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 "" v4.2-rc1
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 https://www.intel.com/content/www/us/en/support/products/122484/memory-and-storage/ssd-software/intel-virtual-raid-on-cpu-intel-vroc.html
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', 'G' or 'T' can be given to indicate Kilobytes,
471 Megabytes, Gigabytes or Terabytes 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', 'G' or 'T' can be given to indicate Kilobytes,
536 Megabytes, Gigabytes or Terabytes 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', 'G' or 'T' can be given to indicate Kilobytes,
555 Megabytes, Gigabytes or Terabytes 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', 'G' or 'T' can be given to indicate Kilobytes,
771 Megabytes, Gigabytes or Terabytes 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', 'G' or 'T' is used to explicitly
861 indicate Kilobytes, Megabytes, Gigabytes or Terabytes 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. This works only for
1136 native. For external metadata it allows to start dirty degraded RAID 4, 5, 6.
1137 An array which requires
1139 to be started may contain data corruption. Use it carefully.
1142 .BR \-R ", " \-\-run
1143 Attempt to start the array even if fewer drives were given than were
1144 present last time the array was active. Normally if not all the
1145 expected drives are found and
1147 is not used, then the array will be assembled but not started.
1150 an attempt will be made to start it anyway.
1154 This is the reverse of
1156 in that it inhibits the startup of array unless all expected drives
1157 are present. This is only needed with
1159 and can be used if the physical connections to devices are
1160 not as reliable as you would like.
1163 .BR \-a ", " "\-\-auto{=no,yes,md,mdp,part}"
1164 See this option under Create and Build options.
1167 .BR \-b ", " \-\-bitmap=
1168 Specify the bitmap file that was given when the array was created. If
1171 bitmap, there is no need to specify this when assembling the array.
1174 .BR \-\-backup\-file=
1177 was used while reshaping an array (e.g. changing number of devices or
1178 chunk size) and the system crashed during the critical section, then the same
1180 must be presented to
1182 to allow possibly corrupted data to be restored, and the reshape
1186 .BR \-\-invalid\-backup
1187 If the file needed for the above option is not available for any
1188 reason an empty file can be given together with this option to
1189 indicate that the backup file is invalid. In this case the data that
1190 was being rearranged at the time of the crash could be irrecoverably
1191 lost, but the rest of the array may still be recoverable. This option
1192 should only be used as a last resort if there is no way to recover the
1197 .BR \-U ", " \-\-update=
1198 Update the superblock on each device while assembling the array. The
1199 argument given to this flag can be one of
1215 .BR layout\-original ,
1216 .BR layout\-alternate ,
1217 .BR layout\-unspecified ,
1224 option will adjust the superblock of an array what was created on a Sparc
1225 machine running a patched 2.2 Linux kernel. This kernel got the
1226 alignment of part of the superblock wrong. You can use the
1227 .B "\-\-examine \-\-sparc2.2"
1230 to see what effect this would have.
1234 option will update the
1235 .B "preferred minor"
1236 field on each superblock to match the minor number of the array being
1238 This can be useful if
1240 reports a different "Preferred Minor" to
1242 In some cases this update will be performed automatically
1243 by the kernel driver. In particular the update happens automatically
1244 at the first write to an array with redundancy (RAID level 1 or
1245 greater) on a 2.6 (or later) kernel.
1249 option will change the uuid of the array. If a UUID is given with the
1251 option that UUID will be used as a new UUID and will
1253 be used to help identify the devices in the array.
1256 is given, a random UUID is chosen.
1260 option will change the
1262 of the array as stored in the superblock. This is only supported for
1263 version-1 superblocks.
1267 option will change the
1269 of the array as stored in the bitmap superblock. This option only
1270 works for a clustered environment.
1274 option will change the
1276 as recorded in the superblock. For version-0 superblocks, this is the
1277 same as updating the UUID.
1278 For version-1 superblocks, this involves updating the name.
1282 option will change the cluster name as recorded in the superblock and
1283 bitmap. This option only works for clustered environment.
1287 option will cause the array to be marked
1289 meaning that any redundancy in the array (e.g. parity for RAID5,
1290 copies for RAID1) may be incorrect. This will cause the RAID system
1291 to perform a "resync" pass to make sure that all redundant information
1296 option allows arrays to be moved between machines with different
1297 byte-order, such as from a big-endian machine like a Sparc or some
1298 MIPS machines, to a little-endian x86_64 machine.
1299 When assembling such an array for the first time after a move, giving
1300 .B "\-\-update=byteorder"
1303 to expect superblocks to have their byteorder reversed, and will
1304 correct that order before assembling the array. This is only valid
1305 with original (Version 0.90) superblocks.
1309 option will correct the summaries in the superblock. That is the
1310 counts of total, working, active, failed, and spare devices.
1314 option will rarely be of use. It applies to version 1.1 and 1.2 metadata
1315 only (where the metadata is at the start of the device) and is only
1316 useful when the component device has changed size (typically become
1317 larger). The version 1 metadata records the amount of the device that
1318 can be used to store data, so if a device in a version 1.1 or 1.2
1319 array becomes larger, the metadata will still be visible, but the
1320 extra space will not. In this case it might be useful to assemble the
1322 .BR \-\-update=devicesize .
1325 to determine the maximum usable amount of space on each device and
1326 update the relevant field in the metadata.
1330 option only works on v0.90 metadata arrays and will convert them to
1331 v1.0 metadata. The array must not be dirty (i.e. it must not need a
1332 sync) and it must not have a write-intent bitmap.
1334 The old metadata will remain on the devices, but will appear older
1335 than the new metadata and so will usually be ignored. The old metadata
1336 (or indeed the new metadata) can be removed by giving the appropriate
1339 .BR \-\-zero\-superblock .
1343 option can be used when an array has an internal bitmap which is
1344 corrupt in some way so that assembling the array normally fails. It
1345 will cause any internal bitmap to be ignored.
1349 option will reserve space in each device for a bad block list. This
1350 will be 4K in size and positioned near the end of any free space
1351 between the superblock and the data.
1355 option will cause any reservation of space for a bad block list to be
1356 removed. If the bad block list contains entries, this will fail, as
1357 removing the list could cause data corruption.
1361 option will enable PPL for a RAID5 array and reserve space for PPL on each
1362 device. There must be enough free space between the data and superblock and a
1363 write-intent bitmap or journal must not be used.
1367 option will disable PPL in the superblock.
1372 .B layout\-alternate
1373 options are for RAID0 arrays with non-uniform devices size that were in
1374 use before Linux 5.4. If the array was being used with Linux 3.13 or
1375 earlier, then to assemble the array on a new kernel,
1376 .B \-\-update=layout\-original
1377 must be given. If the array was created and used with a kernel from Linux 3.14 to
1379 .B \-\-update=layout\-alternate
1380 must be given. This only needs to be given once. Subsequent assembly of the array
1381 will happen normally.
1382 For more information, see
1386 .B layout\-unspecified
1387 option reverts the effect of
1390 .B layout\-alternate
1391 and allows the array to be again used on a kernel prior to Linux 5.3.
