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
304 and to guess for other operations.
305 The default can be overridden by setting the
315 Use the original 0.90 format superblock. This format limits arrays to
316 28 component devices and limits component devices of levels 1 and
317 greater to 2 terabytes.
318 .IP "1, 1.0, 1.1, 1.2 default"
319 Use the new version-1 format superblock. This has few restrictions.
320 The different sub-versions store the superblock at different locations
321 on the device, either at the end (for 1.0), at the start (for 1.1) or
322 4K from the start (for 1.2). '1' is equivalent to '1.0', 'default' is
325 Use the "Industry Standard" DDF (Disk Data Format) format defined by
327 When creating a DDF array a
329 will be created, and normal arrays can be created in that container.
331 Use the Intel(R) Matrix Storage Manager metadata format. This creates a
333 which is managed in a similar manner to DDF, and is supported by an
334 option-rom on some platforms:
336 .B http://www.intel.com/design/chipsets/matrixstorage_sb.htm
342 This will override any
344 setting in the config file and provides the identity of the host which
345 should be considered the home for any arrays.
347 When creating an array, the
349 will be recorded in the metadata. For version-1 superblocks, it will
350 be prefixed to the array name. For version-0.90 superblocks, part of
351 the SHA1 hash of the hostname will be stored in the later half of the
354 When reporting information about an array, any array which is tagged
355 for the given homehost will be reported as such.
357 When using Auto-Assemble, only arrays tagged for the given homehost
358 will be allowed to use 'local' names (i.e. not ending in '_' followed
359 by a digit string). See below under
360 .BR "Auto Assembly" .
362 .SH For create, build, or grow:
365 .BR \-n ", " \-\-raid\-devices=
366 Specify the number of active devices in the array. This, plus the
367 number of spare devices (see below) must equal the number of
369 (including "\fBmissing\fP" devices)
370 that are listed on the command line for
372 Setting a value of 1 is probably
373 a mistake and so requires that
375 be specified first. A value of 1 will then be allowed for linear,
376 multipath, RAID0 and RAID1. It is never allowed for RAID4, RAID5 or RAID6.
378 This number can only be changed using
380 for RAID1, RAID4, RAID5 and RAID6 arrays, and only on kernels which provide
381 the necessary support.
384 .BR \-x ", " \-\-spare\-devices=
385 Specify the number of spare (eXtra) devices in the initial array.
386 Spares can also be added
387 and removed later. The number of component devices listed
388 on the command line must equal the number of RAID devices plus the
389 number of spare devices.
392 .BR \-z ", " \-\-size=
393 Amount (in Kibibytes) of space to use from each drive in RAID levels 1/4/5/6.
394 This must be a multiple of the chunk size, and must leave about 128Kb
395 of space at the end of the drive for the RAID superblock.
396 If this is not specified
397 (as it normally is not) the smallest drive (or partition) sets the
398 size, though if there is a variance among the drives of greater than 1%, a warning is
401 This value can be set with
403 for RAID level 1/4/5/6. If the array was created with a size smaller
404 than the currently active drives, the extra space can be accessed
407 The size can be given as
409 which means to choose the largest size that fits on all current drives.
411 This value can not be used with
413 metadata such as DDF and IMSM.
416 .BR \-Z ", " \-\-array-size=
417 This is only meaningful with
419 and its effect is not persistent: when the array is stopped an
420 restarted the default array size will be restored.
422 Setting the array-size causes the array to appear smaller to programs
423 that access the data. This is particularly needed before reshaping an
424 array so that it will be smaller. As the reshape is not reversible,
425 but setting the size with
427 is, it is required that the array size is reduced as appropriate
428 before the number of devices in the array is reduced.
431 .BR \-c ", " \-\-chunk=
432 Specify chunk size of kibibytes. The default when creating an
433 array is 512KB. To ensure compatibility with earlier versions, the
434 default when Building and array with no persistent metadata is 64KB.
435 This is only meaningful for RAID0, RAID4, RAID5, RAID6, and RAID10.
439 Specify rounding factor for a Linear array. The size of each
440 component will be rounded down to a multiple of this size.
441 This is a synonym for
443 but highlights the different meaning for Linear as compared to other
444 RAID levels. The default is 64K if a kernel earlier than 2.6.16 is in
445 use, and is 0K (i.e. no rounding) in later kernels.
448 .BR \-l ", " \-\-level=
449 Set RAID level. When used with
451 options are: linear, raid0, 0, stripe, raid1, 1, mirror, raid4, 4,
452 raid5, 5, raid6, 6, raid10, 10, multipath, mp, faulty, container.
453 Obviously some of these are synonymous.
457 metadata type is requested, only the
459 level is permitted, and it does not need to be explicitly given.
463 only linear, stripe, raid0, 0, raid1, multipath, mp, and faulty are valid.
465 Not yet supported with
469 .BR \-p ", " \-\-layout=
470 This option configures the fine details of data layout for RAID5, RAID6,
471 and RAID10 arrays, and controls the failure modes for
474 The layout of the RAID5 parity block can be one of
475 .BR left\-asymmetric ,
476 .BR left\-symmetric ,
477 .BR right\-asymmetric ,
478 .BR right\-symmetric ,
479 .BR la ", " ra ", " ls ", " rs .
481 .BR left\-symmetric .
483 It is also possibly to cause RAID5 to use a RAID4-like layout by
489 Finally for RAID5 there are DDF\-compatible layouts,
490 .BR ddf\-zero\-restart ,
491 .BR ddf\-N\-restart ,
493 .BR ddf\-N\-continue .
495 These same layouts are available for RAID6. There are also 4 layouts
496 that will provide an intermediate stage for converting between RAID5
497 and RAID6. These provide a layout which is identical to the
498 corresponding RAID5 layout on the first N\-1 devices, and has the 'Q'
499 syndrome (the second 'parity' block used by RAID6) on the last device.
501 .BR left\-symmetric\-6 ,
502 .BR right\-symmetric\-6 ,
503 .BR left\-asymmetric\-6 ,
504 .BR right\-asymmetric\-6 ,
506 .BR parity\-first\-6 .
508 When setting the failure mode for level
511 .BR write\-transient ", " wt ,
512 .BR read\-transient ", " rt ,
513 .BR write\-persistent ", " wp ,
514 .BR read\-persistent ", " rp ,
516 .BR read\-fixable ", " rf ,
517 .BR clear ", " flush ", " none .
519 Each failure mode can be followed by a number, which is used as a period
520 between fault generation. Without a number, the fault is generated
521 once on the first relevant request. With a number, the fault will be
522 generated after that many requests, and will continue to be generated
523 every time the period elapses.
525 Multiple failure modes can be current simultaneously by using the
527 option to set subsequent failure modes.
529 "clear" or "none" will remove any pending or periodic failure modes,
530 and "flush" will clear any persistent faults.
532 Finally, the layout options for RAID10 are one of 'n', 'o' or 'f' followed
533 by a small number. The default is 'n2'. The supported options are:
536 signals 'near' copies. Multiple copies of one data block are at
537 similar offsets in different devices.
