2 .\" Copyright Neil Brown and others.
3 .\" This program is free software; you can redistribute it and/or modify
4 .\" it under the terms of the GNU General Public License as published by
5 .\" the Free Software Foundation; either version 2 of the License, or
6 .\" (at your option) any later version.
7 .\" See file COPYING in distribution for details.
10 mdadm \- manage MD devices
16 .BI mdadm " [mode] <raiddevice> [options] <component-devices>"
19 RAID devices are virtual devices created from two or more
20 real block devices. This allows multiple devices (typically disk
21 drives or partitions thereof) to be combined into a single device to
22 hold (for example) a single filesystem.
23 Some RAID levels include redundancy and so can survive some degree of
26 Linux Software RAID devices are implemented through the md (Multiple
27 Devices) device driver.
29 Currently, Linux supports
46 is not a Software RAID mechanism, but does involve
48 each device is a path to one common physical storage device.
49 New installations should not use md/multipath as it is not well
50 supported and has no ongoing development. Use the Device Mapper based
51 multipath-tools instead.
54 is also not true RAID, and it only involves one device. It
55 provides a layer over a true device that can be used to inject faults.
60 is a collection of devices that are
61 managed as a set. This is similar to the set of devices connected to
62 a hardware RAID controller. The set of devices may contain a number
63 of different RAID arrays each utilising some (or all) of the blocks from a
64 number of the devices in the set. For example, two devices in a 5-device set
65 might form a RAID1 using the whole devices. The remaining three might
66 have a RAID5 over the first half of each device, and a RAID0 over the
71 there is one set of metadata that describes all of
72 the arrays in the container. So when
76 device, the device just represents the metadata. Other normal arrays (RAID1
77 etc) can be created inside the container.
80 mdadm has several major modes of operation:
83 Assemble the components of a previously created
84 array into an active array. Components can be explicitly given
85 or can be searched for.
87 checks that the components
88 do form a bona fide array, and can, on request, fiddle superblock
89 information so as to assemble a faulty array.
93 Build an array that doesn't have per-device metadata (superblocks). For these
96 cannot differentiate between initial creation and subsequent assembly
97 of an array. It also cannot perform any checks that appropriate
98 components have been requested. Because of this, the
100 mode should only be used together with a complete understanding of
105 Create a new array with per-device metadata (superblocks).
106 Appropriate metadata is written to each device, and then the array
107 comprising those devices is activated. A 'resync' process is started
108 to make sure that the array is consistent (e.g. both sides of a mirror
109 contain the same data) but the content of the device is left otherwise
111 The array can be used as soon as it has been created. There is no
112 need to wait for the initial resync to finish.
115 .B "Follow or Monitor"
116 Monitor one or more md devices and act on any state changes. This is
117 only meaningful for RAID1, 4, 5, 6, 10 or multipath arrays, as
118 only these have interesting state. RAID0 or Linear never have
119 missing, spare, or failed drives, so there is nothing to monitor.
123 Grow (or shrink) an array, or otherwise reshape it in some way.
124 Currently supported growth options including changing the active size
125 of component devices and changing the number of active devices in
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. If not specified, default config file
270 and default conf.d directory will be used. See
274 If the config file given is
276 then nothing will be read, but
278 will act as though the config file contained exactly
280 .B " DEVICE partitions containers"
284 to find a list of devices to scan, and
286 to find a list of containers to examine.
289 is given for the config file, then
291 will act as though the config file were empty.
293 If the name given is of a directory, then
295 will collect all the files contained in the directory with a name ending
298 sort them lexically, and process all of those files as config files.
301 .BR \-s ", " \-\-scan
304 for missing information.
305 In general, this option gives
307 permission to get any missing information (like component devices,
308 array devices, array identities, and alert destination) from the
309 configuration file (see previous option);
310 one exception is MISC mode when using
316 says to get a list of array devices from
320 .BR \-e ", " \-\-metadata=
321 Declare the style of RAID metadata (superblock) to be used. The
322 default is {DEFAULT_METADATA} for
324 and to guess for other operations.
325 The default can be overridden by setting the
334 .ie '{DEFAULT_METADATA}'0.90'
335 .IP "0, 0.90, default"
338 Use the original 0.90 format superblock. This format limits arrays to
339 28 component devices and limits component devices of levels 1 and
340 greater to 2 terabytes. It is also possible for there to be confusion
341 about whether the superblock applies to a whole device or just the
342 last partition, if that partition starts on a 64K boundary.
343 .ie '{DEFAULT_METADATA}'0.90'
344 .IP "1, 1.0, 1.1, 1.2"
346 .IP "1, 1.0, 1.1, 1.2 default"
347 Use the new version-1 format superblock. This has fewer restrictions.
348 It can easily be moved between hosts with different endian-ness, and a
349 recovery operation can be checkpointed and restarted. The different
350 sub-versions store the superblock at different locations on the
351 device, either at the end (for 1.0), at the start (for 1.1) or 4K from
352 the start (for 1.2). "1" is equivalent to "1.2" (the commonly
353 preferred 1.x format).
354 'if '{DEFAULT_METADATA}'1.2' "default" is equivalent to "1.2".
356 Use the "Industry Standard" DDF (Disk Data Format) format defined by
358 When creating a DDF array a
360 will be created, and normal arrays can be created in that container.
362 Use the Intel(R) Matrix Storage Manager metadata format. This creates a
364 which is managed in a similar manner to DDF, and is supported by an
365 option-rom on some platforms:
367 .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
373 This will override any
375 setting in the config file and provides the identity of the host which
376 should be considered the home for any arrays.
378 When creating an array, the
380 will be recorded in the metadata. For version-1 superblocks, it will
381 be prefixed to the array name. For version-0.90 superblocks, part of
382 the SHA1 hash of the hostname will be stored in the later half of the
385 When reporting information about an array, any array which is tagged
386 for the given homehost will be reported as such.
388 When using Auto-Assemble, only arrays tagged for the given homehost
389 will be allowed to use 'local' names (i.e. not ending in '_' followed
390 by a digit string). See below under
391 .BR "Auto Assembly" .
393 The special name "\fBany\fP" can be used as a wild card. If an array
396 then the name "\fBany\fP" will be stored in the array and it can be
397 assembled in the same way on any host. If an array is assembled with
398 this option, then the homehost recorded on the array will be ignored.
404 needs to print the name for a device it normally finds the name in
406 which refers to the device and is shortest. When a path component is
410 will prefer a longer name if it contains that component. For example
411 .B \-\-prefer=by-uuid
412 will prefer a name in a subdirectory of
417 This functionality is currently only provided by
423 .B \-\-home\-cluster=
424 specifies the cluster name for the md device. The md device can be assembled
425 only on the cluster which matches the name specified. If this option is not
426 provided, mdadm tries to detect the cluster name automatically.
428 .SH For create, build, or grow:
431 .BR \-n ", " \-\-raid\-devices=
432 Specify the number of active devices in the array. This, plus the
433 number of spare devices (see below) must equal the number of
435 (including "\fBmissing\fP" devices)
436 that are listed on the command line for
438 Setting a value of 1 is probably
439 a mistake and so requires that
441 be specified first. A value of 1 will then be allowed for linear,
442 multipath, RAID0 and RAID1. It is never allowed for RAID4, RAID5 or RAID6.
444 This number can only be changed using
446 for RAID1, RAID4, RAID5 and RAID6 arrays, and only on kernels which provide
447 the necessary support.
450 .BR \-x ", " \-\-spare\-devices=
451 Specify the number of spare (eXtra) devices in the initial array.
452 Spares can also be added
453 and removed later. The number of component devices listed
454 on the command line must equal the number of RAID devices plus the
455 number of spare devices.
458 .BR \-z ", " \-\-size=
459 Amount (in Kilobytes) of space to use from each drive in RAID levels 1/4/5/6/10
460 and for RAID 0 on external metadata.
461 This must be a multiple of the chunk size, and must leave about 128Kb
462 of space at the end of the drive for the RAID superblock.
463 If this is not specified
464 (as it normally is not) the smallest drive (or partition) sets the
465 size, though if there is a variance among the drives of greater than 1%, a warning is
468 A suffix of 'K', 'M', 'G' or 'T' can be given to indicate Kilobytes,
469 Megabytes, Gigabytes or Terabytes respectively.
471 Sometimes a replacement drive can be a little smaller than the
472 original drives though this should be minimised by IDEMA standards.