1392 This option should be used with great caution.
1395 .BR \-\-freeze\-reshape
1396 Option is intended to be used in start-up scripts during initrd boot phase.
1397 When array under reshape is assembled during initrd phase, this option
1398 stops reshape after reshape critical section is being restored. This happens
1399 before file system pivot operation and avoids loss of file system context.
1400 Losing file system context would cause reshape to be broken.
1402 Reshape can be continued later using the
1404 option for the grow command.
1408 See this option under Create and Build options.
1410 .SH For Manage mode:
1413 .BR \-t ", " \-\-test
1414 Unless a more serious error occurred,
1416 will exit with a status of 2 if no changes were made to the array and
1417 0 if at least one change was made.
1418 This can be useful when an indirect specifier such as
1423 is used in requesting an operation on the array.
1425 will report failure if these specifiers didn't find any match.
1428 .BR \-a ", " \-\-add
1429 hot-add listed devices.
1430 If a device appears to have recently been part of the array
1431 (possibly it failed or was removed) the device is re\-added as described
1433 If that fails or the device was never part of the array, the device is
1434 added as a hot-spare.
1435 If the array is degraded, it will immediately start to rebuild data
1438 Note that this and the following options are only meaningful on array
1439 with redundancy. They don't apply to RAID0 or Linear.
1443 re\-add a device that was previously removed from an array.
1444 If the metadata on the device reports that it is a member of the
1445 array, and the slot that it used is still vacant, then the device will
1446 be added back to the array in the same position. This will normally
1447 cause the data for that device to be recovered. However based on the
1448 event count on the device, the recovery may only require sections that
1449 are flagged a write-intent bitmap to be recovered or may not require
1450 any recovery at all.
1452 When used on an array that has no metadata (i.e. it was built with
1454 it will be assumed that bitmap-based recovery is enough to make the
1455 device fully consistent with the array.
1457 When used with v1.x metadata,
1459 can be accompanied by
1460 .BR \-\-update=devicesize ,
1461 .BR \-\-update=bbl ", or"
1462 .BR \-\-update=no\-bbl .
1463 See the description of these option when used in Assemble mode for an
1464 explanation of their use.
1466 If the device name given is
1470 will try to find any device that looks like it should be
1471 part of the array but isn't and will try to re\-add all such devices.
1473 If the device name given is
1477 will find all devices in the array that are marked
1479 remove them and attempt to immediately re\-add them. This can be
1480 useful if you are certain that the reason for failure has been
1485 Add a device as a spare. This is similar to
1487 except that it does not attempt
1489 first. The device will be added as a spare even if it looks like it
1490 could be an recent member of the array.
1493 .BR \-r ", " \-\-remove
1494 remove listed devices. They must not be active. i.e. they should
1495 be failed or spare devices.
1497 As well as the name of a device file
1507 The first causes all failed device to be removed. The second causes
1508 any device which is no longer connected to the system (i.e an 'open'
1512 The third will remove a set as describe below under
1516 .BR \-f ", " \-\-fail
1517 Mark listed devices as faulty.
1518 As well as the name of a device file, the word
1522 can be given. The former will cause any device that has been detached from
1523 the system to be marked as failed. It can then be removed.
1525 For RAID10 arrays where the number of copies evenly divides the number
1526 of devices, the devices can be conceptually divided into sets where
1527 each set contains a single complete copy of the data on the array.
1528 Sometimes a RAID10 array will be configured so that these sets are on
1529 separate controllers. In this case all the devices in one set can be
1530 failed by giving a name like
1536 The appropriate set names are reported by
1546 Mark listed devices as requiring replacement. As soon as a spare is
1547 available, it will be rebuilt and will replace the marked device.
1548 This is similar to marking a device as faulty, but the device remains
1549 in service during the recovery process to increase resilience against
1550 multiple failures. When the replacement process finishes, the
1551 replaced device will be marked as faulty.
1555 This can follow a list of
1557 devices. The devices listed after
1559 will be preferentially used to replace the devices listed after
1561 These device must already be spare devices in the array.
1564 .BR \-\-write\-mostly
1565 Subsequent devices that are added or re\-added will have the 'write-mostly'
1566 flag set. This is only valid for RAID1 and means that the 'md' driver
1567 will avoid reading from these devices if possible.
1570 Subsequent devices that are added or re\-added will have the 'write-mostly'
1573 .BR \-\-cluster\-confirm
1574 Confirm the existence of the device. This is issued in response to an \-\-add
1575 request by a node in a cluster. When a node adds a device it sends a message
1576 to all nodes in the cluster to look for a device with a UUID. This translates
1577 to a udev notification with the UUID of the device to be added and the slot
1578 number. The receiving node must acknowledge this message
1579 with \-\-cluster\-confirm. Valid arguments are <slot>:<devicename> in case
1580 the device is found or <slot>:missing in case the device is not found.
1584 Add journal to an existing array, or recreate journal for RAID-4/5/6 array
1585 that lost a journal device. To avoid interrupting on-going write opertions,
1587 only works for array in Read-Only state.
1591 Subsequent devices that are added or re\-added will have
1592 the 'failfast' flag set. This is only valid for RAID1 and RAID10 and
1593 means that the 'md' driver will avoid long timeouts on error handling
1597 Subsequent devices that are re\-added will be re\-added without
1598 the 'failfast' flag set.
1601 Each of these options requires that the first device listed is the array
1602 to be acted upon, and the remainder are component devices to be added,
1603 removed, marked as faulty, etc. Several different operations can be
1604 specified for different devices, e.g.
1606 mdadm /dev/md0 \-\-add /dev/sda1 \-\-fail /dev/sdb1 \-\-remove /dev/sdb1
1608 Each operation applies to all devices listed until the next
1611 If an array is using a write-intent bitmap, then devices which have
1612 been removed can be re\-added in a way that avoids a full
1613 reconstruction but instead just updates the blocks that have changed
1614 since the device was removed. For arrays with persistent metadata
1615 (superblocks) this is done automatically. For arrays created with
1617 mdadm needs to be told that this device we removed recently with
1620 Devices can only be removed from an array if they are not in active
1621 use, i.e. that must be spares or failed devices. To remove an active
1622 device, it must first be marked as
1628 .BR \-Q ", " \-\-query
1629 Examine a device to see
1630 (1) if it is an md device and (2) if it is a component of an md
1632 Information about what is discovered is presented.
1635 .BR \-D ", " \-\-detail
1636 Print details of one or more md devices.
1639 .BR \-\-detail\-platform
1640 Print details of the platform's RAID capabilities (firmware / hardware
1641 topology) for a given metadata format. If used without argument, mdadm
1642 will scan all controllers looking for their capabilities. Otherwise, mdadm
1643 will only look at the controller specified by the argument in form of an
1644 absolute filepath or a link, e.g.
1645 .IR /sys/devices/pci0000:00/0000:00:1f.2 .
1648 .BR \-Y ", " \-\-export
1651 .BR \-\-detail-platform ,
1655 output will be formatted as
1657 pairs for easy import into the environment.