540 signals 'offset' copies. Rather than the chunks being duplicated
541 within a stripe, whole stripes are duplicated but are rotated by one
542 device so duplicate blocks are on different devices. Thus subsequent
543 copies of a block are in the next drive, and are one chunk further
548 (multiple copies have very different offsets).
549 See md(4) for more detail about 'near', 'offset', and 'far'.
551 The number is the number of copies of each datablock. 2 is normal, 3
552 can be useful. This number can be at most equal to the number of
553 devices in the array. It does not need to divide evenly into that
554 number (e.g. it is perfectly legal to have an 'n2' layout for an array
555 with an odd number of devices).
557 When an array is converted between RAID5 and RAID6 an intermediate
558 RAID6 layout is used in which the second parity block (Q) is always on
559 the last device. To convert a RAID5 to RAID6 and leave it in this new
560 layout (which does not require re-striping) use
561 .BR \-\-layout=preserve .
562 This will try to avoid any restriping.
564 The converse of this is
565 .B \-\-layout=normalise
566 which will change a non-standard RAID6 layout into a more standard
573 (thus explaining the p of
577 .BR \-b ", " \-\-bitmap=
578 Specify a file to store a write-intent bitmap in. The file should not
581 is also given. The same file should be provided
582 when assembling the array. If the word
584 is given, then the bitmap is stored with the metadata on the array,
585 and so is replicated on all devices. If the word
589 mode, then any bitmap that is present is removed.
591 To help catch typing errors, the filename must contain at least one
592 slash ('/') if it is a real file (not 'internal' or 'none').
594 Note: external bitmaps are only known to work on ext2 and ext3.
595 Storing bitmap files on other filesystems may result in serious problems.
598 .BR \-\-bitmap\-chunk=
599 Set the chunksize of the bitmap. Each bit corresponds to that many
600 Kilobytes of storage.
601 When using a file based bitmap, the default is to use the smallest
602 size that is at-least 4 and requires no more than 2^21 chunks.
605 bitmap, the chunksize defaults to 64Meg, or larger if necessary to
606 fit the bitmap into the available space.
609 .BR \-W ", " \-\-write\-mostly
610 subsequent devices listed in a
615 command will be flagged as 'write-mostly'. This is valid for RAID1
616 only and means that the 'md' driver will avoid reading from these
617 devices if at all possible. This can be useful if mirroring over a
621 .BR \-\-write\-behind=
622 Specify that write-behind mode should be enabled (valid for RAID1
623 only). If an argument is specified, it will set the maximum number
624 of outstanding writes allowed. The default value is 256.
625 A write-intent bitmap is required in order to use write-behind
626 mode, and write-behind is only attempted on drives marked as
630 .BR \-\-assume\-clean
633 that the array pre-existed and is known to be clean. It can be useful
634 when trying to recover from a major failure as you can be sure that no
635 data will be affected unless you actually write to the array. It can
636 also be used when creating a RAID1 or RAID10 if you want to avoid the
637 initial resync, however this practice \(em while normally safe \(em is not
638 recommended. Use this only if you really know what you are doing.
640 When the devices that will be part of a new array were filled
641 with zeros before creation the operator knows the array is
642 actually clean. If that is the case, such as after running
643 badblocks, this argument can be used to tell mdadm the
644 facts the operator knows.
647 .BR \-\-backup\-file=
650 is used to increase the number of
651 raid-devices in a RAID5 if there are no spare devices available.
652 See the GROW MODE section below on RAID\-DEVICES CHANGES. The file
653 should be stored on a separate device, not on the RAID array being
657 .BR \-\-array-size= ", " \-Z
658 Set the size of the array which is seen by users of the device such as
659 filesystems. This can be less that the real size, but never greater.
660 The size set this way does not persist across restarts of the array.
662 This is most useful when reducing the number of devices in a RAID5 or
663 RAID6. Such arrays require the array-size to be reduced before a
664 reshape can be performed that reduces the real size.
668 restores the apparent size of the array to be whatever the real
669 amount of available space is.
672 .BR \-N ", " \-\-name=
675 for the array. This is currently only effective when creating an
676 array with a version-1 superblock, or an array in a DDF container.
677 The name is a simple textual string that can be used to identify array
678 components when assembling. If name is needed but not specified, it
679 is taken from the basename of the device that is being created.
691 run the array, even if some of the components
692 appear to be active in another array or filesystem. Normally
694 will ask for confirmation before including such components in an
695 array. This option causes that question to be suppressed.
698 .BR \-f ", " \-\-force
701 accept the geometry and layout specified without question. Normally
703 will not allow creation of an array with only one device, and will try
704 to create a RAID5 array with one missing drive (as this makes the
705 initial resync work faster). With
708 will not try to be so clever.
711 .BR \-a ", " "\-\-auto{=yes,md,mdp,part,p}{NN}"
712 Instruct mdadm how to create the device file if needed, possibly allocating
713 an unused minor number. "md" causes a non-partitionable array
714 to be used (though since Linux 2.6.28, these array devices are in fact
715 partitionable). "mdp", "part" or "p" causes a partitionable array (2.6 and
716 later) to be used. "yes" requires the named md device to have
717 a 'standard' format, and the type and minor number will be determined
718 from this. With mdadm 3.0, device creation is normally left up to
720 so this option is unlikely to be needed.
721 See DEVICE NAMES below.
723 The argument can also come immediately after
728 is not given on the command line or in the config file, then
734 is also given, then any
736 entries in the config file will override the
738 instruction given on the command line.
740 For partitionable arrays,
742 will create the device file for the whole array and for the first 4
743 partitions. A different number of partitions can be specified at the
744 end of this option (e.g.
746 If the device name ends with a digit, the partition names add a 'p',
748 .IR /dev/md/home1p3 .
749 If there is no trailing digit, then the partition names just have a
751 .IR /dev/md/scratch3 .
753 If the md device name is in a 'standard' format as described in DEVICE
754 NAMES, then it will be created, if necessary, with the appropriate
755 device number based on that name. If the device name is not in one of these
756 formats, then a unused device number will be allocated. The device
757 number will be considered unused if there is no active array for that
758 number, and there is no entry in /dev for that number and with a
759 non-standard name. Names that are not in 'standard' format are only
760 allowed in "/dev/md/".
764 .\".BR \-\-symlink = no
769 .\"to create devices in
771 .\"it will also create symlinks from
773 .\"with names starting with
779 .\"to suppress this, or
780 .\".B \-\-symlink=yes
781 .\"to enforce this even if it is suppressing
789 .BR \-u ", " \-\-uuid=
790 uuid of array to assemble. Devices which don't have this uuid are
794 .BR \-m ", " \-\-super\-minor=
795 Minor number of device that array was created for. Devices which
796 don't have this minor number are excluded. If you create an array as
797 /dev/md1, then all superblocks will contain the minor number 1, even if
798 the array is later assembled as /dev/md2.
800 Giving the literal word "dev" for
804 to use the minor number of the md device that is being assembled.
