible to cause RAID5 to use a RAID4-like layout by
519 Finally for RAID5 there are DDF\-compatible layouts,
520 .BR ddf\-zero\-restart ,
521 .BR ddf\-N\-restart ,
523 .BR ddf\-N\-continue .
525 These same layouts are available for RAID6. There are also 4 layouts
526 that will provide an intermediate stage for converting between RAID5
527 and RAID6. These provide a layout which is identical to the
528 corresponding RAID5 layout on the first N\-1 devices, and has the 'Q'
529 syndrome (the second 'parity' block used by RAID6) on the last device.
531 .BR left\-symmetric\-6 ,
532 .BR right\-symmetric\-6 ,
533 .BR left\-asymmetric\-6 ,
534 .BR right\-asymmetric\-6 ,
536 .BR parity\-first\-6 .
538 When setting the failure mode for level
541 .BR write\-transient ", " wt ,
542 .BR read\-transient ", " rt ,
543 .BR write\-persistent ", " wp ,
544 .BR read\-persistent ", " rp ,
546 .BR read\-fixable ", " rf ,
547 .BR clear ", " flush ", " none .
549 Each failure mode can be followed by a number, which is used as a period
550 between fault generation. Without a number, the fault is generated
551 once on the first relevant request. With a number, the fault will be
552 generated after that many requests, and will continue to be generated
553 every time the period elapses.
555 Multiple failure modes can be current simultaneously by using the
557 option to set subsequent failure modes.
559 "clear" or "none" will remove any pending or periodic failure modes,
560 and "flush" will clear any persistent faults.
562 Finally, the layout options for RAID10 are one of 'n', 'o' or 'f' followed
563 by a small number. The default is 'n2'. The supported options are:
566 signals 'near' copies. Multiple copies of one data block are at
567 similar offsets in different devices.
570 signals 'offset' copies. Rather than the chunks being duplicated
571 within a stripe, whole stripes are duplicated but are rotated by one
572 device so duplicate blocks are on different devices. Thus subsequent
573 copies of a block are in the next drive, and are one chunk further
578 (multiple copies have very different offsets).
579 See md(4) for more detail about 'near', 'offset', and 'far'.
581 The number is the number of copies of each datablock. 2 is normal, 3
582 can be useful. This number can be at most equal to the number of
583 devices in the array. It does not need to divide evenly into that
584 number (e.g. it is perfectly legal to have an 'n2' layout for an array
585 with an odd number of devices).
587 When an array is converted between RAID5 and RAID6 an intermediate
588 RAID6 layout is used in which the second parity block (Q) is always on
589 the last device. To convert a RAID5 to RAID6 and leave it in this new
590 layout (which does not require re-striping) use
591 .BR \-\-layout=preserve .
592 This will try to avoid any restriping.
594 The converse of this is
595 .B \-\-layout=normalise
596 which will change a non-standard RAID6 layout into a more standard
603 (thus explaining the p of
607 .BR \-b ", " \-\-bitmap=
608 Specify a file to store a write-intent bitmap in. The file should not
611 is also given. The same file should be provided
612 when assembling the array. If the word
614 is given, then the bitmap is stored with the metadata on the array,
615 and so is replicated on all devices. If the word
619 mode, then any bitmap that is present is removed.
621 To help catch typing errors, the filename must contain at least one
622 slash ('/') if it is a real file (not 'internal' or 'none').
624 Note: external bitmaps are only known to work on ext2 and ext3.
625 Storing bitmap files on other filesystems may result in serious problems.
628 .BR \-\-bitmap\-chunk=
629 Set the chunksize of the bitmap. Each bit corresponds to that many
630 Kilobytes of storage.
631 When using a file based bitmap, the default is to use the smallest
632 size that is at-least 4 and requires no more than 2^21 chunks.
635 bitmap, the chunksize defaults to 64Meg, or larger if necessary to
636 fit the bitmap into the available space.
638 A suffix of 'M' or 'G' can be given to indicate Megabytes or
639 Gigabytes respectively.
642 .BR \-W ", " \-\-write\-mostly
643 subsequent devices listed in a
648 command will be flagged as 'write-mostly'. This is valid for RAID1
649 only and means that the 'md' driver will avoid reading from these
650 devices if at all possible. This can be useful if mirroring over a
654 .BR \-\-write\-behind=
655 Specify that write-behind mode should be enabled (valid for RAID1
656 only). If an argument is specified, it will set the maximum number
657 of outstanding writes allowed. The default value is 256.
658 A write-intent bitmap is required in order to use write-behind
659 mode, and write-behind is only attempted on drives marked as
663 .BR \-\-assume\-clean
666 that the array pre-existed and is known to be clean. It can be useful
667 when trying to recover from a major failure as you can be sure that no
668 data will be affected unless you actually write to the array. It can
669 also be used when creating a RAID1 or RAID10 if you want to avoid the
670 initial resync, however this practice \(em while normally safe \(em is not
671 recommended. Use this only if you really know what you are doing.
673 When the devices that will be part of a new array were filled
674 with zeros before creation the operator knows the array is
675 actually clean. If that is the case, such as after running
676 badblocks, this argument can be used to tell mdadm the
677 facts the operator knows.
680 .BR \-\-backup\-file=
683 is used to increase the number of raid-devices in a RAID5 or RAID6 if
684 there are no spare devices available, or to shrink, change RAID level
685 or layout. See the GROW MODE section below on RAID\-DEVICES CHANGES.
686 The file must be stored on a separate device, not on the RAID array
690 .BR \-N ", " \-\-name=
693 for the array. This is currently only effective when creating an
694 array with a version-1 superblock, or an array in a DDF container.
695 The name is a simple textual string that can be used to identify array
696 components when assembling. If name is needed but not specified, it
697 is taken from the basename of the device that is being created.
709 run the array, even if some of the components
710 appear to be active in another array or filesystem. Normally
712 will ask for confirmation before including such components in an
713 array. This option causes that question to be suppressed.
716 .BR \-f ", " \-\-force
719 accept the geometry and layout specified without question. Normally
721 will not allow creation of an array with only one device, and will try
722 to create a RAID5 array with one missing drive (as this makes the
723 initial resync work faster). With
726 will not try to be so clever.
729 .BR \-a ", " "\-\-auto{=yes,md,mdp,part,p}{NN}"
730 Instruct mdadm how to create the device file if needed, possibly allocating
731 an unused minor number. "md" causes a non-partitionable array
732 to be used (though since Linux 2.6.28, these array devices are in fact
733 partitionable). "mdp", "part" or "p" causes a partitionable array (2.6 and
734 later) to be used. "yes" requires the named md device to have
735 a 'standard' format, and the type and minor number will be determined
736 from this. With mdadm 3.0, device creation is normally left up to
738 so this option is unlikely to be needed.
