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.
8 .TH MDADM 8 "" v4.1-rc2
10 mdadm \- manage MD devices
16 .BI mdadm " [mode] <raiddevice> [options] <component-devices>"
19 RAID devices are virtual devices created from two or more
20 real block devices. This allows multiple devices (typically disk
21 drives or partitions thereof) to be combined into a single device to
22 hold (for example) a single filesystem.
23 Some RAID levels include redundancy and so can survive some degree of
26 Linux Software RAID devices are implemented through the md (Multiple
27 Devices) device driver.
29 Currently, Linux supports
46 is not a Software RAID mechanism, but does involve
48 each device is a path to one common physical storage device.
49 New installations should not use md/multipath as it is not well
50 supported and has no ongoing development. Use the Device Mapper based
51 multipath-tools instead.
54 is also not true RAID, and it only involves one device. It
55 provides a layer over a true device that can be used to inject faults.
60 is a collection of devices that are
61 managed as a set. This is similar to the set of devices connected to
62 a hardware RAID controller. The set of devices may contain a number
63 of different RAID arrays each utilising some (or all) of the blocks from a
64 number of the devices in the set. For example, two devices in a 5-device set
65 might form a RAID1 using the whole devices. The remaining three might
66 have a RAID5 over the first half of each device, and a RAID0 over the
71 there is one set of metadata that describes all of
72 the arrays in the container. So when
76 device, the device just represents the metadata. Other normal arrays (RAID1
77 etc) can be created inside the container.
80 mdadm has several major modes of operation:
83 Assemble the components of a previously created
84 array into an active array. Components can be explicitly given
85 or can be searched for.
87 checks that the components
88 do form a bona fide array, and can, on request, fiddle superblock
89 information so as to assemble a faulty array.
93 Build an array that doesn't have per-device metadata (superblocks). For these
96 cannot differentiate between initial creation and subsequent assembly
97 of an array. It also cannot perform any checks that appropriate
98 components have been requested. Because of this, the
100 mode should only be used together with a complete understanding of
105 Create a new array with per-device metadata (superblocks).
106 Appropriate metadata is written to each device, and then the array
107 comprising those devices is activated. A 'resync' process is started
108 to make sure that the array is consistent (e.g. both sides of a mirror
109 contain the same data) but the content of the device is left otherwise
111 The array can be used as soon as it has been created. There is no
112 need to wait for the initial resync to finish.
115 .B "Follow or Monitor"
116 Monitor one or more md devices and act on any state changes. This is
117 only meaningful for RAID1, 4, 5, 6, 10 or multipath arrays, as
118 only these have interesting state. RAID0 or Linear never have
119 missing, spare, or failed drives, so there is nothing to monitor.
123 Grow (or shrink) an array, or otherwise reshape it in some way.
124 Currently supported growth options including changing the active size
125 of component devices and changing the number of active devices in
126 Linear and RAID levels 0/1/4/5/6,
127 changing the RAID level between 0, 1, 5, and 6, and between 0 and 10,
128 changing the chunk size and layout for RAID 0,4,5,6,10 as well as adding or
129 removing a write-intent bitmap and changing the array's consistency policy.
132 .B "Incremental Assembly"
133 Add a single device to an appropriate array. If the addition of the
134 device makes the array runnable, the array will be started.
135 This provides a convenient interface to a
137 system. As each device is detected,
139 has a chance to include it in some array as appropriate.
142 flag is passed in we will remove the device from any active array
143 instead of adding it.
149 in this mode, then any arrays within that container will be assembled
154 This is for doing things to specific components of an array such as
155 adding new spares and removing faulty devices.
159 This is an 'everything else' mode that supports operations on active
160 arrays, operations on component devices such as erasing old superblocks, and
161 information gathering operations.
162 .\"This mode allows operations on independent devices such as examine MD
163 .\"superblocks, erasing old superblocks and stopping active arrays.
167 This mode does not act on a specific device or array, but rather it
168 requests the Linux Kernel to activate any auto-detected arrays.
171 .SH Options for selecting a mode are:
174 .BR \-A ", " \-\-assemble
175 Assemble a pre-existing array.
178 .BR \-B ", " \-\-build
179 Build a legacy array without superblocks.
182 .BR \-C ", " \-\-create
186 .BR \-F ", " \-\-follow ", " \-\-monitor
192 .BR \-G ", " \-\-grow
193 Change the size or shape of an active array.
196 .BR \-I ", " \-\-incremental
197 Add/remove a single device to/from an appropriate array, and possibly start the array.
201 Request that the kernel starts any auto-detected arrays. This can only
204 is compiled into the kernel \(em not if it is a module.
205 Arrays can be auto-detected by the kernel if all the components are in
206 primary MS-DOS partitions with partition type
208 and all use v0.90 metadata.
209 In-kernel autodetect is not recommended for new installations. Using
211 to detect and assemble arrays \(em possibly in an
213 \(em is substantially more flexible and should be preferred.
216 If a device is given before any options, or if the first option is
225 then the MANAGE mode is assumed.
226 Anything other than these will cause the
230 .SH Options that are not mode-specific are:
233 .BR \-h ", " \-\-help
234 Display general help message or, after one of the above options, a
235 mode-specific help message.
239 Display more detailed help about command line parsing and some commonly
243 .BR \-V ", " \-\-version
244 Print version information for mdadm.
247 .BR \-v ", " \-\-verbose
248 Be more verbose about what is happening. This can be used twice to be
250 The extra verbosity currently only affects
251 .B \-\-detail \-\-scan
253 .BR "\-\-examine \-\-scan" .
256 .BR \-q ", " \-\-quiet
257 Avoid printing purely informative messages. With this,
259 will be silent unless there is something really important to report.
263 .BR \-f ", " \-\-force
264 Be more forceful about certain operations. See the various modes for
265 the exact meaning of this option in different contexts.
268 .BR \-c ", " \-\-config=
269 Specify the config file or directory. Default is to use
272 .BR /etc/mdadm.conf.d ,
273 or if those are missing then
274 .B /etc/mdadm/mdadm.conf
276 .BR /etc/mdadm/mdadm.conf.d .
277 If the config file given is
279 then nothing will be read, but
281 will act as though the config file contained exactly
283 .B " DEVICE partitions containers"
287 to find a list of devices to scan, and
289 to find a list of containers to examine.
292 is given for the config file, then
294 will act as though the config file were empty.
296 If the name given is of a directory, then
298 will collect all the files contained in the directory with a name ending
301 sort them lexically, and process all of those files as config files.
304 .BR \-s ", " \-\-scan
307 for missing information.
308 In general, this option gives
310 permission to get any missing information (like component devices,
311 array devices, array identities, and alert destination) from the
312 configuration file (see previous option);
313 one exception is MISC mode when using
319 says to get a list of array devices from
323 .BR \-e ", " \-\-metadata=
324 Declare the style of RAID metadata (superblock) to be used. The
325 default is {DEFAULT_METADATA} for
327 and to guess for other operations.
328 The default can be overridden by setting the
337 .ie '{DEFAULT_METADATA}'0.90'
338 .IP "0, 0.90, default"
341 Use the original 0.90 format superblock. This format limits arrays to
342 28 component devices and limits component devices of levels 1 and
343 greater to 2 terabytes. It is also possible for there to be confusion
344 about whether the superblock applies to a whole device or just the
345 last partition, if that partition starts on a 64K boundary.
346 .ie '{DEFAULT_METADATA}'0.90'
347 .IP "1, 1.0, 1.1, 1.2"
349 .IP "1, 1.0, 1.1, 1.2 default"
350 Use the new version-1 format superblock. This has fewer restrictions.
351 It can easily be moved between hosts with different endian-ness, and a
352 recovery operation can be checkpointed and restarted. The different
353 sub-versions store the superblock at different locations on the
354 device, either at the end (for 1.0), at the start (for 1.1) or 4K from
355 the start (for 1.2). "1" is equivalent to "1.2" (the commonly
356 preferred 1.x format).
357 'if '{DEFAULT_METADATA}'1.2' "default" is equivalent to "1.2".
359 Use the "Industry Standard" DDF (Disk Data Format) format defined by
361 When creating a DDF array a
363 will be created, and normal arrays can be created in that container.
365 Use the Intel(R) Matrix Storage Manager metadata format. This creates a
367 which is managed in a similar manner to DDF, and is supported by an
368 option-rom on some platforms:
370 .B http://www.intel.com/design/chipsets/matrixstorage_sb.htm
376 This will override any
378 setting in the config file and provides the identity of the host which
379 should be considered the home for any arrays.
381 When creating an array, the
383 will be recorded in the metadata. For version-1 superblocks, it will
384 be prefixed to the array name. For version-0.90 superblocks, part of
385 the SHA1 hash of the hostname will be stored in the later half of the
388 When reporting information about an array, any array which is tagged
389 for the given homehost will be reported as such.
391 When using Auto-Assemble, only arrays tagged for the given homehost
392 will be allowed to use 'local' names (i.e. not ending in '_' followed
393 by a digit string). See below under
394 .BR "Auto Assembly" .
396 The special name "\fBany\fP" can be used as a wild card. If an array
399 then the name "\fBany\fP" will be stored in the array and it can be
400 assembled in the same way on any host. If an array is assembled with
401 this option, then the homehost recorded on the array will be ignored.
407 needs to print the name for a device it normally finds the name in
409 which refers to the device and is shortest. When a path component is
413 will prefer a longer name if it contains that component. For example
414 .B \-\-prefer=by-uuid
415 will prefer a name in a subdirectory of
420 This functionality is currently only provided by
426 .B \-\-home\-cluster=
427 specifies the cluster name for the md device. The md device can be assembled
428 only on the cluster which matches the name specified. If this option is not
429 provided, mdadm tries to detect the cluster name automatically.
431 .SH For create, build, or grow:
434 .BR \-n ", " \-\-raid\-devices=
435 Specify the number of active devices in the array. This, plus the
436 number of spare devices (see below) must equal the number of
438 (including "\fBmissing\fP" devices)
439 that are listed on the command line for
441 Setting a value of 1 is probably
442 a mistake and so requires that
444 be specified first. A value of 1 will then be allowed for linear,
445 multipath, RAID0 and RAID1. It is never allowed for RAID4, RAID5 or RAID6.
447 This number can only be changed using
449 for RAID1, RAID4, RAID5 and RAID6 arrays, and only on kernels which provide
450 the necessary support.
453 .BR \-x ", " \-\-spare\-devices=
454 Specify the number of spare (eXtra) devices in the initial array.
455 Spares can also be added
456 and removed later. The number of component devices listed
457 on the command line must equal the number of RAID devices plus the
458 number of spare devices.