807 .B \-\-super\-minor=dev
808 will look for super blocks with a minor number of 0.
811 is only relevant for v0.90 metadata, and should not normally be used.
817 .BR \-N ", " \-\-name=
818 Specify the name of the array to assemble. This must be the name
819 that was specified when creating the array. It must either match
820 the name stored in the superblock exactly, or it must match
823 prefixed to the start of the given name.
826 .BR \-f ", " \-\-force
827 Assemble the array even if the metadata on some devices appears to be
830 cannot find enough working devices to start the array, but can find
831 some devices that are recorded as having failed, then it will mark
832 those devices as working so that the array can be started.
833 An array which requires
835 to be started may contain data corruption. Use it carefully.
839 Attempt to start the array even if fewer drives were given than were
840 present last time the array was active. Normally if not all the
841 expected drives are found and
843 is not used, then the array will be assembled but not started.
846 an attempt will be made to start it anyway.
850 This is the reverse of
852 in that it inhibits the startup of array unless all expected drives
853 are present. This is only needed with
855 and can be used if the physical connections to devices are
856 not as reliable as you would like.
859 .BR \-a ", " "\-\-auto{=no,yes,md,mdp,part}"
860 See this option under Create and Build options.
863 .BR \-b ", " \-\-bitmap=
864 Specify the bitmap file that was given when the array was created. If
867 bitmap, there is no need to specify this when assembling the array.
870 .BR \-\-backup\-file=
873 was used to grow the number of raid-devices in a RAID5, and the system
874 crashed during the critical section, then the same
878 to allow possibly corrupted data to be restored.
881 .BR \-U ", " \-\-update=
882 Update the superblock on each device while assembling the array. The
883 argument given to this flag can be one of
897 option will adjust the superblock of an array what was created on a Sparc
898 machine running a patched 2.2 Linux kernel. This kernel got the
899 alignment of part of the superblock wrong. You can use the
900 .B "\-\-examine \-\-sparc2.2"
903 to see what effect this would have.
907 option will update the
909 field on each superblock to match the minor number of the array being
911 This can be useful if
913 reports a different "Preferred Minor" to
915 In some cases this update will be performed automatically
916 by the kernel driver. In particular the update happens automatically
917 at the first write to an array with redundancy (RAID level 1 or
918 greater) on a 2.6 (or later) kernel.
922 option will change the uuid of the array. If a UUID is given with the
924 option that UUID will be used as a new UUID and will
926 be used to help identify the devices in the array.
929 is given, a random UUID is chosen.
933 option will change the
935 of the array as stored in the superblock. This is only supported for
936 version-1 superblocks.
940 option will change the
942 as recorded in the superblock. For version-0 superblocks, this is the
943 same as updating the UUID.
944 For version-1 superblocks, this involves updating the name.
948 option will cause the array to be marked
950 meaning that any redundancy in the array (e.g. parity for RAID5,
951 copies for RAID1) may be incorrect. This will cause the RAID system
952 to perform a "resync" pass to make sure that all redundant information
957 option allows arrays to be moved between machines with different
959 When assembling such an array for the first time after a move, giving
960 .B "\-\-update=byteorder"
963 to expect superblocks to have their byteorder reversed, and will
964 correct that order before assembling the array. This is only valid
965 with original (Version 0.90) superblocks.
969 option will correct the summaries in the superblock. That is the
970 counts of total, working, active, failed, and spare devices.
974 will rarely be of use. It applies to version 1.1 and 1.2 metadata
975 only (where the metadata is at the start of the device) and is only
976 useful when the component device has changed size (typically become
977 larger). The version 1 metadata records the amount of the device that
978 can be used to store data, so if a device in a version 1.1 or 1.2
979 array becomes larger, the metadata will still be visible, but the
980 extra space will not. In this case it might be useful to assemble the
982 .BR \-\-update=devicesize .
985 to determine the maximum usable amount of space on each device and
986 update the relevant field in the metadata.
990 .B \-\-auto\-update\-homehost
991 This flag is only meaningful with auto-assembly (see discussion below).
992 In that situation, if no suitable arrays are found for this homehost,
994 will rescan for any arrays at all and will assemble them and update the
995 homehost to match the current host.
1001 .BR \-a ", " \-\-add
1002 hot-add listed devices. For arrays with redundancy, the listed
1003 devices become available as spares. If the array is degraded, it will
1004 immediately start recovering data on to one of these spares.
1008 re-add a device that was recently removed from an array. This is only
1009 needed for arrays that have be built (i.e. with
1011 For created arrays, devices are always re-added if that is possible.
1012 When re-adding a device, if nothing has changed on the array since the
1013 device was removed, no recovery is performed. Also, if the array has
1014 a write-intent bitmap, then the recovery performed after a re-add will
1015 be limited to those blocks which, according to the bitmap, might have
1016 changed since the device was removed.
1019 .BR \-r ", " \-\-remove
1020 remove listed devices. They must not be active. i.e. they should
1021 be failed or spare devices. As well as the name of a device file
1030 The first causes all failed device to be removed. The second causes
1031 any device which is no longer connected to the system (i.e an 'open'
1034 to be removed. This will only succeed for devices that are spares or
1035 have already been marked as failed.
1038 .BR \-f ", " \-\-fail
1039 mark listed devices as faulty.
1040 As well as the name of a device file, the word
1042 can be given. This will cause any device that has been detached from
1043 the system to be marked as failed. It can then be removed.
1051 .BR \-\-write\-mostly
1052 Subsequent devices that are added or re-added will have the 'write-mostly'
1053 flag set. This is only valid for RAID1 and means that the 'md' driver
1054 will avoid reading from these devices if possible.
1057 Subsequent devices that are added or re-added will have the 'write-mostly'
1061 Each of these options requires that the first device listed is the array
1062 to be acted upon, and the remainder are component devices to be added,
1063 removed, marked as faulty, etc. Several different operations can be
1064 specified for different devices, e.g.
1066 mdadm /dev/md0 \-\-add /dev/sda1 \-\-fail /dev/sdb1 \-\-remove /dev/sdb1
1068 Each operation applies to all devices listed until the next
1071 If an array is using a write-intent bitmap, then devices which have
1072 been removed can be re-added in a way that avoids a full
1073 reconstruction but instead just updates the blocks that have changed
1074 since the device was removed. For arrays with persistent metadata
1075 (superblocks) this is done automatically. For arrays created with
1077 mdadm needs to be told that this device we removed recently with
1080 Devices can only be removed from an array if they are not in active
1081 use, i.e. that must be spares or failed devices. To remove an active
1082 device, it must first be marked as
1088 .BR \-Q ", " \-\-query
1089 Examine a device to see
1090 (1) if it is an md device and (2) if it is a component of an md
1092 Information about what is discovered is presented.
1095 .BR \-D ", " \-\-detail
1096 Print details of one or more md devices.
1099 .BR \-\-detail\-platform
1100 Print details of the platform's RAID capabilities (firmware / hardware
1101 topology) for a given metadata format.