1663 indicates whether an array was started
1665 or not, which may include a reason
1666 .RB ( unsafe ", " nothing ", " no ).
1669 indicates if the array is expected on this host
1671 or seems to be from elsewhere
1675 .BR \-E ", " \-\-examine
1676 Print contents of the metadata stored on the named device(s).
1677 Note the contrast between
1682 applies to devices which are components of an array, while
1684 applies to a whole array which is currently active.
1687 If an array was created on a SPARC machine with a 2.2 Linux kernel
1688 patched with RAID support, the superblock will have been created
1689 incorrectly, or at least incompatibly with 2.4 and later kernels.
1694 will fix the superblock before displaying it. If this appears to do
1695 the right thing, then the array can be successfully assembled using
1696 .BR "\-\-assemble \-\-update=sparc2.2" .
1699 .BR \-X ", " \-\-examine\-bitmap
1700 Report information about a bitmap file.
1701 The argument is either an external bitmap file or an array component
1702 in case of an internal bitmap. Note that running this on an array
1705 does not report the bitmap for that array.
1708 .B \-\-examine\-badblocks
1709 List the bad-blocks recorded for the device, if a bad-blocks list has
1710 been configured. Currently only
1714 metadata support bad-blocks lists.
1717 .BI \-\-dump= directory
1719 .BI \-\-restore= directory
1720 Save metadata from lists devices, or restore metadata to listed devices.
1723 .BR \-R ", " \-\-run
1724 start a partially assembled array. If
1726 did not find enough devices to fully start the array, it might leaving
1727 it partially assembled. If you wish, you can then use
1729 to start the array in degraded mode.
1732 .BR \-S ", " \-\-stop
1733 deactivate array, releasing all resources.
1736 .BR \-o ", " \-\-readonly
1737 mark array as readonly.
1740 .BR \-w ", " \-\-readwrite
1741 mark array as readwrite.
1744 .B \-\-zero\-superblock
1745 If the device contains a valid md superblock, the block is
1746 overwritten with zeros. With
1748 the block where the superblock would be is overwritten even if it
1749 doesn't appear to be valid.
1752 Be careful to call \-\-zero\-superblock with clustered raid, make sure
1753 array isn't used or assembled in other cluster node before execute it.
1756 .B \-\-kill\-subarray=
1757 If the device is a container and the argument to \-\-kill\-subarray
1758 specifies an inactive subarray in the container, then the subarray is
1759 deleted. Deleting all subarrays will leave an 'empty-container' or
1760 spare superblock on the drives. See
1761 .B \-\-zero\-superblock
1763 removing a superblock. Note that some formats depend on the subarray
1764 index for generating a UUID, this command will fail if it would change
1765 the UUID of an active subarray.
1768 .B \-\-update\-subarray=
1769 If the device is a container and the argument to \-\-update\-subarray
1770 specifies a subarray in the container, then attempt to update the given
1771 superblock field in the subarray. See below in
1776 .BR \-t ", " \-\-test
1781 is set to reflect the status of the device. See below in
1786 .BR \-W ", " \-\-wait
1787 For each md device given, wait for any resync, recovery, or reshape
1788 activity to finish before returning.
1790 will return with success if it actually waited for every device
1791 listed, otherwise it will return failure.
1795 For each md device given, or each device in /proc/mdstat if
1797 is given, arrange for the array to be marked clean as soon as possible.
1799 will return with success if the array uses external metadata and we
1800 successfully waited. For native arrays this returns immediately as the
1801 kernel handles dirty-clean transitions at shutdown. No action is taken
1802 if safe-mode handling is disabled.
1806 Set the "sync_action" for all md devices given to one of
1813 will abort any currently running action though some actions will
1814 automatically restart.
1817 will abort any current action and ensure no other action starts
1827 .BR "SCRUBBING AND MISMATCHES" .
1829 .SH For Incremental Assembly mode:
1831 .BR \-\-rebuild\-map ", " \-r
1832 Rebuild the map file
1836 uses to help track which arrays are currently being assembled.
1839 .BR \-\-run ", " \-R
1840 Run any array assembled as soon as a minimal number of devices are
1841 available, rather than waiting until all expected devices are present.
1844 .BR \-\-scan ", " \-s
1845 Only meaningful with
1849 file for arrays that are being incrementally assembled and will try to
1850 start any that are not already started. If any such array is listed
1853 as requiring an external bitmap, that bitmap will be attached first.
1856 .BR \-\-fail ", " \-f
1857 This allows the hot-plug system to remove devices that have fully disappeared
1858 from the kernel. It will first fail and then remove the device from any
1859 array it belongs to.
1860 The device name given should be a kernel device name such as "sda",
1866 Only used with \-\-fail. The 'path' given will be recorded so that if
1867 a new device appears at the same location it can be automatically
1868 added to the same array. This allows the failed device to be
1869 automatically replaced by a new device without metadata if it appears
1870 at specified path. This option is normally only set by a
1874 .SH For Monitor mode:
1876 .BR \-m ", " \-\-mail
1877 Give a mail address to send alerts to.
1880 .BR \-p ", " \-\-program ", " \-\-alert
1881 Give a program to be run whenever an event is detected.
1884 .BR \-y ", " \-\-syslog
1885 Cause all events to be reported through 'syslog'. The messages have
1886 facility of 'daemon' and varying priorities.
1889 .BR \-d ", " \-\-delay
1890 Give a delay in seconds.
1892 polls the md arrays and then waits this many seconds before polling
1893 again. The default is 60 seconds. Since 2.6.16, there is no need to
1894 reduce this as the kernel alerts
1896 immediately when there is any change.
1899 .BR \-r ", " \-\-increment
1900 Give a percentage increment.
1902 will generate RebuildNN events with the given percentage increment.
1905 .BR \-f ", " \-\-daemonise
1908 to run as a background daemon if it decides to monitor anything. This
1909 causes it to fork and run in the child, and to disconnect from the
1910 terminal. The process id of the child is written to stdout.
1913 which will only continue monitoring if a mail address or alert program
1914 is found in the config file.
1917 .BR \-i ", " \-\-pid\-file
1920 is running in daemon mode, write the pid of the daemon process to
1921 the specified file, instead of printing it on standard output.
1924 .BR \-1 ", " \-\-oneshot
1925 Check arrays only once. This will generate
1927 events and more significantly
1933 .B " mdadm \-\-monitor \-\-scan \-1"
1935 from a cron script will ensure regular notification of any degraded arrays.
1938 .BR \-t ", " \-\-test
1941 alert for every array found at startup. This alert gets mailed and
1942 passed to the alert program. This can be used for testing that alert
1943 message do get through successfully.
1947 This inhibits the functionality for moving spares between arrays.
1948 Only one monitoring process started with
1950 but without this flag is allowed, otherwise the two could interfere
1957 .B mdadm \-\-assemble
1958 .I md-device options-and-component-devices...
1961 .B mdadm \-\-assemble \-\-scan
1962 .I md-devices-and-options...
1965 .B mdadm \-\-assemble \-\-scan
1969 This usage assembles one or more RAID arrays from pre-existing components.
1970 For each array, mdadm needs to know the md device, the identity of the
1971 array, and a number of component-devices. These can be found in a number of ways.