461 .BR \-z ", " \-\-size=
462 Amount (in Kilobytes) of space to use from each drive in RAID levels 1/4/5/6.
463 This must be a multiple of the chunk size, and must leave about 128Kb
464 of space at the end of the drive for the RAID superblock.
465 If this is not specified
466 (as it normally is not) the smallest drive (or partition) sets the
467 size, though if there is a variance among the drives of greater than 1%, a warning is
470 A suffix of 'K', 'M' or 'G' can be given to indicate Kilobytes, Megabytes or
471 Gigabytes respectively.
473 Sometimes a replacement drive can be a little smaller than the
474 original drives though this should be minimised by IDEMA standards.
475 Such a replacement drive will be rejected by
477 To guard against this it can be useful to set the initial size
478 slightly smaller than the smaller device with the aim that it will
479 still be larger than any replacement.
481 This value can be set with
483 for RAID level 1/4/5/6 though
484 DDF arrays may not be able to support this.
485 If the array was created with a size smaller than the currently
486 active drives, the extra space can be accessed using
488 The size can be given as
490 which means to choose the largest size that fits on all current drives.
492 Before reducing the size of the array (with
493 .BR "\-\-grow \-\-size=" )
494 you should make sure that space isn't needed. If the device holds a
495 filesystem, you would need to resize the filesystem to use less space.
497 After reducing the array size you should check that the data stored in
498 the device is still available. If the device holds a filesystem, then
499 an 'fsck' of the filesystem is a minimum requirement. If there are
500 problems the array can be made bigger again with no loss with another
501 .B "\-\-grow \-\-size="
504 This value cannot be used when creating a
506 such as with DDF and IMSM metadata, though it perfectly valid when
507 creating an array inside a container.
510 .BR \-Z ", " \-\-array\-size=
511 This is only meaningful with
513 and its effect is not persistent: when the array is stopped and
514 restarted the default array size will be restored.
516 Setting the array-size causes the array to appear smaller to programs
517 that access the data. This is particularly needed before reshaping an
518 array so that it will be smaller. As the reshape is not reversible,
519 but setting the size with
521 is, it is required that the array size is reduced as appropriate
522 before the number of devices in the array is reduced.
524 Before reducing the size of the array you should make sure that space
525 isn't needed. If the device holds a filesystem, you would need to
526 resize the filesystem to use less space.
528 After reducing the array size you should check that the data stored in
529 the device is still available. If the device holds a filesystem, then
530 an 'fsck' of the filesystem is a minimum requirement. If there are
531 problems the array can be made bigger again with no loss with another
532 .B "\-\-grow \-\-array\-size="
535 A suffix of 'K', 'M' or 'G' can be given to indicate Kilobytes, Megabytes or
536 Gigabytes respectively.
539 restores the apparent size of the array to be whatever the real
540 amount of available space is.
542 Clustered arrays do not support this parameter yet.
545 .BR \-c ", " \-\-chunk=
546 Specify chunk size of kilobytes. The default when creating an
547 array is 512KB. To ensure compatibility with earlier versions, the
548 default when building an array with no persistent metadata is 64KB.
549 This is only meaningful for RAID0, RAID4, RAID5, RAID6, and RAID10.
551 RAID4, RAID5, RAID6, and RAID10 require the chunk size to be a power
552 of 2. In any case it must be a multiple of 4KB.
554 A suffix of 'K', 'M' or 'G' can be given to indicate Kilobytes, Megabytes or
555 Gigabytes respectively.
559 Specify rounding factor for a Linear array. The size of each
560 component will be rounded down to a multiple of this size.
561 This is a synonym for
563 but highlights the different meaning for Linear as compared to other
564 RAID levels. The default is 64K if a kernel earlier than 2.6.16 is in
565 use, and is 0K (i.e. no rounding) in later kernels.
568 .BR \-l ", " \-\-level=
569 Set RAID level. When used with
571 options are: linear, raid0, 0, stripe, raid1, 1, mirror, raid4, 4,
572 raid5, 5, raid6, 6, raid10, 10, multipath, mp, faulty, container.
573 Obviously some of these are synonymous.
577 metadata type is requested, only the
579 level is permitted, and it does not need to be explicitly given.
583 only linear, stripe, raid0, 0, raid1, multipath, mp, and faulty are valid.
587 to change the RAID level in some cases. See LEVEL CHANGES below.
590 .BR \-p ", " \-\-layout=
591 This option configures the fine details of data layout for RAID5, RAID6,
592 and RAID10 arrays, and controls the failure modes for
594 It can also be used for working around a kernel bug with RAID0, but generally
595 doesn't need to be used explicitly.
597 The layout of the RAID5 parity block can be one of
598 .BR left\-asymmetric ,
599 .BR left\-symmetric ,
600 .BR right\-asymmetric ,
601 .BR right\-symmetric ,
602 .BR la ", " ra ", " ls ", " rs .
604 .BR left\-symmetric .
606 It is also possible to cause RAID5 to use a RAID4-like layout by
612 Finally for RAID5 there are DDF\-compatible layouts,
613 .BR ddf\-zero\-restart ,
614 .BR ddf\-N\-restart ,
616 .BR ddf\-N\-continue .
618 These same layouts are available for RAID6. There are also 4 layouts
619 that will provide an intermediate stage for converting between RAID5
620 and RAID6. These provide a layout which is identical to the
621 corresponding RAID5 layout on the first N\-1 devices, and has the 'Q'
622 syndrome (the second 'parity' block used by RAID6) on the last device.
624 .BR left\-symmetric\-6 ,
625 .BR right\-symmetric\-6 ,
626 .BR left\-asymmetric\-6 ,
627 .BR right\-asymmetric\-6 ,
629 .BR parity\-first\-6 .
631 When setting the failure mode for level
634 .BR write\-transient ", " wt ,
635 .BR read\-transient ", " rt ,
636 .BR write\-persistent ", " wp ,
637 .BR read\-persistent ", " rp ,
639 .BR read\-fixable ", " rf ,
640 .BR clear ", " flush ", " none .
642 Each failure mode can be followed by a number, which is used as a period
643 between fault generation. Without a number, the fault is generated
644 once on the first relevant request. With a number, the fault will be
645 generated after that many requests, and will continue to be generated
646 every time the period elapses.
648 Multiple failure modes can be current simultaneously by using the
650 option to set subsequent failure modes.
652 "clear" or "none" will remove any pending or periodic failure modes,
653 and "flush" will clear any persistent faults.
655 The layout options for RAID10 are one of 'n', 'o' or 'f' followed
656 by a small number. The default is 'n2'. The supported options are:
659 signals 'near' copies. Multiple copies of one data block are at
660 similar offsets in different devices.
663 signals 'offset' copies. Rather than the chunks being duplicated
664 within a stripe, whole stripes are duplicated but are rotated by one
665 device so duplicate blocks are on different devices. Thus subsequent
666 copies of a block are in the next drive, and are one chunk further
671 (multiple copies have very different offsets).
672 See md(4) for more detail about 'near', 'offset', and 'far'.
674 The number is the number of copies of each datablock. 2 is normal, 3
675 can be useful. This number can be at most equal to the number of
676 devices in the array. It does not need to divide evenly into that
677 number (e.g. it is perfectly legal to have an 'n2' layout for an array
678 with an odd number of devices).
680 A bug introduced in Linux 3.14 means that RAID0 arrays
681 .B "with devices of differing sizes"
682 started using a different layout. This could lead to
683 data corruption. Since Linux 5.4 (and various stable releases that received
684 backports), the kernel will not accept such an array unless
685 a layout is explictly set. It can be set to
689 When creating a new array,
693 by default, so the layout does not normally need to be set.
694 An array created for either
698 will not be recognized by an (unpatched) kernel prior to 5.4. To create
699 a RAID0 array with devices of differing sizes that can be used on an
700 older kernel, you can set the layout to
702 This will use whichever layout the running kernel supports, so the data
703 on the array may become corrupt when changing kernel from pre-3.14 to a
706 When an array is converted between RAID5 and RAID6 an intermediate
707 RAID6 layout is used in which the second parity block (Q) is always on
708 the last device. To convert a RAID5 to RAID6 and leave it in this new
709 layout (which does not require re-striping) use
710 .BR \-\-layout=preserve .
711 This will try to avoid any restriping.
713 The converse of this is
714 .B \-\-layout=normalise
715 which will change a non-standard RAID6 layout into a more standard
722 (thus explaining the p of
726 .BR \-b ", " \-\-bitmap=
727 Specify a file to store a write-intent bitmap in. The file should not
730 is also given. The same file should be provided
731 when assembling the array. If the word
733 is given, then the bitmap is stored with the metadata on the array,
734 and so is replicated on all devices. If the word
738 mode, then any bitmap that is present is removed. If the word
740 is given, the array is created for a clustered environment. One bitmap
741 is created for each node as defined by the
743 parameter and are stored internally.
745 To help catch typing errors, the filename must contain at least one
746 slash ('/') if it is a real file (not 'internal' or 'none').
748 Note: external bitmaps are only known to work on ext2 and ext3.
749 Storing bitmap files on other filesystems may result in serious problems.
751 When creating an array on devices which are 100G or larger,
753 automatically adds an internal bitmap as it will usually be
754 beneficial. This can be suppressed with
756 or by selecting a different consistency policy with
757 .BR \-\-consistency\-policy .
760 .BR \-\-bitmap\-chunk=
761 Set the chunksize of the bitmap. Each bit corresponds to that many
762 Kilobytes of storage.
763 When using a file based bitmap, the default is to use the smallest
764 size that is at-least 4 and requires no more than 2^21 chunks.
767 bitmap, the chunksize defaults to 64Meg, or larger if necessary to
768 fit the bitmap into the available space.
770 A suffix of 'K', 'M' or 'G' can be given to indicate Kilobytes, Megabytes or
771 Gigabytes respectively.
774 .BR \-W ", " \-\-write\-mostly
775 subsequent devices listed in a
780 command will be flagged as 'write\-mostly'. This is valid for RAID1
781 only and means that the 'md' driver will avoid reading from these
782 devices if at all possible. This can be useful if mirroring over a
786 .BR \-\-write\-behind=
787 Specify that write-behind mode should be enabled (valid for RAID1
788 only). If an argument is specified, it will set the maximum number
789 of outstanding writes allowed. The default value is 256.
790 A write-intent bitmap is required in order to use write-behind
791 mode, and write-behind is only attempted on drives marked as
796 subsequent devices listed in a
800 command will be flagged as 'failfast'. This is valid for RAID1 and
801 RAID10 only. IO requests to these devices will be encouraged to fail
802 quickly rather than cause long delays due to error handling. Also no
803 attempt is made to repair a read error on these devices.