1104 .BR \-Y ", " \-\-export
1109 output will be formatted as
1111 pairs for easy import into the environment.
1114 .BR \-E ", " \-\-examine
1115 Print contents of the metadata stored on the named device(s).
1116 Note the contrast between
1121 applies to devices which are components of an array, while
1123 applies to a whole array which is currently active.
1126 If an array was created on a SPARC machine with a 2.2 Linux kernel
1127 patched with RAID support, the superblock will have been created
1128 incorrectly, or at least incompatibly with 2.4 and later kernels.
1133 will fix the superblock before displaying it. If this appears to do
1134 the right thing, then the array can be successfully assembled using
1135 .BR "\-\-assemble \-\-update=sparc2.2" .
1138 .BR \-X ", " \-\-examine\-bitmap
1139 Report information about a bitmap file.
1140 The argument is either an external bitmap file or an array component
1141 in case of an internal bitmap. Note that running this on an array
1144 does not report the bitmap for that array.
1147 .BR \-R ", " \-\-run
1148 start a partially assembled array. If
1150 did not find enough devices to fully start the array, it might leaving
1151 it partially assembled. If you wish, you can then use
1153 to start the array in degraded mode.
1156 .BR \-S ", " \-\-stop
1157 deactivate array, releasing all resources.
1160 .BR \-o ", " \-\-readonly
1161 mark array as readonly.
1164 .BR \-w ", " \-\-readwrite
1165 mark array as readwrite.
1168 .B \-\-zero\-superblock
1169 If the device contains a valid md superblock, the block is
1170 overwritten with zeros. With
1172 the block where the superblock would be is overwritten even if it
1173 doesn't appear to be valid.
1176 .B \-\-kill\-subarray=
1177 If the device is a container and the argument to \-\-kill\-subarray
1178 specifies an inactive subarray in the container, then the subarray is
1179 deleted. Deleting all subarrays will leave an 'empty-container' or
1180 spare superblock on the drives. See \-\-zero\-superblock for completely
1181 removing a superblock. Note that some formats depend on the subarray
1182 index for generating a UUID, this command will fail if it would change
1183 the UUID of an active subarray.
1186 .BR \-t ", " \-\-test
1191 is set to reflect the status of the device. See below in
1196 .BR \-W ", " \-\-wait
1197 For each md device given, wait for any resync, recovery, or reshape
1198 activity to finish before returning.
1200 will return with success if it actually waited for every device
1201 listed, otherwise it will return failure.
1205 For each md device given, or each device in /proc/mdstat if
1207 is given, arrange for the array to be marked clean as soon as possible.
1208 Also, quiesce resync so that the monitor for external metadata arrays
1209 (mdmon) has an opportunity to checkpoint the resync position.
1211 will return with success if the array uses external metadata and we
1212 successfully waited. For native arrays this returns immediately as the
1213 kernel handles both dirty-clean transitions and resync checkpointing in
1214 the kernel at shutdown. No action is taken if safe-mode handling is
1217 .SH For Incremental Assembly mode:
1219 .BR \-\-rebuild\-map ", " \-r
1220 Rebuild the map file
1221 .RB ( /var/run/mdadm/map )
1224 uses to help track which arrays are currently being assembled.
1227 .BR \-\-run ", " \-R
1228 Run any array assembled as soon as a minimal number of devices are
1229 available, rather than waiting until all expected devices are present.
1233 This allows the hot-plug system to prevent arrays from running when it knows
1234 that more disks may arrive later in the discovery process.
1237 .BR \-\-scan ", " \-s
1238 Only meaningful with
1242 file for arrays that are being incrementally assembled and will try to
1243 start any that are not already started. If any such array is listed
1246 as requiring an external bitmap, that bitmap will be attached first.
1248 .SH For Monitor mode:
1250 .BR \-m ", " \-\-mail
1251 Give a mail address to send alerts to.
1254 .BR \-p ", " \-\-program ", " \-\-alert
1255 Give a program to be run whenever an event is detected.
1258 .BR \-y ", " \-\-syslog
1259 Cause all events to be reported through 'syslog'. The messages have
1260 facility of 'daemon' and varying priorities.
1263 .BR \-d ", " \-\-delay
1264 Give a delay in seconds.
1266 polls the md arrays and then waits this many seconds before polling
1267 again. The default is 60 seconds. Since 2.6.16, there is no need to
1268 reduce this as the kernel alerts
1270 immediately when there is any change.
1273 .BR \-r ", " \-\-increment
1274 Give a percentage increment.
1276 will generate RebuildNN events with the given percentage increment.
1279 .BR \-f ", " \-\-daemonise
1282 to run as a background daemon if it decides to monitor anything. This
1283 causes it to fork and run in the child, and to disconnect from the
1284 terminal. The process id of the child is written to stdout.
1287 which will only continue monitoring if a mail address or alert program
1288 is found in the config file.
1291 .BR \-i ", " \-\-pid\-file
1294 is running in daemon mode, write the pid of the daemon process to
1295 the specified file, instead of printing it on standard output.
1298 .BR \-1 ", " \-\-oneshot
1299 Check arrays only once. This will generate
1301 events and more significantly
1307 .B " mdadm \-\-monitor \-\-scan \-1"
1309 from a cron script will ensure regular notification of any degraded arrays.
1312 .BR \-t ", " \-\-test
1315 alert for every array found at startup. This alert gets mailed and
1316 passed to the alert program. This can be used for testing that alert
1317 message do get through successfully.
1323 .B mdadm \-\-assemble
1324 .I md-device options-and-component-devices...
1327 .B mdadm \-\-assemble \-\-scan
1328 .I md-devices-and-options...
1331 .B mdadm \-\-assemble \-\-scan
1335 This usage assembles one or more RAID arrays from pre-existing components.
1336 For each array, mdadm needs to know the md device, the identity of the
1337 array, and a number of component-devices. These can be found in a number of ways.
1339 In the first usage example (without the
1341 the first device given is the md device.
1342 In the second usage example, all devices listed are treated as md
1343 devices and assembly is attempted.
1344 In the third (where no devices are listed) all md devices that are
1345 listed in the configuration file are assembled. If not arrays are
1346 described by the configuration file, then any arrays that
1347 can be found on unused devices will be assembled.
1349 If precisely one device is listed, but
1355 was given and identity information is extracted from the configuration file.
1357 The identity can be given with the
1363 option, will be taken from the md-device record in the config file, or
1364 will be taken from the super block of the first component-device
1365 listed on the command line.
1367 Devices can be given on the
1369 command line or in the config file. Only devices which have an md
1370 superblock which contains the right identity will be considered for
1373 The config file is only used if explicitly named with
1375 or requested with (a possibly implicit)
1380 .B /etc/mdadm/mdadm.conf
1385 is not given, then the config file will only be used to find the
1386 identity of md arrays.
1388 Normally the array will be started after it is assembled. However if
1390 is not given and not all expected drives were listed, then the array
1391 is not started (to guard against usage errors). To insist that the
1392 array be started in this case (as may work for RAID1, 4, 5, 6, or 10),
1401 does not create any entries in
1405 It does record information in
1406 .B /var/run/mdadm/map
1409 to choose the correct name.