1973 In the first usage example (without the
1975 the first device given is the md device.
1976 In the second usage example, all devices listed are treated as md
1977 devices and assembly is attempted.
1978 In the third (where no devices are listed) all md devices that are
1979 listed in the configuration file are assembled. If no arrays are
1980 described by the configuration file, then any arrays that
1981 can be found on unused devices will be assembled.
1983 If precisely one device is listed, but
1989 was given and identity information is extracted from the configuration file.
1991 The identity can be given with the
1997 option, will be taken from the md-device record in the config file, or
1998 will be taken from the super block of the first component-device
1999 listed on the command line.
2001 Devices can be given on the
2003 command line or in the config file. Only devices which have an md
2004 superblock which contains the right identity will be considered for
2007 The config file is only used if explicitly named with
2009 or requested with (a possibly implicit)
2014 .B /etc/mdadm/mdadm.conf
2019 is not given, then the config file will only be used to find the
2020 identity of md arrays.
2022 Normally the array will be started after it is assembled. However if
2024 is not given and not all expected drives were listed, then the array
2025 is not started (to guard against usage errors). To insist that the
2026 array be started in this case (as may work for RAID1, 4, 5, 6, or 10),
2035 does not create any entries in
2039 It does record information in
2043 to choose the correct name.
2047 detects that udev is not configured, it will create the devices in
2051 In Linux kernels prior to version 2.6.28 there were two distinctly
2052 different types of md devices that could be created: one that could be
2053 partitioned using standard partitioning tools and one that could not.
2054 Since 2.6.28 that distinction is no longer relevant as both type of
2055 devices can be partitioned.
2057 will normally create the type that originally could not be partitioned
2058 as it has a well defined major number (9).
2060 Prior to 2.6.28, it is important that mdadm chooses the correct type
2061 of array device to use. This can be controlled with the
2063 option. In particular, a value of "mdp" or "part" or "p" tells mdadm
2064 to use a partitionable device rather than the default.
2066 In the no-udev case, the value given to
2068 can be suffixed by a number. This tells
2070 to create that number of partition devices rather than the default of 4.
2074 can also be given in the configuration file as a word starting
2076 on the ARRAY line for the relevant array.
2083 and no devices are listed,
2085 will first attempt to assemble all the arrays listed in the config
2088 If no arrays are listed in the config (other than those marked
2090 it will look through the available devices for possible arrays and
2091 will try to assemble anything that it finds. Arrays which are tagged
2092 as belonging to the given homehost will be assembled and started
2093 normally. Arrays which do not obviously belong to this host are given
2094 names that are expected not to conflict with anything local, and are
2095 started "read-auto" so that nothing is written to any device until the
2096 array is written to. i.e. automatic resync etc is delayed.
2100 finds a consistent set of devices that look like they should comprise
2101 an array, and if the superblock is tagged as belonging to the given
2102 home host, it will automatically choose a device name and try to
2103 assemble the array. If the array uses version-0.90 metadata, then the
2105 number as recorded in the superblock is used to create a name in
2109 If the array uses version-1 metadata, then the
2111 from the superblock is used to similarly create a name in
2113 (the name will have any 'host' prefix stripped first).
2115 This behaviour can be modified by the
2119 configuration file. This line can indicate that specific metadata
2120 type should, or should not, be automatically assembled. If an array
2121 is found which is not listed in
2123 and has a metadata format that is denied by the
2125 line, then it will not be assembled.
2128 line can also request that all arrays identified as being for this
2129 homehost should be assembled regardless of their metadata type.
2132 for further details.
2134 Note: Auto assembly cannot be used for assembling and activating some
2135 arrays which are undergoing reshape. In particular as the
2137 cannot be given, any reshape which requires a backup-file to continue
2138 cannot be started by auto assembly. An array which is growing to more
2139 devices and has passed the critical section can be assembled using
2150 .BI \-\-raid\-devices= Z
2154 This usage is similar to
2156 The difference is that it creates an array without a superblock. With
2157 these arrays there is no difference between initially creating the array and
2158 subsequently assembling the array, except that hopefully there is useful
2159 data there in the second case.
2161 The level may raid0, linear, raid1, raid10, multipath, or faulty, or
2162 one of their synonyms. All devices must be listed and the array will
2163 be started once complete. It will often be appropriate to use
2164 .B \-\-assume\-clean
2165 with levels raid1 or raid10.
2176 .BI \-\-raid\-devices= Z
2180 This usage will initialise a new md array, associate some devices with
2181 it, and activate the array.
2183 The named device will normally not exist when
2184 .I "mdadm \-\-create"
2185 is run, but will be created by
2187 once the array becomes active.
2189 As devices are added, they are checked to see if they contain RAID
2190 superblocks or filesystems. They are also checked to see if the variance in
2191 device size exceeds 1%.
2193 If any discrepancy is found, the array will not automatically be run, though
2196 can override this caution.
2198 To create a "degraded" array in which some devices are missing, simply
2199 give the word "\fBmissing\fP"
2200 in place of a device name. This will cause
2202 to leave the corresponding slot in the array empty.
2203 For a RAID4 or RAID5 array at most one slot can be
2204 "\fBmissing\fP"; for a RAID6 array at most two slots.
2205 For a RAID1 array, only one real device needs to be given. All of the
2209 When creating a RAID5 array,
2211 will automatically create a degraded array with an extra spare drive.
2212 This is because building the spare into a degraded array is in general
2213 faster than resyncing the parity on a non-degraded, but not clean,
2214 array. This feature can be overridden with the
2218 When creating an array with version-1 metadata a name for the array is
2220 If this is not given with the
2224 will choose a name based on the last component of the name of the
2225 device being created. So if
2227 is being created, then the name
2232 is being created, then the name
2236 When creating a partition based array, using
2238 with version-1.x metadata, the partition type should be set to
2240 (non fs-data). This type selection allows for greater precision since
2241 using any other [RAID auto-detect (0xFD) or a GNU/Linux partition (0x83)],
2242 might create problems in the event of array recovery through a live cdrom.
2244 A new array will normally get a randomly assigned 128bit UUID which is
2245 very likely to be unique. If you have a specific need, you can choose
2246 a UUID for the array by giving the
2248 option. Be warned that creating two arrays with the same UUID is a
2249 recipe for disaster. Also, using
2251 when creating a v0.90 array will silently override any
2256 .\"option is given, it is not necessary to list any component-devices in this command.
2257 .\"They can be added later, before a
2261 .\"is given, the apparent size of the smallest drive given is used.
2263 If the array type supports a write-intent bitmap, and if the devices
2264 in the array exceed 100G is size, an internal write-intent bitmap
2265 will automatically be added unless some other option is explicitly
2268 option or a different consistency policy is selected with the
2269 .B \-\-consistency\-policy
2270 option. In any case space for a bitmap will be reserved so that one
2271 can be added later with
2272 .BR "\-\-grow \-\-bitmap=internal" .
