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.
144 in this mode, then any arrays within that container will be assembled
149 This is for doing things to specific components of an array such as
150 adding new spares and removing faulty devices.
154 This is an 'everything else' mode that supports operations on active
155 arrays, operations on component devices such as erasing old superblocks, and
156 information gathering operations.
157 .\"This mode allows operations on independent devices such as examine MD
158 .\"superblocks, erasing old superblocks and stopping active arrays.
162 This mode does not act on a specific device or array, but rather it
163 requests the Linux Kernel to activate any auto-detected arrays.
166 .SH Options for selecting a mode are:
169 .BR \-A ", " \-\-assemble
170 Assemble a pre-existing array.
173 .BR \-B ", " \-\-build
174 Build a legacy array without superblocks.
177 .BR \-C ", " \-\-create
181 .BR \-F ", " \-\-follow ", " \-\-monitor
187 .BR \-G ", " \-\-grow
188 Change the size or shape of an active array.
191 .BR \-I ", " \-\-incremental
192 Add a single device into an appropriate array, and possibly start the array.
196 Request that the kernel starts any auto-detected arrays. This can only
199 is compiled into the kernel \(em not if it is a module.
200 Arrays can be auto-detected by the kernel if all the components are in
201 primary MS-DOS partitions with partition type
203 and all use v0.90 metadata.
204 In-kernel autodetect is not recommended for new installations. Using
206 to detect and assemble arrays \(em possibly in an
208 \(em is substantially more flexible and should be preferred.
211 If a device is given before any options, or if the first option is
216 then the MANAGE mode is assumed.
217 Anything other than these will cause the
221 .SH Options that are not mode-specific are:
224 .BR \-h ", " \-\-help
225 Display general help message or, after one of the above options, a
226 mode-specific help message.
230 Display more detailed help about command line parsing and some commonly
234 .BR \-V ", " \-\-version
235 Print version information for mdadm.
238 .BR \-v ", " \-\-verbose
239 Be more verbose about what is happening. This can be used twice to be
241 The extra verbosity currently only affects
242 .B \-\-detail \-\-scan
244 .BR "\-\-examine \-\-scan" .
247 .BR \-q ", " \-\-quiet
248 Avoid printing purely informative messages. With this,
250 will be silent unless there is something really important to report.
253 .BR \-f ", " \-\-force
254 Be more forceful about certain operations. See the various modes for
255 the exact meaning of this option in different contexts.
258 .BR \-c ", " \-\-config=
259 Specify the config file. Default is to use
260 .BR /etc/mdadm.conf ,
261 or if that is missing then
262 .BR /etc/mdadm/mdadm.conf .
263 If the config file given is
265 then nothing will be read, but
267 will act as though the config file contained exactly
268 .B "DEVICE partitions containers"
271 to find a list of devices to scan, and
273 to find a list of containers to examine.
276 is given for the config file, then
278 will act as though the config file were empty.
281 .BR \-s ", " \-\-scan
284 for missing information.
285 In general, this option gives
287 permission to get any missing information (like component devices,
288 array devices, array identities, and alert destination) from the
289 configuration file (see previous option);
290 one exception is MISC mode when using
296 says to get a list of array devices from
300 .BR \-e ", " \-\-metadata=
301 Declare the style of RAID metadata (superblock) to be used. The
302 default is {DEFAULT_METADATA} for
304 and to guess for other operations.
305 The default can be overridden by setting the
314 .ie '{DEFAULT_METADATA}'0.90'
315 .IP "0, 0.90, default"
319 Use the original 0.90 format superblock. This format limits arrays to
320 28 component devices and limits component devices of levels 1 and
321 greater to 2 terabytes.
322 .ie '{DEFAULT_METADATA}'0.90'
323 .IP "1, 1.0, 1.1, 1.2"
325 .IP "1, 1.0, 1.1, 1.2 default"
327 Use the new version-1 format superblock. This has few restrictions.
328 The different sub-versions store the superblock at different locations
329 on the device, either at the end (for 1.0), at the start (for 1.1) or
330 4K from the start (for 1.2). "1" is equivalent to "1.0".
331 'if '{DEFAULT_METADATA}'1.2' "default" is equivalent to "1.2".
333 Use the "Industry Standard" DDF (Disk Data Format) format defined by
335 When creating a DDF array a
337 will be created, and normal arrays can be created in that container.
339 Use the Intel(R) Matrix Storage Manager metadata format. This creates a
341 which is managed in a similar manner to DDF, and is supported by an
342 option-rom on some platforms:
344 .B http://www.intel.com/design/chipsets/matrixstorage_sb.htm
350 This will override any
352 setting in the config file and provides the identity of the host which
353 should be considered the home for any arrays.
355 When creating an array, the
357 will be recorded in the metadata. For version-1 superblocks, it will
358 be prefixed to the array name. For version-0.90 superblocks, part of
359 the SHA1 hash of the hostname will be stored in the later half of the
362 When reporting information about an array, any array which is tagged
363 for the given homehost will be reported as such.
365 When using Auto-Assemble, only arrays tagged for the given homehost
366 will be allowed to use 'local' names (i.e. not ending in '_' followed
367 by a digit string). See below under
368 .BR "Auto Assembly" .
370 .SH For create, build, or grow:
373 .BR \-n ", " \-\-raid\-devices=
374 Specify the number of active devices in the array. This, plus the
375 number of spare devices (see below) must equal the number of
377 (including "\fBmissing\fP" devices)
378 that are listed on the command line for
380 Setting a value of 1 is probably
381 a mistake and so requires that
383 be specified first. A value of 1 will then be allowed for linear,
384 multipath, RAID0 and RAID1. It is never allowed for RAID4, RAID5 or RAID6.
386 This number can only be changed using
388 for RAID1, RAID4, RAID5 and RAID6 arrays, and only on kernels which provide
389 the necessary support.
392 .BR \-x ", " \-\-spare\-devices=
393 Specify the number of spare (eXtra) devices in the initial array.
394 Spares can also be added
395 and removed later. The number of component devices listed
396 on the command line must equal the number of RAID devices plus the
397 number of spare devices.
400 .BR \-z ", " \-\-size=
401 Amount (in Kibibytes) of space to use from each drive in RAID levels 1/4/5/6.
402 This must be a multiple of the chunk size, and must leave about 128Kb
403 of space at the end of the drive for the RAID superblock.
404 If this is not specified
405 (as it normally is not) the smallest drive (or partition) sets the
406 size, though if there is a variance among the drives of greater than 1%, a warning is
409 This value can be set with
411 for RAID level 1/4/5/6. If the array was created with a size smaller
412 than the currently active drives, the extra space can be accessed
415 The size can be given as
417 which means to choose the largest size that fits on all current drives.
419 This value can not be used with
421 metadata such as DDF and IMSM.
424 .BR \-Z ", " \-\-array-size=
425 This is only meaningful with
427 and its effect is not persistent: when the array is stopped an
428 restarted the default array size will be restored.
430 Setting the array-size causes the array to appear smaller to programs
431 that access the data. This is particularly needed before reshaping an
432 array so that it will be smaller. As the reshape is not reversible,
433 but setting the size with
435 is, it is required that the array size is reduced as appropriate
436 before the number of devices in the array is reduced.
439 .BR \-c ", " \-\-chunk=
440 Specify chunk size of kibibytes. The default when creating an
441 array is 512KB. To ensure compatibility with earlier versions, the
442 default when Building and array with no persistent metadata is 64KB.