473 Such a replacement drive will be rejected by
475 To guard against this it can be useful to set the initial size
476 slightly smaller than the smaller device with the aim that it will
477 still be larger than any replacement.
479 This option can be used with
481 for determining initial size of an array. For external metadata,
482 it can be used on a volume, but not on a container itself.
483 Setting initial size of
485 array is only valid for external metadata.
487 This value can be set with
489 for RAID level 1/4/5/6/10 though
490 DDF arrays may not be able to support this.
491 RAID 0 array size cannot be changed.
492 If the array was created with a size smaller than the currently
493 active drives, the extra space can be accessed using
495 The size can be given as
497 which means to choose the largest size that fits on all current drives.
499 Before reducing the size of the array (with
500 .BR "\-\-grow \-\-size=" )
501 you should make sure that space isn't needed. If the device holds a
502 filesystem, you would need to resize the filesystem to use less space.
504 After reducing the array size you should check that the data stored in
505 the device is still available. If the device holds a filesystem, then
506 an 'fsck' of the filesystem is a minimum requirement. If there are
507 problems the array can be made bigger again with no loss with another
508 .B "\-\-grow \-\-size="
512 .BR \-Z ", " \-\-array\-size=
513 This is only meaningful with
515 and its effect is not persistent: when the array is stopped and
516 restarted the default array size will be restored.
518 Setting the array-size causes the array to appear smaller to programs
519 that access the data. This is particularly needed before reshaping an
520 array so that it will be smaller. As the reshape is not reversible,
521 but setting the size with
523 is, it is required that the array size is reduced as appropriate
524 before the number of devices in the array is reduced.
526 Before reducing the size of the array you should make sure that space
527 isn't needed. If the device holds a filesystem, you would need to
528 resize the filesystem to use less space.
530 After reducing the array size you should check that the data stored in
531 the device is still available. If the device holds a filesystem, then
532 an 'fsck' of the filesystem is a minimum requirement. If there are
533 problems the array can be made bigger again with no loss with another
534 .B "\-\-grow \-\-array\-size="
537 A suffix of 'K', 'M', 'G' or 'T' can be given to indicate Kilobytes,
538 Megabytes, Gigabytes or Terabytes respectively.
541 restores the apparent size of the array to be whatever the real
542 amount of available space is.
544 Clustered arrays do not support this parameter yet.
547 .BR \-c ", " \-\-chunk=
548 Specify chunk size of kilobytes. The default when creating an
549 array is 512KB. To ensure compatibility with earlier versions, the
550 default when building an array with no persistent metadata is 64KB.
551 This is only meaningful for RAID0, RAID4, RAID5, RAID6, and RAID10.
553 RAID4, RAID5, RAID6, and RAID10 require the chunk size to be a power
554 of 2. In any case it must be a multiple of 4KB.
556 A suffix of 'K', 'M', 'G' or 'T' can be given to indicate Kilobytes,
557 Megabytes, Gigabytes or Terabytes respectively.
561 Specify rounding factor for a Linear array. The size of each
562 component will be rounded down to a multiple of this size.
563 This is a synonym for
565 but highlights the different meaning for Linear as compared to other
566 RAID levels. The default is 64K if a kernel earlier than 2.6.16 is in
567 use, and is 0K (i.e. no rounding) in later kernels.
570 .BR \-l ", " \-\-level=
571 Set RAID level. When used with
573 options are: linear, raid0, 0, stripe, raid1, 1, mirror, raid4, 4,
574 raid5, 5, raid6, 6, raid10, 10, multipath, mp, faulty, container.
575 Obviously some of these are synonymous.
579 metadata type is requested, only the
581 level is permitted, and it does not need to be explicitly given.
585 only linear, stripe, raid0, 0, raid1, multipath, mp, and faulty are valid.
589 to change the RAID level in some cases. See LEVEL CHANGES below.
592 .BR \-p ", " \-\-layout=
593 This option configures the fine details of data layout for RAID5, RAID6,
594 and RAID10 arrays, and controls the failure modes for
596 It can also be used for working around a kernel bug with RAID0, but generally
597 doesn't need to be used explicitly.
599 The layout of the RAID5 parity block can be one of
600 .BR left\-asymmetric ,
601 .BR left\-symmetric ,
602 .BR right\-asymmetric ,
603 .BR right\-symmetric ,
604 .BR la ", " ra ", " ls ", " rs .
606 .BR left\-symmetric .
608 It is also possible to cause RAID5 to use a RAID4-like layout by
614 Finally for RAID5 there are DDF\-compatible layouts,
615 .BR ddf\-zero\-restart ,
616 .BR ddf\-N\-restart ,
618 .BR ddf\-N\-continue .
620 These same layouts are available for RAID6. There are also 4 layouts
621 that will provide an intermediate stage for converting between RAID5
622 and RAID6. These provide a layout which is identical to the
623 corresponding RAID5 layout on the first N\-1 devices, and has the 'Q'
624 syndrome (the second 'parity' block used by RAID6) on the last device.
626 .BR left\-symmetric\-6 ,
627 .BR right\-symmetric\-6 ,
628 .BR left\-asymmetric\-6 ,
629 .BR right\-asymmetric\-6 ,
631 .BR parity\-first\-6 .
633 When setting the failure mode for level
636 .BR write\-transient ", " wt ,
637 .BR read\-transient ", " rt ,
638 .BR write\-persistent ", " wp ,
639 .BR read\-persistent ", " rp ,
641 .BR read\-fixable ", " rf ,
642 .BR clear ", " flush ", " none .
644 Each failure mode can be followed by a number, which is used as a period
645 between fault generation. Without a number, the fault is generated
646 once on the first relevant request. With a number, the fault will be
647 generated after that many requests, and will continue to be generated
648 every time the period elapses.
650 Multiple failure modes can be current simultaneously by using the
652 option to set subsequent failure modes.
654 "clear" or "none" will remove any pending or periodic failure modes,
655 and "flush" will clear any persistent faults.
657 The layout options for RAID10 are one of 'n', 'o' or 'f' followed
658 by a small number. The default is 'n2'. The supported options are:
661 signals 'near' copies. Multiple copies of one data block are at
662 similar offsets in different devices.
665 signals 'offset' copies. Rather than the chunks being duplicated
666 within a stripe, whole stripes are duplicated but are rotated by one
667 device so duplicate blocks are on different devices. Thus subsequent
668 copies of a block are in the next drive, and are one chunk further
673 (multiple copies have very different offsets).
674 See md(4) for more detail about 'near', 'offset', and 'far'.
676 The number is the number of copies of each datablock. 2 is normal, 3
677 can be useful. This number can be at most equal to the number of
678 devices in the array. It does not need to divide evenly into that
679 number (e.g. it is perfectly legal to have an 'n2' layout for an array
680 with an odd number of devices).
682 A bug introduced in Linux 3.14 means that RAID0 arrays
683 .B "with devices of differing sizes"
684 started using a different layout. This could lead to
685 data corruption. Since Linux 5.4 (and various stable releases that received
686 backports), the kernel will not accept such an array unless
687 a layout is explictly set. It can be set to
691 When creating a new array,
695 by default, so the layout does not normally need to be set.
696 An array created for either
700 will not be recognized by an (unpatched) kernel prior to 5.4. To create
701 a RAID0 array with devices of differing sizes that can be used on an
702 older kernel, you can set the layout to
704 This will use whichever layout the running kernel supports, so the data
705 on the array may become corrupt when changing kernel from pre-3.14 to a
708 When an array is converted between RAID5 and RAID6 an intermediate
709 RAID6 layout is used in which the second parity block (Q) is always on
710 the last device. To convert a RAID5 to RAID6 and leave it in this new
711 layout (which does not require re-striping) use
712 .BR \-\-layout=preserve .
713 This will try to avoid any restriping.
715 The converse of this is
716 .B \-\-layout=normalise
717 which will change a non-standard RAID6 layout into a more standard
724 (thus explaining the p of
728 .BR \-b ", " \-\-bitmap=
729 Specify a file to store a write-intent bitmap in. The file should not
732 is also given. The same file should be provided
733 when assembling the array. If the word
735 is given, then the bitmap is stored with the metadata on the array,
736 and so is replicated on all devices. If the word
740 mode, then any bitmap that is present is removed. If the word
742 is given, the array is created for a clustered environment. One bitmap
743 is created for each node as defined by the
745 parameter and are stored internally.
747 To help catch typing errors, the filename must contain at least one
748 slash ('/') if it is a real file (not 'internal' or 'none').