2274 If the metadata type supports it (currently only 1.x and IMSM metadata),
2275 space will be allocated to store a bad block list. This allows a modest
2276 number of bad blocks to be recorded, allowing the drive to remain in
2277 service while only partially functional.
2279 When creating an array within a
2282 can be given either the list of devices to use, or simply the name of
2283 the container. The former case gives control over which devices in
2284 the container will be used for the array. The latter case allows
2286 to automatically choose which devices to use based on how much spare
2289 The General Management options that are valid with
2294 insist on running the array even if some devices look like they might
2299 start the array in readonly mode.
2306 .I options... devices...
2309 This usage will allow individual devices in an array to be failed,
2310 removed or added. It is possible to perform multiple operations with
2311 on command. For example:
2313 .B " mdadm /dev/md0 \-f /dev/hda1 \-r /dev/hda1 \-a /dev/hda1"
2319 and will then remove it from the array and finally add it back
2320 in as a spare. However only one md array can be affected by a single
2323 When a device is added to an active array, mdadm checks to see if it
2324 has metadata on it which suggests that it was recently a member of the
2325 array. If it does, it tries to "re\-add" the device. If there have
2326 been no changes since the device was removed, or if the array has a
2327 write-intent bitmap which has recorded whatever changes there were,
2328 then the device will immediately become a full member of the array and
2329 those differences recorded in the bitmap will be resolved.
2339 MISC mode includes a number of distinct operations that
2340 operate on distinct devices. The operations are:
2343 The device is examined to see if it is
2344 (1) an active md array, or
2345 (2) a component of an md array.
2346 The information discovered is reported.
2350 The device should be an active md device.
2352 will display a detailed description of the array.
2356 will cause the output to be less detailed and the format to be
2357 suitable for inclusion in
2361 will normally be 0 unless
2363 failed to get useful information about the device(s); however, if the
2365 option is given, then the exit status will be:
2369 The array is functioning normally.
2372 The array has at least one failed device.
2375 The array has multiple failed devices such that it is unusable.
2378 There was an error while trying to get information about the device.
2382 .B \-\-detail\-platform
2383 Print detail of the platform's RAID capabilities (firmware / hardware
2384 topology). If the metadata is specified with
2388 then the return status will be:
2392 metadata successfully enumerated its platform components on this system
2395 metadata is platform independent
2398 metadata failed to find its platform components on this system
2402 .B \-\-update\-subarray=
2403 If the device is a container and the argument to \-\-update\-subarray
2404 specifies a subarray in the container, then attempt to update the given
2405 superblock field in the subarray. Similar to updating an array in
2406 "assemble" mode, the field to update is selected by
2410 option. The supported options are
2420 option updates the subarray name in the metadata, it may not affect the
2421 device node name or the device node symlink until the subarray is
2422 re\-assembled. If updating
2424 would change the UUID of an active subarray this operation is blocked,
2425 and the command will end in an error.
2431 options enable and disable PPL in the metadata. Currently supported only for
2438 options enable and disable write-intent bitmap in the metadata. Currently supported only for
2443 The device should be a component of an md array.
2445 will read the md superblock of the device and display the contents.
2450 is given, then multiple devices that are components of the one array
2451 are grouped together and reported in a single entry suitable
2457 without listing any devices will cause all devices listed in the
2458 config file to be examined.
2461 .BI \-\-dump= directory
2462 If the device contains RAID metadata, a file will be created in the
2464 and the metadata will be written to it. The file will be the same
2465 size as the device and have the metadata written in the file at the
2466 same locate that it exists in the device. However the file will be "sparse" so
2467 that only those blocks containing metadata will be allocated. The
2468 total space used will be small.
2470 The file name used in the
2472 will be the base name of the device. Further if any links appear in
2474 which point to the device, then hard links to the file will be created
2481 Multiple devices can be listed and their metadata will all be stored
2482 in the one directory.
2485 .BI \-\-restore= directory
2486 This is the reverse of
2489 will locate a file in the directory that has a name appropriate for
2490 the given device and will restore metadata from it. Names that match
2492 names are preferred, however if two of those refer to different files,
2494 will not choose between them but will abort the operation.
2496 If a file name is given instead of a
2500 will restore from that file to a single device, always provided the
2501 size of the file matches that of the device, and the file contains
2505 The devices should be active md arrays which will be deactivated, as
2506 long as they are not currently in use.
2510 This will fully activate a partially assembled md array.
2514 This will mark an active array as read-only, providing that it is
2515 not currently being used.
2521 array back to being read/write.
2525 For all operations except
2528 will cause the operation to be applied to all arrays listed in
2533 causes all devices listed in the config file to be examined.
2536 .BR \-b ", " \-\-brief
2537 Be less verbose. This is used with
2545 gives an intermediate level of verbosity.
2551 .B mdadm \-\-monitor
2552 .I options... devices...
2557 to periodically poll a number of md arrays and to report on any events
2560 will never exit once it decides that there are arrays to be checked,
2561 so it should normally be run in the background.
2563 As well as reporting events,
2565 may move a spare drive from one array to another if they are in the
2570 and if the destination array has a failed drive but no spares.
2572 If any devices are listed on the command line,
2574 will only monitor those devices. Otherwise all arrays listed in the
2575 configuration file will be monitored. Further, if
2577 is given, then any other md devices that appear in
2579 will also be monitored.
2581 The result of monitoring the arrays is the generation of events.
2582 These events are passed to a separate program (if specified) and may
2583 be mailed to a given E-mail address.
2585 When passing events to a program, the program is run once for each event,
2586 and is given 2 or 3 command-line arguments: the first is the
2587 name of the event (see below), the second is the name of the
2588 md device which is affected, and the third is the name of a related
2589 device if relevant (such as a component device that has failed).
2593 is given, then a program or an E-mail address must be specified on the
2594 command line or in the config file. If neither are available, then
2596 will not monitor anything.
2600 will continue monitoring as long as something was found to monitor. If
2601 no program or email is given, then each event is reported to
2604 The different events are:
2608 .B DeviceDisappeared
2609 An md array which previously was configured appears to no longer be
2610 configured. (syslog priority: Critical)
2614 was told to monitor an array which is RAID0 or Linear, then it will
2616 .B DeviceDisappeared
2617 with the extra information
2619 This is because RAID0 and Linear do not support the device-failed,
2620 hot-spare and resync operations which are monitored.
2624 An md array started reconstruction (e.g. recovery, resync, reshape,
2625 check, repair). (syslog priority: Warning)
2631 is a two-digit number (ie. 05, 48). This indicates that rebuild
2632 has passed that many percent of the total. The events are generated
2633 with fixed increment since 0. Increment size may be specified with
2634 a commandline option (default is 20). (syslog priority: Warning)
2638 An md array that was rebuilding, isn't any more, either because it
2639 finished normally or was aborted. (syslog priority: Warning)
2643 An active component device of an array has been marked as
2644 faulty. (syslog priority: Critical)
2648 A spare component device which was being rebuilt to replace a faulty
2649 device has failed. (syslog priority: Critical)
2653 A spare component device which was being rebuilt to replace a faulty
2654 device has been successfully rebuilt and has been made active.