1413 detects that udev is not configured, it will create the devices in
1417 In Linux kernels prior to version 2.6.28 there were two distinctly
1418 different types of md devices that could be created: one that could be
1419 partitioned using standard partitioning tools and one that could not.
1420 Since 2.6.28 that distinction is no longer relevant as both type of
1421 devices can be partitioned.
1423 will normally create the type that originally could not be partitioned
1424 as it has a well defined major number (9).
1426 Prior to 2.6.28, it is important that mdadm chooses the correct type
1427 of array device to use. This can be controlled with the
1429 option. In particular, a value of "mdp" or "part" or "p" tells mdadm
1430 to use a partitionable device rather than the default.
1432 In the no-udev case, the value given to
1434 can be suffixed by a number. This tells
1436 to create that number of partition devices rather than the default of 4.
1440 can also be given in the configuration file as a word starting
1442 on the ARRAY line for the relevant array.
1449 and no devices are listed,
1451 will first attempt to assemble all the arrays listed in the config
1454 In no array at listed in the config (other than those marked
1456 it will look through the available devices for possible arrays and
1457 will try to assemble anything that it finds. Arrays which are tagged
1458 as belonging to the given homehost will be assembled and started
1459 normally. Arrays which do not obviously belong to this host are given
1460 names that are expected not to conflict with anything local, and are
1461 started "read-auto" so that nothing is written to any device until the
1462 array is written to. i.e. automatic resync etc is delayed.
1466 finds a consistent set of devices that look like they should comprise
1467 an array, and if the superblock is tagged as belonging to the given
1468 home host, it will automatically choose a device name and try to
1469 assemble the array. If the array uses version-0.90 metadata, then the
1471 number as recorded in the superblock is used to create a name in
1475 If the array uses version-1 metadata, then the
1477 from the superblock is used to similarly create a name in
1479 (the name will have any 'host' prefix stripped first).
1481 This behaviour can be modified by the
1485 configuration file. This line can indicate that specific metadata
1486 type should, or should not, be automatically assembled. If an array
1487 is found which is not listed in
1489 and has a metadata format that is denied by the
1491 line, then it will not be assembled.
1494 line can also request that all arrays identified as being for this
1495 homehost should be assembled regardless of their metadata type.
1498 for further details.
1503 cannot find any array for the given host at all, and if
1504 .B \-\-auto\-update\-homehost
1507 will search again for any array (not just an array created for this
1508 host) and will assemble each assuming
1509 .BR \-\-update=homehost .
1510 This will change the host tag in the superblock so that on the next run,
1511 these arrays will be found without the second pass. The intention of
1512 this feature is to support transitioning a set of md arrays to using
1515 The reason for requiring arrays to be tagged with the homehost for
1516 auto assembly is to guard against problems that can arise when moving
1517 devices from one host to another.
1528 .BI \-\-raid\-devices= Z
1532 This usage is similar to
1534 The difference is that it creates an array without a superblock. With
1535 these arrays there is no difference between initially creating the array and
1536 subsequently assembling the array, except that hopefully there is useful
1537 data there in the second case.
1539 The level may raid0, linear, raid1, raid10, multipath, or faulty, or
1540 one of their synonyms. All devices must be listed and the array will
1541 be started once complete. It will often be appropriate to use
1542 .B \-\-assume\-clean
1543 with levels raid1 or raid10.
1554 .BI \-\-raid\-devices= Z
1558 This usage will initialise a new md array, associate some devices with
1559 it, and activate the array.
1561 The named device will normally not exist when
1562 .I "mdadm \-\-create"
1563 is run, but will be created by
1565 once the array becomes active.
1567 As devices are added, they are checked to see if they contain RAID
1568 superblocks or filesystems. They are also checked to see if the variance in
1569 device size exceeds 1%.
1571 If any discrepancy is found, the array will not automatically be run, though
1574 can override this caution.
1576 To create a "degraded" array in which some devices are missing, simply
1577 give the word "\fBmissing\fP"
1578 in place of a device name. This will cause
1580 to leave the corresponding slot in the array empty.
1581 For a RAID4 or RAID5 array at most one slot can be
1582 "\fBmissing\fP"; for a RAID6 array at most two slots.
1583 For a RAID1 array, only one real device needs to be given. All of the
1587 When creating a RAID5 array,
1589 will automatically create a degraded array with an extra spare drive.
1590 This is because building the spare into a degraded array is in general
1591 faster than resyncing the parity on a non-degraded, but not clean,
1592 array. This feature can be overridden with the
1596 When creating an array with version-1 metadata a name for the array is
1598 If this is not given with the
1602 will choose a name based on the last component of the name of the
1603 device being created. So if
1605 is being created, then the name
1610 is being created, then the name
1614 When creating a partition based array, using
1616 with version-1.x metadata, the partition type should be set to
1618 (non fs-data). This type selection allows for greater precision since
1619 using any other [RAID auto-detect (0xFD) or a GNU/Linux partition (0x83)],
1620 might create problems in the event of array recovery through a live cdrom.
1622 A new array will normally get a randomly assigned 128bit UUID which is
1623 very likely to be unique. If you have a specific need, you can choose
1624 a UUID for the array by giving the
1626 option. Be warned that creating two arrays with the same UUID is a
1627 recipe for disaster. Also, using
1629 when creating a v0.90 array will silently override any
1634 .\"option is given, it is not necessary to list any component-devices in this command.
1635 .\"They can be added later, before a
1639 .\"is given, the apparent size of the smallest drive given is used.
1641 When creating an array within a
1644 can be given either the list of devices to use, or simply the name of
1645 the container. The former case gives control over which devices in
1646 the container will be used for the array. The latter case allows
1648 to automatically choose which devices to use based on how much spare
1651 The General Management options that are valid with
1656 insist on running the array even if some devices look like they might
1661 start the array readonly \(em not supported yet.
1668 .I options... devices...
1671 This usage will allow individual devices in an array to be failed,
1672 removed or added. It is possible to perform multiple operations with
1673 on command. For example:
1675 .B " mdadm /dev/md0 \-f /dev/hda1 \-r /dev/hda1 \-a /dev/hda1"
1681 and will then remove it from the array and finally add it back
1682 in as a spare. However only one md array can be affected by a single
1685 When a device is added to an active array, mdadm checks to see if it
1686 has metadata on it which suggests that it was recently a member of the
1687 array. If it does, it tried to "re-add" the device. If there have
1688 been no changes since the device was removed, or if the array has a
1689 write-intent bitmap which has recorded whatever changes there were,
1690 then the device will immediately become a full member of the array and
1691 those differences recorded in the bitmap will be resolved.
1701 MISC mode includes a number of distinct operations that
1702 operate on distinct devices. The operations are:
1705 The device is examined to see if it is
1706 (1) an active md array, or
1707 (2) a component of an md array.
1708 The information discovered is reported.
1712 The device should be an active md device.
1714 will display a detailed description of the array.