750 Note: external bitmaps are only known to work on ext2 and ext3.
751 Storing bitmap files on other filesystems may result in serious problems.
753 When creating an array on devices which are 100G or larger,
755 automatically adds an internal bitmap as it will usually be
756 beneficial. This can be suppressed with
758 or by selecting a different consistency policy with
759 .BR \-\-consistency\-policy .
762 .BR \-\-bitmap\-chunk=
763 Set the chunksize of the bitmap. Each bit corresponds to that many
764 Kilobytes of storage.
765 When using a file based bitmap, the default is to use the smallest
766 size that is at-least 4 and requires no more than 2^21 chunks.
769 bitmap, the chunksize defaults to 64Meg, or larger if necessary to
770 fit the bitmap into the available space.
772 A suffix of 'K', 'M', 'G' or 'T' can be given to indicate Kilobytes,
773 Megabytes, Gigabytes or Terabytes respectively.
776 .BR \-W ", " \-\-write\-mostly
777 subsequent devices listed in a
782 command will be flagged as 'write\-mostly'. This is valid for RAID1
783 only and means that the 'md' driver will avoid reading from these
784 devices if at all possible. This can be useful if mirroring over a
788 .BR \-\-write\-behind=
789 Specify that write-behind mode should be enabled (valid for RAID1
790 only). If an argument is specified, it will set the maximum number
791 of outstanding writes allowed. The default value is 256.
792 A write-intent bitmap is required in order to use write-behind
793 mode, and write-behind is only attempted on drives marked as
798 subsequent devices listed in a
802 command will be flagged as 'failfast'. This is valid for RAID1 and
803 RAID10 only. IO requests to these devices will be encouraged to fail
804 quickly rather than cause long delays due to error handling. Also no
805 attempt is made to repair a read error on these devices.
807 If an array becomes degraded so that the 'failfast' device is the only
808 usable device, the 'failfast' flag will then be ignored and extended
809 delays will be preferred to complete failure.
811 The 'failfast' flag is appropriate for storage arrays which have a
812 low probability of true failure, but which may sometimes
813 cause unacceptable delays due to internal maintenance functions.
816 .BR \-\-assume\-clean
819 that the array pre-existed and is known to be clean. It can be useful
820 when trying to recover from a major failure as you can be sure that no
821 data will be affected unless you actually write to the array. It can
822 also be used when creating a RAID1 or RAID10 if you want to avoid the
823 initial resync, however this practice \(em while normally safe \(em is not
824 recommended. Use this only if you really know what you are doing.
826 When the devices that will be part of a new array were filled
827 with zeros before creation the operator knows the array is
828 actually clean. If that is the case, such as after running
829 badblocks, this argument can be used to tell mdadm the
830 facts the operator knows.
832 When an array is resized to a larger size with
833 .B "\-\-grow \-\-size="
834 the new space is normally resynced in that same way that the whole
835 array is resynced at creation. From Linux version 3.0,
837 can be used with that command to avoid the automatic resync.
840 .BR \-\-backup\-file=
843 is used to increase the number of raid-devices in a RAID5 or RAID6 if
844 there are no spare devices available, or to shrink, change RAID level
845 or layout. See the GROW MODE section below on RAID\-DEVICES CHANGES.
846 The file must be stored on a separate device, not on the RAID array
851 Arrays with 1.x metadata can leave a gap between the start of the
852 device and the start of array data. This gap can be used for various
853 metadata. The start of data is known as the
855 Normally an appropriate data offset is computed automatically.
856 However it can be useful to set it explicitly such as when re-creating
857 an array which was originally created using a different version of
859 which computed a different offset.
861 Setting the offset explicitly over-rides the default. The value given
862 is in Kilobytes unless a suffix of 'K', 'M', 'G' or 'T' is used to explicitly
863 indicate Kilobytes, Megabytes, Gigabytes or Terabytes respectively.
867 can also be used with
869 for some RAID levels (initially on RAID10). This allows the
870 data\-offset to be changed as part of the reshape process. When the
871 data offset is changed, no backup file is required as the difference
872 in offsets is used to provide the same functionality.
874 When the new offset is earlier than the old offset, the number of
875 devices in the array cannot shrink. When it is after the old offset,
876 the number of devices in the array cannot increase.
878 When creating an array,
882 In the case each member device is expected to have a offset appended
883 to the name, separated by a colon. This makes it possible to recreate
884 exactly an array which has varying data offsets (as can happen when
885 different versions of
887 are used to add different devices).
891 This option is complementary to the
892 .B \-\-freeze-reshape
893 option for assembly. It is needed when
895 operation is interrupted and it is not restarted automatically due to
896 .B \-\-freeze-reshape
897 usage during array assembly. This option is used together with
901 ) command and device for a pending reshape to be continued.
902 All parameters required for reshape continuation will be read from array metadata.
906 .BR \-\-backup\-file=
907 option to be set, continuation option will require to have exactly the same
908 backup file given as well.
910 Any other parameter passed together with
912 option will be ignored.
915 .BR \-N ", " \-\-name=
918 for the array. This is currently only effective when creating an
919 array with a version-1 superblock, or an array in a DDF container.
920 The name is a simple textual string that can be used to identify array
921 components when assembling. If name is needed but not specified, it
922 is taken from the basename of the device that is being created.
934 run the array, even if some of the components
935 appear to be active in another array or filesystem. Normally
937 will ask for confirmation before including such components in an
938 array. This option causes that question to be suppressed.
941 .BR \-f ", " \-\-force
944 accept the geometry and layout specified without question. Normally
946 will not allow creation of an array with only one device, and will try
947 to create a RAID5 array with one missing drive (as this makes the
948 initial resync work faster). With
951 will not try to be so clever.
954 .BR \-o ", " \-\-readonly
957 rather than read-write as normal. No writes will be allowed to the
958 array, and no resync, recovery, or reshape will be started. It works with
959 Create, Assemble, Manage and Misc mode.
962 .BR \-a ", " "\-\-auto{=yes,md,mdp,part,p}{NN}"
963 Instruct mdadm how to create the device file if needed, possibly allocating
964 an unused minor number. "md" causes a non-partitionable array
965 to be used (though since Linux 2.6.28, these array devices are in fact
966 partitionable). "mdp", "part" or "p" causes a partitionable array (2.6 and
967 later) to be used. "yes" requires the named md device to have
968 a 'standard' format, and the type and minor number will be determined
969 from this. With mdadm 3.0, device creation is normally left up to
971 so this option is unlikely to be needed.
972 See DEVICE NAMES below.
974 The argument can also come immediately after
979 is not given on the command line or in the config file, then
985 is also given, then any
987 entries in the config file will override the
989 instruction given on the command line.
991 For partitionable arrays,
993 will create the device file for the whole array and for the first 4
994 partitions. A different number of partitions can be specified at the
995 end of this option (e.g.
997 If the device name ends with a digit, the partition names add a 'p',
999 .IR /dev/md/home1p3 .
1000 If there is no trailing digit, then the partition names just have a
1002 .IR /dev/md/scratch3 .
1004 If the md device name is in a 'standard' format as described in DEVICE
1005 NAMES, then it will be created, if necessary, with the appropriate
1006 device number based on that name. If the device name is not in one of these
1007 formats, then a unused device number will be allocated. The device
1008 number will be considered unused if there is no active array for that
1009 number, and there is no entry in /dev for that number and with a
1010 non-standard name. Names that are not in 'standard' format are only
1011 allowed in "/dev/md/".
1013 This is meaningful with
1019 .BR \-a ", " "\-\-add"
1020 This option can be used in Grow mode in two cases.
1022 If the target array is a Linear array, then
1024 can be used to add one or more devices to the array. They
1025 are simply catenated on to the end of the array. Once added, the
1026 devices cannot be removed.
1030 option is being used to increase the number of devices in an array,
1033 can be used to add some extra devices to be included in the array.
1034 In most cases this is not needed as the extra devices can be added as
1035 spares first, and then the number of raid-disks can be changed.
1036 However for RAID0, it is not possible to add spares. So to increase
1037 the number of devices in a RAID0, it is necessary to set the new
1038 number of devices, and to add the new devices, in the same command.
1042 Only works when the array is for clustered environment. It specifies
1043 the maximum number of nodes in the cluster that will use this device
1044 simultaneously. If not specified, this defaults to 4.
1047 .BR \-\-write-journal
1048 Specify journal device for the RAID-4/5/6 array. The journal device
1049 should be a SSD with reasonable lifetime.