805 If an array becomes degraded so that the 'failfast' device is the only
806 usable device, the 'failfast' flag will then be ignored and extended
807 delays will be preferred to complete failure.
809 The 'failfast' flag is appropriate for storage arrays which have a
810 low probability of true failure, but which may sometimes
811 cause unacceptable delays due to internal maintenance functions.
814 .BR \-\-assume\-clean
817 that the array pre-existed and is known to be clean. It can be useful
818 when trying to recover from a major failure as you can be sure that no
819 data will be affected unless you actually write to the array. It can
820 also be used when creating a RAID1 or RAID10 if you want to avoid the
821 initial resync, however this practice \(em while normally safe \(em is not
822 recommended. Use this only if you really know what you are doing.
824 When the devices that will be part of a new array were filled
825 with zeros before creation the operator knows the array is
826 actually clean. If that is the case, such as after running
827 badblocks, this argument can be used to tell mdadm the
828 facts the operator knows.
830 When an array is resized to a larger size with
831 .B "\-\-grow \-\-size="
832 the new space is normally resynced in that same way that the whole
833 array is resynced at creation. From Linux version 3.0,
835 can be used with that command to avoid the automatic resync.
838 .BR \-\-backup\-file=
841 is used to increase the number of raid-devices in a RAID5 or RAID6 if
842 there are no spare devices available, or to shrink, change RAID level
843 or layout. See the GROW MODE section below on RAID\-DEVICES CHANGES.
844 The file must be stored on a separate device, not on the RAID array
849 Arrays with 1.x metadata can leave a gap between the start of the
850 device and the start of array data. This gap can be used for various
851 metadata. The start of data is known as the
853 Normally an appropriate data offset is computed automatically.
854 However it can be useful to set it explicitly such as when re-creating
855 an array which was originally created using a different version of
857 which computed a different offset.
859 Setting the offset explicitly over-rides the default. The value given
860 is in Kilobytes unless a suffix of 'K', 'M' or 'G' is used to explicitly
861 indicate Kilobytes, Megabytes or Gigabytes respectively.
865 can also be used with
867 for some RAID levels (initially on RAID10). This allows the
868 data\-offset to be changed as part of the reshape process. When the
869 data offset is changed, no backup file is required as the difference
870 in offsets is used to provide the same functionality.
872 When the new offset is earlier than the old offset, the number of
873 devices in the array cannot shrink. When it is after the old offset,
874 the number of devices in the array cannot increase.
876 When creating an array,
880 In the case each member device is expected to have a offset appended
881 to the name, separated by a colon. This makes it possible to recreate
882 exactly an array which has varying data offsets (as can happen when
883 different versions of
885 are used to add different devices).
889 This option is complementary to the
890 .B \-\-freeze-reshape
891 option for assembly. It is needed when
893 operation is interrupted and it is not restarted automatically due to
894 .B \-\-freeze-reshape
895 usage during array assembly. This option is used together with
899 ) command and device for a pending reshape to be continued.
900 All parameters required for reshape continuation will be read from array metadata.
904 .BR \-\-backup\-file=
905 option to be set, continuation option will require to have exactly the same
906 backup file given as well.
908 Any other parameter passed together with
910 option will be ignored.
913 .BR \-N ", " \-\-name=
916 for the array. This is currently only effective when creating an
917 array with a version-1 superblock, or an array in a DDF container.
918 The name is a simple textual string that can be used to identify array
919 components when assembling. If name is needed but not specified, it
920 is taken from the basename of the device that is being created.
932 run the array, even if some of the components
933 appear to be active in another array or filesystem. Normally
935 will ask for confirmation before including such components in an
936 array. This option causes that question to be suppressed.
939 .BR \-f ", " \-\-force
942 accept the geometry and layout specified without question. Normally
944 will not allow creation of an array with only one device, and will try
945 to create a RAID5 array with one missing drive (as this makes the
946 initial resync work faster). With
949 will not try to be so clever.
952 .BR \-o ", " \-\-readonly
955 rather than read-write as normal. No writes will be allowed to the
956 array, and no resync, recovery, or reshape will be started. It works with
957 Create, Assemble, Manage and Misc mode.
960 .BR \-a ", " "\-\-auto{=yes,md,mdp,part,p}{NN}"
961 Instruct mdadm how to create the device file if needed, possibly allocating
962 an unused minor number. "md" causes a non-partitionable array
963 to be used (though since Linux 2.6.28, these array devices are in fact
964 partitionable). "mdp", "part" or "p" causes a partitionable array (2.6 and
965 later) to be used. "yes" requires the named md device to have
966 a 'standard' format, and the type and minor number will be determined
967 from this. With mdadm 3.0, device creation is normally left up to
969 so this option is unlikely to be needed.
970 See DEVICE NAMES below.
972 The argument can also come immediately after
977 is not given on the command line or in the config file, then
983 is also given, then any
985 entries in the config file will override the
987 instruction given on the command line.
989 For partitionable arrays,
991 will create the device file for the whole array and for the first 4
992 partitions. A different number of partitions can be specified at the
993 end of this option (e.g.
995 If the device name ends with a digit, the partition names add a 'p',
997 .IR /dev/md/home1p3 .
998 If there is no trailing digit, then the partition names just have a
1000 .IR /dev/md/scratch3 .
1002 If the md device name is in a 'standard' format as described in DEVICE
1003 NAMES, then it will be created, if necessary, with the appropriate
1004 device number based on that name. If the device name is not in one of these
1005 formats, then a unused device number will be allocated. The device
1006 number will be considered unused if there is no active array for that
1007 number, and there is no entry in /dev for that number and with a
1008 non-standard name. Names that are not in 'standard' format are only
1009 allowed in "/dev/md/".
1011 This is meaningful with
1017 .BR \-a ", " "\-\-add"
1018 This option can be used in Grow mode in two cases.
1020 If the target array is a Linear array, then
1022 can be used to add one or more devices to the array. They
1023 are simply catenated on to the end of the array. Once added, the
1024 devices cannot be removed.
1028 option is being used to increase the number of devices in an array,
1031 can be used to add some extra devices to be included in the array.
1032 In most cases this is not needed as the extra devices can be added as
1033 spares first, and then the number of raid-disks can be changed.
1034 However for RAID0, it is not possible to add spares. So to increase
1035 the number of devices in a RAID0, it is necessary to set the new
1036 number of devices, and to add the new devices, in the same command.
1040 Only works when the array is for clustered environment. It specifies
1041 the maximum number of nodes in the cluster that will use this device
1042 simultaneously. If not specified, this defaults to 4.
1045 .BR \-\-write-journal
1046 Specify journal device for the RAID-4/5/6 array. The journal device
1047 should be a SSD with reasonable lifetime.
1051 Auto creation of symlinks in /dev to /dev/md, option --symlinks must
1052 be 'no' or 'yes' and work with --create and --build.
1055 .BR \-k ", " \-\-consistency\-policy=
1056 Specify how the array maintains consistency in case of unexpected shutdown.
1057 Only relevant for RAID levels with redundancy.
1058 Currently supported options are:
1063 Full resync is performed and all redundancy is regenerated when the array is
1064 started after unclean shutdown.
1068 Resync assisted by a write-intent bitmap. Implicitly selected when using
1073 For RAID levels 4/5/6, journal device is used to log transactions and replay
1074 after unclean shutdown. Implicitly selected when using
1075 .BR \-\-write\-journal .
1079 For RAID5 only, Partial Parity Log is used to close the write hole and
1080 eliminate resync. PPL is stored in the metadata region of RAID member drives,
1081 no additional journal drive is needed.
1084 Can be used with \-\-grow to change the consistency policy of an active array
1085 in some cases. See CONSISTENCY POLICY CHANGES below.
1092 .BR \-u ", " \-\-uuid=
1093 uuid of array to assemble. Devices which don't have this uuid are
1097 .BR \-m ", " \-\-super\-minor=
1098 Minor number of device that array was created for. Devices which
1099 don't have this minor number are excluded. If you create an array as
1100 /dev/md1, then all superblocks will contain the minor number 1, even if
1101 the array is later assembled as /dev/md2.
1103 Giving the literal word "dev" for
1107 to use the minor number of the md device that is being assembled.
1108 e.g. when assembling
1110 .B \-\-super\-minor=dev
1111 will look for super blocks with a minor number of 0.
1114 is only relevant for v0.90 metadata, and should not normally be used.
1120 .BR \-N ", " \-\-name=
1121 Specify the name of the array to assemble. This must be the name
1122 that was specified when creating the array. It must either match
1123 the name stored in the superblock exactly, or it must match
1126 prefixed to the start of the given name.
1129 .BR \-f ", " \-\-force
1130 Assemble the array even if the metadata on some devices appears to be
1133 cannot find enough working devices to start the array, but can find
1134 some devices that are recorded as having failed, then it will mark
1135 those devices as working so that the array can be started.
1136 An array which requires
1138 to be started may contain data corruption. Use it carefully.
1141 .BR \-R ", " \-\-run
1142 Attempt to start the array even if fewer drives were given than were
1143 present last time the array was active. Normally if not all the
1144 expected drives are found and
1146 is not used, then the array will be assembled but not started.
1149 an attempt will be made to start it anyway.
1153 This is the reverse of
1155 in that it inhibits the startup of array unless all expected drives
1156 are present. This is only needed with
1158 and can be used if the physical connections to devices are
1159 not as reliable as you would like.
1162 .BR \-a ", " "\-\-auto{=no,yes,md,mdp,part}"
1163 See this option under Create and Build options.
1166 .BR \-b ", " \-\-bitmap=
1167 Specify the bitmap file that was given when the array was created. If
1170 bitmap, there is no need to specify this when assembling the array.
1173 .BR \-\-backup\-file=
1176 was used while reshaping an array (e.g. changing number of devices or
1177 chunk size) and the system crashed during the critical section, then the same
1179 must be presented to
1181 to allow possibly corrupted data to be restored, and the reshape
1185 .BR \-\-invalid\-backup
1186 If the file needed for the above option is not available for any
1187 reason an empty file can be given together with this option to
1188 indicate that the backup file is invalid. In this case the data that
1189 was being rearranged at the time of the crash could be irrecoverably
1190 lost, but the rest of the array may still be recoverable. This option
1191 should only be used as a last resort if there is no way to recover the
1196 .BR \-U ", " \-\-update=
1197 Update the superblock on each device while assembling the array. The
1198 argument given to this flag can be one of
1214 .BR layout\-original ,
1215 .BR layout\-alternate ,
1222 option will adjust the superblock of an array what was created on a Sparc
1223 machine running a patched 2.2 Linux kernel. This kernel got the
1224 alignment of part of the superblock wrong. You can use the
1225 .B "\-\-examine \-\-sparc2.2"
1228 to see what effect this would have.