1718 will cause the output to be less detailed and the format to be
1719 suitable for inclusion in
1720 .BR /etc/mdadm.conf .
1723 will normally be 0 unless
1725 failed to get useful information about the device(s); however, if the
1727 option is given, then the exit status will be:
1731 The array is functioning normally.
1734 The array has at least one failed device.
1737 The array has multiple failed devices such that it is unusable.
1740 There was an error while trying to get information about the device.
1744 .B \-\-detail\-platform
1745 Print detail of the platform's RAID capabilities (firmware / hardware
1746 topology). If the metadata is specified with
1750 then the return status will be:
1754 metadata successfully enumerated its platform components on this system
1757 metadata is platform independent
1760 metadata failed to find its platform components on this system
1765 The device should be a component of an md array.
1767 will read the md superblock of the device and display the contents.
1772 is given, then multiple devices that are components of the one array
1773 are grouped together and reported in a single entry suitable
1775 .BR /etc/mdadm.conf .
1779 without listing any devices will cause all devices listed in the
1780 config file to be examined.
1784 The devices should be active md arrays which will be deactivated, as
1785 long as they are not currently in use.
1789 This will fully activate a partially assembled md array.
1793 This will mark an active array as read-only, providing that it is
1794 not currently being used.
1800 array back to being read/write.
1804 For all operations except
1807 will cause the operation to be applied to all arrays listed in
1812 causes all devices listed in the config file to be examined.
1815 .BR \-b ", " \-\-brief
1816 Be less verbose. This is used with
1824 gives an intermediate level of verbosity.
1830 .B mdadm \-\-monitor
1831 .I options... devices...
1836 to periodically poll a number of md arrays and to report on any events
1839 will never exit once it decides that there are arrays to be checked,
1840 so it should normally be run in the background.
1842 As well as reporting events,
1844 may move a spare drive from one array to another if they are in the
1847 and if the destination array has a failed drive but no spares.
1849 If any devices are listed on the command line,
1851 will only monitor those devices. Otherwise all arrays listed in the
1852 configuration file will be monitored. Further, if
1854 is given, then any other md devices that appear in
1856 will also be monitored.
1858 The result of monitoring the arrays is the generation of events.
1859 These events are passed to a separate program (if specified) and may
1860 be mailed to a given E-mail address.
1862 When passing events to a program, the program is run once for each event,
1863 and is given 2 or 3 command-line arguments: the first is the
1864 name of the event (see below), the second is the name of the
1865 md device which is affected, and the third is the name of a related
1866 device if relevant (such as a component device that has failed).
1870 is given, then a program or an E-mail address must be specified on the
1871 command line or in the config file. If neither are available, then
1873 will not monitor anything.
1877 will continue monitoring as long as something was found to monitor. If
1878 no program or email is given, then each event is reported to
1881 The different events are:
1885 .B DeviceDisappeared
1886 An md array which previously was configured appears to no longer be
1887 configured. (syslog priority: Critical)
1891 was told to monitor an array which is RAID0 or Linear, then it will
1893 .B DeviceDisappeared
1894 with the extra information
1896 This is because RAID0 and Linear do not support the device-failed,
1897 hot-spare and resync operations which are monitored.
1901 An md array started reconstruction. (syslog priority: Warning)
1907 is a two-digit number (ie. 05, 48). This indicates that rebuild
1908 has passed that many percent of the total. The events are generated
1909 with fixed increment since 0. Increment size may be specified with
1910 a commandline option (default is 20). (syslog priority: Warning)
1914 An md array that was rebuilding, isn't any more, either because it
1915 finished normally or was aborted. (syslog priority: Warning)
1919 An active component device of an array has been marked as
1920 faulty. (syslog priority: Critical)
1924 A spare component device which was being rebuilt to replace a faulty
1925 device has failed. (syslog priority: Critical)
1929 A spare component device which was being rebuilt to replace a faulty
1930 device has been successfully rebuilt and has been made active.
1931 (syslog priority: Info)
1935 A new md array has been detected in the
1937 file. (syslog priority: Info)
1941 A newly noticed array appears to be degraded. This message is not
1944 notices a drive failure which causes degradation, but only when
1946 notices that an array is degraded when it first sees the array.
1947 (syslog priority: Critical)
1951 A spare drive has been moved from one array in a
1953 to another to allow a failed drive to be replaced.
1954 (syslog priority: Info)
1960 has been told, via the config file, that an array should have a certain
1961 number of spare devices, and
1963 detects that it has fewer than this number when it first sees the
1964 array, it will report a
1967 (syslog priority: Warning)
1971 An array was found at startup, and the
1974 (syslog priority: Info)
1984 cause Email to be sent. All events cause the program to be run.
1985 The program is run with two or three arguments: the event
1986 name, the array device and possibly a second device.
1988 Each event has an associated array device (e.g.
1990 and possibly a second device. For
1995 the second device is the relevant component device.
1998 the second device is the array that the spare was moved from.
2002 to move spares from one array to another, the different arrays need to
2003 be labeled with the same
2005 in the configuration file. The
2007 name can be any string; it is only necessary that different spare
2008 groups use different names.
2012 detects that an array in a spare group has fewer active
2013 devices than necessary for the complete array, and has no spare
2014 devices, it will look for another array in the same spare group that
2015 has a full complement of working drive and a spare. It will then
2016 attempt to remove the spare from the second drive and add it to the
2018 If the removal succeeds but the adding fails, then it is added back to
2022 The GROW mode is used for changing the size or shape of an active
2024 For this to work, the kernel must support the necessary change.
2025 Various types of growth are being added during 2.6 development,
2026 including restructuring a RAID5 array to have more active devices.
2028 Currently the only support available is to
2030 change the "size" attribute
2031 for RAID1, RAID5 and RAID6.
2033 increase or decrease the "raid\-devices" attribute of RAID1, RAID5,
2036 change the chunk-size and layout of RAID5 and RAID6.
2038 convert between RAID1 and RAID5, and between RAID5 and RAID6.
2040 add a write-intent bitmap to any array which supports these bitmaps, or
2041 remove a write-intent bitmap from such an array.
2044 GROW mode is not currently supported for
2046 or arrays inside containers.
2049 Normally when an array is built the "size" it taken from the smallest
2050 of the drives. If all the small drives in an arrays are, one at a
2051 time, removed and replaced with larger drives, then you could have an
2052 array of large drives with only a small amount used. In this
2053 situation, changing the "size" with "GROW" mode will allow the extra
2054 space to start being used. If the size is increased in this way, a
2055 "resync" process will start to make sure the new parts of the array
2058 Note that when an array changes size, any filesystem that may be
2059 stored in the array will not automatically grow to use the space. The
2060 filesystem will need to be explicitly told to use the extra space.
2062 Also the size of an array cannot be changed while it has an active
2063 bitmap. If an array has a bitmap, it must be removed before the size
2064 can be changed. Once the change it complete a new bitmap can be created.