739 See DEVICE NAMES below.
741 The argument can also come immediately after
746 is not given on the command line or in the config file, then
752 is also given, then any
754 entries in the config file will override the
756 instruction given on the command line.
758 For partitionable arrays,
760 will create the device file for the whole array and for the first 4
761 partitions. A different number of partitions can be specified at the
762 end of this option (e.g.
764 If the device name ends with a digit, the partition names add a 'p',
766 .IR /dev/md/home1p3 .
767 If there is no trailing digit, then the partition names just have a
769 .IR /dev/md/scratch3 .
771 If the md device name is in a 'standard' format as described in DEVICE
772 NAMES, then it will be created, if necessary, with the appropriate
773 device number based on that name. If the device name is not in one of these
774 formats, then a unused device number will be allocated. The device
775 number will be considered unused if there is no active array for that
776 number, and there is no entry in /dev for that number and with a
777 non-standard name. Names that are not in 'standard' format are only
778 allowed in "/dev/md/".
782 .\".BR \-\-symlink = no
787 .\"to create devices in
789 .\"it will also create symlinks from
791 .\"with names starting with
797 .\"to suppress this, or
798 .\".B \-\-symlink=yes
799 .\"to enforce this even if it is suppressing
807 .BR \-u ", " \-\-uuid=
808 uuid of array to assemble. Devices which don't have this uuid are
812 .BR \-m ", " \-\-super\-minor=
813 Minor number of device that array was created for. Devices which
814 don't have this minor number are excluded. If you create an array as
815 /dev/md1, then all superblocks will contain the minor number 1, even if
816 the array is later assembled as /dev/md2.
818 Giving the literal word "dev" for
822 to use the minor number of the md device that is being assembled.
825 .B \-\-super\-minor=dev
826 will look for super blocks with a minor number of 0.
829 is only relevant for v0.90 metadata, and should not normally be used.
835 .BR \-N ", " \-\-name=
836 Specify the name of the array to assemble. This must be the name
837 that was specified when creating the array. It must either match
838 the name stored in the superblock exactly, or it must match
841 prefixed to the start of the given name.
844 .BR \-f ", " \-\-force
845 Assemble the array even if the metadata on some devices appears to be
848 cannot find enough working devices to start the array, but can find
849 some devices that are recorded as having failed, then it will mark
850 those devices as working so that the array can be started.
851 An array which requires
853 to be started may contain data corruption. Use it carefully.
857 Attempt to start the array even if fewer drives were given than were
858 present last time the array was active. Normally if not all the
859 expected drives are found and
861 is not used, then the array will be assembled but not started.
864 an attempt will be made to start it anyway.
868 This is the reverse of
870 in that it inhibits the startup of array unless all expected drives
871 are present. This is only needed with
873 and can be used if the physical connections to devices are
874 not as reliable as you would like.
877 .BR \-a ", " "\-\-auto{=no,yes,md,mdp,part}"
878 See this option under Create and Build options.
881 .BR \-b ", " \-\-bitmap=
882 Specify the bitmap file that was given when the array was created. If
885 bitmap, there is no need to specify this when assembling the array.
888 .BR \-\-backup\-file=
891 was used while reshaping an array (e.g. changing number of devices or
892 chunk size) and the system crashed during the critical section, then the same
896 to allow possibly corrupted data to be restored, and the reshape
900 .BR \-\-invalid\-backup
901 If the file needed for the above option is not available for any
902 reason an empty file can be given together with this option to
903 indicate that the backup file is invalid. In this case the data that
904 was being rearranged at the time of the crash could be irrecoverably
905 lost, but the rest of the array may still be recoverable. This option
906 should only be used as a last resort if there is no way to recover the
911 .BR \-U ", " \-\-update=
912 Update the superblock on each device while assembling the array. The
913 argument given to this flag can be one of
928 option will adjust the superblock of an array what was created on a Sparc
929 machine running a patched 2.2 Linux kernel. This kernel got the
930 alignment of part of the superblock wrong. You can use the
931 .B "\-\-examine \-\-sparc2.2"
934 to see what effect this would have.
938 option will update the
940 field on each superblock to match the minor number of the array being
942 This can be useful if
944 reports a different "Preferred Minor" to
946 In some cases this update will be performed automatically
947 by the kernel driver. In particular the update happens automatically
948 at the first write to an array with redundancy (RAID level 1 or
949 greater) on a 2.6 (or later) kernel.
953 option will change the uuid of the array. If a UUID is given with the
955 option that UUID will be used as a new UUID and will
957 be used to help identify the devices in the array.
960 is given, a random UUID is chosen.
964 option will change the
966 of the array as stored in the superblock. This is only supported for
967 version-1 superblocks.
971 option will change the
973 as recorded in the superblock. For version-0 superblocks, this is the
974 same as updating the UUID.
975 For version-1 superblocks, this involves updating the name.
979 option will cause the array to be marked
981 meaning that any redundancy in the array (e.g. parity for RAID5,
982 copies for RAID1) may be incorrect. This will cause the RAID system
983 to perform a "resync" pass to make sure that all redundant information
988 option allows arrays to be moved between machines with different
990 When assembling such an array for the first time after a move, giving
991 .B "\-\-update=byteorder"
994 to expect superblocks to have their byteorder reversed, and will
995 correct that order before assembling the array. This is only valid
996 with original (Version 0.90) superblocks.
1000 option will correct the summaries in the superblock. That is the
1001 counts of total, working, active, failed, and spare devices.
1005 option will rarely be of use. It applies to version 1.1 and 1.2 metadata
1006 only (where the metadata is at the start of the device) and is only
1007 useful when the component device has changed size (typically become
1008 larger). The version 1 metadata records the amount of the device that
1009 can be used to store data, so if a device in a version 1.1 or 1.2
1010 array becomes larger, the metadata will still be visible, but the
1011 extra space will not. In this case it might be useful to assemble the
1013 .BR \-\-update=devicesize .
1016 to determine the maximum usable amount of space on each device and
1017 update the relevant field in the metadata.
1021 option can be used when an array has an internal bitmap which is
1022 corrupt in some way so that assembling the array normally fails. It
1023 will cause any internal bitmap to be ignored.
1027 .B \-\-auto\-update\-homehost
1028 This flag is only meaningful with auto-assembly (see discussion below).
1029 In that situation, if no suitable arrays are found for this homehost,
1031 will rescan for any arrays at all and will assemble them and update the
1032 homehost to match the current host.
1035 .SH For Manage mode:
1038 .BR \-t ", " \-\-test
1039 Unless a more serious error occurred,
1041 will exit with a status of 2 if no changes were made to the array and
1042 0 if at least one change was made.