443 This is only meaningful for RAID0, RAID4, RAID5, RAID6, and RAID10.
447 Specify rounding factor for a Linear array. The size of each
448 component will be rounded down to a multiple of this size.
449 This is a synonym for
451 but highlights the different meaning for Linear as compared to other
452 RAID levels. The default is 64K if a kernel earlier than 2.6.16 is in
453 use, and is 0K (i.e. no rounding) in later kernels.
456 .BR \-l ", " \-\-level=
457 Set RAID level. When used with
459 options are: linear, raid0, 0, stripe, raid1, 1, mirror, raid4, 4,
460 raid5, 5, raid6, 6, raid10, 10, multipath, mp, faulty, container.
461 Obviously some of these are synonymous.
465 metadata type is requested, only the
467 level is permitted, and it does not need to be explicitly given.
471 only linear, stripe, raid0, 0, raid1, multipath, mp, and faulty are valid.
473 Not yet supported with
477 .BR \-p ", " \-\-layout=
478 This option configures the fine details of data layout for RAID5, RAID6,
479 and RAID10 arrays, and controls the failure modes for
482 The layout of the RAID5 parity block can be one of
483 .BR left\-asymmetric ,
484 .BR left\-symmetric ,
485 .BR right\-asymmetric ,
486 .BR right\-symmetric ,
487 .BR la ", " ra ", " ls ", " rs .
489 .BR left\-symmetric .
491 It is also possibly to cause RAID5 to use a RAID4-like layout by
497 Finally for RAID5 there are DDF\-compatible layouts,
498 .BR ddf\-zero\-restart ,
499 .BR ddf\-N\-restart ,
501 .BR ddf\-N\-continue .
503 These same layouts are available for RAID6. There are also 4 layouts
504 that will provide an intermediate stage for converting between RAID5
505 and RAID6. These provide a layout which is identical to the
506 corresponding RAID5 layout on the first N\-1 devices, and has the 'Q'
507 syndrome (the second 'parity' block used by RAID6) on the last device.
509 .BR left\-symmetric\-6 ,
510 .BR right\-symmetric\-6 ,
511 .BR left\-asymmetric\-6 ,
512 .BR right\-asymmetric\-6 ,
514 .BR parity\-first\-6 .
516 When setting the failure mode for level
519 .BR write\-transient ", " wt ,
520 .BR read\-transient ", " rt ,
521 .BR write\-persistent ", " wp ,
522 .BR read\-persistent ", " rp ,
524 .BR read\-fixable ", " rf ,
525 .BR clear ", " flush ", " none .
527 Each failure mode can be followed by a number, which is used as a period
528 between fault generation. Without a number, the fault is generated
529 once on the first relevant request. With a number, the fault will be
530 generated after that many requests, and will continue to be generated
531 every time the period elapses.
533 Multiple failure modes can be current simultaneously by using the
535 option to set subsequent failure modes.
537 "clear" or "none" will remove any pending or periodic failure modes,
538 and "flush" will clear any persistent faults.
540 Finally, the layout options for RAID10 are one of 'n', 'o' or 'f' followed
541 by a small number. The default is 'n2'. The supported options are:
544 signals 'near' copies. Multiple copies of one data block are at
545 similar offsets in different devices.
548 signals 'offset' copies. Rather than the chunks being duplicated
549 within a stripe, whole stripes are duplicated but are rotated by one
550 device so duplicate blocks are on different devices. Thus subsequent
551 copies of a block are in the next drive, and are one chunk further
556 (multiple copies have very different offsets).
557 See md(4) for more detail about 'near', 'offset', and 'far'.
559 The number is the number of copies of each datablock. 2 is normal, 3
560 can be useful. This number can be at most equal to the number of
561 devices in the array. It does not need to divide evenly into that
562 number (e.g. it is perfectly legal to have an 'n2' layout for an array
563 with an odd number of devices).
565 When an array is converted between RAID5 and RAID6 an intermediate
566 RAID6 layout is used in which the second parity block (Q) is always on
567 the last device. To convert a RAID5 to RAID6 and leave it in this new
568 layout (which does not require re-striping) use
569 .BR \-\-layout=preserve .
570 This will try to avoid any restriping.
572 The converse of this is
573 .B \-\-layout=normalise
574 which will change a non-standard RAID6 layout into a more standard
581 (thus explaining the p of
585 .BR \-b ", " \-\-bitmap=
586 Specify a file to store a write-intent bitmap in. The file should not
589 is also given. The same file should be provided
590 when assembling the array. If the word
592 is given, then the bitmap is stored with the metadata on the array,
593 and so is replicated on all devices. If the word
597 mode, then any bitmap that is present is removed.
599 To help catch typing errors, the filename must contain at least one
600 slash ('/') if it is a real file (not 'internal' or 'none').
602 Note: external bitmaps are only known to work on ext2 and ext3.
603 Storing bitmap files on other filesystems may result in serious problems.
606 .BR \-\-bitmap\-chunk=
607 Set the chunksize of the bitmap. Each bit corresponds to that many
608 Kilobytes of storage.
609 When using a file based bitmap, the default is to use the smallest
610 size that is at-least 4 and requires no more than 2^21 chunks.
613 bitmap, the chunksize defaults to 64Meg, or larger if necessary to
614 fit the bitmap into the available space.
617 .BR \-W ", " \-\-write\-mostly
618 subsequent devices listed in a
623 command will be flagged as 'write-mostly'. This is valid for RAID1
624 only and means that the 'md' driver will avoid reading from these
625 devices if at all possible. This can be useful if mirroring over a
629 .BR \-\-write\-behind=
630 Specify that write-behind mode should be enabled (valid for RAID1
631 only). If an argument is specified, it will set the maximum number
632 of outstanding writes allowed. The default value is 256.
633 A write-intent bitmap is required in order to use write-behind
634 mode, and write-behind is only attempted on drives marked as
638 .BR \-\-assume\-clean
641 that the array pre-existed and is known to be clean. It can be useful
642 when trying to recover from a major failure as you can be sure that no
643 data will be affected unless you actually write to the array. It can
644 also be used when creating a RAID1 or RAID10 if you want to avoid the
645 initial resync, however this practice \(em while normally safe \(em is not
646 recommended. Use this only if you really know what you are doing.
648 When the devices that will be part of a new array were filled
649 with zeros before creation the operator knows the array is
650 actually clean. If that is the case, such as after running
651 badblocks, this argument can be used to tell mdadm the
652 facts the operator knows.
655 .BR \-\-backup\-file=
658 is used to increase the number of
659 raid-devices in a RAID5 if there are no spare devices available.
660 See the GROW MODE section below on RAID\-DEVICES CHANGES. The file
661 should be stored on a separate device, not on the RAID array being
665 .BR \-\-array-size= ", " \-Z
666 Set the size of the array which is seen by users of the device such as
667 filesystems. This can be less that the real size, but never greater.
668 The size set this way does not persist across restarts of the array.
670 This is most useful when reducing the number of devices in a RAID5 or
671 RAID6. Such arrays require the array-size to be reduced before a
672 reshape can be performed that reduces the real size.
676 restores the apparent size of the array to be whatever the real
677 amount of available space is.
680 .BR \-N ", " \-\-name=
683 for the array. This is currently only effective when creating an
684 array with a version-1 superblock, or an array in a DDF container.