2066 .SS RAID\-DEVICES CHANGES
2068 A RAID1 array can work with any number of devices from 1 upwards
2069 (though 1 is not very useful). There may be times which you want to
2070 increase or decrease the number of active devices. Note that this is
2071 different to hot-add or hot-remove which changes the number of
2074 When reducing the number of devices in a RAID1 array, the slots which
2075 are to be removed from the array must already be vacant. That is, the
2076 devices which were in those slots must be failed and removed.
2078 When the number of devices is increased, any hot spares that are
2079 present will be activated immediately.
2081 Changing the number of active devices in a RAID5 or RAID6 is much more
2082 effort. Every block in the array will need to be read and written
2083 back to a new location. From 2.6.17, the Linux Kernel is able to
2084 increase the number of devices in a RAID5 safely, including restarting
2085 an interrupted "reshape". From 2.6.31, the Linux Kernel is able to
2086 increase or decrease the number of devices in a RAID5 or RAID6.
2088 When decreasing the number of devices, the size of the array will also
2089 decrease. If there was data in the array, it could get destroyed and
2090 this is not reversible. To help prevent accidents,
2092 requires that the size of the array be decreased first with
2093 .BR "mdadm --grow --array-size" .
2094 This is a reversible change which simply makes the end of the array
2095 inaccessible. The integrity of any data can then be checked before
2096 the non-reversible reduction in the number of devices is request.
2098 When relocating the first few stripes on a RAID5, it is not possible
2099 to keep the data on disk completely consistent and crash-proof. To
2100 provide the required safety, mdadm disables writes to the array while
2101 this "critical section" is reshaped, and takes a backup of the data
2102 that is in that section. This backup is normally stored in any spare
2103 devices that the array has, however it can also be stored in a
2104 separate file specified with the
2106 option. If this option is used, and the system does crash during the
2107 critical period, the same file must be passed to
2109 to restore the backup and reassemble the array.
2113 Changing the RAID level of any array happens instantaneously. However
2114 in the RAID to RAID6 case this requires a non-standard layout of the
2115 RAID6 data, and in the RAID6 to RAID5 case that non-standard layout is
2116 required before the change can be accomplish. So while the level
2117 change is instant, the accompanying layout change can take quite a
2120 .SS CHUNK-SIZE AND LAYOUT CHANGES
2122 Changing the chunk-size of layout without also changing the number of
2123 devices as the same time will involve re-writing all blocks in-place.
2124 To ensure against data loss in the case of a crash, a
2126 must be provided for these changes. Small sections of the array will
2127 be copied to the backup file while they are being rearranged.
2129 If the reshape is interrupted for any reason, this backup file must be
2131 .B "mdadm --assemble"
2132 so the array can be reassembled. Consequently the file cannot be
2133 stored on the device being reshaped.
2138 A write-intent bitmap can be added to, or removed from, an active
2139 array. Either internal bitmaps, or bitmaps stored in a separate file,
2140 can be added. Note that if you add a bitmap stored in a file which is
2141 in a filesystem that is on the RAID array being affected, the system
2142 will deadlock. The bitmap must be on a separate filesystem.
2144 .SH INCREMENTAL MODE
2148 .B mdadm \-\-incremental
2154 .B mdadm \-\-incremental \-\-rebuild
2157 .B mdadm \-\-incremental \-\-run \-\-scan
2160 This mode is designed to be used in conjunction with a device
2161 discovery system. As devices are found in a system, they can be
2163 .B "mdadm \-\-incremental"
2164 to be conditionally added to an appropriate array.
2166 If the device passed is a
2168 device created by a previous call to
2170 then rather than trying to add that device to an array, all the arrays
2171 described by the metadata of the container will be started.
2174 performs a number of tests to determine if the device is part of an
2175 array, and which array it should be part of. If an appropriate array
2176 is found, or can be created,
2178 adds the device to the array and conditionally starts the array.
2182 will only add devices to an array which were previously working
2183 (active or spare) parts of that array. It does not currently support
2184 automatic inclusion of a new drive as a spare in some array.
2188 makes are as follow:
2190 Is the device permitted by
2192 That is, is it listed in a
2194 line in that file. If
2196 is absent then the default it to allow any device. Similar if
2198 contains the special word
2200 then any device is allowed. Otherwise the device name given to
2202 must match one of the names or patterns in a
2207 Does the device have a valid md superblock. If a specific metadata
2208 version is request with
2212 then only that style of metadata is accepted, otherwise
2214 finds any known version of metadata. If no
2216 metadata is found, the device is rejected.
2220 Does the metadata match an expected array?
2221 The metadata can match in two ways. Either there is an array listed
2224 which identifies the array (either by UUID, by name, by device list,
2225 or by minor-number), or the array was created with a
2231 or on the command line.
2234 is not able to positively identify the array as belonging to the
2235 current host, the device will be rejected.
2239 keeps a list of arrays that it has partially assembled in
2240 .B /var/run/mdadm/map
2242 .B /var/run/mdadm.map
2243 if the directory doesn't exist. Or maybe even
2244 .BR /dev/.mdadm.map ).
2245 If no array exists which matches
2246 the metadata on the new device,
2248 must choose a device name and unit number. It does this based on any
2251 or any name information stored in the metadata. If this name
2252 suggests a unit number, that number will be used, otherwise a free
2253 unit number will be chosen. Normally
2255 will prefer to create a partitionable array, however if the
2259 suggests that a non-partitionable array is preferred, that will be
2262 If the array is not found in the config file and its metadata does not
2263 identify it as belonging to the "homehost", then
2265 will choose a name for the array which is certain not to conflict with
2266 any array which does belong to this host. It does this be adding an
2267 underscore and a small number to the name preferred by the metadata.
2269 Once an appropriate array is found or created and the device is added,
2271 must decide if the array is ready to be started. It will
2272 normally compare the number of available (non-spare) devices to the
2273 number of devices that the metadata suggests need to be active. If
2274 there are at least that many, the array will be started. This means
2275 that if any devices are missing the array will not be restarted.
2281 in which case the array will be run as soon as there are enough
2282 devices present for the data to be accessible. For a RAID1, that
2283 means one device will start the array. For a clean RAID5, the array
2284 will be started as soon as all but one drive is present.
2286 Note that neither of these approaches is really ideal. If it can
2287 be known that all device discovery has completed, then
2291 can be run which will try to start all arrays that are being
2292 incrementally assembled. They are started in "read-auto" mode in
2293 which they are read-only until the first write request. This means
2294 that no metadata updates are made and no attempt at resync or recovery
2295 happens. Further devices that are found before the first write can
2296 still be added safely.
2299 This section describes environment variables that affect how mdadm
2304 Setting this value to 1 will prevent mdadm from automatically launching
2305 mdmon. This variable is intended primarily for debugging mdadm/mdmon.
2311 does not create any device nodes in /dev, but leaves that task to
2315 appears not to be configured, or if this environment variable is set
2318 will create and devices that are needed.
2322 .B " mdadm \-\-query /dev/name-of-device"
2324 This will find out if a given device is a RAID array, or is part of
2325 one, and will provide brief information about the device.