1043 This can be useful when an indirect specifier such as
1048 is used in requesting an operation on the array.
1050 will report failure if these specifiers didn't find any match.
1053 .BR \-a ", " \-\-add
1054 hot-add listed devices.
1055 If a device appears to have recently been part of the array
1056 (possibly it failed or was removed) the device is re-added as describe
1058 If that fails or the device was never part of the array, the device is
1059 added as a hot-spare.
1060 If the array is degraded, it will immediately start to rebuild data
1063 Note that this and the following options are only meaningful on array
1064 with redundancy. They don't apply to RAID0 or Linear.
1068 re\-add a device that was previous removed from an array.
1069 If the metadata on the device reports that it is a member of the
1070 array, and the slot that it used is still vacant, then the device will
1071 be added back to the array in the same position. This will normally
1072 cause the data for that device to be recovered. However based on the
1073 event count on the device, the recovery may only require sections that
1074 are flagged a write-intent bitmap to be recovered or may not require
1075 any recovery at all.
1077 When used on an array that has no metadata (i.e. it was built with
1079 it will be assumed that bitmap-based recovery is enough to make the
1080 device fully consistent with the array.
1082 If the device name given is
1084 then mdadm will try to find any device that looks like it should be
1085 part of the array but isn't and will try to re\-add all such devices.
1088 .BR \-r ", " \-\-remove
1089 remove listed devices. They must not be active. i.e. they should
1090 be failed or spare devices. As well as the name of a device file
1099 The first causes all failed device to be removed. The second causes
1100 any device which is no longer connected to the system (i.e an 'open'
1103 to be removed. This will only succeed for devices that are spares or
1104 have already been marked as failed.
1107 .BR \-f ", " \-\-fail
1108 mark listed devices as faulty.
1109 As well as the name of a device file, the word
1111 can be given. This will cause any device that has been detached from
1112 the system to be marked as failed. It can then be removed.
1120 .BR \-\-write\-mostly
1121 Subsequent devices that are added or re\-added will have the 'write-mostly'
1122 flag set. This is only valid for RAID1 and means that the 'md' driver
1123 will avoid reading from these devices if possible.
1126 Subsequent devices that are added or re\-added will have the 'write-mostly'
1130 Each of these options requires that the first device listed is the array
1131 to be acted upon, and the remainder are component devices to be added,
1132 removed, marked as faulty, etc. Several different operations can be
1133 specified for different devices, e.g.
1135 mdadm /dev/md0 \-\-add /dev/sda1 \-\-fail /dev/sdb1 \-\-remove /dev/sdb1
1137 Each operation applies to all devices listed until the next
1140 If an array is using a write-intent bitmap, then devices which have
1141 been removed can be re\-added in a way that avoids a full
1142 reconstruction but instead just updates the blocks that have changed
1143 since the device was removed. For arrays with persistent metadata
1144 (superblocks) this is done automatically. For arrays created with
1146 mdadm needs to be told that this device we removed recently with
1149 Devices can only be removed from an array if they are not in active
1150 use, i.e. that must be spares or failed devices. To remove an active
1151 device, it must first be marked as
1157 .BR \-Q ", " \-\-query
1158 Examine a device to see
1159 (1) if it is an md device and (2) if it is a component of an md
1161 Information about what is discovered is presented.
1164 .BR \-D ", " \-\-detail
1165 Print details of one or more md devices.
1168 .BR \-\-detail\-platform
1169 Print details of the platform's RAID capabilities (firmware / hardware
1170 topology) for a given metadata format.
1173 .BR \-Y ", " \-\-export
1178 output will be formatted as
1180 pairs for easy import into the environment.
1183 .BR \-E ", " \-\-examine
1184 Print contents of the metadata stored on the named device(s).
1185 Note the contrast between
1190 applies to devices which are components of an array, while
1192 applies to a whole array which is currently active.
1195 If an array was created on a SPARC machine with a 2.2 Linux kernel
1196 patched with RAID support, the superblock will have been created
1197 incorrectly, or at least incompatibly with 2.4 and later kernels.
1202 will fix the superblock before displaying it. If this appears to do
1203 the right thing, then the array can be successfully assembled using
1204 .BR "\-\-assemble \-\-update=sparc2.2" .
1207 .BR \-X ", " \-\-examine\-bitmap
1208 Report information about a bitmap file.
1209 The argument is either an external bitmap file or an array component
1210 in case of an internal bitmap. Note that running this on an array
1213 does not report the bitmap for that array.
1216 .BR \-R ", " \-\-run
1217 start a partially assembled array. If
1219 did not find enough devices to fully start the array, it might leaving
1220 it partially assembled. If you wish, you can then use
1222 to start the array in degraded mode.
1225 .BR \-S ", " \-\-stop
1226 deactivate array, releasing all resources.
1229 .BR \-o ", " \-\-readonly
1230 mark array as readonly.
1233 .BR \-w ", " \-\-readwrite
1234 mark array as readwrite.
1237 .B \-\-zero\-superblock
1238 If the device contains a valid md superblock, the block is
1239 overwritten with zeros. With
1241 the block where the superblock would be is overwritten even if it
1242 doesn't appear to be valid.
1245 .B \-\-kill\-subarray=
1246 If the device is a container and the argument to \-\-kill\-subarray
1247 specifies an inactive subarray in the container, then the subarray is
1248 deleted. Deleting all subarrays will leave an 'empty-container' or
1249 spare superblock on the drives. See \-\-zero\-superblock for completely
1250 removing a superblock. Note that some formats depend on the subarray
1251 index for generating a UUID, this command will fail if it would change
1252 the UUID of an active subarray.
1255 .B \-\-update\-subarray=
1256 If the device is a container and the argument to \-\-update\-subarray
1257 specifies a subarray in the container, then attempt to update the given
1258 superblock field in the subarray. See below in
1263 .BR \-t ", " \-\-test
1268 is set to reflect the status of the device. See below in
1273 .BR \-W ", " \-\-wait
1274 For each md device given, wait for any resync, recovery, or reshape
1275 activity to finish before returning.
1277 will return with success if it actually waited for every device
1278 listed, otherwise it will return failure.
1282 For each md device given, or each device in /proc/mdstat if
1284 is given, arrange for the array to be marked clean as soon as possible.
1286 will return with success if the array uses external metadata and we
1287 successfully waited. For native arrays this returns immediately as the
1288 kernel handles dirty-clean transitions at shutdown. No action is taken
1289 if safe-mode handling is disabled.
1291 .SH For Incremental Assembly mode:
1293 .BR \-\-rebuild\-map ", " \-r
1294 Rebuild the map file
1295 .RB ( /var/run/mdadm/map )
1298 uses to help track which arrays are currently being assembled.