1052 .BR \-k ", " \-\-consistency\-policy=
1053 Specify how the array maintains consistency in case of unexpected shutdown.
1054 Only relevant for RAID levels with redundancy.
1055 Currently supported options are:
1060 Full resync is performed and all redundancy is regenerated when the array is
1061 started after unclean shutdown.
1065 Resync assisted by a write-intent bitmap. Implicitly selected when using
1070 For RAID levels 4/5/6, journal device is used to log transactions and replay
1071 after unclean shutdown. Implicitly selected when using
1072 .BR \-\-write\-journal .
1076 For RAID5 only, Partial Parity Log is used to close the write hole and
1077 eliminate resync. PPL is stored in the metadata region of RAID member drives,
1078 no additional journal drive is needed.
1081 Can be used with \-\-grow to change the consistency policy of an active array
1082 in some cases. See CONSISTENCY POLICY CHANGES below.
1089 .BR \-u ", " \-\-uuid=
1090 uuid of array to assemble. Devices which don't have this uuid are
1094 .BR \-m ", " \-\-super\-minor=
1095 Minor number of device that array was created for. Devices which
1096 don't have this minor number are excluded. If you create an array as
1097 /dev/md1, then all superblocks will contain the minor number 1, even if
1098 the array is later assembled as /dev/md2.
1100 Giving the literal word "dev" for
1104 to use the minor number of the md device that is being assembled.
1105 e.g. when assembling
1107 .B \-\-super\-minor=dev
1108 will look for super blocks with a minor number of 0.
1111 is only relevant for v0.90 metadata, and should not normally be used.
1117 .BR \-N ", " \-\-name=
1118 Specify the name of the array to assemble. This must be the name
1119 that was specified when creating the array. It must either match
1120 the name stored in the superblock exactly, or it must match
1123 prefixed to the start of the given name.
1126 .BR \-f ", " \-\-force
1127 Assemble the array even if the metadata on some devices appears to be
1130 cannot find enough working devices to start the array, but can find
1131 some devices that are recorded as having failed, then it will mark
1132 those devices as working so that the array can be started. This works only for
1133 native. For external metadata it allows to start dirty degraded RAID 4, 5, 6.
1134 An array which requires
1136 to be started may contain data corruption. Use it carefully.
1139 .BR \-R ", " \-\-run
1140 Attempt to start the array even if fewer drives were given than were
1141 present last time the array was active. Normally if not all the
1142 expected drives are found and
1144 is not used, then the array will be assembled but not started.
1147 an attempt will be made to start it anyway.
1151 This is the reverse of
1153 in that it inhibits the startup of array unless all expected drives
1154 are present. This is only needed with
1156 and can be used if the physical connections to devices are
1157 not as reliable as you would like.
1160 .BR \-a ", " "\-\-auto{=no,yes,md,mdp,part}"
1161 See this option under Create and Build options.
1164 .BR \-b ", " \-\-bitmap=
1165 Specify the bitmap file that was given when the array was created. If
1168 bitmap, there is no need to specify this when assembling the array.
1171 .BR \-\-backup\-file=
1174 was used while reshaping an array (e.g. changing number of devices or
1175 chunk size) and the system crashed during the critical section, then the same
1177 must be presented to
1179 to allow possibly corrupted data to be restored, and the reshape
1183 .BR \-\-invalid\-backup
1184 If the file needed for the above option is not available for any
1185 reason an empty file can be given together with this option to
1186 indicate that the backup file is invalid. In this case the data that
1187 was being rearranged at the time of the crash could be irrecoverably
1188 lost, but the rest of the array may still be recoverable. This option
1189 should only be used as a last resort if there is no way to recover the
1194 .BR \-U ", " \-\-update=
1195 Update the superblock on each device while assembling the array. The
1196 argument given to this flag can be one of
1212 .BR layout\-original ,
1213 .BR layout\-alternate ,
1214 .BR layout\-unspecified ,
1221 option will adjust the superblock of an array what was created on a Sparc
1222 machine running a patched 2.2 Linux kernel. This kernel got the
1223 alignment of part of the superblock wrong. You can use the
1224 .B "\-\-examine \-\-sparc2.2"
1227 to see what effect this would have.
1231 option will update the
1232 .B "preferred minor"
1233 field on each superblock to match the minor number of the array being
1235 This can be useful if
1237 reports a different "Preferred Minor" to
1239 In some cases this update will be performed automatically
1240 by the kernel driver. In particular the update happens automatically
1241 at the first write to an array with redundancy (RAID level 1 or
1242 greater) on a 2.6 (or later) kernel.
1246 option will change the uuid of the array. If a UUID is given with the
1248 option that UUID will be used as a new UUID and will
1250 be used to help identify the devices in the array.
1253 is given, a random UUID is chosen.
1257 option will change the
1259 of the array as stored in the superblock. This is only supported for
1260 version-1 superblocks.
1264 option will change the
1266 of the array as stored in the bitmap superblock. This option only
1267 works for a clustered environment.
1271 option will change the
1273 as recorded in the superblock. For version-0 superblocks, this is the
1274 same as updating the UUID.
1275 For version-1 superblocks, this involves updating the name.
1279 option will change the cluster name as recorded in the superblock and
1280 bitmap. This option only works for clustered environment.
1284 option will cause the array to be marked
1286 meaning that any redundancy in the array (e.g. parity for RAID5,
1287 copies for RAID1) may be incorrect. This will cause the RAID system
1288 to perform a "resync" pass to make sure that all redundant information
1293 option allows arrays to be moved between machines with different
1294 byte-order, such as from a big-endian machine like a Sparc or some
1295 MIPS machines, to a little-endian x86_64 machine.
1296 When assembling such an array for the first time after a move, giving
1297 .B "\-\-update=byteorder"
1300 to expect superblocks to have their byteorder reversed, and will
1301 correct that order before assembling the array. This is only valid
1302 with original (Version 0.90) superblocks.
1306 option will correct the summaries in the superblock. That is the
1307 counts of total, working, active, failed, and spare devices.
1311 option will rarely be of use. It applies to version 1.1 and 1.2 metadata
1312 only (where the metadata is at the start of the device) and is only
1313 useful when the component device has changed size (typically become
1314 larger). The version 1 metadata records the amount of the device that
1315 can be used to store data, so if a device in a version 1.1 or 1.2
1316 array becomes larger, the metadata will still be visible, but the
1317 extra space will not. In this case it might be useful to assemble the
1319 .BR \-\-update=devicesize .
1322 to determine the maximum usable amount of space on each device and
1323 update the relevant field in the metadata.
1327 option only works on v0.90 metadata arrays and will convert them to
1328 v1.0 metadata. The array must not be dirty (i.e. it must not need a
1329 sync) and it must not have a write-intent bitmap.
1331 The old metadata will remain on the devices, but will appear older
1332 than the new metadata and so will usually be ignored. The old metadata
1333 (or indeed the new metadata) can be removed by giving the appropriate
1336 .BR \-\-zero\-superblock .
1340 option can be used when an array has an internal bitmap which is
1341 corrupt in some way so that assembling the array normally fails. It
1342 will cause any internal bitmap to be ignored.
1346 option will reserve space in each device for a bad block list. This
1347 will be 4K in size and positioned near the end of any free space
1348 between the superblock and the data.
1352 option will cause any reservation of space for a bad block list to be
1353 removed. If the bad block list contains entries, this will fail, as
1354 removing the list could cause data corruption.
1358 option will enable PPL for a RAID5 array and reserve space for PPL on each
1359 device. There must be enough free space between the data and superblock and a
1360 write-intent bitmap or journal must not be used.
1364 option will disable PPL in the superblock.
1369 .B layout\-alternate
1370 options are for RAID0 arrays with non-uniform devices size that were in
1371 use before Linux 5.4. If the array was being used with Linux 3.13 or
1372 earlier, then to assemble the array on a new kernel,
1373 .B \-\-update=layout\-original
1374 must be given. If the array was created and used with a kernel from Linux 3.14 to
1376 .B \-\-update=layout\-alternate
1377 must be given. This only needs to be given once. Subsequent assembly of the array
1378 will happen normally.
1379 For more information, see
1383 .B layout\-unspecified
1384 option reverts the effect of
1387 .B layout\-alternate
1388 and allows the array to be again used on a kernel prior to Linux 5.3.