1232 option will update the
1233 .B "preferred minor"
1234 field on each superblock to match the minor number of the array being
1236 This can be useful if
1238 reports a different "Preferred Minor" to
1240 In some cases this update will be performed automatically
1241 by the kernel driver. In particular the update happens automatically
1242 at the first write to an array with redundancy (RAID level 1 or
1243 greater) on a 2.6 (or later) kernel.
1247 option will change the uuid of the array. If a UUID is given with the
1249 option that UUID will be used as a new UUID and will
1251 be used to help identify the devices in the array.
1254 is given, a random UUID is chosen.
1258 option will change the
1260 of the array as stored in the superblock. This is only supported for
1261 version-1 superblocks.
1265 option will change the
1267 of the array as stored in the bitmap superblock. This option only
1268 works for a clustered environment.
1272 option will change the
1274 as recorded in the superblock. For version-0 superblocks, this is the
1275 same as updating the UUID.
1276 For version-1 superblocks, this involves updating the name.
1280 option will change the cluster name as recorded in the superblock and
1281 bitmap. This option only works for clustered environment.
1285 option will cause the array to be marked
1287 meaning that any redundancy in the array (e.g. parity for RAID5,
1288 copies for RAID1) may be incorrect. This will cause the RAID system
1289 to perform a "resync" pass to make sure that all redundant information
1294 option allows arrays to be moved between machines with different
1295 byte-order, such as from a big-endian machine like a Sparc or some
1296 MIPS machines, to a little-endian x86_64 machine.
1297 When assembling such an array for the first time after a move, giving
1298 .B "\-\-update=byteorder"
1301 to expect superblocks to have their byteorder reversed, and will
1302 correct that order before assembling the array. This is only valid
1303 with original (Version 0.90) superblocks.
1307 option will correct the summaries in the superblock. That is the
1308 counts of total, working, active, failed, and spare devices.
1312 option will rarely be of use. It applies to version 1.1 and 1.2 metadata
1313 only (where the metadata is at the start of the device) and is only
1314 useful when the component device has changed size (typically become
1315 larger). The version 1 metadata records the amount of the device that
1316 can be used to store data, so if a device in a version 1.1 or 1.2
1317 array becomes larger, the metadata will still be visible, but the
1318 extra space will not. In this case it might be useful to assemble the
1320 .BR \-\-update=devicesize .
1323 to determine the maximum usable amount of space on each device and
1324 update the relevant field in the metadata.
1328 option only works on v0.90 metadata arrays and will convert them to
1329 v1.0 metadata. The array must not be dirty (i.e. it must not need a
1330 sync) and it must not have a write-intent bitmap.
1332 The old metadata will remain on the devices, but will appear older
1333 than the new metadata and so will usually be ignored. The old metadata
1334 (or indeed the new metadata) can be removed by giving the appropriate
1337 .BR \-\-zero\-superblock .
1341 option can be used when an array has an internal bitmap which is
1342 corrupt in some way so that assembling the array normally fails. It
1343 will cause any internal bitmap to be ignored.
1347 option will reserve space in each device for a bad block list. This
1348 will be 4K in size and positioned near the end of any free space
1349 between the superblock and the data.
1353 option will cause any reservation of space for a bad block list to be
1354 removed. If the bad block list contains entries, this will fail, as
1355 removing the list could cause data corruption.
1359 option will enable PPL for a RAID5 array and reserve space for PPL on each
1360 device. There must be enough free space between the data and superblock and a
1361 write-intent bitmap or journal must not be used.
1365 option will disable PPL in the superblock.
1370 .B layout\-alternate
1371 options are for RAID0 arrays in use before Linux 5.4. If the array was being
1372 used with Linux 3.13 or earlier, then to assemble the array on a new kernel,
1373 .B \-\-update=layout\-original
1374 must be given. If the array was created and used with a kernel from Linux 3.14 to
1376 .B \-\-update=layout\-alternate
1377 must be given. This only needs to be given once. Subsequent assembly of the array
1378 will happen normally.
1379 For more information, see
1383 .BR \-\-freeze\-reshape
1384 Option is intended to be used in start-up scripts during initrd boot phase.
1385 When array under reshape is assembled during initrd phase, this option
1386 stops reshape after reshape critical section is being restored. This happens
1387 before file system pivot operation and avoids loss of file system context.
1388 Losing file system context would cause reshape to be broken.
1390 Reshape can be continued later using the
1392 option for the grow command.
1396 See this option under Create and Build options.
1398 .SH For Manage mode:
1401 .BR \-t ", " \-\-test
1402 Unless a more serious error occurred,
1404 will exit with a status of 2 if no changes were made to the array and
1405 0 if at least one change was made.
1406 This can be useful when an indirect specifier such as
1411 is used in requesting an operation on the array.
1413 will report failure if these specifiers didn't find any match.
1416 .BR \-a ", " \-\-add
1417 hot-add listed devices.
1418 If a device appears to have recently been part of the array
1419 (possibly it failed or was removed) the device is re\-added as described
1421 If that fails or the device was never part of the array, the device is
1422 added as a hot-spare.
1423 If the array is degraded, it will immediately start to rebuild data
1426 Note that this and the following options are only meaningful on array
1427 with redundancy. They don't apply to RAID0 or Linear.
1431 re\-add a device that was previously removed from an array.
1432 If the metadata on the device reports that it is a member of the
1433 array, and the slot that it used is still vacant, then the device will
1434 be added back to the array in the same position. This will normally
1435 cause the data for that device to be recovered. However based on the
1436 event count on the device, the recovery may only require sections that
1437 are flagged a write-intent bitmap to be recovered or may not require
1438 any recovery at all.
1440 When used on an array that has no metadata (i.e. it was built with
1442 it will be assumed that bitmap-based recovery is enough to make the
1443 device fully consistent with the array.
1445 When used with v1.x metadata,
1447 can be accompanied by
1448 .BR \-\-update=devicesize ,
1449 .BR \-\-update=bbl ", or"
1450 .BR \-\-update=no\-bbl .
1451 See the description of these option when used in Assemble mode for an
1452 explanation of their use.
1454 If the device name given is
1458 will try to find any device that looks like it should be
1459 part of the array but isn't and will try to re\-add all such devices.
1461 If the device name given is
1465 will find all devices in the array that are marked
1467 remove them and attempt to immediately re\-add them. This can be
1468 useful if you are certain that the reason for failure has been
1473 Add a device as a spare. This is similar to
1475 except that it does not attempt
1477 first. The device will be added as a spare even if it looks like it
1478 could be an recent member of the array.
1481 .BR \-r ", " \-\-remove
1482 remove listed devices. They must not be active. i.e. they should
1483 be failed or spare devices.
1485 As well as the name of a device file
1495 The first causes all failed device to be removed. The second causes
1496 any device which is no longer connected to the system (i.e an 'open'
1500 The third will remove a set as describe below under
1504 .BR \-f ", " \-\-fail
1505 Mark listed devices as faulty.
1506 As well as the name of a device file, the word
1510 can be given. The former will cause any device that has been detached from
1511 the system to be marked as failed. It can then be removed.
1513 For RAID10 arrays where the number of copies evenly divides the number
1514 of devices, the devices can be conceptually divided into sets where
1515 each set contains a single complete copy of the data on the array.
1516 Sometimes a RAID10 array will be configured so that these sets are on
1517 separate controllers. In this case all the devices in one set can be
1518 failed by giving a name like
1524 The appropriate set names are reported by
1534 Mark listed devices as requiring replacement. As soon as a spare is
1535 available, it will be rebuilt and will replace the marked device.
1536 This is similar to marking a device as faulty, but the device remains
1537 in service during the recovery process to increase resilience against
1538 multiple failures. When the replacement process finishes, the
1539 replaced device will be marked as faulty.
1543 This can follow a list of
1545 devices. The devices listed after
1547 will be preferentially used to replace the devices listed after
1549 These device must already be spare devices in the array.
1552 .BR \-\-write\-mostly
1553 Subsequent devices that are added or re\-added will have the 'write-mostly'
1554 flag set. This is only valid for RAID1 and means that the 'md' driver
1555 will avoid reading from these devices if possible.
1558 Subsequent devices that are added or re\-added will have the 'write-mostly'
1561 .BR \-\-cluster\-confirm
1562 Confirm the existence of the device. This is issued in response to an \-\-add
1563 request by a node in a cluster. When a node adds a device it sends a message
1564 to all nodes in the cluster to look for a device with a UUID. This translates
1565 to a udev notification with the UUID of the device to be added and the slot
1566 number. The receiving node must acknowledge this message
1567 with \-\-cluster\-confirm. Valid arguments are <slot>:<devicename> in case
1568 the device is found or <slot>:missing in case the device is not found.
1572 Add journal to an existing array, or recreate journal for RAID-4/5/6 array
1573 that lost a journal device. To avoid interrupting on-going write opertions,
1575 only works for array in Read-Only state.
1579 Subsequent devices that are added or re\-added will have
1580 the 'failfast' flag set. This is only valid for RAID1 and RAID10 and
1581 means that the 'md' driver will avoid long timeouts on error handling
1585 Subsequent devices that are re\-added will be re\-added without
1586 the 'failfast' flag set.
1589 Each of these options requires that the first device listed is the array
1590 to be acted upon, and the remainder are component devices to be added,
1591 removed, marked as faulty, etc. Several different operations can be
1592 specified for different devices, e.g.
1594 mdadm /dev/md0 \-\-add /dev/sda1 \-\-fail /dev/sdb1 \-\-remove /dev/sdb1
1596 Each operation applies to all devices listed until the next
1599 If an array is using a write-intent bitmap, then devices which have
1600 been removed can be re\-added in a way that avoids a full
1601 reconstruction but instead just updates the blocks that have changed
1602 since the device was removed. For arrays with persistent metadata
1603 (superblocks) this is done automatically. For arrays created with
1605 mdadm needs to be told that this device we removed recently with
1608 Devices can only be removed from an array if they are not in active
1609 use, i.e. that must be spares or failed devices. To remove an active
1610 device, it must first be marked as
1616 .BR \-Q ", " \-\-query
1617 Examine a device to see
1618 (1) if it is an md device and (2) if it is a component of an md
1620 Information about what is discovered is presented.
1623 .BR \-D ", " \-\-detail
1624 Print details of one or more md devices.
1627 .BR \-\-detail\-platform
1628 Print details of the platform's RAID capabilities (firmware / hardware
1629 topology) for a given metadata format. If used without argument, mdadm
1630 will scan all controllers looking for their capabilities. Otherwise, mdadm
1631 will only look at the controller specified by the argument in form of an
1632 absolute filepath or a link, e.g.