685 The name is a simple textual string that can be used to identify array
686 components when assembling. If name is needed but not specified, it
687 is taken from the basename of the device that is being created.
699 run the array, even if some of the components
700 appear to be active in another array or filesystem. Normally
702 will ask for confirmation before including such components in an
703 array. This option causes that question to be suppressed.
706 .BR \-f ", " \-\-force
709 accept the geometry and layout specified without question. Normally
711 will not allow creation of an array with only one device, and will try
712 to create a RAID5 array with one missing drive (as this makes the
713 initial resync work faster). With
716 will not try to be so clever.
719 .BR \-a ", " "\-\-auto{=yes,md,mdp,part,p}{NN}"
720 Instruct mdadm how to create the device file if needed, possibly allocating
721 an unused minor number. "md" causes a non-partitionable array
722 to be used (though since Linux 2.6.28, these array devices are in fact
723 partitionable). "mdp", "part" or "p" causes a partitionable array (2.6 and
724 later) to be used. "yes" requires the named md device to have
725 a 'standard' format, and the type and minor number will be determined
726 from this. With mdadm 3.0, device creation is normally left up to
728 so this option is unlikely to be needed.
729 See DEVICE NAMES below.
731 The argument can also come immediately after
736 is not given on the command line or in the config file, then
742 is also given, then any
744 entries in the config file will override the
746 instruction given on the command line.
748 For partitionable arrays,
750 will create the device file for the whole array and for the first 4
751 partitions. A different number of partitions can be specified at the
752 end of this option (e.g.
754 If the device name ends with a digit, the partition names add a 'p',
756 .IR /dev/md/home1p3 .
757 If there is no trailing digit, then the partition names just have a
759 .IR /dev/md/scratch3 .
761 If the md device name is in a 'standard' format as described in DEVICE
762 NAMES, then it will be created, if necessary, with the appropriate
763 device number based on that name. If the device name is not in one of these
764 formats, then a unused device number will be allocated. The device
765 number will be considered unused if there is no active array for that
766 number, and there is no entry in /dev for that number and with a
767 non-standard name. Names that are not in 'standard' format are only
768 allowed in "/dev/md/".
772 .\".BR \-\-symlink = no
777 .\"to create devices in
779 .\"it will also create symlinks from
781 .\"with names starting with
787 .\"to suppress this, or
788 .\".B \-\-symlink=yes
789 .\"to enforce this even if it is suppressing
797 .BR \-u ", " \-\-uuid=
798 uuid of array to assemble. Devices which don't have this uuid are
802 .BR \-m ", " \-\-super\-minor=
803 Minor number of device that array was created for. Devices which
804 don't have this minor number are excluded. If you create an array as
805 /dev/md1, then all superblocks will contain the minor number 1, even if
806 the array is later assembled as /dev/md2.
808 Giving the literal word "dev" for
812 to use the minor number of the md device that is being assembled.
815 .B \-\-super\-minor=dev
816 will look for super blocks with a minor number of 0.
819 is only relevant for v0.90 metadata, and should not normally be used.
825 .BR \-N ", " \-\-name=
826 Specify the name of the array to assemble. This must be the name
827 that was specified when creating the array. It must either match
828 the name stored in the superblock exactly, or it must match
831 prefixed to the start of the given name.
834 .BR \-f ", " \-\-force
835 Assemble the array even if the metadata on some devices appears to be
838 cannot find enough working devices to start the array, but can find
839 some devices that are recorded as having failed, then it will mark
840 those devices as working so that the array can be started.
841 An array which requires
843 to be started may contain data corruption. Use it carefully.
847 Attempt to start the array even if fewer drives were given than were
848 present last time the array was active. Normally if not all the
849 expected drives are found and
851 is not used, then the array will be assembled but not started.
854 an attempt will be made to start it anyway.
858 This is the reverse of
860 in that it inhibits the startup of array unless all expected drives
861 are present. This is only needed with
863 and can be used if the physical connections to devices are
864 not as reliable as you would like.
867 .BR \-a ", " "\-\-auto{=no,yes,md,mdp,part}"
868 See this option under Create and Build options.
871 .BR \-b ", " \-\-bitmap=
872 Specify the bitmap file that was given when the array was created. If
875 bitmap, there is no need to specify this when assembling the array.
878 .BR \-\-backup\-file=
881 was used to grow the number of raid-devices in a RAID5, and the system
882 crashed during the critical section, then the same
886 to allow possibly corrupted data to be restored.
889 .BR \-U ", " \-\-update=
890 Update the superblock on each device while assembling the array. The
891 argument given to this flag can be one of
905 option will adjust the superblock of an array what was created on a Sparc
906 machine running a patched 2.2 Linux kernel. This kernel got the
907 alignment of part of the superblock wrong. You can use the
908 .B "\-\-examine \-\-sparc2.2"
911 to see what effect this would have.
915 option will update the
917 field on each superblock to match the minor number of the array being
919 This can be useful if
921 reports a different "Preferred Minor" to
923 In some cases this update will be performed automatically
924 by the kernel driver. In particular the update happens automatically
925 at the first write to an array with redundancy (RAID level 1 or
926 greater) on a 2.6 (or later) kernel.
930 option will change the uuid of the array. If a UUID is given with the
932 option that UUID will be used as a new UUID and will
934 be used to help identify the devices in the array.
937 is given, a random UUID is chosen.
941 option will change the
943 of the array as stored in the superblock. This is only supported for
944 version-1 superblocks.
948 option will change the
950 as recorded in the superblock. For version-0 superblocks, this is the
951 same as updating the UUID.
952 For version-1 superblocks, this involves updating the name.
956 option will cause the array to be marked
958 meaning that any redundancy in the array (e.g. parity for RAID5,
959 copies for RAID1) may be incorrect. This will cause the RAID system
960 to perform a "resync" pass to make sure that all redundant information
965 option allows arrays to be moved between machines with different
967 When assembling such an array for the first time after a move, giving
968 .B "\-\-update=byteorder"
971 to expect superblocks to have their byteorder reversed, and will
972 correct that order before assembling the array. This is only valid
973 with original (Version 0.90) superblocks.
977 option will correct the summaries in the superblock. That is the
978 counts of total, working, active, failed, and spare devices.
982 will rarely be of use. It applies to version 1.1 and 1.2 metadata
983 only (where the metadata is at the start of the device) and is only
984 useful when the component device has changed size (typically become
985 larger). The version 1 metadata records the amount of the device that
986 can be used to store data, so if a device in a version 1.1 or 1.2
987 array becomes larger, the metadata will still be visible, but the
988 extra space will not. In this case it might be useful to assemble the
990 .BR \-\-update=devicesize .
993 to determine the maximum usable amount of space on each device and
994 update the relevant field in the metadata.
998 .B \-\-auto\-update\-homehost
999 This flag is only meaningful with auto-assembly (see discussion below).
1000 In that situation, if no suitable arrays are found for this homehost,
1002 will rescan for any arrays at all and will assemble them and update the
1003 homehost to match the current host.
1006 .SH For Manage mode:
1009 .BR \-a ", " \-\-add
1010 hot-add listed devices. For arrays with redundancy, the listed
1011 devices become available as spares. If the array is degraded, it will
1012 immediately start recovering data on to one of these spares.