1389 This option should be used with great caution.
1392 .BR \-\-freeze\-reshape
1393 Option is intended to be used in start-up scripts during initrd boot phase.
1394 When array under reshape is assembled during initrd phase, this option
1395 stops reshape after reshape critical section is being restored. This happens
1396 before file system pivot operation and avoids loss of file system context.
1397 Losing file system context would cause reshape to be broken.
1399 Reshape can be continued later using the
1401 option for the grow command.
1403 .SH For Manage mode:
1406 .BR \-t ", " \-\-test
1407 Unless a more serious error occurred,
1409 will exit with a status of 2 if no changes were made to the array and
1410 0 if at least one change was made.
1411 This can be useful when an indirect specifier such as
1416 is used in requesting an operation on the array.
1418 will report failure if these specifiers didn't find any match.
1421 .BR \-a ", " \-\-add
1422 hot-add listed devices.
1423 If a device appears to have recently been part of the array
1424 (possibly it failed or was removed) the device is re\-added as described
1426 If that fails or the device was never part of the array, the device is
1427 added as a hot-spare.
1428 If the array is degraded, it will immediately start to rebuild data
1431 Note that this and the following options are only meaningful on array
1432 with redundancy. They don't apply to RAID0 or Linear.
1436 re\-add a device that was previously removed from an array.
1437 If the metadata on the device reports that it is a member of the
1438 array, and the slot that it used is still vacant, then the device will
1439 be added back to the array in the same position. This will normally
1440 cause the data for that device to be recovered. However based on the
1441 event count on the device, the recovery may only require sections that
1442 are flagged a write-intent bitmap to be recovered or may not require
1443 any recovery at all.
1445 When used on an array that has no metadata (i.e. it was built with
1447 it will be assumed that bitmap-based recovery is enough to make the
1448 device fully consistent with the array.
1450 When used with v1.x metadata,
1452 can be accompanied by
1453 .BR \-\-update=devicesize ,
1454 .BR \-\-update=bbl ", or"
1455 .BR \-\-update=no\-bbl .
1456 See the description of these option when used in Assemble mode for an
1457 explanation of their use.
1459 If the device name given is
1463 will try to find any device that looks like it should be
1464 part of the array but isn't and will try to re\-add all such devices.
1466 If the device name given is
1470 will find all devices in the array that are marked
1472 remove them and attempt to immediately re\-add them. This can be
1473 useful if you are certain that the reason for failure has been
1478 Add a device as a spare. This is similar to
1480 except that it does not attempt
1482 first. The device will be added as a spare even if it looks like it
1483 could be an recent member of the array.
1486 .BR \-r ", " \-\-remove
1487 remove listed devices. They must not be active. i.e. they should
1488 be failed or spare devices.
1490 As well as the name of a device file
1500 The first causes all failed device to be removed. The second causes
1501 any device which is no longer connected to the system (i.e an 'open'
1505 The third will remove a set as describe below under
1509 .BR \-f ", " \-\-fail
1510 Mark listed devices as faulty.
1511 As well as the name of a device file, the word
1515 can be given. The former will cause any device that has been detached from
1516 the system to be marked as failed. It can then be removed.
1518 For RAID10 arrays where the number of copies evenly divides the number
1519 of devices, the devices can be conceptually divided into sets where
1520 each set contains a single complete copy of the data on the array.
1521 Sometimes a RAID10 array will be configured so that these sets are on
1522 separate controllers. In this case all the devices in one set can be
1523 failed by giving a name like
1529 The appropriate set names are reported by
1539 Mark listed devices as requiring replacement. As soon as a spare is
1540 available, it will be rebuilt and will replace the marked device.
1541 This is similar to marking a device as faulty, but the device remains
1542 in service during the recovery process to increase resilience against
1543 multiple failures. When the replacement process finishes, the
1544 replaced device will be marked as faulty.
1548 This can follow a list of
1550 devices. The devices listed after
1552 will be preferentially used to replace the devices listed after
1554 These device must already be spare devices in the array.
1557 .BR \-\-write\-mostly
1558 Subsequent devices that are added or re\-added will have the 'write-mostly'
1559 flag set. This is only valid for RAID1 and means that the 'md' driver
1560 will avoid reading from these devices if possible.
1563 Subsequent devices that are added or re\-added will have the 'write-mostly'
1566 .BR \-\-cluster\-confirm
1567 Confirm the existence of the device. This is issued in response to an \-\-add
1568 request by a node in a cluster. When a node adds a device it sends a message
1569 to all nodes in the cluster to look for a device with a UUID. This translates
1570 to a udev notification with the UUID of the device to be added and the slot
1571 number. The receiving node must acknowledge this message
1572 with \-\-cluster\-confirm. Valid arguments are <slot>:<devicename> in case
1573 the device is found or <slot>:missing in case the device is not found.
1577 Add journal to an existing array, or recreate journal for RAID-4/5/6 array
1578 that lost a journal device. To avoid interrupting on-going write opertions,
1580 only works for array in Read-Only state.
1584 Subsequent devices that are added or re\-added will have
1585 the 'failfast' flag set. This is only valid for RAID1 and RAID10 and
1586 means that the 'md' driver will avoid long timeouts on error handling
1590 Subsequent devices that are re\-added will be re\-added without
1591 the 'failfast' flag set.
1594 Each of these options requires that the first device listed is the array
1595 to be acted upon, and the remainder are component devices to be added,
1596 removed, marked as faulty, etc. Several different operations can be
1597 specified for different devices, e.g.
1599 mdadm /dev/md0 \-\-add /dev/sda1 \-\-fail /dev/sdb1 \-\-remove /dev/sdb1
1601 Each operation applies to all devices listed until the next
1604 If an array is using a write-intent bitmap, then devices which have
1605 been removed can be re\-added in a way that avoids a full
1606 reconstruction but instead just updates the blocks that have changed
1607 since the device was removed. For arrays with persistent metadata
1608 (superblocks) this is done automatically. For arrays created with
1610 mdadm needs to be told that this device we removed recently with
1613 Devices can only be removed from an array if they are not in active
1614 use, i.e. that must be spares or failed devices. To remove an active
1615 device, it must first be marked as
1621 .BR \-Q ", " \-\-query
1622 Examine a device to see
1623 (1) if it is an md device and (2) if it is a component of an md
1625 Information about what is discovered is presented.
1628 .BR \-D ", " \-\-detail
1629 Print details of one or more md devices.
1632 .BR \-\-detail\-platform
1633 Print details of the platform's RAID capabilities (firmware / hardware
1634 topology) for a given metadata format. If used without argument, mdadm
1635 will scan all controllers looking for their capabilities. Otherwise, mdadm
1636 will only look at the controller specified by the argument in form of an
1637 absolute filepath or a link, e.g.
1638 .IR /sys/devices/pci0000:00/0000:00:1f.2 .
1641 .BR \-Y ", " \-\-export
1644 .BR \-\-detail-platform ,
1648 output will be formatted as
1650 pairs for easy import into the environment.
1656 indicates whether an array was started
1658 or not, which may include a reason
1659 .RB ( unsafe ", " nothing ", " no ).
1662 indicates if the array is expected on this host
1664 or seems to be from elsewhere
1668 .BR \-E ", " \-\-examine
1669 Print contents of the metadata stored on the named device(s).
1670 Note the contrast between
1675 applies to devices which are components of an array, while
1677 applies to a whole array which is currently active.
1680 If an array was created on a SPARC machine with a 2.2 Linux kernel
1681 patched with RAID support, the superblock will have been created
1682 incorrectly, or at least incompatibly with 2.4 and later kernels.
1687 will fix the superblock before displaying it. If this appears to do
1688 the right thing, then the array can be successfully assembled using
1689 .BR "\-\-assemble \-\-update=sparc2.2" .
1692 .BR \-X ", " \-\-examine\-bitmap
1693 Report information about a bitmap file.
1694 The argument is either an external bitmap file or an array component
1695 in case of an internal bitmap. Note that running this on an array
1698 does not report the bitmap for that array.
1701 .B \-\-examine\-badblocks
1702 List the bad-blocks recorded for the device, if a bad-blocks list has
1703 been configured. Currently only
1707 metadata support bad-blocks lists.
1710 .BI \-\-dump= directory
1712 .BI \-\-restore= directory
1713 Save metadata from lists devices, or restore metadata to listed devices.
1716 .BR \-R ", " \-\-run
1717 start a partially assembled array. If
1719 did not find enough devices to fully start the array, it might leaving
1720 it partially assembled. If you wish, you can then use
1722 to start the array in degraded mode.