1633 .IR /sys/devices/pci0000:00/0000:00:1f.2 .
1636 .BR \-Y ", " \-\-export
1639 .BR \-\-detail-platform ,
1643 output will be formatted as
1645 pairs for easy import into the environment.
1651 indicates whether an array was started
1653 or not, which may include a reason
1654 .RB ( unsafe ", " nothing ", " no ).
1657 indicates if the array is expected on this host
1659 or seems to be from elsewhere
1663 .BR \-E ", " \-\-examine
1664 Print contents of the metadata stored on the named device(s).
1665 Note the contrast between
1670 applies to devices which are components of an array, while
1672 applies to a whole array which is currently active.
1675 If an array was created on a SPARC machine with a 2.2 Linux kernel
1676 patched with RAID support, the superblock will have been created
1677 incorrectly, or at least incompatibly with 2.4 and later kernels.
1682 will fix the superblock before displaying it. If this appears to do
1683 the right thing, then the array can be successfully assembled using
1684 .BR "\-\-assemble \-\-update=sparc2.2" .
1687 .BR \-X ", " \-\-examine\-bitmap
1688 Report information about a bitmap file.
1689 The argument is either an external bitmap file or an array component
1690 in case of an internal bitmap. Note that running this on an array
1693 does not report the bitmap for that array.
1696 .B \-\-examine\-badblocks
1697 List the bad-blocks recorded for the device, if a bad-blocks list has
1698 been configured. Currently only
1700 metadata supports bad-blocks lists.
1703 .BI \-\-dump= directory
1705 .BI \-\-restore= directory
1706 Save metadata from lists devices, or restore metadata to listed devices.
1709 .BR \-R ", " \-\-run
1710 start a partially assembled array. If
1712 did not find enough devices to fully start the array, it might leaving
1713 it partially assembled. If you wish, you can then use
1715 to start the array in degraded mode.
1718 .BR \-S ", " \-\-stop
1719 deactivate array, releasing all resources.
1722 .BR \-o ", " \-\-readonly
1723 mark array as readonly.
1726 .BR \-w ", " \-\-readwrite
1727 mark array as readwrite.
1730 .B \-\-zero\-superblock
1731 If the device contains a valid md superblock, the block is
1732 overwritten with zeros. With
1734 the block where the superblock would be is overwritten even if it
1735 doesn't appear to be valid.
1738 Be careful to call \-\-zero\-superblock with clustered raid, make sure
1739 array isn't used or assembled in other cluster node before execute it.
1742 .B \-\-kill\-subarray=
1743 If the device is a container and the argument to \-\-kill\-subarray
1744 specifies an inactive subarray in the container, then the subarray is
1745 deleted. Deleting all subarrays will leave an 'empty-container' or
1746 spare superblock on the drives. See
1747 .B \-\-zero\-superblock
1749 removing a superblock. Note that some formats depend on the subarray
1750 index for generating a UUID, this command will fail if it would change
1751 the UUID of an active subarray.
1754 .B \-\-update\-subarray=
1755 If the device is a container and the argument to \-\-update\-subarray
1756 specifies a subarray in the container, then attempt to update the given
1757 superblock field in the subarray. See below in
1762 .BR \-t ", " \-\-test
1767 is set to reflect the status of the device. See below in
1772 .BR \-W ", " \-\-wait
1773 For each md device given, wait for any resync, recovery, or reshape
1774 activity to finish before returning.
1776 will return with success if it actually waited for every device
1777 listed, otherwise it will return failure.
1781 For each md device given, or each device in /proc/mdstat if
1783 is given, arrange for the array to be marked clean as soon as possible.
1785 will return with success if the array uses external metadata and we
1786 successfully waited. For native arrays this returns immediately as the
1787 kernel handles dirty-clean transitions at shutdown. No action is taken
1788 if safe-mode handling is disabled.
1792 Set the "sync_action" for all md devices given to one of
1799 will abort any currently running action though some actions will
1800 automatically restart.
1803 will abort any current action and ensure no other action starts
1813 .BR "SCRUBBING AND MISMATCHES" .
1815 .SH For Incremental Assembly mode:
1817 .BR \-\-rebuild\-map ", " \-r
1818 Rebuild the map file
1822 uses to help track which arrays are currently being assembled.
1825 .BR \-\-run ", " \-R
1826 Run any array assembled as soon as a minimal number of devices are
1827 available, rather than waiting until all expected devices are present.
1830 .BR \-\-scan ", " \-s
1831 Only meaningful with
1835 file for arrays that are being incrementally assembled and will try to
1836 start any that are not already started. If any such array is listed
1839 as requiring an external bitmap, that bitmap will be attached first.
1842 .BR \-\-fail ", " \-f
1843 This allows the hot-plug system to remove devices that have fully disappeared
1844 from the kernel. It will first fail and then remove the device from any
1845 array it belongs to.
1846 The device name given should be a kernel device name such as "sda",
1852 Only used with \-\-fail. The 'path' given will be recorded so that if
1853 a new device appears at the same location it can be automatically
1854 added to the same array. This allows the failed device to be
1855 automatically replaced by a new device without metadata if it appears
1856 at specified path. This option is normally only set by a
1860 .SH For Monitor mode:
1862 .BR \-m ", " \-\-mail
1863 Give a mail address to send alerts to.
1866 .BR \-p ", " \-\-program ", " \-\-alert
1867 Give a program to be run whenever an event is detected.
1870 .BR \-y ", " \-\-syslog
1871 Cause all events to be reported through 'syslog'. The messages have
1872 facility of 'daemon' and varying priorities.
1875 .BR \-d ", " \-\-delay
1876 Give a delay in seconds.
1878 polls the md arrays and then waits this many seconds before polling
1879 again. The default is 60 seconds. Since 2.6.16, there is no need to
1880 reduce this as the kernel alerts
1882 immediately when there is any change.
1885 .BR \-r ", " \-\-increment
1886 Give a percentage increment.
1888 will generate RebuildNN events with the given percentage increment.
1891 .BR \-f ", " \-\-daemonise
1894 to run as a background daemon if it decides to monitor anything. This
1895 causes it to fork and run in the child, and to disconnect from the
1896 terminal. The process id of the child is written to stdout.
1899 which will only continue monitoring if a mail address or alert program
1900 is found in the config file.
1903 .BR \-i ", " \-\-pid\-file
1906 is running in daemon mode, write the pid of the daemon process to
1907 the specified file, instead of printing it on standard output.
1910 .BR \-1 ", " \-\-oneshot
1911 Check arrays only once. This will generate
1913 events and more significantly
1919 .B " mdadm \-\-monitor \-\-scan \-1"
1921 from a cron script will ensure regular notification of any degraded arrays.
1924 .BR \-t ", " \-\-test
1927 alert for every array found at startup. This alert gets mailed and
1928 passed to the alert program. This can be used for testing that alert
1929 message do get through successfully.
1933 This inhibits the functionality for moving spares between arrays.
1934 Only one monitoring process started with
1936 but without this flag is allowed, otherwise the two could interfere
1943 .B mdadm \-\-assemble
1944 .I md-device options-and-component-devices...
1947 .B mdadm \-\-assemble \-\-scan
1948 .I md-devices-and-options...
1951 .B mdadm \-\-assemble \-\-scan
1955 This usage assembles one or more RAID arrays from pre-existing components.
1956 For each array, mdadm needs to know the md device, the identity of the
1957 array, and a number of component-devices. These can be found in a number of ways.
1959 In the first usage example (without the
1961 the first device given is the md device.
1962 In the second usage example, all devices listed are treated as md
1963 devices and assembly is attempted.
1964 In the third (where no devices are listed) all md devices that are
1965 listed in the configuration file are assembled. If no arrays are
1966 described by the configuration file, then any arrays that
1967 can be found on unused devices will be assembled.
1969 If precisely one device is listed, but
1975 was given and identity information is extracted from the configuration file.
1977 The identity can be given with the
1983 option, will be taken from the md-device record in the config file, or
1984 will be taken from the super block of the first component-device
1985 listed on the command line.
1987 Devices can be given on the
1989 command line or in the config file. Only devices which have an md
1990 superblock which contains the right identity will be considered for
1993 The config file is only used if explicitly named with
1995 or requested with (a possibly implicit)
2000 .B /etc/mdadm/mdadm.conf
2005 is not given, then the config file will only be used to find the
2006 identity of md arrays.
2008 Normally the array will be started after it is assembled. However if
2010 is not given and not all expected drives were listed, then the array
2011 is not started (to guard against usage errors). To insist that the
2012 array be started in this case (as may work for RAID1, 4, 5, 6, or 10),
2021 does not create any entries in
2025 It does record information in
2029 to choose the correct name.
2033 detects that udev is not configured, it will create the devices in
2037 In Linux kernels prior to version 2.6.28 there were two distinctly
2038 different types of md devices that could be created: one that could be
2039 partitioned using standard partitioning tools and one that could not.
2040 Since 2.6.28 that distinction is no longer relevant as both type of
2041 devices can be partitioned.
2043 will normally create the type that originally could not be partitioned
2044 as it has a well defined major number (9).
2046 Prior to 2.6.28, it is important that mdadm chooses the correct type
2047 of array device to use. This can be controlled with the
2049 option. In particular, a value of "mdp" or "part" or "p" tells mdadm
2050 to use a partitionable device rather than the default.
2052 In the no-udev case, the value given to
2054 can be suffixed by a number. This tells
2056 to create that number of partition devices rather than the default of 4.
2060 can also be given in the configuration file as a word starting
2062 on the ARRAY line for the relevant array.
2069 and no devices are listed,
2071 will first attempt to assemble all the arrays listed in the config
2074 If no arrays are listed in the config (other than those marked
2076 it will look through the available devices for possible arrays and
2077 will try to assemble anything that it finds. Arrays which are tagged
2078 as belonging to the given homehost will be assembled and started
2079 normally. Arrays which do not obviously belong to this host are given
2080 names that are expected not to conflict with anything local, and are
2081 started "read-auto" so that nothing is written to any device until the
2082 array is written to. i.e. automatic resync etc is delayed.