1016 re-add a device that was recently removed from an array. This is only
1017 needed for arrays that have be built (i.e. with
1019 For created arrays, devices are always re-added if that is possible.
1020 When re-adding a device, if nothing has changed on the array since the
1021 device was removed, no recovery is performed. Also, if the array has
1022 a write-intent bitmap, then the recovery performed after a re-add will
1023 be limited to those blocks which, according to the bitmap, might have
1024 changed since the device was removed.
1027 .BR \-r ", " \-\-remove
1028 remove listed devices. They must not be active. i.e. they should
1029 be failed or spare devices. As well as the name of a device file
1038 The first causes all failed device to be removed. The second causes
1039 any device which is no longer connected to the system (i.e an 'open'
1042 to be removed. This will only succeed for devices that are spares or
1043 have already been marked as failed.
1046 .BR \-f ", " \-\-fail
1047 mark listed devices as faulty.
1048 As well as the name of a device file, the word
1050 can be given. This will cause any device that has been detached from
1051 the system to be marked as failed. It can then be removed.
1059 .BR \-\-write\-mostly
1060 Subsequent devices that are added or re-added will have the 'write-mostly'
1061 flag set. This is only valid for RAID1 and means that the 'md' driver
1062 will avoid reading from these devices if possible.
1065 Subsequent devices that are added or re-added will have the 'write-mostly'
1069 Each of these options requires that the first device listed is the array
1070 to be acted upon, and the remainder are component devices to be added,
1071 removed, marked as faulty, etc. Several different operations can be
1072 specified for different devices, e.g.
1074 mdadm /dev/md0 \-\-add /dev/sda1 \-\-fail /dev/sdb1 \-\-remove /dev/sdb1
1076 Each operation applies to all devices listed until the next
1079 If an array is using a write-intent bitmap, then devices which have
1080 been removed can be re-added in a way that avoids a full
1081 reconstruction but instead just updates the blocks that have changed
1082 since the device was removed. For arrays with persistent metadata
1083 (superblocks) this is done automatically. For arrays created with
1085 mdadm needs to be told that this device we removed recently with
1088 Devices can only be removed from an array if they are not in active
1089 use, i.e. that must be spares or failed devices. To remove an active
1090 device, it must first be marked as
1096 .BR \-Q ", " \-\-query
1097 Examine a device to see
1098 (1) if it is an md device and (2) if it is a component of an md
1100 Information about what is discovered is presented.
1103 .BR \-D ", " \-\-detail
1104 Print details of one or more md devices.
1107 .BR \-\-detail\-platform
1108 Print details of the platform's RAID capabilities (firmware / hardware
1109 topology) for a given metadata format.
1112 .BR \-Y ", " \-\-export
1117 output will be formatted as
1119 pairs for easy import into the environment.
1122 .BR \-E ", " \-\-examine
1123 Print contents of the metadata stored on the named device(s).
1124 Note the contrast between
1129 applies to devices which are components of an array, while
1131 applies to a whole array which is currently active.
1134 If an array was created on a SPARC machine with a 2.2 Linux kernel
1135 patched with RAID support, the superblock will have been created
1136 incorrectly, or at least incompatibly with 2.4 and later kernels.
1141 will fix the superblock before displaying it. If this appears to do
1142 the right thing, then the array can be successfully assembled using
1143 .BR "\-\-assemble \-\-update=sparc2.2" .
1146 .BR \-X ", " \-\-examine\-bitmap
1147 Report information about a bitmap file.
1148 The argument is either an external bitmap file or an array component
1149 in case of an internal bitmap. Note that running this on an array
1152 does not report the bitmap for that array.
1155 .BR \-R ", " \-\-run
1156 start a partially assembled array. If
1158 did not find enough devices to fully start the array, it might leaving
1159 it partially assembled. If you wish, you can then use
1161 to start the array in degraded mode.
1164 .BR \-S ", " \-\-stop
1165 deactivate array, releasing all resources.
1168 .BR \-o ", " \-\-readonly
1169 mark array as readonly.
1172 .BR \-w ", " \-\-readwrite
1173 mark array as readwrite.
1176 .B \-\-zero\-superblock
1177 If the device contains a valid md superblock, the block is
1178 overwritten with zeros. With
1180 the block where the superblock would be is overwritten even if it
1181 doesn't appear to be valid.
1184 .BR \-t ", " \-\-test
1189 is set to reflect the status of the device. See below in
1194 .BR \-W ", " \-\-wait
1195 For each md device given, wait for any resync, recovery, or reshape
1196 activity to finish before returning.
1198 will return with success if it actually waited for every device
1199 listed, otherwise it will return failure.
1203 For each md device given, or each device in /proc/mdstat if
1205 is given, arrange for the array to be marked clean as soon as possible.
1206 Also, quiesce resync so that the monitor for external metadata arrays
1207 (mdmon) has an opportunity to checkpoint the resync position.
1209 will return with success if the array uses external metadata and we
1210 successfully waited. For native arrays this returns immediately as the
1211 kernel handles both dirty-clean transitions and resync checkpointing in
1212 the kernel at shutdown. No action is taken if safe-mode handling is
1215 .SH For Incremental Assembly mode:
1217 .BR \-\-rebuild\-map ", " \-r
1218 Rebuild the map file
1219 .RB ( /var/run/mdadm/map )
1222 uses to help track which arrays are currently being assembled.
1225 .BR \-\-run ", " \-R
1226 Run any array assembled as soon as a minimal number of devices are
1227 available, rather than waiting until all expected devices are present.
1230 .BR \-\-scan ", " \-s
1231 Only meaningful with
1235 file for arrays that are being incrementally assembled and will try to
1236 start any that are not already started. If any such array is listed
1239 as requiring an external bitmap, that bitmap will be attached first.
1241 .SH For Monitor mode:
1243 .BR \-m ", " \-\-mail
1244 Give a mail address to send alerts to.
1247 .BR \-p ", " \-\-program ", " \-\-alert
1248 Give a program to be run whenever an event is detected.
1251 .BR \-y ", " \-\-syslog
1252 Cause all events to be reported through 'syslog'. The messages have
1253 facility of 'daemon' and varying priorities.
1256 .BR \-d ", " \-\-delay
1257 Give a delay in seconds.
1259 polls the md arrays and then waits this many seconds before polling
1260 again. The default is 60 seconds. Since 2.6.16, there is no need to
1261 reduce this as the kernel alerts
1263 immediately when there is any change.
1266 .BR \-r ", " \-\-increment
1267 Give a percentage increment.
1269 will generate RebuildNN events with the given percentage increment.
1272 .BR \-f ", " \-\-daemonise
1275 to run as a background daemon if it decides to monitor anything. This
1276 causes it to fork and run in the child, and to disconnect from the
1277 terminal. The process id of the child is written to stdout.
1280 which will only continue monitoring if a mail address or alert program
1281 is found in the config file.
1284 .BR \-i ", " \-\-pid\-file
1287 is running in daemon mode, write the pid of the daemon process to
1288 the specified file, instead of printing it on standard output.
1291 .BR \-1 ", " \-\-oneshot
1292 Check arrays only once. This will generate
1294 events and more significantly
1300 .B " mdadm \-\-monitor \-\-scan \-1"
1302 from a cron script will ensure regular notification of any degraded arrays.
1305 .BR \-t ", " \-\-test
1308 alert for every array found at startup. This alert gets mailed and
1309 passed to the alert program. This can be used for testing that alert
1310 message do get through successfully.
1316 .B mdadm \-\-assemble
1317 .I md-device options-and-component-devices...