1301 .BR \-\-run ", " \-R
1302 Run any array assembled as soon as a minimal number of devices are
1303 available, rather than waiting until all expected devices are present.
1306 .BR \-\-scan ", " \-s
1307 Only meaningful with
1311 file for arrays that are being incrementally assembled and will try to
1312 start any that are not already started. If any such array is listed
1315 as requiring an external bitmap, that bitmap will be attached first.
1318 .BR \-\-fail ", " \-f
1319 This allows the hot-plug system to remove devices that have fully disappeared
1320 from the kernel. It will first fail and then remove the device from any
1321 array it belongs to.
1322 The device name given should be a kernel device name such as "sda",
1326 .SH For Monitor mode:
1328 .BR \-m ", " \-\-mail
1329 Give a mail address to send alerts to.
1332 .BR \-p ", " \-\-program ", " \-\-alert
1333 Give a program to be run whenever an event is detected.
1336 .BR \-y ", " \-\-syslog
1337 Cause all events to be reported through 'syslog'. The messages have
1338 facility of 'daemon' and varying priorities.
1341 .BR \-d ", " \-\-delay
1342 Give a delay in seconds.
1344 polls the md arrays and then waits this many seconds before polling
1345 again. The default is 60 seconds. Since 2.6.16, there is no need to
1346 reduce this as the kernel alerts
1348 immediately when there is any change.
1351 .BR \-r ", " \-\-increment
1352 Give a percentage increment.
1354 will generate RebuildNN events with the given percentage increment.
1357 .BR \-f ", " \-\-daemonise
1360 to run as a background daemon if it decides to monitor anything. This
1361 causes it to fork and run in the child, and to disconnect from the
1362 terminal. The process id of the child is written to stdout.
1365 which will only continue monitoring if a mail address or alert program
1366 is found in the config file.
1369 .BR \-i ", " \-\-pid\-file
1372 is running in daemon mode, write the pid of the daemon process to
1373 the specified file, instead of printing it on standard output.
1376 .BR \-1 ", " \-\-oneshot
1377 Check arrays only once. This will generate
1379 events and more significantly
1385 .B " mdadm \-\-monitor \-\-scan \-1"
1387 from a cron script will ensure regular notification of any degraded arrays.
1390 .BR \-t ", " \-\-test
1393 alert for every array found at startup. This alert gets mailed and
1394 passed to the alert program. This can be used for testing that alert
1395 message do get through successfully.
1401 .B mdadm \-\-assemble
1402 .I md-device options-and-component-devices...
1405 .B mdadm \-\-assemble \-\-scan
1406 .I md-devices-and-options...
1409 .B mdadm \-\-assemble \-\-scan
1413 This usage assembles one or more RAID arrays from pre-existing components.
1414 For each array, mdadm needs to know the md device, the identity of the
1415 array, and a number of component-devices. These can be found in a number of ways.
1417 In the first usage example (without the
1419 the first device given is the md device.
1420 In the second usage example, all devices listed are treated as md
1421 devices and assembly is attempted.
1422 In the third (where no devices are listed) all md devices that are
1423 listed in the configuration file are assembled. If not arrays are
1424 described by the configuration file, then any arrays that
1425 can be found on unused devices will be assembled.
1427 If precisely one device is listed, but
1433 was given and identity information is extracted from the configuration file.
1435 The identity can be given with the
1441 option, will be taken from the md-device record in the config file, or
1442 will be taken from the super block of the first component-device
1443 listed on the command line.
1445 Devices can be given on the
1447 command line or in the config file. Only devices which have an md
1448 superblock which contains the right identity will be considered for
1451 The config file is only used if explicitly named with
1453 or requested with (a possibly implicit)
1458 .B /etc/mdadm/mdadm.conf
1463 is not given, then the config file will only be used to find the
1464 identity of md arrays.
1466 Normally the array will be started after it is assembled. However if
1468 is not given and not all expected drives were listed, then the array
1469 is not started (to guard against usage errors). To insist that the
1470 array be started in this case (as may work for RAID1, 4, 5, 6, or 10),
1479 does not create any entries in
1483 It does record information in
1484 .B /var/run/mdadm/map
1487 to choose the correct name.
1491 detects that udev is not configured, it will create the devices in
1495 In Linux kernels prior to version 2.6.28 there were two distinctly
1496 different types of md devices that could be created: one that could be
1497 partitioned using standard partitioning tools and one that could not.
1498 Since 2.6.28 that distinction is no longer relevant as both type of
1499 devices can be partitioned.
1501 will normally create the type that originally could not be partitioned
1502 as it has a well defined major number (9).
1504 Prior to 2.6.28, it is important that mdadm chooses the correct type
1505 of array device to use. This can be controlled with the
1507 option. In particular, a value of "mdp" or "part" or "p" tells mdadm
1508 to use a partitionable device rather than the default.
1510 In the no-udev case, the value given to
1512 can be suffixed by a number. This tells
1514 to create that number of partition devices rather than the default of 4.
1518 can also be given in the configuration file as a word starting
1520 on the ARRAY line for the relevant array.
1527 and no devices are listed,
1529 will first attempt to assemble all the arrays listed in the config
1532 In no array at listed in the config (other than those marked
1534 it will look through the available devices for possible arrays and
1535 will try to assemble anything that it finds. Arrays which are tagged
1536 as belonging to the given homehost will be assembled and started
1537 normally. Arrays which do not obviously belong to this host are given
1538 names that are expected not to conflict with anything local, and are
1539 started "read-auto" so that nothing is written to any device until the
1540 array is written to. i.e. automatic resync etc is delayed.
1544 finds a consistent set of devices that look like they should comprise
1545 an array, and if the superblock is tagged as belonging to the given
1546 home host, it will automatically choose a device name and try to
1547 assemble the array. If the array uses version-0.90 metadata, then the
1549 number as recorded in the superblock is used to create a name in
1553 If the array uses version-1 metadata, then the
1555 from the superblock is used to similarly create a name in
1557 (the name will have any 'host' prefix stripped first).
1559 This behaviour can be modified by the
1563 configuration file. This line can indicate that specific metadata
1564 type should, or should not, be automatically assembled. If an array
1565 is found which is not listed in
1567 and has a metadata format that is denied by the
1569 line, then it will not be assembled.
1572 line can also request that all arrays identified as being for this
1573 homehost should be assembled regardless of their metadata type.
1576 for further details.
1581 cannot find any array for the given host at all, and if
1582 .B \-\-auto\-update\-homehost
1585 will search again for any array (not just an array created for this
1586 host) and will assemble each assuming
1587 .BR \-\-update=homehost .