2086 finds a consistent set of devices that look like they should comprise
2087 an array, and if the superblock is tagged as belonging to the given
2088 home host, it will automatically choose a device name and try to
2089 assemble the array. If the array uses version-0.90 metadata, then the
2091 number as recorded in the superblock is used to create a name in
2095 If the array uses version-1 metadata, then the
2097 from the superblock is used to similarly create a name in
2099 (the name will have any 'host' prefix stripped first).
2101 This behaviour can be modified by the
2105 configuration file. This line can indicate that specific metadata
2106 type should, or should not, be automatically assembled. If an array
2107 is found which is not listed in
2109 and has a metadata format that is denied by the
2111 line, then it will not be assembled.
2114 line can also request that all arrays identified as being for this
2115 homehost should be assembled regardless of their metadata type.
2118 for further details.
2120 Note: Auto assembly cannot be used for assembling and activating some
2121 arrays which are undergoing reshape. In particular as the
2123 cannot be given, any reshape which requires a backup-file to continue
2124 cannot be started by auto assembly. An array which is growing to more
2125 devices and has passed the critical section can be assembled using
2136 .BI \-\-raid\-devices= Z
2140 This usage is similar to
2142 The difference is that it creates an array without a superblock. With
2143 these arrays there is no difference between initially creating the array and
2144 subsequently assembling the array, except that hopefully there is useful
2145 data there in the second case.
2147 The level may raid0, linear, raid1, raid10, multipath, or faulty, or
2148 one of their synonyms. All devices must be listed and the array will
2149 be started once complete. It will often be appropriate to use
2150 .B \-\-assume\-clean
2151 with levels raid1 or raid10.
2162 .BI \-\-raid\-devices= Z
2166 This usage will initialise a new md array, associate some devices with
2167 it, and activate the array.
2169 The named device will normally not exist when
2170 .I "mdadm \-\-create"
2171 is run, but will be created by
2173 once the array becomes active.
2175 As devices are added, they are checked to see if they contain RAID
2176 superblocks or filesystems. They are also checked to see if the variance in
2177 device size exceeds 1%.
2179 If any discrepancy is found, the array will not automatically be run, though
2182 can override this caution.
2184 To create a "degraded" array in which some devices are missing, simply
2185 give the word "\fBmissing\fP"
2186 in place of a device name. This will cause
2188 to leave the corresponding slot in the array empty.
2189 For a RAID4 or RAID5 array at most one slot can be
2190 "\fBmissing\fP"; for a RAID6 array at most two slots.
2191 For a RAID1 array, only one real device needs to be given. All of the
2195 When creating a RAID5 array,
2197 will automatically create a degraded array with an extra spare drive.
2198 This is because building the spare into a degraded array is in general
2199 faster than resyncing the parity on a non-degraded, but not clean,
2200 array. This feature can be overridden with the
2204 When creating an array with version-1 metadata a name for the array is
2206 If this is not given with the
2210 will choose a name based on the last component of the name of the
2211 device being created. So if
2213 is being created, then the name
2218 is being created, then the name
2222 When creating a partition based array, using
2224 with version-1.x metadata, the partition type should be set to
2226 (non fs-data). This type selection allows for greater precision since
2227 using any other [RAID auto-detect (0xFD) or a GNU/Linux partition (0x83)],
2228 might create problems in the event of array recovery through a live cdrom.
2230 A new array will normally get a randomly assigned 128bit UUID which is
2231 very likely to be unique. If you have a specific need, you can choose
2232 a UUID for the array by giving the
2234 option. Be warned that creating two arrays with the same UUID is a
2235 recipe for disaster. Also, using
2237 when creating a v0.90 array will silently override any
2242 .\"option is given, it is not necessary to list any component-devices in this command.
2243 .\"They can be added later, before a
2247 .\"is given, the apparent size of the smallest drive given is used.
2249 If the array type supports a write-intent bitmap, and if the devices
2250 in the array exceed 100G is size, an internal write-intent bitmap
2251 will automatically be added unless some other option is explicitly
2254 option or a different consistency policy is selected with the
2255 .B \-\-consistency\-policy
2256 option. In any case space for a bitmap will be reserved so that one
2257 can be added later with
2258 .BR "\-\-grow \-\-bitmap=internal" .
2260 If the metadata type supports it (currently only 1.x and IMSM metadata),
2261 space will be allocated to store a bad block list. This allows a modest
2262 number of bad blocks to be recorded, allowing the drive to remain in
2263 service while only partially functional.
2265 When creating an array within a
2268 can be given either the list of devices to use, or simply the name of
2269 the container. The former case gives control over which devices in
2270 the container will be used for the array. The latter case allows
2272 to automatically choose which devices to use based on how much spare
2275 The General Management options that are valid with
2280 insist on running the array even if some devices look like they might
2285 start the array in readonly mode.
2292 .I options... devices...
2295 This usage will allow individual devices in an array to be failed,
2296 removed or added. It is possible to perform multiple operations with
2297 on command. For example:
2299 .B " mdadm /dev/md0 \-f /dev/hda1 \-r /dev/hda1 \-a /dev/hda1"
2305 and will then remove it from the array and finally add it back
2306 in as a spare. However only one md array can be affected by a single
2309 When a device is added to an active array, mdadm checks to see if it
2310 has metadata on it which suggests that it was recently a member of the
2311 array. If it does, it tries to "re\-add" the device. If there have
2312 been no changes since the device was removed, or if the array has a
2313 write-intent bitmap which has recorded whatever changes there were,
2314 then the device will immediately become a full member of the array and
2315 those differences recorded in the bitmap will be resolved.
2325 MISC mode includes a number of distinct operations that
2326 operate on distinct devices. The operations are:
2329 The device is examined to see if it is
2330 (1) an active md array, or
2331 (2) a component of an md array.
2332 The information discovered is reported.
2336 The device should be an active md device.
2338 will display a detailed description of the array.
2342 will cause the output to be less detailed and the format to be
2343 suitable for inclusion in
2347 will normally be 0 unless
2349 failed to get useful information about the device(s); however, if the
2351 option is given, then the exit status will be:
2355 The array is functioning normally.
2358 The array has at least one failed device.
2361 The array has multiple failed devices such that it is unusable.
2364 There was an error while trying to get information about the device.
2368 .B \-\-detail\-platform
2369 Print detail of the platform's RAID capabilities (firmware / hardware
2370 topology). If the metadata is specified with
2374 then the return status will be:
2378 metadata successfully enumerated its platform components on this system
2381 metadata is platform independent
2384 metadata failed to find its platform components on this system
2388 .B \-\-update\-subarray=
2389 If the device is a container and the argument to \-\-update\-subarray
2390 specifies a subarray in the container, then attempt to update the given
2391 superblock field in the subarray. Similar to updating an array in
2392 "assemble" mode, the field to update is selected by
2396 option. The supported options are
2404 option updates the subarray name in the metadata, it may not affect the
2405 device node name or the device node symlink until the subarray is
2406 re\-assembled. If updating
2408 would change the UUID of an active subarray this operation is blocked,
2409 and the command will end in an error.
2415 options enable and disable PPL in the metadata. Currently supported only for
2420 The device should be a component of an md array.
2422 will read the md superblock of the device and display the contents.
2427 is given, then multiple devices that are components of the one array
2428 are grouped together and reported in a single entry suitable
2434 without listing any devices will cause all devices listed in the
2435 config file to be examined.
2438 .BI \-\-dump= directory
2439 If the device contains RAID metadata, a file will be created in the
2441 and the metadata will be written to it. The file will be the same
2442 size as the device and have the metadata written in the file at the
2443 same locate that it exists in the device. However the file will be "sparse" so
2444 that only those blocks containing metadata will be allocated. The
2445 total space used will be small.
2447 The file name used in the
2449 will be the base name of the device. Further if any links appear in
2451 which point to the device, then hard links to the file will be created
2458 Multiple devices can be listed and their metadata will all be stored
2459 in the one directory.
2462 .BI \-\-restore= directory
2463 This is the reverse of
2466 will locate a file in the directory that has a name appropriate for
2467 the given device and will restore metadata from it. Names that match
2469 names are preferred, however if two of those refer to different files,
2471 will not choose between them but will abort the operation.
2473 If a file name is given instead of a
2477 will restore from that file to a single device, always provided the
2478 size of the file matches that of the device, and the file contains
2482 The devices should be active md arrays which will be deactivated, as
2483 long as they are not currently in use.
2487 This will fully activate a partially assembled md array.
2491 This will mark an active array as read-only, providing that it is
2492 not currently being used.
2498 array back to being read/write.
2502 For all operations except
2505 will cause the operation to be applied to all arrays listed in
2510 causes all devices listed in the config file to be examined.
2513 .BR \-b ", " \-\-brief
2514 Be less verbose. This is used with
2522 gives an intermediate level of verbosity.
2528 .B mdadm \-\-monitor
2529 .I options... devices...
2534 to periodically poll a number of md arrays and to report on any events
2537 will never exit once it decides that there are arrays to be checked,
2538 so it should normally be run in the background.
2540 As well as reporting events,
2542 may move a spare drive from one array to another if they are in the
2547 and if the destination array has a failed drive but no spares.
2549 If any devices are listed on the command line,
2551 will only monitor those devices. Otherwise all arrays listed in the
2552 configuration file will be monitored. Further, if
2554 is given, then any other md devices that appear in
2556 will also be monitored.
2558 The result of monitoring the arrays is the generation of events.
2559 These events are passed to a separate program (if specified) and may
2560 be mailed to a given E-mail address.
2562 When passing events to a program, the program is run once for each event,
2563 and is given 2 or 3 command-line arguments: the first is the
2564 name of the event (see below), the second is the name of the
2565 md device which is affected, and the third is the name of a related
2566 device if relevant (such as a component device that has failed).
2570 is given, then a program or an E-mail address must be specified on the
2571 command line or in the config file. If neither are available, then
2573 will not monitor anything.
2577 will continue monitoring as long as something was found to monitor. If
2578 no program or email is given, then each event is reported to
2581 The different events are:
2585 .B DeviceDisappeared
2586 An md array which previously was configured appears to no longer be
2587 configured. (syslog priority: Critical)
2591 was told to monitor an array which is RAID0 or Linear, then it will
2593 .B DeviceDisappeared
2594 with the extra information
2596 This is because RAID0 and Linear do not support the device-failed,
2597 hot-spare and resync operations which are monitored.