1725 .BR \-S ", " \-\-stop
1726 deactivate array, releasing all resources.
1729 .BR \-o ", " \-\-readonly
1730 mark array as readonly.
1733 .BR \-w ", " \-\-readwrite
1734 mark array as readwrite.
1737 .B \-\-zero\-superblock
1738 If the device contains a valid md superblock, the block is
1739 overwritten with zeros. With
1741 the block where the superblock would be is overwritten even if it
1742 doesn't appear to be valid.
1745 Be careful to call \-\-zero\-superblock with clustered raid, make sure
1746 array isn't used or assembled in other cluster node before execute it.
1749 .B \-\-kill\-subarray=
1750 If the device is a container and the argument to \-\-kill\-subarray
1751 specifies an inactive subarray in the container, then the subarray is
1752 deleted. Deleting all subarrays will leave an 'empty-container' or
1753 spare superblock on the drives. See
1754 .B \-\-zero\-superblock
1756 removing a superblock. Note that some formats depend on the subarray
1757 index for generating a UUID, this command will fail if it would change
1758 the UUID of an active subarray.
1761 .B \-\-update\-subarray=
1762 If the device is a container and the argument to \-\-update\-subarray
1763 specifies a subarray in the container, then attempt to update the given
1764 superblock field in the subarray. See below in
1769 .BR \-t ", " \-\-test
1774 is set to reflect the status of the device. See below in
1779 .BR \-W ", " \-\-wait
1780 For each md device given, wait for any resync, recovery, or reshape
1781 activity to finish before returning.
1783 will return with success if it actually waited for every device
1784 listed, otherwise it will return failure.
1788 For each md device given, or each device in /proc/mdstat if
1790 is given, arrange for the array to be marked clean as soon as possible.
1792 will return with success if the array uses external metadata and we
1793 successfully waited. For native arrays this returns immediately as the
1794 kernel handles dirty-clean transitions at shutdown. No action is taken
1795 if safe-mode handling is disabled.
1799 Set the "sync_action" for all md devices given to one of
1806 will abort any currently running action though some actions will
1807 automatically restart.
1810 will abort any current action and ensure no other action starts
1820 .BR "SCRUBBING AND MISMATCHES" .
1822 .SH For Incremental Assembly mode:
1824 .BR \-\-rebuild\-map ", " \-r
1825 Rebuild the map file
1829 uses to help track which arrays are currently being assembled.
1832 .BR \-\-run ", " \-R
1833 Run any array assembled as soon as a minimal number of devices are
1834 available, rather than waiting until all expected devices are present.
1837 .BR \-\-scan ", " \-s
1838 Only meaningful with
1842 file for arrays that are being incrementally assembled and will try to
1843 start any that are not already started. If any such array is listed
1846 as requiring an external bitmap, that bitmap will be attached first.
1849 .BR \-\-fail ", " \-f
1850 This allows the hot-plug system to remove devices that have fully disappeared
1851 from the kernel. It will first fail and then remove the device from any
1852 array it belongs to.
1853 The device name given should be a kernel device name such as "sda",
1859 Only used with \-\-fail. The 'path' given will be recorded so that if
1860 a new device appears at the same location it can be automatically
1861 added to the same array. This allows the failed device to be
1862 automatically replaced by a new device without metadata if it appears
1863 at specified path. This option is normally only set by a
1867 .SH For Monitor mode:
1869 .BR \-m ", " \-\-mail
1870 Give a mail address to send alerts to.
1873 .BR \-p ", " \-\-program ", " \-\-alert
1874 Give a program to be run whenever an event is detected.
1877 .BR \-y ", " \-\-syslog
1878 Cause all events to be reported through 'syslog'. The messages have
1879 facility of 'daemon' and varying priorities.
1882 .BR \-d ", " \-\-delay
1883 Give a delay in seconds.
1885 polls the md arrays and then waits this many seconds before polling
1886 again. The default is 60 seconds. Since 2.6.16, there is no need to
1887 reduce this as the kernel alerts
1889 immediately when there is any change.
1892 .BR \-r ", " \-\-increment
1893 Give a percentage increment.
1895 will generate RebuildNN events with the given percentage increment.
1898 .BR \-f ", " \-\-daemonise
1901 to run as a background daemon if it decides to monitor anything. This
1902 causes it to fork and run in the child, and to disconnect from the
1903 terminal. The process id of the child is written to stdout.
1906 which will only continue monitoring if a mail address or alert program
1907 is found in the config file.
1910 .BR \-i ", " \-\-pid\-file
1913 is running in daemon mode, write the pid of the daemon process to
1914 the specified file, instead of printing it on standard output.
1917 .BR \-1 ", " \-\-oneshot
1918 Check arrays only once. This will generate
1920 events and more significantly
1926 .B " mdadm \-\-monitor \-\-scan \-1"
1928 from a cron script will ensure regular notification of any degraded arrays.
1931 .BR \-t ", " \-\-test
1934 alert for every array found at startup. This alert gets mailed and
1935 passed to the alert program. This can be used for testing that alert
1936 message do get through successfully.
1940 This inhibits the functionality for moving spares between arrays.
1941 Only one monitoring process started with
1943 but without this flag is allowed, otherwise the two could interfere
1950 .B mdadm \-\-assemble
1951 .I md-device options-and-component-devices...
1954 .B mdadm \-\-assemble \-\-scan
1955 .I md-devices-and-options...
1958 .B mdadm \-\-assemble \-\-scan
1962 This usage assembles one or more RAID arrays from pre-existing components.
1963 For each array, mdadm needs to know the md device, the identity of the
1964 array, and a number of component-devices. These can be found in a number of ways.
1966 In the first usage example (without the
1968 the first device given is the md device.
1969 In the second usage example, all devices listed are treated as md
1970 devices and assembly is attempted.
1971 In the third (where no devices are listed) all md devices that are
1972 listed in the configuration file are assembled. If no arrays are
1973 described by the configuration file, then any arrays that
1974 can be found on unused devices will be assembled.
1976 If precisely one device is listed, but
1982 was given and identity information is extracted from the configuration file.
1984 The identity can be given with the
1990 option, will be taken from the md-device record in the config file, or
1991 will be taken from the super block of the first component-device
1992 listed on the command line.
1994 Devices can be given on the
1996 command line or in the config file. Only devices which have an md
1997 superblock which contains the right identity will be considered for
2000 The config file is only used if explicitly named with
2002 or requested with (a possibly implicit)
2004 In the later case, default config file is used. See
2010 is not given, then the config file will only be used to find the
2011 identity of md arrays.
2013 Normally the array will be started after it is assembled. However if
2015 is not given and not all expected drives were listed, then the array
2016 is not started (to guard against usage errors). To insist that the
2017 array be started in this case (as may work for RAID1, 4, 5, 6, or 10),
2026 does not create any entries in
2030 It does record information in
2034 to choose the correct name.
2038 detects that udev is not configured, it will create the devices in
2042 In Linux kernels prior to version 2.6.28 there were two distinctly
2043 different types of md devices that could be created: one that could be
2044 partitioned using standard partitioning tools and one that could not.
2045 Since 2.6.28 that distinction is no longer relevant as both type of
2046 devices can be partitioned.
2048 will normally create the type that originally could not be partitioned
2049 as it has a well defined major number (9).
2051 Prior to 2.6.28, it is important that mdadm chooses the correct type
2052 of array device to use. This can be controlled with the
2054 option. In particular, a value of "mdp" or "part" or "p" tells mdadm
2055 to use a partitionable device rather than the default.
2057 In the no-udev case, the value given to
2059 can be suffixed by a number. This tells
2061 to create that number of partition devices rather than the default of 4.
2065 can also be given in the configuration file as a word starting
2067 on the ARRAY line for the relevant array.
2074 and no devices are listed,
2076 will first attempt to assemble all the arrays listed in the config
2079 If no arrays are listed in the config (other than those marked
2081 it will look through the available devices for possible arrays and
2082 will try to assemble anything that it finds. Arrays which are tagged
2083 as belonging to the given homehost will be assembled and started
2084 normally. Arrays which do not obviously belong to this host are given
2085 names that are expected not to conflict with anything local, and are
2086 started "read-auto" so that nothing is written to any device until the
2087 array is written to. i.e. automatic resync etc is delayed.