1588 This will change the host tag in the superblock so that on the next run,
1589 these arrays will be found without the second pass. The intention of
1590 this feature is to support transitioning a set of md arrays to using
1593 The reason for requiring arrays to be tagged with the homehost for
1594 auto assembly is to guard against problems that can arise when moving
1595 devices from one host to another.
1606 .BI \-\-raid\-devices= Z
1610 This usage is similar to
1612 The difference is that it creates an array without a superblock. With
1613 these arrays there is no difference between initially creating the array and
1614 subsequently assembling the array, except that hopefully there is useful
1615 data there in the second case.
1617 The level may raid0, linear, raid1, raid10, multipath, or faulty, or
1618 one of their synonyms. All devices must be listed and the array will
1619 be started once complete. It will often be appropriate to use
1620 .B \-\-assume\-clean
1621 with levels raid1 or raid10.
1632 .BI \-\-raid\-devices= Z
1636 This usage will initialise a new md array, associate some devices with
1637 it, and activate the array.
1639 The named device will normally not exist when
1640 .I "mdadm \-\-create"
1641 is run, but will be created by
1643 once the array becomes active.
1645 As devices are added, they are checked to see if they contain RAID
1646 superblocks or filesystems. They are also checked to see if the variance in
1647 device size exceeds 1%.
1649 If any discrepancy is found, the array will not automatically be run, though
1652 can override this caution.
1654 To create a "degraded" array in which some devices are missing, simply
1655 give the word "\fBmissing\fP"
1656 in place of a device name. This will cause
1658 to leave the corresponding slot in the array empty.
1659 For a RAID4 or RAID5 array at most one slot can be
1660 "\fBmissing\fP"; for a RAID6 array at most two slots.
1661 For a RAID1 array, only one real device needs to be given. All of the
1665 When creating a RAID5 array,
1667 will automatically create a degraded array with an extra spare drive.
1668 This is because building the spare into a degraded array is in general
1669 faster than resyncing the parity on a non-degraded, but not clean,
1670 array. This feature can be overridden with the
1674 When creating an array with version-1 metadata a name for the array is
1676 If this is not given with the
1680 will choose a name based on the last component of the name of the
1681 device being created. So if
1683 is being created, then the name
1688 is being created, then the name
1692 When creating a partition based array, using
1694 with version-1.x metadata, the partition type should be set to
1696 (non fs-data). This type selection allows for greater precision since
1697 using any other [RAID auto-detect (0xFD) or a GNU/Linux partition (0x83)],
1698 might create problems in the event of array recovery through a live cdrom.
1700 A new array will normally get a randomly assigned 128bit UUID which is
1701 very likely to be unique. If you have a specific need, you can choose
1702 a UUID for the array by giving the
1704 option. Be warned that creating two arrays with the same UUID is a
1705 recipe for disaster. Also, using
1707 when creating a v0.90 array will silently override any
1712 .\"option is given, it is not necessary to list any component-devices in this command.
1713 .\"They can be added later, before a
1717 .\"is given, the apparent size of the smallest drive given is used.
1719 When creating an array within a
1722 can be given either the list of devices to use, or simply the name of
1723 the container. The former case gives control over which devices in
1724 the container will be used for the array. The latter case allows
1726 to automatically choose which devices to use based on how much spare
1729 The General Management options that are valid with
1734 insist on running the array even if some devices look like they might
1739 start the array readonly \(em not supported yet.
1746 .I options... devices...
1749 This usage will allow individual devices in an array to be failed,
1750 removed or added. It is possible to perform multiple operations with
1751 on command. For example:
1753 .B " mdadm /dev/md0 \-f /dev/hda1 \-r /dev/hda1 \-a /dev/hda1"
1759 and will then remove it from the array and finally add it back
1760 in as a spare. However only one md array can be affected by a single
1763 When a device is added to an active array, mdadm checks to see if it
1764 has metadata on it which suggests that it was recently a member of the
1765 array. If it does, it tries to "re\-add" the device. If there have
1766 been no changes since the device was removed, or if the array has a
1767 write-intent bitmap which has recorded whatever changes there were,
1768 then the device will immediately become a full member of the array and
1769 those differences recorded in the bitmap will be resolved.
1779 MISC mode includes a number of distinct operations that
1780 operate on distinct devices. The operations are:
1783 The device is examined to see if it is
1784 (1) an active md array, or
1785 (2) a component of an md array.
1786 The information discovered is reported.
1790 The device should be an active md device.
1792 will display a detailed description of the array.
1796 will cause the output to be less detailed and the format to be
1797 suitable for inclusion in
1798 .BR /etc/mdadm.conf .
1801 will normally be 0 unless
1803 failed to get useful information about the device(s); however, if the
1805 option is given, then the exit status will be:
1809 The array is functioning normally.
1812 The array has at least one failed device.
1815 The array has multiple failed devices such that it is unusable.
1818 There was an error while trying to get information about the device.
1822 .B \-\-detail\-platform
1823 Print detail of the platform's RAID capabilities (firmware / hardware
1824 topology). If the metadata is specified with
1828 then the return status will be:
1832 metadata successfully enumerated its platform components on this system
1835 metadata is platform independent
1838 metadata failed to find its platform components on this system
1842 .B \-\-update\-subarray=
1843 If the device is a container and the argument to \-\-update\-subarray
1844 specifies a subarray in the container, then attempt to update the given
1845 superblock field in the subarray. Similar to updating an array in
1846 "assemble" mode, the field to update is selected by
1850 option. Currently only
1856 option updates the subarray name in the metadata, it may not affect the
1857 device node name or the device node symlink until the subarray is
1858 re\-assembled. If updating
1860 would change the UUID of an active subarray this operation is blocked,
1861 and the command will end in an error.
1865 The device should be a component of an md array.
1867 will read the md superblock of the device and display the contents.
1872 is given, then multiple devices that are components of the one array
1873 are grouped together and reported in a single entry suitable
1875 .BR /etc/mdadm.conf .
1879 without listing any devices will cause all devices listed in the
1880 config file to be examined.
1884 The devices should be active md arrays which will be deactivated, as
1885 long as they are not currently in use.
1889 This will fully activate a partially assembled md array.
1893 This will mark an active array as read-only, providing that it is
1894 not currently being used.
1900 array back to being read/write.
1904 For all operations except
1907 will cause the operation to be applied to all arrays listed in
1912 causes all devices listed in the config file to be examined.
1915 .BR \-b ", " \-\-brief
1916 Be less verbose. This is used with
1924 gives an intermediate level of verbosity.
1930 .B mdadm \-\-monitor
1931 .I options... devices...
1936 to periodically poll a number of md arrays and to report on any events
1939 will never exit once it decides that there are arrays to be checked,
1940 so it should normally be run in the background.