2601 An md array started reconstruction (e.g. recovery, resync, reshape,
2602 check, repair). (syslog priority: Warning)
2608 is a two-digit number (ie. 05, 48). This indicates that rebuild
2609 has passed that many percent of the total. The events are generated
2610 with fixed increment since 0. Increment size may be specified with
2611 a commandline option (default is 20). (syslog priority: Warning)
2615 An md array that was rebuilding, isn't any more, either because it
2616 finished normally or was aborted. (syslog priority: Warning)
2620 An active component device of an array has been marked as
2621 faulty. (syslog priority: Critical)
2625 A spare component device which was being rebuilt to replace a faulty
2626 device has failed. (syslog priority: Critical)
2630 A spare component device which was being rebuilt to replace a faulty
2631 device has been successfully rebuilt and has been made active.
2632 (syslog priority: Info)
2636 A new md array has been detected in the
2638 file. (syslog priority: Info)
2642 A newly noticed array appears to be degraded. This message is not
2645 notices a drive failure which causes degradation, but only when
2647 notices that an array is degraded when it first sees the array.
2648 (syslog priority: Critical)
2652 A spare drive has been moved from one array in a
2656 to another to allow a failed drive to be replaced.
2657 (syslog priority: Info)
2663 has been told, via the config file, that an array should have a certain
2664 number of spare devices, and
2666 detects that it has fewer than this number when it first sees the
2667 array, it will report a
2670 (syslog priority: Warning)
2674 An array was found at startup, and the
2677 (syslog priority: Info)
2687 cause Email to be sent. All events cause the program to be run.
2688 The program is run with two or three arguments: the event
2689 name, the array device and possibly a second device.
2691 Each event has an associated array device (e.g.
2693 and possibly a second device. For
2698 the second device is the relevant component device.
2701 the second device is the array that the spare was moved from.
2705 to move spares from one array to another, the different arrays need to
2706 be labeled with the same
2708 or the spares must be allowed to migrate through matching POLICY domains
2709 in the configuration file. The
2711 name can be any string; it is only necessary that different spare
2712 groups use different names.
2716 detects that an array in a spare group has fewer active
2717 devices than necessary for the complete array, and has no spare
2718 devices, it will look for another array in the same spare group that
2719 has a full complement of working drive and a spare. It will then
2720 attempt to remove the spare from the second drive and add it to the
2722 If the removal succeeds but the adding fails, then it is added back to
2725 If the spare group for a degraded array is not defined,
2727 will look at the rules of spare migration specified by POLICY lines in
2729 and then follow similar steps as above if a matching spare is found.
2732 The GROW mode is used for changing the size or shape of an active
2734 For this to work, the kernel must support the necessary change.
2735 Various types of growth are being added during 2.6 development.
2737 Currently the supported changes include
2739 change the "size" attribute for RAID1, RAID4, RAID5 and RAID6.
2741 increase or decrease the "raid\-devices" attribute of RAID0, RAID1, RAID4,
2744 change the chunk-size and layout of RAID0, RAID4, RAID5, RAID6 and RAID10.
2746 convert between RAID1 and RAID5, between RAID5 and RAID6, between
2747 RAID0, RAID4, and RAID5, and between RAID0 and RAID10 (in the near-2 mode).
2749 add a write-intent bitmap to any array which supports these bitmaps, or
2750 remove a write-intent bitmap from such an array.
2752 change the array's consistency policy.
2755 Using GROW on containers is currently supported only for Intel's IMSM
2756 container format. The number of devices in a container can be
2757 increased - which affects all arrays in the container - or an array
2758 in a container can be converted between levels where those levels are
2759 supported by the container, and the conversion is on of those listed
2765 Intel's native checkpointing doesn't use
2767 option and it is transparent for assembly feature.
2769 Roaming between Windows(R) and Linux systems for IMSM metadata is not
2770 supported during grow process.
2773 Normally when an array is built the "size" is taken from the smallest
2774 of the drives. If all the small drives in an arrays are, one at a
2775 time, removed and replaced with larger drives, then you could have an
2776 array of large drives with only a small amount used. In this
2777 situation, changing the "size" with "GROW" mode will allow the extra
2778 space to start being used. If the size is increased in this way, a
2779 "resync" process will start to make sure the new parts of the array
2782 Note that when an array changes size, any filesystem that may be
2783 stored in the array will not automatically grow or shrink to use or
2784 vacate the space. The
2785 filesystem will need to be explicitly told to use the extra space
2786 after growing, or to reduce its size
2788 to shrinking the array.
2790 Also the size of an array cannot be changed while it has an active
2791 bitmap. If an array has a bitmap, it must be removed before the size
2792 can be changed. Once the change is complete a new bitmap can be created.
2797 is not yet supported for external file bitmap.
2799 .SS RAID\-DEVICES CHANGES
2801 A RAID1 array can work with any number of devices from 1 upwards
2802 (though 1 is not very useful). There may be times which you want to
2803 increase or decrease the number of active devices. Note that this is
2804 different to hot-add or hot-remove which changes the number of
2807 When reducing the number of devices in a RAID1 array, the slots which
2808 are to be removed from the array must already be vacant. That is, the
2809 devices which were in those slots must be failed and removed.
2811 When the number of devices is increased, any hot spares that are
2812 present will be activated immediately.
2814 Changing the number of active devices in a RAID5 or RAID6 is much more
2815 effort. Every block in the array will need to be read and written
2816 back to a new location. From 2.6.17, the Linux Kernel is able to
2817 increase the number of devices in a RAID5 safely, including restarting
2818 an interrupted "reshape". From 2.6.31, the Linux Kernel is able to
2819 increase or decrease the number of devices in a RAID5 or RAID6.
2821 From 2.6.35, the Linux Kernel is able to convert a RAID0 in to a RAID4
2824 uses this functionality and the ability to add
2825 devices to a RAID4 to allow devices to be added to a RAID0. When
2826 requested to do this,
2828 will convert the RAID0 to a RAID4, add the necessary disks and make
2829 the reshape happen, and then convert the RAID4 back to RAID0.
2831 When decreasing the number of devices, the size of the array will also
2832 decrease. If there was data in the array, it could get destroyed and
2833 this is not reversible, so you should firstly shrink the filesystem on
2834 the array to fit within the new size. To help prevent accidents,
2836 requires that the size of the array be decreased first with
2837 .BR "mdadm --grow --array-size" .
2838 This is a reversible change which simply makes the end of the array
2839 inaccessible. The integrity of any data can then be checked before
2840 the non-reversible reduction in the number of devices is request.
2842 When relocating the first few stripes on a RAID5 or RAID6, it is not
2843 possible to keep the data on disk completely consistent and
2844 crash-proof. To provide the required safety, mdadm disables writes to
2845 the array while this "critical section" is reshaped, and takes a
2846 backup of the data that is in that section. For grows, this backup may be
2847 stored in any spare devices that the array has, however it can also be
2848 stored in a separate file specified with the
2850 option, and is required to be specified for shrinks, RAID level
2851 changes and layout changes. If this option is used, and the system
2852 does crash during the critical period, the same file must be passed to
2854 to restore the backup and reassemble the array. When shrinking rather
2855 than growing the array, the reshape is done from the end towards the
2856 beginning, so the "critical section" is at the end of the reshape.
2860 Changing the RAID level of any array happens instantaneously. However
2861 in the RAID5 to RAID6 case this requires a non-standard layout of the
2862 RAID6 data, and in the RAID6 to RAID5 case that non-standard layout is
2863 required before the change can be accomplished. So while the level
2864 change is instant, the accompanying layout change can take quite a
2867 is required. If the array is not simultaneously being grown or
2868 shrunk, so that the array size will remain the same - for example,
2869 reshaping a 3-drive RAID5 into a 4-drive RAID6 - the backup file will
2870 be used not just for a "cricital section" but throughout the reshape
2871 operation, as described below under LAYOUT CHANGES.
2873 .SS CHUNK-SIZE AND LAYOUT CHANGES
2875 Changing the chunk-size of layout without also changing the number of
2876 devices as the same time will involve re-writing all blocks in-place.
2877 To ensure against data loss in the case of a crash, a
2879 must be provided for these changes. Small sections of the array will
2880 be copied to the backup file while they are being rearranged. This
2881 means that all the data is copied twice, once to the backup and once
2882 to the new layout on the array, so this type of reshape will go very
2885 If the reshape is interrupted for any reason, this backup file must be
2887 .B "mdadm --assemble"
2888 so the array can be reassembled. Consequently the file cannot be
2889 stored on the device being reshaped.
2894 A write-intent bitmap can be added to, or removed from, an active
2895 array. Either internal bitmaps, or bitmaps stored in a separate file,
2896 can be added. Note that if you add a bitmap stored in a file which is
2897 in a filesystem that is on the RAID array being affected, the system
2898 will deadlock. The bitmap must be on a separate filesystem.
2900 .SS CONSISTENCY POLICY CHANGES
2902 The consistency policy of an active array can be changed by using the
2903 .B \-\-consistency\-policy
2904 option in Grow mode. Currently this works only for the
2908 policies and allows to enable or disable the RAID5 Partial Parity Log (PPL).
2910 .SH INCREMENTAL MODE
2914 .B mdadm \-\-incremental
2918 .RI [ optional-aliases-for-device ]
2921 .B mdadm \-\-incremental \-\-fail
2925 .B mdadm \-\-incremental \-\-rebuild\-map
2928 .B mdadm \-\-incremental \-\-run \-\-scan
2931 This mode is designed to be used in conjunction with a device
2932 discovery system. As devices are found in a system, they can be
2934 .B "mdadm \-\-incremental"
2935 to be conditionally added to an appropriate array.
2937 Conversely, it can also be used with the
2939 flag to do just the opposite and find whatever array a particular device
2940 is part of and remove the device from that array.
2942 If the device passed is a
2944 device created by a previous call to
2946 then rather than trying to add that device to an array, all the arrays
2947 described by the metadata of the container will be started.
2950 performs a number of tests to determine if the device is part of an
2951 array, and which array it should be part of. If an appropriate array
2952 is found, or can be created,
2954 adds the device to the array and conditionally starts the array.
2958 will normally only add devices to an array which were previously working
2959 (active or spare) parts of that array. The support for automatic
2960 inclusion of a new drive as a spare in some array requires
2961 a configuration through POLICY in config file.
2965 makes are as follow:
2967 Is the device permitted by
2969 That is, is it listed in a
2971 line in that file. If
2973 is absent then the default it to allow any device. Similarly if
2975 contains the special word
2977 then any device is allowed. Otherwise the device name given to
2979 or one of the aliases given, or an alias found in the filesystem,
2980 must match one of the names or patterns in a
2984 This is the only context where the aliases are used. They are
2985 usually provided by a
2988 .BR $env{DEVLINKS} .
2991 Does the device have a valid md superblock? If a specific metadata
2992 version is requested with
2996 then only that style of metadata is accepted, otherwise
2998 finds any known version of metadata. If no
3000 metadata is found, the device may be still added to an array
3001 as a spare if POLICY allows.