1320 .B mdadm \-\-assemble \-\-scan
1321 .I md-devices-and-options...
1324 .B mdadm \-\-assemble \-\-scan
1328 This usage assembles one or more RAID arrays from pre-existing components.
1329 For each array, mdadm needs to know the md device, the identity of the
1330 array, and a number of component-devices. These can be found in a number of ways.
1332 In the first usage example (without the
1334 the first device given is the md device.
1335 In the second usage example, all devices listed are treated as md
1336 devices and assembly is attempted.
1337 In the third (where no devices are listed) all md devices that are
1338 listed in the configuration file are assembled. If not arrays are
1339 described by the configuration file, then any arrays that
1340 can be found on unused devices will be assembled.
1342 If precisely one device is listed, but
1348 was given and identity information is extracted from the configuration file.
1350 The identity can be given with the
1356 option, will be taken from the md-device record in the config file, or
1357 will be taken from the super block of the first component-device
1358 listed on the command line.
1360 Devices can be given on the
1362 command line or in the config file. Only devices which have an md
1363 superblock which contains the right identity will be considered for
1366 The config file is only used if explicitly named with
1368 or requested with (a possibly implicit)
1373 .B /etc/mdadm/mdadm.conf
1378 is not given, then the config file will only be used to find the
1379 identity of md arrays.
1381 Normally the array will be started after it is assembled. However if
1383 is not given and not all expected drives were listed, then the array
1384 is not started (to guard against usage errors). To insist that the
1385 array be started in this case (as may work for RAID1, 4, 5, 6, or 10),
1394 does not create any entries in
1398 It does record information in
1399 .B /var/run/mdadm/map
1402 to choose the correct name.
1406 detects that udev is not configured, it will create the devices in
1410 In Linux kernels prior to version 2.6.28 there were two distinctly
1411 different types of md devices that could be created: one that could be
1412 partitioned using standard partitioning tools and one that could not.
1413 Since 2.6.28 that distinction is no longer relevant as both type of
1414 devices can be partitioned.
1416 will normally create the type that originally could not be partitioned
1417 as it has a well defined major number (9).
1419 Prior to 2.6.28, it is important that mdadm chooses the correct type
1420 of array device to use. This can be controlled with the
1422 option. In particular, a value of "mdp" or "part" or "p" tells mdadm
1423 to use a partitionable device rather than the default.
1425 In the no-udev case, the value given to
1427 can be suffixed by a number. This tells
1429 to create that number of partition devices rather than the default of 4.
1433 can also be given in the configuration file as a word starting
1435 on the ARRAY line for the relevant array.
1442 and no devices are listed,
1444 will first attempt to assemble all the arrays listed in the config
1447 In no array at listed in the config (other than those marked
1449 it will look through the available devices for possible arrays and
1450 will try to assemble anything that it finds. Arrays which are tagged
1451 as belonging to the given homehost will be assembled and started
1452 normally. Arrays which do not obviously belong to this host are given
1453 names that are expected not to conflict with anything local, and are
1454 started "read-auto" so that nothing is written to any device until the
1455 array is written to. i.e. automatic resync etc is delayed.
1459 finds a consistent set of devices that look like they should comprise
1460 an array, and if the superblock is tagged as belonging to the given
1461 home host, it will automatically choose a device name and try to
1462 assemble the array. If the array uses version-0.90 metadata, then the
1464 number as recorded in the superblock is used to create a name in
1468 If the array uses version-1 metadata, then the
1470 from the superblock is used to similarly create a name in
1472 (the name will have any 'host' prefix stripped first).
1474 This behaviour can be modified by the
1478 configuration file. This line can indicate that specific metadata
1479 type should, or should not, be automatically assembled. If an array
1480 is found which is not listed in
1482 and has a metadata format that is denied by the
1484 line, then it will not be assembled.
1487 line can also request that all arrays identified as being for this
1488 homehost should be assembled regardless of their metadata type.
1491 for further details.
1496 cannot find any array for the given host at all, and if
1497 .B \-\-auto\-update\-homehost
1500 will search again for any array (not just an array created for this
1501 host) and will assemble each assuming
1502 .BR \-\-update=homehost .
1503 This will change the host tag in the superblock so that on the next run,
1504 these arrays will be found without the second pass. The intention of
1505 this feature is to support transitioning a set of md arrays to using
1508 The reason for requiring arrays to be tagged with the homehost for
1509 auto assembly is to guard against problems that can arise when moving
1510 devices from one host to another.
1521 .BI \-\-raid\-devices= Z
1525 This usage is similar to
1527 The difference is that it creates an array without a superblock. With
1528 these arrays there is no difference between initially creating the array and
1529 subsequently assembling the array, except that hopefully there is useful
1530 data there in the second case.
1532 The level may raid0, linear, raid1, raid10, multipath, or faulty, or
1533 one of their synonyms. All devices must be listed and the array will
1534 be started once complete. It will often be appropriate to use
1535 .B \-\-assume\-clean
1536 with levels raid1 or raid10.
1547 .BI \-\-raid\-devices= Z
1551 This usage will initialise a new md array, associate some devices with
1552 it, and activate the array.
1554 The named device will normally not exist when
1555 .I "mdadm \-\-create"
1556 is run, but will be created by
1558 once the array becomes active.
1560 As devices are added, they are checked to see if they contain RAID
1561 superblocks or filesystems. They are also checked to see if the variance in
1562 device size exceeds 1%.
1564 If any discrepancy is found, the array will not automatically be run, though
1567 can override this caution.
1569 To create a "degraded" array in which some devices are missing, simply
1570 give the word "\fBmissing\fP"
1571 in place of a device name. This will cause
1573 to leave the corresponding slot in the array empty.
1574 For a RAID4 or RAID5 array at most one slot can be
1575 "\fBmissing\fP"; for a RAID6 array at most two slots.
1576 For a RAID1 array, only one real device needs to be given. All of the
1580 When creating a RAID5 array,
1582 will automatically create a degraded array with an extra spare drive.
1583 This is because building the spare into a degraded array is in general
1584 faster than resyncing the parity on a non-degraded, but not clean,
1585 array. This feature can be overridden with the
1589 When creating an array with version-1 metadata a name for the array is
1591 If this is not given with the
1595 will choose a name based on the last component of the name of the
1596 device being created. So if
1598 is being created, then the name
1603 is being created, then the name
1607 When creating a partition based array, using
1609 with version-1.x metadata, the partition type should be set to
1611 (non fs-data). This type selection allows for greater precision since
1612 using any other [RAID auto-detect (0xFD) or a GNU/Linux partition (0x83)],
1613 might create problems in the event of array recovery through a live cdrom.
1615 A new array will normally get a randomly assigned 128bit UUID which is
1616 very likely to be unique. If you have a specific need, you can choose
1617 a UUID for the array by giving the
1619 option. Be warned that creating two arrays with the same UUID is a
1620 recipe for disaster. Also, using
1622 when creating a v0.90 array will silently override any
1627 .\"option is given, it is not necessary to list any component-devices in this command.
1628 .\"They can be added later, before a
1632 .\"is given, the apparent size of the smallest drive given is used.
1634 When creating an array within a
1637 can be given either the list of devices to use, or simply the name of
1638 the container. The former case gives control over which devices in
1639 the container will be used for the array. The latter case allows
1641 to automatically choose which devices to use based on how much spare
1644 The General Management options that are valid with
1649 insist on running the array even if some devices look like they might
1654 start the array readonly \(em not supported yet.