2327 .B " mdadm \-\-assemble \-\-scan"
2329 This will assemble and start all arrays listed in the standard config
2330 file. This command will typically go in a system startup file.
2332 .B " mdadm \-\-stop \-\-scan"
2334 This will shut down all arrays that can be shut down (i.e. are not
2335 currently in use). This will typically go in a system shutdown script.
2337 .B " mdadm \-\-follow \-\-scan \-\-delay=120"
2339 If (and only if) there is an Email address or program given in the
2340 standard config file, then
2341 monitor the status of all arrays listed in that file by
2342 polling them ever 2 minutes.
2344 .B " mdadm \-\-create /dev/md0 \-\-level=1 \-\-raid\-devices=2 /dev/hd[ac]1"
2346 Create /dev/md0 as a RAID1 array consisting of /dev/hda1 and /dev/hdc1.
2349 .B " echo 'DEVICE /dev/hd*[0\-9] /dev/sd*[0\-9]' > mdadm.conf"
2351 .B " mdadm \-\-detail \-\-scan >> mdadm.conf"
2353 This will create a prototype config file that describes currently
2354 active arrays that are known to be made from partitions of IDE or SCSI drives.
2355 This file should be reviewed before being used as it may
2356 contain unwanted detail.
2358 .B " echo 'DEVICE /dev/hd[a\-z] /dev/sd*[a\-z]' > mdadm.conf"
2360 .B " mdadm \-\-examine \-\-scan \-\-config=mdadm.conf >> mdadm.conf"
2362 This will find arrays which could be assembled from existing IDE and
2363 SCSI whole drives (not partitions), and store the information in the
2364 format of a config file.
2365 This file is very likely to contain unwanted detail, particularly
2368 entries. It should be reviewed and edited before being used as an
2371 .B " mdadm \-\-examine \-\-brief \-\-scan \-\-config=partitions"
2373 .B " mdadm \-Ebsc partitions"
2375 Create a list of devices by reading
2376 .BR /proc/partitions ,
2377 scan these for RAID superblocks, and printout a brief listing of all
2380 .B " mdadm \-Ac partitions \-m 0 /dev/md0"
2382 Scan all partitions and devices listed in
2383 .BR /proc/partitions
2386 out of all such devices with a RAID superblock with a minor number of 0.
2388 .B " mdadm \-\-monitor \-\-scan \-\-daemonise > /var/run/mdadm"
2390 If config file contains a mail address or alert program, run mdadm in
2391 the background in monitor mode monitoring all md devices. Also write
2392 pid of mdadm daemon to
2393 .BR /var/run/mdadm .
2395 .B " mdadm \-Iq /dev/somedevice"
2397 Try to incorporate newly discovered device into some array as
2400 .B " mdadm \-\-incremental \-\-rebuild \-\-run \-\-scan"
2402 Rebuild the array map from any current arrays, and then start any that
2405 .B " mdadm /dev/md4 --fail detached --remove detached"
2407 Any devices which are components of /dev/md4 will be marked as faulty
2408 and then remove from the array.
2410 .B " mdadm --grow /dev/md4 --level=6 --backup-file=/root/backup-md4
2414 which is currently a RAID5 array will be converted to RAID6. There
2415 should normally already be a spare drive attached to the array as a
2416 RAID6 needs one more drive than a matching RAID5.
2418 .B " mdadm --create /dev/md/ddf --metadata=ddf --raid-disks 6 /dev/sd[a-f]"
2420 Create a DDF array over 6 devices.
2422 .B " mdadm --create /dev/md/home -n3 -l5 -z 30000000 /dev/md/ddf"
2424 Create a RAID5 array over any 3 devices in the given DDF set. Use
2425 only 30 gigabytes of each device.
2427 .B " mdadm -A /dev/md/ddf1 /dev/sd[a-f]"
2429 Assemble a pre-exist ddf array.
2431 .B " mdadm -I /dev/md/ddf1"
2433 Assemble all arrays contained in the ddf array, assigning names as
2436 .B " mdadm \-\-create \-\-help"
2438 Provide help about the Create mode.
2440 .B " mdadm \-\-config \-\-help"
2442 Provide help about the format of the config file.
2444 .B " mdadm \-\-help"
2446 Provide general help.
2456 lists all active md devices with information about them.
2458 uses this to find arrays when
2460 is given in Misc mode, and to monitor array reconstruction
2465 The config file lists which devices may be scanned to see if
2466 they contain MD super block, and gives identifying information
2467 (e.g. UUID) about known MD arrays. See
2471 .SS /var/run/mdadm/map
2474 mode is used, this file gets a list of arrays currently being created.
2477 does not exist as a directory, then
2478 .B /var/run/mdadm.map
2481 is not available (as may be the case during early boot),
2483 is used on the basis that
2485 is usually available very early in boot.
2490 understand two sorts of names for array devices.
2492 The first is the so-called 'standard' format name, which matches the
2493 names used by the kernel and which appear in
2496 The second sort can be freely chosen, but must reside in
2498 When giving a device name to
2500 to create or assemble an array, either full path name such as
2504 can be given, or just the suffix of the second sort of name, such as
2510 chooses device names during auto-assembly or incremental assembly, it
2511 will sometimes add a small sequence number to the end of the name to
2512 avoid conflicted between multiple arrays that have the same name. If
2514 can reasonably determine that the array really is meant for this host,
2515 either by a hostname in the metadata, or by the presence of the array
2516 in /etc/mdadm.conf, then it will leave off the suffix if possible.
2517 Also if the homehost is specified as
2520 will only use a suffix if a different array of the same name already
2521 exists or is listed in the config file.
2523 The standard names for non-partitioned arrays (the only sort of md
2524 array available in 2.4 and earlier) are of the form
2528 where NN is a number.
2529 The standard names for partitionable arrays (as available from 2.6
2530 onwards) are of the form
2534 Partition numbers should be indicated by added "pMM" to these, thus "/dev/md/d1p2".
2536 From kernel version, 2.6.28 the "non-partitioned array" can actually
2537 be partitioned. So the "md_dNN" names are no longer needed, and
2538 partitions such as "/dev/mdNNpXX" are possible.
2542 was previously known as
2546 is completely separate from the
2548 package, and does not use the
2550 configuration file at all.
2553 For further information on mdadm usage, MD and the various levels of
2556 .B http://linux\-raid.osdl.org/
2558 (based upon Jakob \(/Ostergaard's Software\-RAID.HOWTO)
2560 .\"for new releases of the RAID driver check out:
2563 .\".UR ftp://ftp.kernel.org/pub/linux/kernel/people/mingo/raid-patches
2564 .\"ftp://ftp.kernel.org/pub/linux/kernel/people/mingo/raid-patches
2569 .\".UR http://www.cse.unsw.edu.au/~neilb/patches/linux-stable/
2570 .\"http://www.cse.unsw.edu.au/~neilb/patches/linux-stable/
2573 The latest version of
2575 should always be available from
2577 .B http://www.kernel.org/pub/linux/utils/raid/mdadm/
projects / thirdparty / mdadm.git / blob