2091 finds a consistent set of devices that look like they should comprise
2092 an array, and if the superblock is tagged as belonging to the given
2093 home host, it will automatically choose a device name and try to
2094 assemble the array. If the array uses version-0.90 metadata, then the
2096 number as recorded in the superblock is used to create a name in
2100 If the array uses version-1 metadata, then the
2102 from the superblock is used to similarly create a name in
2104 (the name will have any 'host' prefix stripped first).
2106 This behaviour can be modified by the
2110 configuration file. This line can indicate that specific metadata
2111 type should, or should not, be automatically assembled. If an array
2112 is found which is not listed in
2114 and has a metadata format that is denied by the
2116 line, then it will not be assembled.
2119 line can also request that all arrays identified as being for this
2120 homehost should be assembled regardless of their metadata type.
2123 for further details.
2125 Note: Auto assembly cannot be used for assembling and activating some
2126 arrays which are undergoing reshape. In particular as the
2128 cannot be given, any reshape which requires a backup-file to continue
2129 cannot be started by auto assembly. An array which is growing to more
2130 devices and has passed the critical section can be assembled using
2141 .BI \-\-raid\-devices= Z
2145 This usage is similar to
2147 The difference is that it creates an array without a superblock. With
2148 these arrays there is no difference between initially creating the array and
2149 subsequently assembling the array, except that hopefully there is useful
2150 data there in the second case.
2152 The level may raid0, linear, raid1, raid10, multipath, or faulty, or
2153 one of their synonyms. All devices must be listed and the array will
2154 be started once complete. It will often be appropriate to use
2155 .B \-\-assume\-clean
2156 with levels raid1 or raid10.
2167 .BI \-\-raid\-devices= Z
2171 This usage will initialise a new md array, associate some devices with
2172 it, and activate the array.
2174 The named device will normally not exist when
2175 .I "mdadm \-\-create"
2176 is run, but will be created by
2178 once the array becomes active.
2180 The max length md-device name is limited to 32 characters.
2181 Different metadata types have more strict limitation
2182 (like IMSM where only 16 characters are allowed).
2183 For that reason, long name could be truncated or rejected, it depends on metadata policy.
2185 As devices are added, they are checked to see if they contain RAID
2186 superblocks or filesystems. They are also checked to see if the variance in
2187 device size exceeds 1%.
2189 If any discrepancy is found, the array will not automatically be run, though
2192 can override this caution.
2194 To create a "degraded" array in which some devices are missing, simply
2195 give the word "\fBmissing\fP"
2196 in place of a device name. This will cause
2198 to leave the corresponding slot in the array empty.
2199 For a RAID4 or RAID5 array at most one slot can be
2200 "\fBmissing\fP"; for a RAID6 array at most two slots.
2201 For a RAID1 array, only one real device needs to be given. All of the
2205 When creating a RAID5 array,
2207 will automatically create a degraded array with an extra spare drive.
2208 This is because building the spare into a degraded array is in general
2209 faster than resyncing the parity on a non-degraded, but not clean,
2210 array. This feature can be overridden with the
2214 When creating an array with version-1 metadata a name for the array is
2216 If this is not given with the
2220 will choose a name based on the last component of the name of the
2221 device being created. So if
2223 is being created, then the name
2228 is being created, then the name
2232 When creating a partition based array, using
2234 with version-1.x metadata, the partition type should be set to
2236 (non fs-data). This type selection allows for greater precision since
2237 using any other [RAID auto-detect (0xFD) or a GNU/Linux partition (0x83)],
2238 might create problems in the event of array recovery through a live cdrom.
2240 A new array will normally get a randomly assigned 128bit UUID which is
2241 very likely to be unique. If you have a specific need, you can choose
2242 a UUID for the array by giving the
2244 option. Be warned that creating two arrays with the same UUID is a
2245 recipe for disaster. Also, using
2247 when creating a v0.90 array will silently override any
2252 .\"option is given, it is not necessary to list any component-devices in this command.
2253 .\"They can be added later, before a
2257 .\"is given, the apparent size of the smallest drive given is used.
2259 If the array type supports a write-intent bitmap, and if the devices
2260 in the array exceed 100G is size, an internal write-intent bitmap
2261 will automatically be added unless some other option is explicitly
2264 option or a different consistency policy is selected with the
2265 .B \-\-consistency\-policy
2266 option. In any case space for a bitmap will be reserved so that one
2267 can be added later with
2268 .BR "\-\-grow \-\-bitmap=internal" .
2270 If the metadata type supports it (currently only 1.x and IMSM metadata),
2271 space will be allocated to store a bad block list. This allows a modest
2272 number of bad blocks to be recorded, allowing the drive to remain in
2273 service while only partially functional.
2275 When creating an array within a
2278 can be given either the list of devices to use, or simply the name of
2279 the container. The former case gives control over which devices in
2280 the container will be used for the array. The latter case allows
2282 to automatically choose which devices to use based on how much spare
2285 The General Management options that are valid with
2290 insist on running the array even if some devices look like they might
2295 start the array in readonly mode.
2302 .I options... devices...
2305 This usage will allow individual devices in an array to be failed,
2306 removed or added. It is possible to perform multiple operations with
2307 on command. For example:
2309 .B " mdadm /dev/md0 \-f /dev/hda1 \-r /dev/hda1 \-a /dev/hda1"
2315 and will then remove it from the array and finally add it back
2316 in as a spare. However only one md array can be affected by a single
2319 When a device is added to an active array, mdadm checks to see if it
2320 has metadata on it which suggests that it was recently a member of the
2321 array. If it does, it tries to "re\-add" the device. If there have
2322 been no changes since the device was removed, or if the array has a
2323 write-intent bitmap which has recorded whatever changes there were,
2324 then the device will immediately become a full member of the array and
2325 those differences recorded in the bitmap will be resolved.
2335 MISC mode includes a number of distinct operations that
2336 operate on distinct devices. The operations are:
2339 The device is examined to see if it is
2340 (1) an active md array, or
2341 (2) a component of an md array.
2342 The information discovered is reported.
2346 The device should be an active md device.
2348 will display a detailed description of the array.
2352 will cause the output to be less detailed and the format to be
2353 suitable for inclusion in
2357 will normally be 0 unless
2359 failed to get useful information about the device(s); however, if the
2361 option is given, then the exit status will be:
2365 The array is functioning normally.
2368 The array has at least one failed device.
2371 The array has multiple failed devices such that it is unusable.
2374 There was an error while trying to get information about the device.
2378 .B \-\-detail\-platform
2379 Print detail of the platform's RAID capabilities (firmware / hardware
2380 topology). If the metadata is specified with
2384 then the return status will be:
2388 metadata successfully enumerated its platform components on this system
2391 metadata is platform independent
2394 metadata failed to find its platform components on this system
2398 .B \-\-update\-subarray=
2399 If the device is a container and the argument to \-\-update\-subarray
2400 specifies a subarray in the container, then attempt to update the given
2401 superblock field in the subarray. Similar to updating an array in
2402 "assemble" mode, the field to update is selected by
2406 option. The supported options are
2416 option updates the subarray name in the metadata, it may not affect the
2417 device node name or the device node symlink until the subarray is
2418 re\-assembled. If updating
2420 would change the UUID of an active subarray this operation is blocked,
2421 and the command will end in an error.
2427 options enable and disable PPL in the metadata. Currently supported only for
2434 options enable and disable write-intent bitmap in the metadata. Currently supported only for
2439 The device should be a component of an md array.
2441 will read the md superblock of the device and display the contents.
2446 is given, then multiple devices that are components of the one array
2447 are grouped together and reported in a single entry suitable
2453 without listing any devices will cause all devices listed in the
2454 config file to be examined.
2457 .BI \-\-dump= directory
2458 If the device contains RAID metadata, a file will be created in the
2460 and the metadata will be written to it. The file will be the same
2461 size as the device and have the metadata written in the file at the
2462 same locate that it exists in the device. However the file will be "sparse" so
2463 that only those blocks containing metadata will be allocated. The
2464 total space used will be small.
2466 The file name used in the
2468 will be the base name of the device. Further if any links appear in
2470 which point to the device, then hard links to the file will be created
2477 Multiple devices can be listed and their metadata will all be stored
2478 in the one directory.
2481 .BI \-\-restore= directory
2482 This is the reverse of
2485 will locate a file in the directory that has a name appropriate for
2486 the given device and will restore metadata from it. Names that match
2488 names are preferred, however if two of those refer to different files,
2490 will not choose between them but will abort the operation.