1661 .I options... devices...
1664 This usage will allow individual devices in an array to be failed,
1665 removed or added. It is possible to perform multiple operations with
1666 on command. For example:
1668 .B " mdadm /dev/md0 \-f /dev/hda1 \-r /dev/hda1 \-a /dev/hda1"
1674 and will then remove it from the array and finally add it back
1675 in as a spare. However only one md array can be affected by a single
1678 When a device is added to an active array, mdadm checks to see if it
1679 has metadata on it which suggests that it was recently a member of the
1680 array. If it does, it tried to "re-add" the device. If there have
1681 been no changes since the device was removed, or if the array has a
1682 write-intent bitmap which has recorded whatever changes there were,
1683 then the device will immediately become a full member of the array and
1684 those differences recorded in the bitmap will be resolved.
1694 MISC mode includes a number of distinct operations that
1695 operate on distinct devices. The operations are:
1698 The device is examined to see if it is
1699 (1) an active md array, or
1700 (2) a component of an md array.
1701 The information discovered is reported.
1705 The device should be an active md device.
1707 will display a detailed description of the array.
1711 will cause the output to be less detailed and the format to be
1712 suitable for inclusion in
1713 .BR /etc/mdadm.conf .
1716 will normally be 0 unless
1718 failed to get useful information about the device(s); however, if the
1720 option is given, then the exit status will be:
1724 The array is functioning normally.
1727 The array has at least one failed device.
1730 The array has multiple failed devices such that it is unusable.
1733 There was an error while trying to get information about the device.
1737 .B \-\-detail\-platform
1738 Print detail of the platform's RAID capabilities (firmware / hardware
1739 topology). If the metadata is specified with
1743 then the return status will be:
1747 metadata successfully enumerated its platform components on this system
1750 metadata is platform independent
1753 metadata failed to find its platform components on this system
1758 The device should be a component of an md array.
1760 will read the md superblock of the device and display the contents.
1765 is given, then multiple devices that are components of the one array
1766 are grouped together and reported in a single entry suitable
1768 .BR /etc/mdadm.conf .
1772 without listing any devices will cause all devices listed in the
1773 config file to be examined.
1777 The devices should be active md arrays which will be deactivated, as
1778 long as they are not currently in use.
1782 This will fully activate a partially assembled md array.
1786 This will mark an active array as read-only, providing that it is
1787 not currently being used.
1793 array back to being read/write.
1797 For all operations except
1800 will cause the operation to be applied to all arrays listed in
1805 causes all devices listed in the config file to be examined.
1808 .BR \-b ", " \-\-brief
1809 Be less verbose. This is used with
1817 gives an intermediate level of verbosity.
1823 .B mdadm \-\-monitor
1824 .I options... devices...
1829 to periodically poll a number of md arrays and to report on any events
1832 will never exit once it decides that there are arrays to be checked,
1833 so it should normally be run in the background.
1835 As well as reporting events,
1837 may move a spare drive from one array to another if they are in the
1840 and if the destination array has a failed drive but no spares.
1842 If any devices are listed on the command line,
1844 will only monitor those devices. Otherwise all arrays listed in the
1845 configuration file will be monitored. Further, if
1847 is given, then any other md devices that appear in
1849 will also be monitored.
1851 The result of monitoring the arrays is the generation of events.
1852 These events are passed to a separate program (if specified) and may
1853 be mailed to a given E-mail address.
1855 When passing events to a program, the program is run once for each event,
1856 and is given 2 or 3 command-line arguments: the first is the
1857 name of the event (see below), the second is the name of the
1858 md device which is affected, and the third is the name of a related
1859 device if relevant (such as a component device that has failed).
1863 is given, then a program or an E-mail address must be specified on the
1864 command line or in the config file. If neither are available, then
1866 will not monitor anything.
1870 will continue monitoring as long as something was found to monitor. If
1871 no program or email is given, then each event is reported to
1874 The different events are:
1878 .B DeviceDisappeared
1879 An md array which previously was configured appears to no longer be
1880 configured. (syslog priority: Critical)
1884 was told to monitor an array which is RAID0 or Linear, then it will
1886 .B DeviceDisappeared
1887 with the extra information
1889 This is because RAID0 and Linear do not support the device-failed,
1890 hot-spare and resync operations which are monitored.
1894 An md array started reconstruction. (syslog priority: Warning)
1900 is a two-digit number (ie. 05, 48). This indicates that rebuild
1901 has passed that many percent of the total. The events are generated
1902 with fixed increment since 0. Increment size may be specified with
1903 a commandline option (default is 20). (syslog priority: Warning)
1907 An md array that was rebuilding, isn't any more, either because it
1908 finished normally or was aborted. (syslog priority: Warning)
1912 An active component device of an array has been marked as
1913 faulty. (syslog priority: Critical)
1917 A spare component device which was being rebuilt to replace a faulty
1918 device has failed. (syslog priority: Critical)
1922 A spare component device which was being rebuilt to replace a faulty
1923 device has been successfully rebuilt and has been made active.
1924 (syslog priority: Info)
1928 A new md array has been detected in the
1930 file. (syslog priority: Info)
1934 A newly noticed array appears to be degraded. This message is not
1937 notices a drive failure which causes degradation, but only when
1939 notices that an array is degraded when it first sees the array.
1940 (syslog priority: Critical)
1944 A spare drive has been moved from one array in a
1946 to another to allow a failed drive to be replaced.
1947 (syslog priority: Info)
1953 has been told, via the config file, that an array should have a certain
1954 number of spare devices, and
1956 detects that it has fewer than this number when it first sees the
1957 array, it will report a
1960 (syslog priority: Warning)
1964 An array was found at startup, and the
1967 (syslog priority: Info)
1977 cause Email to be sent. All events cause the program to be run.
1978 The program is run with two or three arguments: the event
1979 name, the array device and possibly a second device.
1981 Each event has an associated array device (e.g.
1983 and possibly a second device. For
1988 the second device is the relevant component device.
1991 the second device is the array that the spare was moved from.
1995 to move spares from one array to another, the different arrays need to
1996 be labeled with the same
1998 in the configuration file. The
2000 name can be any string; it is only necessary that different spare
2001 groups use different names.
2005 detects that an array in a spare group has fewer active
2006 devices than necessary for the complete array, and has no spare
2007 devices, it will look for another array in the same spare group that
2008 has a full complement of working drive and a spare. It will then
2009 attempt to remove the spare from the second drive and add it to the
2011 If the removal succeeds but the adding fails, then it is added back to
2015 The GROW mode is used for changing the size or shape of an active
2017 For this to work, the kernel must support the necessary change.
2018 Various types of growth are being added during 2.6 development,
2019 including restructuring a RAID5 array to have more active devices.
2021 Currently the only support available is to
2023 change the "size" attribute
2024 for RAID1, RAID5 and RAID6.
2026 increase or decrease the "raid\-devices" attribute of RAID1, RAID5,
2029 change the chunk-size and layout of RAID5 and RAID6.
2031 convert between RAID1 and RAID5, and between RAID5 and RAID6.
2033 add a write-intent bitmap to any array which supports these bitmaps, or
2034 remove a write-intent bitmap from such an array.
2037 GROW mode is not currently supported for
2039 or arrays inside containers.