2655 (syslog priority: Info)
2659 A new md array has been detected in the
2661 file. (syslog priority: Info)
2665 A newly noticed array appears to be degraded. This message is not
2668 notices a drive failure which causes degradation, but only when
2670 notices that an array is degraded when it first sees the array.
2671 (syslog priority: Critical)
2675 A spare drive has been moved from one array in a
2679 to another to allow a failed drive to be replaced.
2680 (syslog priority: Info)
2686 has been told, via the config file, that an array should have a certain
2687 number of spare devices, and
2689 detects that it has fewer than this number when it first sees the
2690 array, it will report a
2693 (syslog priority: Warning)
2697 An array was found at startup, and the
2700 (syslog priority: Info)
2710 cause Email to be sent. All events cause the program to be run.
2711 The program is run with two or three arguments: the event
2712 name, the array device and possibly a second device.
2714 Each event has an associated array device (e.g.
2716 and possibly a second device. For
2721 the second device is the relevant component device.
2724 the second device is the array that the spare was moved from.
2728 to move spares from one array to another, the different arrays need to
2729 be labeled with the same
2731 or the spares must be allowed to migrate through matching POLICY domains
2732 in the configuration file. The
2734 name can be any string; it is only necessary that different spare
2735 groups use different names.
2739 detects that an array in a spare group has fewer active
2740 devices than necessary for the complete array, and has no spare
2741 devices, it will look for another array in the same spare group that
2742 has a full complement of working drive and a spare. It will then
2743 attempt to remove the spare from the second drive and add it to the
2745 If the removal succeeds but the adding fails, then it is added back to
2748 If the spare group for a degraded array is not defined,
2750 will look at the rules of spare migration specified by POLICY lines in
2752 and then follow similar steps as above if a matching spare is found.
2755 The GROW mode is used for changing the size or shape of an active
2757 For this to work, the kernel must support the necessary change.
2758 Various types of growth are being added during 2.6 development.
2760 Currently the supported changes include
2762 change the "size" attribute for RAID1, RAID4, RAID5 and RAID6.
2764 increase or decrease the "raid\-devices" attribute of RAID0, RAID1, RAID4,
2767 change the chunk-size and layout of RAID0, RAID4, RAID5, RAID6 and RAID10.
2769 convert between RAID1 and RAID5, between RAID5 and RAID6, between
2770 RAID0, RAID4, and RAID5, and between RAID0 and RAID10 (in the near-2 mode).
2772 add a write-intent bitmap to any array which supports these bitmaps, or
2773 remove a write-intent bitmap from such an array.
2775 change the array's consistency policy.
2778 Using GROW on containers is currently supported only for Intel's IMSM
2779 container format. The number of devices in a container can be
2780 increased - which affects all arrays in the container - or an array
2781 in a container can be converted between levels where those levels are
2782 supported by the container, and the conversion is on of those listed
2788 Intel's native checkpointing doesn't use
2790 option and it is transparent for assembly feature.
2792 Roaming between Windows(R) and Linux systems for IMSM metadata is not
2793 supported during grow process.
2795 When growing a raid0 device, the new component disk size (or external
2796 backup size) should be larger than LCM(old, new) * chunk-size * 2,
2797 where LCM() is the least common multiple of the old and new count of
2798 component disks, and "* 2" comes from the fact that mdadm refuses to
2799 use more than half of a spare device for backup space.
2802 Normally when an array is built the "size" is taken from the smallest
2803 of the drives. If all the small drives in an arrays are, one at a
2804 time, removed and replaced with larger drives, then you could have an
2805 array of large drives with only a small amount used. In this
2806 situation, changing the "size" with "GROW" mode will allow the extra
2807 space to start being used. If the size is increased in this way, a
2808 "resync" process will start to make sure the new parts of the array
2811 Note that when an array changes size, any filesystem that may be
2812 stored in the array will not automatically grow or shrink to use or
2813 vacate the space. The
2814 filesystem will need to be explicitly told to use the extra space
2815 after growing, or to reduce its size
2817 to shrinking the array.
2819 Also the size of an array cannot be changed while it has an active
2820 bitmap. If an array has a bitmap, it must be removed before the size
2821 can be changed. Once the change is complete a new bitmap can be created.
2826 is not yet supported for external file bitmap.
2828 .SS RAID\-DEVICES CHANGES
2830 A RAID1 array can work with any number of devices from 1 upwards
2831 (though 1 is not very useful). There may be times which you want to
2832 increase or decrease the number of active devices. Note that this is
2833 different to hot-add or hot-remove which changes the number of
2836 When reducing the number of devices in a RAID1 array, the slots which
2837 are to be removed from the array must already be vacant. That is, the
2838 devices which were in those slots must be failed and removed.
2840 When the number of devices is increased, any hot spares that are
2841 present will be activated immediately.
2843 Changing the number of active devices in a RAID5 or RAID6 is much more
2844 effort. Every block in the array will need to be read and written
2845 back to a new location. From 2.6.17, the Linux Kernel is able to
2846 increase the number of devices in a RAID5 safely, including restarting
2847 an interrupted "reshape". From 2.6.31, the Linux Kernel is able to
2848 increase or decrease the number of devices in a RAID5 or RAID6.
2850 From 2.6.35, the Linux Kernel is able to convert a RAID0 in to a RAID4
2853 uses this functionality and the ability to add
2854 devices to a RAID4 to allow devices to be added to a RAID0. When
2855 requested to do this,
2857 will convert the RAID0 to a RAID4, add the necessary disks and make
2858 the reshape happen, and then convert the RAID4 back to RAID0.
2860 When decreasing the number of devices, the size of the array will also
2861 decrease. If there was data in the array, it could get destroyed and
2862 this is not reversible, so you should firstly shrink the filesystem on
2863 the array to fit within the new size. To help prevent accidents,
2865 requires that the size of the array be decreased first with
2866 .BR "mdadm --grow --array-size" .
2867 This is a reversible change which simply makes the end of the array
2868 inaccessible. The integrity of any data can then be checked before
2869 the non-reversible reduction in the number of devices is request.
2871 When relocating the first few stripes on a RAID5 or RAID6, it is not
2872 possible to keep the data on disk completely consistent and
2873 crash-proof. To provide the required safety, mdadm disables writes to
2874 the array while this "critical section" is reshaped, and takes a
2875 backup of the data that is in that section. For grows, this backup may be
2876 stored in any spare devices that the array has, however it can also be
2877 stored in a separate file specified with the
2879 option, and is required to be specified for shrinks, RAID level
2880 changes and layout changes. If this option is used, and the system
2881 does crash during the critical period, the same file must be passed to
2883 to restore the backup and reassemble the array. When shrinking rather
2884 than growing the array, the reshape is done from the end towards the
2885 beginning, so the "critical section" is at the end of the reshape.