1942 As well as reporting events,
1944 may move a spare drive from one array to another if they are in the
1947 and if the destination array has a failed drive but no spares.
1949 If any devices are listed on the command line,
1951 will only monitor those devices. Otherwise all arrays listed in the
1952 configuration file will be monitored. Further, if
1954 is given, then any other md devices that appear in
1956 will also be monitored.
1958 The result of monitoring the arrays is the generation of events.
1959 These events are passed to a separate program (if specified) and may
1960 be mailed to a given E-mail address.
1962 When passing events to a program, the program is run once for each event,
1963 and is given 2 or 3 command-line arguments: the first is the
1964 name of the event (see below), the second is the name of the
1965 md device which is affected, and the third is the name of a related
1966 device if relevant (such as a component device that has failed).
1970 is given, then a program or an E-mail address must be specified on the
1971 command line or in the config file. If neither are available, then
1973 will not monitor anything.
1977 will continue monitoring as long as something was found to monitor. If
1978 no program or email is given, then each event is reported to
1981 The different events are:
1985 .B DeviceDisappeared
1986 An md array which previously was configured appears to no longer be
1987 configured. (syslog priority: Critical)
1991 was told to monitor an array which is RAID0 or Linear, then it will
1993 .B DeviceDisappeared
1994 with the extra information
1996 This is because RAID0 and Linear do not support the device-failed,
1997 hot-spare and resync operations which are monitored.
2001 An md array started reconstruction. (syslog priority: Warning)
2007 is a two-digit number (ie. 05, 48). This indicates that rebuild
2008 has passed that many percent of the total. The events are generated
2009 with fixed increment since 0. Increment size may be specified with
2010 a commandline option (default is 20). (syslog priority: Warning)
2014 An md array that was rebuilding, isn't any more, either because it
2015 finished normally or was aborted. (syslog priority: Warning)
2019 An active component device of an array has been marked as
2020 faulty. (syslog priority: Critical)
2024 A spare component device which was being rebuilt to replace a faulty
2025 device has failed. (syslog priority: Critical)
2029 A spare component device which was being rebuilt to replace a faulty
2030 device has been successfully rebuilt and has been made active.
2031 (syslog priority: Info)
2035 A new md array has been detected in the
2037 file. (syslog priority: Info)
2041 A newly noticed array appears to be degraded. This message is not
2044 notices a drive failure which causes degradation, but only when
2046 notices that an array is degraded when it first sees the array.
2047 (syslog priority: Critical)
2051 A spare drive has been moved from one array in a
2053 to another to allow a failed drive to be replaced.
2054 (syslog priority: Info)
2060 has been told, via the config file, that an array should have a certain
2061 number of spare devices, and
2063 detects that it has fewer than this number when it first sees the
2064 array, it will report a
2067 (syslog priority: Warning)
2071 An array was found at startup, and the
2074 (syslog priority: Info)
2084 cause Email to be sent. All events cause the program to be run.
2085 The program is run with two or three arguments: the event
2086 name, the array device and possibly a second device.
2088 Each event has an associated array device (e.g.
2090 and possibly a second device. For
2095 the second device is the relevant component device.
2098 the second device is the array that the spare was moved from.
2102 to move spares from one array to another, the different arrays need to
2103 be labeled with the same
2105 in the configuration file. The
2107 name can be any string; it is only necessary that different spare
2108 groups use different names.
2112 detects that an array in a spare group has fewer active
2113 devices than necessary for the complete array, and has no spare
2114 devices, it will look for another array in the same spare group that
2115 has a full complement of working drive and a spare. It will then
2116 attempt to remove the spare from the second drive and add it to the
2118 If the removal succeeds but the adding fails, then it is added back to
2122 The GROW mode is used for changing the size or shape of an active
2124 For this to work, the kernel must support the necessary change.
2125 Various types of growth are being added during 2.6 development,
2126 including restructuring a RAID5 array to have more active devices.
2128 Currently the only support available is to
2130 change the "size" attribute
2131 for RAID1, RAID5 and RAID6.
2133 increase or decrease the "raid\-devices" attribute of RAID1, RAID5,
2136 change the chunk-size and layout of RAID5 and RAID6.
2138 convert between RAID1 and RAID5, and between RAID5 and RAID6.
2140 add a write-intent bitmap to any array which supports these bitmaps, or
2141 remove a write-intent bitmap from such an array.
2144 GROW mode is not currently supported for
2146 or arrays inside containers.
2149 Normally when an array is built the "size" it taken from the smallest
2150 of the drives. If all the small drives in an arrays are, one at a
2151 time, removed and replaced with larger drives, then you could have an
2152 array of large drives with only a small amount used. In this
2153 situation, changing the "size" with "GROW" mode will allow the extra
2154 space to start being used. If the size is increased in this way, a
2155 "resync" process will start to make sure the new parts of the array
2158 Note that when an array changes size, any filesystem that may be
2159 stored in the array will not automatically grow to use the space. The
2160 filesystem will need to be explicitly told to use the extra space.
2162 Also the size of an array cannot be changed while it has an active
2163 bitmap. If an array has a bitmap, it must be removed before the size
2164 can be changed. Once the change it complete a new bitmap can be created.
2166 .SS RAID\-DEVICES CHANGES
2168 A RAID1 array can work with any number of devices from 1 upwards
2169 (though 1 is not very useful). There may be times which you want to
2170 increase or decrease the number of active devices. Note that this is
2171 different to hot-add or hot-remove which changes the number of
2174 When reducing the number of devices in a RAID1 array, the slots which
2175 are to be removed from the array must already be vacant. That is, the
2176 devices which were in those slots must be failed and removed.
2178 When the number of devices is increased, any hot spares that are
2179 present will be activated immediately.
2181 Changing the number of active devices in a RAID5 or RAID6 is much more
2182 effort. Every block in the array will need to be read and written
2183 back to a new location. From 2.6.17, the Linux Kernel is able to
2184 increase the number of devices in a RAID5 safely, including restarting
2185 an interrupted "reshape". From 2.6.31, the Linux Kernel is able to
2186 increase or decrease the number of devices in a RAID5 or RAID6.
2188 When decreasing the number of devices, the size of the array will also
2189 decrease. If there was data in the array, it could get destroyed and
2190 this is not reversible. To help prevent accidents,
2192 requires that the size of the array be decreased first with
2193 .BR "mdadm --grow --array-size" .
2194 This is a reversible change which simply makes the end of the array
2195 inaccessible. The integrity of any data can then be checked before
2196 the non-reversible reduction in the number of devices is request.