2042 Normally when an array is built the "size" it taken from the smallest
2043 of the drives. If all the small drives in an arrays are, one at a
2044 time, removed and replaced with larger drives, then you could have an
2045 array of large drives with only a small amount used. In this
2046 situation, changing the "size" with "GROW" mode will allow the extra
2047 space to start being used. If the size is increased in this way, a
2048 "resync" process will start to make sure the new parts of the array
2051 Note that when an array changes size, any filesystem that may be
2052 stored in the array will not automatically grow to use the space. The
2053 filesystem will need to be explicitly told to use the extra space.
2055 Also the size of an array cannot be changed while it has an active
2056 bitmap. If an array has a bitmap, it must be removed before the size
2057 can be changed. Once the change it complete a new bitmap can be created.
2059 .SS RAID\-DEVICES CHANGES
2061 A RAID1 array can work with any number of devices from 1 upwards
2062 (though 1 is not very useful). There may be times which you want to
2063 increase or decrease the number of active devices. Note that this is
2064 different to hot-add or hot-remove which changes the number of
2067 When reducing the number of devices in a RAID1 array, the slots which
2068 are to be removed from the array must already be vacant. That is, the
2069 devices which were in those slots must be failed and removed.
2071 When the number of devices is increased, any hot spares that are
2072 present will be activated immediately.
2074 Changing the number of active devices in a RAID5 or RAID6 is much more
2075 effort. Every block in the array will need to be read and written
2076 back to a new location. From 2.6.17, the Linux Kernel is able to
2077 increase the number of devices in a RAID5 safely, including restarting
2078 an interrupted "reshape". From 2.6.31, the Linux Kernel is able to
2079 increase or decrease the number of devices in a RAID5 or RAID6.
2081 When decreasing the number of devices, the size of the array will also
2082 decrease. If there was data in the array, it could get destroyed and
2083 this is not reversible. To help prevent accidents,
2085 requires that the size of the array be decreased first with
2086 .BR "mdadm --grow --array-size" .
2087 This is a reversible change which simply makes the end of the array
2088 inaccessible. The integrity of any data can then be checked before
2089 the non-reversible reduction in the number of devices is request.
2091 When relocating the first few stripes on a RAID5, it is not possible
2092 to keep the data on disk completely consistent and crash-proof. To
2093 provide the required safety, mdadm disables writes to the array while
2094 this "critical section" is reshaped, and takes a backup of the data
2095 that is in that section. This backup is normally stored in any spare
2096 devices that the array has, however it can also be stored in a
2097 separate file specified with the
2099 option. If this option is used, and the system does crash during the
2100 critical period, the same file must be passed to
2102 to restore the backup and reassemble the array.
2106 Changing the RAID level of any array happens instantaneously. However
2107 in the RAID to RAID6 case this requires a non-standard layout of the
2108 RAID6 data, and in the RAID6 to RAID5 case that non-standard layout is
2109 required before the change can be accomplish. So while the level
2110 change is instant, the accompanying layout change can take quite a
2113 .SS CHUNK-SIZE AND LAYOUT CHANGES
2115 Changing the chunk-size of layout without also changing the number of
2116 devices as the same time will involve re-writing all blocks in-place.
2117 To ensure against data loss in the case of a crash, a
2119 must be provided for these changes. Small sections of the array will
2120 be copied to the backup file while they are being rearranged.
2122 If the reshape is interrupted for any reason, this backup file must be
2124 .B "mdadm --assemble"
2125 so the array can be reassembled. Consequently the file cannot be
2126 stored on the device being reshaped.
2131 A write-intent bitmap can be added to, or removed from, an active
2132 array. Either internal bitmaps, or bitmaps stored in a separate file,
2133 can be added. Note that if you add a bitmap stored in a file which is
2134 in a filesystem that is on the RAID array being affected, the system
2135 will deadlock. The bitmap must be on a separate filesystem.
2137 .SH INCREMENTAL MODE
2141 .B mdadm \-\-incremental
2147 .B mdadm \-\-incremental \-\-rebuild
2150 .B mdadm \-\-incremental \-\-run \-\-scan
2153 This mode is designed to be used in conjunction with a device
2154 discovery system. As devices are found in a system, they can be
2156 .B "mdadm \-\-incremental"
2157 to be conditionally added to an appropriate array.
2159 If the device passed is a
2161 device created by a previous call to
2163 then rather than trying to add that device to an array, all the arrays
2164 described by the metadata of the container will be started.
2167 performs a number of tests to determine if the device is part of an
2168 array, and which array it should be part of. If an appropriate array
2169 is found, or can be created,
2171 adds the device to the array and conditionally starts the array.
2175 will only add devices to an array which were previously working
2176 (active or spare) parts of that array. It does not currently support
2177 automatic inclusion of a new drive as a spare in some array.
2181 makes are as follow:
2183 Is the device permitted by
2185 That is, is it listed in a
2187 line in that file. If
2189 is absent then the default it to allow any device. Similar if
2191 contains the special word
2193 then any device is allowed. Otherwise the device name given to
2195 must match one of the names or patterns in a
2200 Does the device have a valid md superblock. If a specific metadata
2201 version is request with
2205 then only that style of metadata is accepted, otherwise
2207 finds any known version of metadata. If no
2209 metadata is found, the device is rejected.
2213 Does the metadata match an expected array?
2214 The metadata can match in two ways. Either there is an array listed
2217 which identifies the array (either by UUID, by name, by device list,
2218 or by minor-number), or the array was created with a
2224 or on the command line.
2227 is not able to positively identify the array as belonging to the
2228 current host, the device will be rejected.
2232 keeps a list of arrays that it has partially assembled in
2233 .B /var/run/mdadm/map
2235 .B /var/run/mdadm.map
2236 if the directory doesn't exist. Or maybe even
2237 .BR /dev/.mdadm.map ).
2238 If no array exists which matches
2239 the metadata on the new device,
2241 must choose a device name and unit number. It does this based on any
2244 or any name information stored in the metadata. If this name
2245 suggests a unit number, that number will be used, otherwise a free
2246 unit number will be chosen. Normally
2248 will prefer to create a partitionable array, however if the
2252 suggests that a non-partitionable array is preferred, that will be
2255 If the array is not found in the config file and its metadata does not
2256 identify it as belonging to the "homehost", then
2258 will choose a name for the array which is certain not to conflict with
2259 any array which does belong to this host. It does this be adding an
2260 underscore and a small number to the name preferred by the metadata.
2262 Once an appropriate array is found or created and the device is added,
2264 must decide if the array is ready to be started. It will
2265 normally compare the number of available (non-spare) devices to the
2266 number of devices that the metadata suggests need to be active. If
2267 there are at least that many, the array will be started. This means
2268 that if any devices are missing the array will not be restarted.
2274 in which case the array will be run as soon as there are enough
2275 devices present for the data to be accessible. For a RAID1, that
2276 means one device will start the array. For a clean RAID5, the array
2277 will be started as soon as all but one drive is present.
2279 Note that neither of these approaches is really ideal. If it can
2280 be known that all device discovery has completed, then
2284 can be run which will try to start all arrays that are being
2285 incrementally assembled. They are started in "read-auto" mode in
2286 which they are read-only until the first write request. This means
2287 that no metadata updates are made and no attempt at resync or recovery
2288 happens. Further devices that are found before the first write can
2289 still be added safely.
2292 This section describes environment variables that affect how mdadm
2297 Setting this value to 1 will prevent mdadm from automatically launching
2298 mdmon. This variable is intended primarily for debugging mdadm/mdmon.