2889 Changing the RAID level of any array happens instantaneously. However
2890 in the RAID5 to RAID6 case this requires a non-standard layout of the
2891 RAID6 data, and in the RAID6 to RAID5 case that non-standard layout is
2892 required before the change can be accomplished. So while the level
2893 change is instant, the accompanying layout change can take quite a
2896 is required. If the array is not simultaneously being grown or
2897 shrunk, so that the array size will remain the same - for example,
2898 reshaping a 3-drive RAID5 into a 4-drive RAID6 - the backup file will
2899 be used not just for a "cricital section" but throughout the reshape
2900 operation, as described below under LAYOUT CHANGES.
2902 .SS CHUNK-SIZE AND LAYOUT CHANGES
2904 Changing the chunk-size or layout without also changing the number of
2905 devices as the same time will involve re-writing all blocks in-place.
2906 To ensure against data loss in the case of a crash, a
2908 must be provided for these changes. Small sections of the array will
2909 be copied to the backup file while they are being rearranged. This
2910 means that all the data is copied twice, once to the backup and once
2911 to the new layout on the array, so this type of reshape will go very
2914 If the reshape is interrupted for any reason, this backup file must be
2916 .B "mdadm --assemble"
2917 so the array can be reassembled. Consequently the file cannot be
2918 stored on the device being reshaped.
2923 A write-intent bitmap can be added to, or removed from, an active
2924 array. Either internal bitmaps, or bitmaps stored in a separate file,
2925 can be added. Note that if you add a bitmap stored in a file which is
2926 in a filesystem that is on the RAID array being affected, the system
2927 will deadlock. The bitmap must be on a separate filesystem.
2929 .SS CONSISTENCY POLICY CHANGES
2931 The consistency policy of an active array can be changed by using the
2932 .B \-\-consistency\-policy
2933 option in Grow mode. Currently this works only for the
2937 policies and allows to enable or disable the RAID5 Partial Parity Log (PPL).
2939 .SH INCREMENTAL MODE
2943 .B mdadm \-\-incremental
2947 .RI [ optional-aliases-for-device ]
2950 .B mdadm \-\-incremental \-\-fail
2954 .B mdadm \-\-incremental \-\-rebuild\-map
2957 .B mdadm \-\-incremental \-\-run \-\-scan
2960 This mode is designed to be used in conjunction with a device
2961 discovery system. As devices are found in a system, they can be
2963 .B "mdadm \-\-incremental"
2964 to be conditionally added to an appropriate array.
2966 Conversely, it can also be used with the
2968 flag to do just the opposite and find whatever array a particular device
2969 is part of and remove the device from that array.
2971 If the device passed is a
2973 device created by a previous call to
2975 then rather than trying to add that device to an array, all the arrays
2976 described by the metadata of the container will be started.
2979 performs a number of tests to determine if the device is part of an
2980 array, and which array it should be part of. If an appropriate array
2981 is found, or can be created,
2983 adds the device to the array and conditionally starts the array.
2987 will normally only add devices to an array which were previously working
2988 (active or spare) parts of that array. The support for automatic
2989 inclusion of a new drive as a spare in some array requires
2990 a configuration through POLICY in config file.
2994 makes are as follow:
2996 Is the device permitted by
2998 That is, is it listed in a
3000 line in that file. If
3002 is absent then the default it to allow any device. Similarly if
3004 contains the special word
3006 then any device is allowed. Otherwise the device name given to
3008 or one of the aliases given, or an alias found in the filesystem,
3009 must match one of the names or patterns in a
3013 This is the only context where the aliases are used. They are
3014 usually provided by a
3017 .BR $env{DEVLINKS} .
3020 Does the device have a valid md superblock? If a specific metadata
3021 version is requested with
3025 then only that style of metadata is accepted, otherwise
3027 finds any known version of metadata. If no
3029 metadata is found, the device may be still added to an array
3030 as a spare if POLICY allows.
3034 Does the metadata match an expected array?
3035 The metadata can match in two ways. Either there is an array listed
3038 which identifies the array (either by UUID, by name, by device list,
3039 or by minor-number), or the array was created with a
3045 or on the command line.
3048 is not able to positively identify the array as belonging to the
3049 current host, the device will be rejected.
3054 keeps a list of arrays that it has partially assembled in
3056 If no array exists which matches
3057 the metadata on the new device,
3059 must choose a device name and unit number. It does this based on any
3062 or any name information stored in the metadata. If this name
3063 suggests a unit number, that number will be used, otherwise a free
3064 unit number will be chosen. Normally
3066 will prefer to create a partitionable array, however if the
3070 suggests that a non-partitionable array is preferred, that will be
3073 If the array is not found in the config file and its metadata does not
3074 identify it as belonging to the "homehost", then
3076 will choose a name for the array which is certain not to conflict with
3077 any array which does belong to this host. It does this be adding an
3078 underscore and a small number to the name preferred by the metadata.
3080 Once an appropriate array is found or created and the device is added,
3082 must decide if the array is ready to be started. It will
3083 normally compare the number of available (non-spare) devices to the
3084 number of devices that the metadata suggests need to be active. If
3085 there are at least that many, the array will be started. This means
3086 that if any devices are missing the array will not be restarted.
3092 in which case the array will be run as soon as there are enough
3093 devices present for the data to be accessible. For a RAID1, that
3094 means one device will start the array. For a clean RAID5, the array
3095 will be started as soon as all but one drive is present.
3097 Note that neither of these approaches is really ideal. If it can
3098 be known that all device discovery has completed, then
3102 can be run which will try to start all arrays that are being
3103 incrementally assembled. They are started in "read-auto" mode in
3104 which they are read-only until the first write request. This means
3105 that no metadata updates are made and no attempt at resync or recovery
3106 happens. Further devices that are found before the first write can
3107 still be added safely.
3110 This section describes environment variables that affect how mdadm
3115 Setting this value to 1 will prevent mdadm from automatically launching
3116 mdmon. This variable is intended primarily for debugging mdadm/mdmon.
3122 does not create any device nodes in /dev, but leaves that task to
3126 appears not to be configured, or if this environment variable is set
3129 will create and devices that are needed.
3132 .B MDADM_NO_SYSTEMCTL
3137 is in use it will normally request
3139 to start various background tasks (particularly
3141 rather than forking and running them in the background. This can be
3142 suppressed by setting
3143 .BR MDADM_NO_SYSTEMCTL=1 .
3147 A key value of IMSM metadata is that it allows interoperability with
3148 boot ROMs on Intel platforms, and with other major operating systems.
3151 will only allow an IMSM array to be created or modified if detects
3152 that it is running on an Intel platform which supports IMSM, and
3153 supports the particular configuration of IMSM that is being requested
3154 (some functionality requires newer OROM support).
3156 These checks can be suppressed by setting IMSM_NO_PLATFORM=1 in the
3157 environment. This can be useful for testing or for disaster
3158 recovery. You should be aware that interoperability may be
3159 compromised by setting this value.