2198 When relocating the first few stripes on a RAID5 or RAID6, it is not
2199 possible to keep the data on disk completely consistent and
2200 crash-proof. To provide the required safety, mdadm disables writes to
2201 the array while this "critical section" is reshaped, and takes a
2202 backup of the data that is in that section. For grows, this backup may be
2203 stored in any spare devices that the array has, however it can also be
2204 stored in a separate file specified with the
2206 option, and is required to be specified for shrinks, RAID level
2207 changes and layout changes. If this option is used, and the system
2208 does crash during the critical period, the same file must be passed to
2210 to restore the backup and reassemble the array. When shrinking rather
2211 than growing the array, the reshape is done from the end towards the
2212 beginning, so the "critical section" is at the end of the reshape.
2216 Changing the RAID level of any array happens instantaneously. However
2217 in the RAID5 to RAID6 case this requires a non-standard layout of the
2218 RAID6 data, and in the RAID6 to RAID5 case that non-standard layout is
2219 required before the change can be accomplished. So while the level
2220 change is instant, the accompanying layout change can take quite a
2223 is required. If the array is not simultaneously being grown or
2224 shrunk, so that the array size will remain the same - for example,
2225 reshaping a 3-drive RAID5 into a 4-drive RAID6 - the backup file will
2226 be used not just for a "cricital section" but throughout the reshape
2227 operation, as described below under LAYOUT CHANGES.
2229 .SS CHUNK-SIZE AND LAYOUT CHANGES
2231 Changing the chunk-size of layout without also changing the number of
2232 devices as the same time will involve re-writing all blocks in-place.
2233 To ensure against data loss in the case of a crash, a
2235 must be provided for these changes. Small sections of the array will
2236 be copied to the backup file while they are being rearranged. This
2237 means that all the data is copied twice, once to the backup and once
2238 to the new layout on the array, so this type of reshape will go very
2241 If the reshape is interrupted for any reason, this backup file must be
2243 .B "mdadm --assemble"
2244 so the array can be reassembled. Consequently the file cannot be
2245 stored on the device being reshaped.
2250 A write-intent bitmap can be added to, or removed from, an active
2251 array. Either internal bitmaps, or bitmaps stored in a separate file,
2252 can be added. Note that if you add a bitmap stored in a file which is
2253 in a filesystem that is on the RAID array being affected, the system
2254 will deadlock. The bitmap must be on a separate filesystem.
2256 .SH INCREMENTAL MODE
2260 .B mdadm \-\-incremental
2266 .B mdadm \-\-incremental \-\-fail
2270 .B mdadm \-\-incremental \-\-rebuild\-map
2273 .B mdadm \-\-incremental \-\-run \-\-scan
2276 This mode is designed to be used in conjunction with a device
2277 discovery system. As devices are found in a system, they can be
2279 .B "mdadm \-\-incremental"
2280 to be conditionally added to an appropriate array.
2282 Conversely, it can also be used with the
2284 flag to do just the opposite and find whatever array a particular device
2285 is part of and remove the device from that array.
2287 If the device passed is a
2289 device created by a previous call to
2291 then rather than trying to add that device to an array, all the arrays
2292 described by the metadata of the container will be started.
2295 performs a number of tests to determine if the device is part of an
2296 array, and which array it should be part of. If an appropriate array
2297 is found, or can be created,
2299 adds the device to the array and conditionally starts the array.
2303 will only add devices to an array which were previously working
2304 (active or spare) parts of that array. It does not currently support
2305 automatic inclusion of a new drive as a spare in some array.
2309 makes are as follow:
2311 Is the device permitted by
2313 That is, is it listed in a
2315 line in that file. If
2317 is absent then the default it to allow any device. Similar if
2319 contains the special word
2321 then any device is allowed. Otherwise the device name given to
2323 must match one of the names or patterns in a
2328 Does the device have a valid md superblock. If a specific metadata
2329 version is request with
2333 then only that style of metadata is accepted, otherwise
2335 finds any known version of metadata. If no
2337 metadata is found, the device is rejected.
2341 Does the metadata match an expected array?
2342 The metadata can match in two ways. Either there is an array listed
2345 which identifies the array (either by UUID, by name, by device list,
2346 or by minor-number), or the array was created with a
2352 or on the command line.
2355 is not able to positively identify the array as belonging to the
2356 current host, the device will be rejected.
2360 keeps a list of arrays that it has partially assembled in
2361 .B /var/run/mdadm/map
2363 .B /var/run/mdadm.map
2364 if the directory doesn't exist. Or maybe even
2365 .BR /dev/.mdadm.map ).
2366 If no array exists which matches
2367 the metadata on the new device,
2369 must choose a device name and unit number. It does this based on any
2372 or any name information stored in the metadata. If this name
2373 suggests a unit number, that number will be used, otherwise a free
2374 unit number will be chosen. Normally
2376 will prefer to create a partitionable array, however if the
2380 suggests that a non-partitionable array is preferred, that will be
2383 If the array is not found in the config file and its metadata does not
2384 identify it as belonging to the "homehost", then
2386 will choose a name for the array which is certain not to conflict with
2387 any array which does belong to this host. It does this be adding an
2388 underscore and a small number to the name preferred by the metadata.
2390 Once an appropriate array is found or created and the device is added,
2392 must decide if the array is ready to be started. It will
2393 normally compare the number of available (non-spare) devices to the
2394 number of devices that the metadata suggests need to be active. If
2395 there are at least that many, the array will be started. This means
2396 that if any devices are missing the array will not be restarted.
2402 in which case the array will be run as soon as there are enough
2403 devices present for the data to be accessible. For a RAID1, that
2404 means one device will start the array. For a clean RAID5, the array
2405 will be started as soon as all but one drive is present.
2407 Note that neither of these approaches is really ideal. If it can
2408 be known that all device discovery has completed, then
2412 can be run which will try to start all arrays that are being
2413 incrementally assembled. They are started in "read-auto" mode in
2414 which they are read-only until the first write request. This means
2415 that no metadata updates are made and no attempt at resync or recovery
2416 happens. Further devices that are found before the first write can
2417 still be added safely.
2420 This section describes environment variables that affect how mdadm
2425 Setting this value to 1 will prevent mdadm from automatically launching
2426 mdmon. This variable is intended primarily for debugging mdadm/mdmon.
2432 does not create any device nodes in /dev, but leaves that task to
2436 appears not to be configured, or if this environment variable is set
2439 will create and devices that are needed.
2443 .B " mdadm \-\-query /dev/name-of-device"
2445 This will find out if a given device is a RAID array, or is part of
2446 one, and will provide brief information about the device.
2448 .B " mdadm \-\-assemble \-\-scan"
2450 This will assemble and start all arrays listed in the standard config
2451 file. This command will typically go in a system startup file.
2453 .B " mdadm \-\-stop \-\-scan"
2455 This will shut down all arrays that can be shut down (i.e. are not
2456 currently in use). This will typically go in a system shutdown script.