3005 Does the metadata match an expected array?
3006 The metadata can match in two ways. Either there is an array listed
3009 which identifies the array (either by UUID, by name, by device list,
3010 or by minor-number), or the array was created with a
3016 or on the command line.
3019 is not able to positively identify the array as belonging to the
3020 current host, the device will be rejected.
3025 keeps a list of arrays that it has partially assembled in
3027 If no array exists which matches
3028 the metadata on the new device,
3030 must choose a device name and unit number. It does this based on any
3033 or any name information stored in the metadata. If this name
3034 suggests a unit number, that number will be used, otherwise a free
3035 unit number will be chosen. Normally
3037 will prefer to create a partitionable array, however if the
3041 suggests that a non-partitionable array is preferred, that will be
3044 If the array is not found in the config file and its metadata does not
3045 identify it as belonging to the "homehost", then
3047 will choose a name for the array which is certain not to conflict with
3048 any array which does belong to this host. It does this be adding an
3049 underscore and a small number to the name preferred by the metadata.
3051 Once an appropriate array is found or created and the device is added,
3053 must decide if the array is ready to be started. It will
3054 normally compare the number of available (non-spare) devices to the
3055 number of devices that the metadata suggests need to be active. If
3056 there are at least that many, the array will be started. This means
3057 that if any devices are missing the array will not be restarted.
3063 in which case the array will be run as soon as there are enough
3064 devices present for the data to be accessible. For a RAID1, that
3065 means one device will start the array. For a clean RAID5, the array
3066 will be started as soon as all but one drive is present.
3068 Note that neither of these approaches is really ideal. If it can
3069 be known that all device discovery has completed, then
3073 can be run which will try to start all arrays that are being
3074 incrementally assembled. They are started in "read-auto" mode in
3075 which they are read-only until the first write request. This means
3076 that no metadata updates are made and no attempt at resync or recovery
3077 happens. Further devices that are found before the first write can
3078 still be added safely.
3081 This section describes environment variables that affect how mdadm
3086 Setting this value to 1 will prevent mdadm from automatically launching
3087 mdmon. This variable is intended primarily for debugging mdadm/mdmon.
3093 does not create any device nodes in /dev, but leaves that task to
3097 appears not to be configured, or if this environment variable is set
3100 will create and devices that are needed.
3103 .B MDADM_NO_SYSTEMCTL
3108 is in use it will normally request
3110 to start various background tasks (particularly
3112 rather than forking and running them in the background. This can be
3113 suppressed by setting
3114 .BR MDADM_NO_SYSTEMCTL=1 .
3118 A key value of IMSM metadata is that it allows interoperability with
3119 boot ROMs on Intel platforms, and with other major operating systems.
3122 will only allow an IMSM array to be created or modified if detects
3123 that it is running on an Intel platform which supports IMSM, and
3124 supports the particular configuration of IMSM that is being requested
3125 (some functionality requires newer OROM support).
3127 These checks can be suppressed by setting IMSM_NO_PLATFORM=1 in the
3128 environment. This can be useful for testing or for disaster
3129 recovery. You should be aware that interoperability may be
3130 compromised by setting this value.
3133 .B MDADM_GROW_ALLOW_OLD
3134 If an array is stopped while it is performing a reshape and that
3135 reshape was making use of a backup file, then when the array is
3138 will sometimes complain that the backup file is too old. If this
3139 happens and you are certain it is the right backup file, you can
3140 over-ride this check by setting
3141 .B MDADM_GROW_ALLOW_OLD=1
3146 Any string given in this variable is added to the start of the
3148 line in the config file, or treated as the whole
3150 line if none is given. It can be used to disable certain metadata
3153 is called from a boot script. For example
3155 .B " export MDADM_CONF_AUTO='-ddf -imsm'
3159 does not automatically assemble any DDF or
3160 IMSM arrays that are found. This can be useful on systems configured
3161 to manage such arrays with
3167 .B " mdadm \-\-query /dev/name-of-device"
3169 This will find out if a given device is a RAID array, or is part of
3170 one, and will provide brief information about the device.
3172 .B " mdadm \-\-assemble \-\-scan"
3174 This will assemble and start all arrays listed in the standard config
3175 file. This command will typically go in a system startup file.
3177 .B " mdadm \-\-stop \-\-scan"
3179 This will shut down all arrays that can be shut down (i.e. are not
3180 currently in use). This will typically go in a system shutdown script.
3182 .B " mdadm \-\-follow \-\-scan \-\-delay=120"
3184 If (and only if) there is an Email address or program given in the
3185 standard config file, then
3186 monitor the status of all arrays listed in that file by
3187 polling them ever 2 minutes.
3189 .B " mdadm \-\-create /dev/md0 \-\-level=1 \-\-raid\-devices=2 /dev/hd[ac]1"
3191 Create /dev/md0 as a RAID1 array consisting of /dev/hda1 and /dev/hdc1.
3194 .B " echo 'DEVICE /dev/hd*[0\-9] /dev/sd*[0\-9]' > mdadm.conf"
3196 .B " mdadm \-\-detail \-\-scan >> mdadm.conf"
3198 This will create a prototype config file that describes currently
3199 active arrays that are known to be made from partitions of IDE or SCSI drives.
3200 This file should be reviewed before being used as it may
3201 contain unwanted detail.
3203 .B " echo 'DEVICE /dev/hd[a\-z] /dev/sd*[a\-z]' > mdadm.conf"
3205 .B " mdadm \-\-examine \-\-scan \-\-config=mdadm.conf >> mdadm.conf"
3207 This will find arrays which could be assembled from existing IDE and
3208 SCSI whole drives (not partitions), and store the information in the
3209 format of a config file.
3210 This file is very likely to contain unwanted detail, particularly
3213 entries. It should be reviewed and edited before being used as an
3216 .B " mdadm \-\-examine \-\-brief \-\-scan \-\-config=partitions"
3218 .B " mdadm \-Ebsc partitions"
3220 Create a list of devices by reading
3221 .BR /proc/partitions ,
3222 scan these for RAID superblocks, and printout a brief listing of all
3225 .B " mdadm \-Ac partitions \-m 0 /dev/md0"
3227 Scan all partitions and devices listed in
3228 .BR /proc/partitions
3231 out of all such devices with a RAID superblock with a minor number of 0.
3233 .B " mdadm \-\-monitor \-\-scan \-\-daemonise > /run/mdadm/mon.pid"
3235 If config file contains a mail address or alert program, run mdadm in
3236 the background in monitor mode monitoring all md devices. Also write
3237 pid of mdadm daemon to
3238 .BR /run/mdadm/mon.pid .
3240 .B " mdadm \-Iq /dev/somedevice"
3242 Try to incorporate newly discovered device into some array as
3245 .B " mdadm \-\-incremental \-\-rebuild\-map \-\-run \-\-scan"
3247 Rebuild the array map from any current arrays, and then start any that
3250 .B " mdadm /dev/md4 --fail detached --remove detached"
3252 Any devices which are components of /dev/md4 will be marked as faulty
3253 and then remove from the array.
3255 .B " mdadm --grow /dev/md4 --level=6 --backup-file=/root/backup-md4"
3259 which is currently a RAID5 array will be converted to RAID6. There
3260 should normally already be a spare drive attached to the array as a
3261 RAID6 needs one more drive than a matching RAID5.
3263 .B " mdadm --create /dev/md/ddf --metadata=ddf --raid-disks 6 /dev/sd[a-f]"
3265 Create a DDF array over 6 devices.
3267 .B " mdadm --create /dev/md/home -n3 -l5 -z 30000000 /dev/md/ddf"
3269 Create a RAID5 array over any 3 devices in the given DDF set. Use
3270 only 30 gigabytes of each device.
3272 .B " mdadm -A /dev/md/ddf1 /dev/sd[a-f]"
3274 Assemble a pre-exist ddf array.
3276 .B " mdadm -I /dev/md/ddf1"
3278 Assemble all arrays contained in the ddf array, assigning names as
3281 .B " mdadm \-\-create \-\-help"
3283 Provide help about the Create mode.
3285 .B " mdadm \-\-config \-\-help"
3287 Provide help about the format of the config file.
3289 .B " mdadm \-\-help"
3291 Provide general help.
3301 lists all active md devices with information about them.
3303 uses this to find arrays when
3305 is given in Misc mode, and to monitor array reconstruction
3310 The config file lists which devices may be scanned to see if
3311 they contain MD super block, and gives identifying information
3312 (e.g. UUID) about known MD arrays. See
3316 .SS /etc/mdadm.conf.d
3318 A directory containing configuration files which are read in lexical
3324 mode is used, this file gets a list of arrays currently being created.
3329 understand two sorts of names for array devices.
3331 The first is the so-called 'standard' format name, which matches the
3332 names used by the kernel and which appear in
3335 The second sort can be freely chosen, but must reside in
3337 When giving a device name to
3339 to create or assemble an array, either full path name such as
3343 can be given, or just the suffix of the second sort of name, such as
3349 chooses device names during auto-assembly or incremental assembly, it
3350 will sometimes add a small sequence number to the end of the name to
3351 avoid conflicted between multiple arrays that have the same name. If
3353 can reasonably determine that the array really is meant for this host,
3354 either by a hostname in the metadata, or by the presence of the array
3357 then it will leave off the suffix if possible.
3358 Also if the homehost is specified as
3361 will only use a suffix if a different array of the same name already
3362 exists or is listed in the config file.
3364 The standard names for non-partitioned arrays (the only sort of md
3365 array available in 2.4 and earlier) are of the form
3369 where NN is a number.
3370 The standard names for partitionable arrays (as available from 2.6
3371 onwards) are of the form:
3375 Partition numbers should be indicated by adding "pMM" to these, thus "/dev/md/d1p2".
3377 From kernel version 2.6.28 the "non-partitioned array" can actually
3378 be partitioned. So the "md_d\fBNN\fP"
3379 names are no longer needed, and
3380 partitions such as "/dev/md\fBNN\fPp\fBXX\fP"
3383 From kernel version 2.6.29 standard names can be non-numeric following
3390 is any string. These names are supported by
3392 since version 3.3 provided they are enabled in
3397 was previously known as
3401 For further information on mdadm usage, MD and the various levels of
3404 .B http://raid.wiki.kernel.org/
3406 (based upon Jakob \(/Ostergaard's Software\-RAID.HOWTO)
3408 The latest version of
3410 should always be available from
3412 .B http://www.kernel.org/pub/linux/utils/raid/mdadm/
projects / thirdparty / mdadm.git / blob