3162 .B MDADM_GROW_ALLOW_OLD
3163 If an array is stopped while it is performing a reshape and that
3164 reshape was making use of a backup file, then when the array is
3167 will sometimes complain that the backup file is too old. If this
3168 happens and you are certain it is the right backup file, you can
3169 over-ride this check by setting
3170 .B MDADM_GROW_ALLOW_OLD=1
3175 Any string given in this variable is added to the start of the
3177 line in the config file, or treated as the whole
3179 line if none is given. It can be used to disable certain metadata
3182 is called from a boot script. For example
3184 .B " export MDADM_CONF_AUTO='-ddf -imsm'
3188 does not automatically assemble any DDF or
3189 IMSM arrays that are found. This can be useful on systems configured
3190 to manage such arrays with
3196 .B " mdadm \-\-query /dev/name-of-device"
3198 This will find out if a given device is a RAID array, or is part of
3199 one, and will provide brief information about the device.
3201 .B " mdadm \-\-assemble \-\-scan"
3203 This will assemble and start all arrays listed in the standard config
3204 file. This command will typically go in a system startup file.
3206 .B " mdadm \-\-stop \-\-scan"
3208 This will shut down all arrays that can be shut down (i.e. are not
3209 currently in use). This will typically go in a system shutdown script.
3211 .B " mdadm \-\-follow \-\-scan \-\-delay=120"
3213 If (and only if) there is an Email address or program given in the
3214 standard config file, then
3215 monitor the status of all arrays listed in that file by
3216 polling them ever 2 minutes.
3218 .B " mdadm \-\-create /dev/md0 \-\-level=1 \-\-raid\-devices=2 /dev/hd[ac]1"
3220 Create /dev/md0 as a RAID1 array consisting of /dev/hda1 and /dev/hdc1.
3223 .B " echo 'DEVICE /dev/hd*[0\-9] /dev/sd*[0\-9]' > mdadm.conf"
3225 .B " mdadm \-\-detail \-\-scan >> mdadm.conf"
3227 This will create a prototype config file that describes currently
3228 active arrays that are known to be made from partitions of IDE or SCSI drives.
3229 This file should be reviewed before being used as it may
3230 contain unwanted detail.
3232 .B " echo 'DEVICE /dev/hd[a\-z] /dev/sd*[a\-z]' > mdadm.conf"
3234 .B " mdadm \-\-examine \-\-scan \-\-config=mdadm.conf >> mdadm.conf"
3236 This will find arrays which could be assembled from existing IDE and
3237 SCSI whole drives (not partitions), and store the information in the
3238 format of a config file.
3239 This file is very likely to contain unwanted detail, particularly
3242 entries. It should be reviewed and edited before being used as an
3245 .B " mdadm \-\-examine \-\-brief \-\-scan \-\-config=partitions"
3247 .B " mdadm \-Ebsc partitions"
3249 Create a list of devices by reading
3250 .BR /proc/partitions ,
3251 scan these for RAID superblocks, and printout a brief listing of all
3254 .B " mdadm \-Ac partitions \-m 0 /dev/md0"
3256 Scan all partitions and devices listed in
3257 .BR /proc/partitions
3260 out of all such devices with a RAID superblock with a minor number of 0.
3262 .B " mdadm \-\-monitor \-\-scan \-\-daemonise > /run/mdadm/mon.pid"
3264 If config file contains a mail address or alert program, run mdadm in
3265 the background in monitor mode monitoring all md devices. Also write
3266 pid of mdadm daemon to
3267 .BR /run/mdadm/mon.pid .
3269 .B " mdadm \-Iq /dev/somedevice"
3271 Try to incorporate newly discovered device into some array as
3274 .B " mdadm \-\-incremental \-\-rebuild\-map \-\-run \-\-scan"
3276 Rebuild the array map from any current arrays, and then start any that
3279 .B " mdadm /dev/md4 --fail detached --remove detached"
3281 Any devices which are components of /dev/md4 will be marked as faulty
3282 and then remove from the array.
3284 .B " mdadm --grow /dev/md4 --level=6 --backup-file=/root/backup-md4"
3288 which is currently a RAID5 array will be converted to RAID6. There
3289 should normally already be a spare drive attached to the array as a
3290 RAID6 needs one more drive than a matching RAID5.
3292 .B " mdadm --create /dev/md/ddf --metadata=ddf --raid-disks 6 /dev/sd[a-f]"
3294 Create a DDF array over 6 devices.
3296 .B " mdadm --create /dev/md/home -n3 -l5 -z 30000000 /dev/md/ddf"
3298 Create a RAID5 array over any 3 devices in the given DDF set. Use
3299 only 30 gigabytes of each device.
3301 .B " mdadm -A /dev/md/ddf1 /dev/sd[a-f]"
3303 Assemble a pre-exist ddf array.
3305 .B " mdadm -I /dev/md/ddf1"
3307 Assemble all arrays contained in the ddf array, assigning names as
3310 .B " mdadm \-\-create \-\-help"
3312 Provide help about the Create mode.
3314 .B " mdadm \-\-config \-\-help"
3316 Provide help about the format of the config file.
3318 .B " mdadm \-\-help"
3320 Provide general help.
3330 lists all active md devices with information about them.
3332 uses this to find arrays when
3334 is given in Misc mode, and to monitor array reconstruction
3339 The config file lists which devices may be scanned to see if
3340 they contain MD super block, and gives identifying information
3341 (e.g. UUID) about known MD arrays. See
3345 .SS /etc/mdadm.conf.d
3347 A directory containing configuration files which are read in lexical
3353 mode is used, this file gets a list of arrays currently being created.
3358 understand two sorts of names for array devices.
3360 The first is the so-called 'standard' format name, which matches the
3361 names used by the kernel and which appear in
3364 The second sort can be freely chosen, but must reside in
3366 When giving a device name to
3368 to create or assemble an array, either full path name such as
3372 can be given, or just the suffix of the second sort of name, such as
3378 chooses device names during auto-assembly or incremental assembly, it
3379 will sometimes add a small sequence number to the end of the name to
3380 avoid conflicted between multiple arrays that have the same name. If
3382 can reasonably determine that the array really is meant for this host,
3383 either by a hostname in the metadata, or by the presence of the array
3386 then it will leave off the suffix if possible.
3387 Also if the homehost is specified as
3390 will only use a suffix if a different array of the same name already
3391 exists or is listed in the config file.
3393 The standard names for non-partitioned arrays (the only sort of md
3394 array available in 2.4 and earlier) are of the form
3398 where NN is a number.
3399 The standard names for partitionable arrays (as available from 2.6
3400 onwards) are of the form:
3404 Partition numbers should be indicated by adding "pMM" to these, thus "/dev/md/d1p2".
3406 From kernel version 2.6.28 the "non-partitioned array" can actually
3407 be partitioned. So the "md_d\fBNN\fP"
3408 names are no longer needed, and
3409 partitions such as "/dev/md\fBNN\fPp\fBXX\fP"
3412 From kernel version 2.6.29 standard names can be non-numeric following
3419 is any string. These names are supported by
3421 since version 3.3 provided they are enabled in
3426 was previously known as
3430 For further information on mdadm usage, MD and the various levels of
3433 .B https://raid.wiki.kernel.org/
3435 (based upon Jakob \(/Ostergaard's Software\-RAID.HOWTO)
3437 The latest version of
3439 should always be available from
3441 .B https://www.kernel.org/pub/linux/utils/raid/mdadm/
projects / thirdparty / mdadm.git / blob