2304 does not create any device nodes in /dev, but leaves that task to
2308 appears not to be configured, or if this environment variable is set
2311 will create and devices that are needed.
2315 .B " mdadm \-\-query /dev/name-of-device"
2317 This will find out if a given device is a RAID array, or is part of
2318 one, and will provide brief information about the device.
2320 .B " mdadm \-\-assemble \-\-scan"
2322 This will assemble and start all arrays listed in the standard config
2323 file. This command will typically go in a system startup file.
2325 .B " mdadm \-\-stop \-\-scan"
2327 This will shut down all arrays that can be shut down (i.e. are not
2328 currently in use). This will typically go in a system shutdown script.
2330 .B " mdadm \-\-follow \-\-scan \-\-delay=120"
2332 If (and only if) there is an Email address or program given in the
2333 standard config file, then
2334 monitor the status of all arrays listed in that file by
2335 polling them ever 2 minutes.
2337 .B " mdadm \-\-create /dev/md0 \-\-level=1 \-\-raid\-devices=2 /dev/hd[ac]1"
2339 Create /dev/md0 as a RAID1 array consisting of /dev/hda1 and /dev/hdc1.
2342 .B " echo 'DEVICE /dev/hd*[0\-9] /dev/sd*[0\-9]' > mdadm.conf"
2344 .B " mdadm \-\-detail \-\-scan >> mdadm.conf"
2346 This will create a prototype config file that describes currently
2347 active arrays that are known to be made from partitions of IDE or SCSI drives.
2348 This file should be reviewed before being used as it may
2349 contain unwanted detail.
2351 .B " echo 'DEVICE /dev/hd[a\-z] /dev/sd*[a\-z]' > mdadm.conf"
2353 .B " mdadm \-\-examine \-\-scan \-\-config=mdadm.conf >> mdadm.conf"
2355 This will find arrays which could be assembled from existing IDE and
2356 SCSI whole drives (not partitions), and store the information in the
2357 format of a config file.
2358 This file is very likely to contain unwanted detail, particularly
2361 entries. It should be reviewed and edited before being used as an
2364 .B " mdadm \-\-examine \-\-brief \-\-scan \-\-config=partitions"
2366 .B " mdadm \-Ebsc partitions"
2368 Create a list of devices by reading
2369 .BR /proc/partitions ,
2370 scan these for RAID superblocks, and printout a brief listing of all
2373 .B " mdadm \-Ac partitions \-m 0 /dev/md0"
2375 Scan all partitions and devices listed in
2376 .BR /proc/partitions
2379 out of all such devices with a RAID superblock with a minor number of 0.
2381 .B " mdadm \-\-monitor \-\-scan \-\-daemonise > /var/run/mdadm"
2383 If config file contains a mail address or alert program, run mdadm in
2384 the background in monitor mode monitoring all md devices. Also write
2385 pid of mdadm daemon to
2386 .BR /var/run/mdadm .
2388 .B " mdadm \-Iq /dev/somedevice"
2390 Try to incorporate newly discovered device into some array as
2393 .B " mdadm \-\-incremental \-\-rebuild \-\-run \-\-scan"
2395 Rebuild the array map from any current arrays, and then start any that
2398 .B " mdadm /dev/md4 --fail detached --remove detached"
2400 Any devices which are components of /dev/md4 will be marked as faulty
2401 and then remove from the array.
2403 .B " mdadm --grow /dev/md4 --level=6 --backup-file=/root/backup-md4
2407 which is currently a RAID5 array will be converted to RAID6. There
2408 should normally already be a spare drive attached to the array as a
2409 RAID6 needs one more drive than a matching RAID5.
2411 .B " mdadm --create /dev/md/ddf --metadata=ddf --raid-disks 6 /dev/sd[a-f]"
2413 Create a DDF array over 6 devices.
2415 .B " mdadm --create /dev/md/home -n3 -l5 -z 30000000 /dev/md/ddf"
2417 Create a RAID5 array over any 3 devices in the given DDF set. Use
2418 only 30 gigabytes of each device.
2420 .B " mdadm -A /dev/md/ddf1 /dev/sd[a-f]"
2422 Assemble a pre-exist ddf array.
2424 .B " mdadm -I /dev/md/ddf1"
2426 Assemble all arrays contained in the ddf array, assigning names as
2429 .B " mdadm \-\-create \-\-help"
2431 Provide help about the Create mode.
2433 .B " mdadm \-\-config \-\-help"
2435 Provide help about the format of the config file.
2437 .B " mdadm \-\-help"
2439 Provide general help.
2449 lists all active md devices with information about them.
2451 uses this to find arrays when
2453 is given in Misc mode, and to monitor array reconstruction
2458 The config file lists which devices may be scanned to see if
2459 they contain MD super block, and gives identifying information
2460 (e.g. UUID) about known MD arrays. See
2464 .SS /var/run/mdadm/map
2467 mode is used, this file gets a list of arrays currently being created.
2470 does not exist as a directory, then
2471 .B /var/run/mdadm.map
2474 is not available (as may be the case during early boot),
2476 is used on the basis that
2478 is usually available very early in boot.
2483 understand two sorts of names for array devices.
2485 The first is the so-called 'standard' format name, which matches the
2486 names used by the kernel and which appear in
2489 The second sort can be freely chosen, but must reside in
2491 When giving a device name to
2493 to create or assemble an array, either full path name such as
2497 can be given, or just the suffix of the second sort of name, such as
2503 chooses device names during auto-assembly or incremental assembly, it
2504 will sometimes add a small sequence number to the end of the name to
2505 avoid conflicted between multiple arrays that have the same name. If
2507 can reasonably determine that the array really is meant for this host,
2508 either by a hostname in the metadata, or by the presence of the array
2509 in /etc/mdadm.conf, then it will leave off the suffix if possible.
2510 Also if the homehost is specified as
2513 will only use a suffix if a different array of the same name already
2514 exists or is listed in the config file.
2516 The standard names for non-partitioned arrays (the only sort of md
2517 array available in 2.4 and earlier) are of the form
2521 where NN is a number.
2522 The standard names for partitionable arrays (as available from 2.6
2523 onwards) are of the form
2527 Partition numbers should be indicated by added "pMM" to these, thus "/dev/md/d1p2".
2529 From kernel version, 2.6.28 the "non-partitioned array" can actually
2530 be partitioned. So the "md_dNN" names are no longer needed, and
2531 partitions such as "/dev/mdNNpXX" are possible.
2535 was previously known as
2539 is completely separate from the
2541 package, and does not use the
2543 configuration file at all.
2546 For further information on mdadm usage, MD and the various levels of
2549 .B http://linux\-raid.osdl.org/
2551 (based upon Jakob \(/Ostergaard's Software\-RAID.HOWTO)
2553 .\"for new releases of the RAID driver check out:
2556 .\".UR ftp://ftp.kernel.org/pub/linux/kernel/people/mingo/raid-patches
2557 .\"ftp://ftp.kernel.org/pub/linux/kernel/people/mingo/raid-patches
2562 .\".UR http://www.cse.unsw.edu.au/~neilb/patches/linux-stable/
2563 .\"http://www.cse.unsw.edu.au/~neilb/patches/linux-stable/
2566 The latest version of
2568 should always be available from
2570 .B http://www.kernel.org/pub/linux/utils/raid/mdadm/
projects / thirdparty / mdadm.git / blob