2458 .B " mdadm \-\-follow \-\-scan \-\-delay=120"
2460 If (and only if) there is an Email address or program given in the
2461 standard config file, then
2462 monitor the status of all arrays listed in that file by
2463 polling them ever 2 minutes.
2465 .B " mdadm \-\-create /dev/md0 \-\-level=1 \-\-raid\-devices=2 /dev/hd[ac]1"
2467 Create /dev/md0 as a RAID1 array consisting of /dev/hda1 and /dev/hdc1.
2470 .B " echo 'DEVICE /dev/hd*[0\-9] /dev/sd*[0\-9]' > mdadm.conf"
2472 .B " mdadm \-\-detail \-\-scan >> mdadm.conf"
2474 This will create a prototype config file that describes currently
2475 active arrays that are known to be made from partitions of IDE or SCSI drives.
2476 This file should be reviewed before being used as it may
2477 contain unwanted detail.
2479 .B " echo 'DEVICE /dev/hd[a\-z] /dev/sd*[a\-z]' > mdadm.conf"
2481 .B " mdadm \-\-examine \-\-scan \-\-config=mdadm.conf >> mdadm.conf"
2483 This will find arrays which could be assembled from existing IDE and
2484 SCSI whole drives (not partitions), and store the information in the
2485 format of a config file.
2486 This file is very likely to contain unwanted detail, particularly
2489 entries. It should be reviewed and edited before being used as an
2492 .B " mdadm \-\-examine \-\-brief \-\-scan \-\-config=partitions"
2494 .B " mdadm \-Ebsc partitions"
2496 Create a list of devices by reading
2497 .BR /proc/partitions ,
2498 scan these for RAID superblocks, and printout a brief listing of all
2501 .B " mdadm \-Ac partitions \-m 0 /dev/md0"
2503 Scan all partitions and devices listed in
2504 .BR /proc/partitions
2507 out of all such devices with a RAID superblock with a minor number of 0.
2509 .B " mdadm \-\-monitor \-\-scan \-\-daemonise > /var/run/mdadm"
2511 If config file contains a mail address or alert program, run mdadm in
2512 the background in monitor mode monitoring all md devices. Also write
2513 pid of mdadm daemon to
2514 .BR /var/run/mdadm .
2516 .B " mdadm \-Iq /dev/somedevice"
2518 Try to incorporate newly discovered device into some array as
2521 .B " mdadm \-\-incremental \-\-rebuild\-map \-\-run \-\-scan"
2523 Rebuild the array map from any current arrays, and then start any that
2526 .B " mdadm /dev/md4 --fail detached --remove detached"
2528 Any devices which are components of /dev/md4 will be marked as faulty
2529 and then remove from the array.
2531 .B " mdadm --grow /dev/md4 --level=6 --backup-file=/root/backup-md4
2535 which is currently a RAID5 array will be converted to RAID6. There
2536 should normally already be a spare drive attached to the array as a
2537 RAID6 needs one more drive than a matching RAID5.
2539 .B " mdadm --create /dev/md/ddf --metadata=ddf --raid-disks 6 /dev/sd[a-f]"
2541 Create a DDF array over 6 devices.
2543 .B " mdadm --create /dev/md/home -n3 -l5 -z 30000000 /dev/md/ddf"
2545 Create a RAID5 array over any 3 devices in the given DDF set. Use
2546 only 30 gigabytes of each device.
2548 .B " mdadm -A /dev/md/ddf1 /dev/sd[a-f]"
2550 Assemble a pre-exist ddf array.
2552 .B " mdadm -I /dev/md/ddf1"
2554 Assemble all arrays contained in the ddf array, assigning names as
2557 .B " mdadm \-\-create \-\-help"
2559 Provide help about the Create mode.
2561 .B " mdadm \-\-config \-\-help"
2563 Provide help about the format of the config file.
2565 .B " mdadm \-\-help"
2567 Provide general help.
2577 lists all active md devices with information about them.
2579 uses this to find arrays when
2581 is given in Misc mode, and to monitor array reconstruction
2586 The config file lists which devices may be scanned to see if
2587 they contain MD super block, and gives identifying information
2588 (e.g. UUID) about known MD arrays. See
2592 .SS /var/run/mdadm/map
2595 mode is used, this file gets a list of arrays currently being created.
2598 does not exist as a directory, then
2599 .B /var/run/mdadm.map
2602 is not available (as may be the case during early boot),
2604 is used on the basis that
2606 is usually available very early in boot.
2611 understand two sorts of names for array devices.
2613 The first is the so-called 'standard' format name, which matches the
2614 names used by the kernel and which appear in
2617 The second sort can be freely chosen, but must reside in
2619 When giving a device name to
2621 to create or assemble an array, either full path name such as
2625 can be given, or just the suffix of the second sort of name, such as
2631 chooses device names during auto-assembly or incremental assembly, it
2632 will sometimes add a small sequence number to the end of the name to
2633 avoid conflicted between multiple arrays that have the same name. If
2635 can reasonably determine that the array really is meant for this host,
2636 either by a hostname in the metadata, or by the presence of the array
2637 in /etc/mdadm.conf, then it will leave off the suffix if possible.
2638 Also if the homehost is specified as
2641 will only use a suffix if a different array of the same name already
2642 exists or is listed in the config file.
2644 The standard names for non-partitioned arrays (the only sort of md
2645 array available in 2.4 and earlier) are of the form
2649 where NN is a number.
2650 The standard names for partitionable arrays (as available from 2.6
2651 onwards) are of the form
2655 Partition numbers should be indicated by added "pMM" to these, thus "/dev/md/d1p2".
2657 From kernel version, 2.6.28 the "non-partitioned array" can actually
2658 be partitioned. So the "md_dNN" names are no longer needed, and
2659 partitions such as "/dev/mdNNpXX" are possible.
2663 was previously known as
2667 is completely separate from the
2669 package, and does not use the
2671 configuration file at all.
2674 For further information on mdadm usage, MD and the various levels of
2677 .B http://linux\-raid.osdl.org/
2679 (based upon Jakob \(/Ostergaard's Software\-RAID.HOWTO)
2681 .\"for new releases of the RAID driver check out:
2684 .\".UR ftp://ftp.kernel.org/pub/linux/kernel/people/mingo/raid-patches
2685 .\"ftp://ftp.kernel.org/pub/linux/kernel/people/mingo/raid-patches
2690 .\".UR http://www.cse.unsw.edu.au/~neilb/patches/linux-stable/
2691 .\"http://www.cse.unsw.edu.au/~neilb/patches/linux-stable/
2694 The latest version of
2696 should always be available from
2698 .B http://www.kernel.org/pub/linux/utils/raid/mdadm/