2492 If a file name is given instead of a
2496 will restore from that file to a single device, always provided the
2497 size of the file matches that of the device, and the file contains
2501 The devices should be active md arrays which will be deactivated, as
2502 long as they are not currently in use.
2506 This will fully activate a partially assembled md array.
2510 This will mark an active array as read-only, providing that it is
2511 not currently being used.
2517 array back to being read/write.
2521 For all operations except
2524 will cause the operation to be applied to all arrays listed in
2529 causes all devices listed in the config file to be examined.
2532 .BR \-b ", " \-\-brief
2533 Be less verbose. This is used with
2541 gives an intermediate level of verbosity.
2547 .B mdadm \-\-monitor
2548 .I options... devices...
2553 to periodically poll a number of md arrays and to report on any events
2556 will never exit once it decides that there are arrays to be checked,
2557 so it should normally be run in the background.
2559 As well as reporting events,
2561 may move a spare drive from one array to another if they are in the
2566 and if the destination array has a failed drive but no spares.
2568 If any devices are listed on the command line,
2570 will only monitor those devices. Otherwise all arrays listed in the
2571 configuration file will be monitored. Further, if
2573 is given, then any other md devices that appear in
2575 will also be monitored.
2577 The result of monitoring the arrays is the generation of events.
2578 These events are passed to a separate program (if specified) and may
2579 be mailed to a given E-mail address.
2581 When passing events to a program, the program is run once for each event,
2582 and is given 2 or 3 command-line arguments: the first is the
2583 name of the event (see below), the second is the name of the
2584 md device which is affected, and the third is the name of a related
2585 device if relevant (such as a component device that has failed).
2589 is given, then a program or an E-mail address must be specified on the
2590 command line or in the config file. If neither are available, then
2592 will not monitor anything.
2596 will continue monitoring as long as something was found to monitor. If
2597 no program or email is given, then each event is reported to
2600 The different events are:
2604 .B DeviceDisappeared
2605 An md array which previously was configured appears to no longer be
2606 configured. (syslog priority: Critical)
2610 was told to monitor an array which is RAID0 or Linear, then it will
2612 .B DeviceDisappeared
2613 with the extra information
2615 This is because RAID0 and Linear do not support the device-failed,
2616 hot-spare and resync operations which are monitored.
2620 An md array started reconstruction (e.g. recovery, resync, reshape,
2621 check, repair). (syslog priority: Warning)
2627 is a two-digit number (ie. 05, 48). This indicates that rebuild
2628 has passed that many percent of the total. The events are generated
2629 with fixed increment since 0. Increment size may be specified with
2630 a commandline option (default is 20). (syslog priority: Warning)
2634 An md array that was rebuilding, isn't any more, either because it
2635 finished normally or was aborted. (syslog priority: Warning)
2639 An active component device of an array has been marked as
2640 faulty. (syslog priority: Critical)
2644 A spare component device which was being rebuilt to replace a faulty
2645 device has failed. (syslog priority: Critical)
2649 A spare component device which was being rebuilt to replace a faulty
2650 device has been successfully rebuilt and has been made active.
2651 (syslog priority: Info)
2655 A new md array has been detected in the
2657 file. (syslog priority: Info)
2661 A newly noticed array appears to be degraded. This message is not
2664 notices a drive failure which causes degradation, but only when
2666 notices that an array is degraded when it first sees the array.
2667 (syslog priority: Critical)
2671 A spare drive has been moved from one array in a
2675 to another to allow a failed drive to be replaced.
2676 (syslog priority: Info)
2682 has been told, via the config file, that an array should have a certain
2683 number of spare devices, and
2685 detects that it has fewer than this number when it first sees the
2686 array, it will report a
2689 (syslog priority: Warning)
2693 An array was found at startup, and the
2696 (syslog priority: Info)
2706 cause Email to be sent. All events cause the program to be run.
2707 The program is run with two or three arguments: the event
2708 name, the array device and possibly a second device.
2710 Each event has an associated array device (e.g.
2712 and possibly a second device. For
2717 the second device is the relevant component device.
2720 the second device is the array that the spare was moved from.
2724 to move spares from one array to another, the different arrays need to
2725 be labeled with the same
2727 or the spares must be allowed to migrate through matching POLICY domains
2728 in the configuration file. The
2730 name can be any string; it is only necessary that different spare
2731 groups use different names.
2735 detects that an array in a spare group has fewer active
2736 devices than necessary for the complete array, and has no spare
2737 devices, it will look for another array in the same spare group that
2738 has a full complement of working drive and a spare. It will then
2739 attempt to remove the spare from the second drive and add it to the
2741 If the removal succeeds but the adding fails, then it is added back to
2744 If the spare group for a degraded array is not defined,
2746 will look at the rules of spare migration specified by POLICY lines in
2748 and then follow similar steps as above if a matching spare is found.
2751 The GROW mode is used for changing the size or shape of an active
2753 For this to work, the kernel must support the necessary change.
2754 Various types of growth are being added during 2.6 development.
2756 Currently the supported changes include
2758 change the "size" attribute for RAID1, RAID4, RAID5 and RAID6.
2760 increase or decrease the "raid\-devices" attribute of RAID0, RAID1, RAID4,
2763 change the chunk-size and layout of RAID0, RAID4, RAID5, RAID6 and RAID10.
2765 convert between RAID1 and RAID5, between RAID5 and RAID6, between
2766 RAID0, RAID4, and RAID5, and between RAID0 and RAID10 (in the near-2 mode).
2768 add a write-intent bitmap to any array which supports these bitmaps, or
2769 remove a write-intent bitmap from such an array.
2771 change the array's consistency policy.
2774 Using GROW on containers is currently supported only for Intel's IMSM
2775 container format. The number of devices in a container can be
2776 increased - which affects all arrays in the container - or an array
2777 in a container can be converted between levels where those levels are
2778 supported by the container, and the conversion is on of those listed
2784 Intel's native checkpointing doesn't use
2786 option and it is transparent for assembly feature.
2788 Roaming between Windows(R) and Linux systems for IMSM metadata is not
2789 supported during grow process.
2791 When growing a raid0 device, the new component disk size (or external
2792 backup size) should be larger than LCM(old, new) * chunk-size * 2,
2793 where LCM() is the least common multiple of the old and new count of
2794 component disks, and "* 2" comes from the fact that mdadm refuses to
2795 use more than half of a spare device for backup space.
2798 Normally when an array is built the "size" is taken from the smallest
2799 of the drives. If all the small drives in an arrays are, one at a
2800 time, removed and replaced with larger drives, then you could have an
2801 array of large drives with only a small amount used. In this
2802 situation, changing the "size" with "GROW" mode will allow the extra
2803 space to start being used. If the size is increased in this way, a
2804 "resync" process will start to make sure the new parts of the array
2807 Note that when an array changes size, any filesystem that may be
2808 stored in the array will not automatically grow or shrink to use or
2809 vacate the space. The
2810 filesystem will need to be explicitly told to use the extra space
2811 after growing, or to reduce its size
2813 to shrinking the array.
2815 Also the size of an array cannot be changed while it has an active
2816 bitmap. If an array has a bitmap, it must be removed before the size
2817 can be changed. Once the change is complete a new bitmap can be created.
2822 is not yet supported for external file bitmap.
2824 .SS RAID\-DEVICES CHANGES
2826 A RAID1 array can work with any number of devices from 1 upwards
2827 (though 1 is not very useful). There may be times which you want to
2828 increase or decrease the number of active devices. Note that this is
2829 different to hot-add or hot-remove which changes the number of
2832 When reducing the number of devices in a RAID1 array, the slots which
2833 are to be removed from the array must already be vacant. That is, the
2834 devices which were in those slots must be failed and removed.
2836 When the number of devices is increased, any hot spares that are
2837 present will be activated immediately.
2839 Changing the number of active devices in a RAID5 or RAID6 is much more
2840 effort. Every block in the array will need to be read and written
2841 back to a new location. From 2.6.17, the Linux Kernel is able to
2842 increase the number of devices in a RAID5 safely, including restarting
2843 an interrupted "reshape". From 2.6.31, the Linux Kernel is able to
2844 increase or decrease the number of devices in a RAID5 or RAID6.
2846 From 2.6.35, the Linux Kernel is able to convert a RAID0 in to a RAID4
2849 uses this functionality and the ability to add
2850 devices to a RAID4 to allow devices to be added to a RAID0. When
2851 requested to do this,
2853 will convert the RAID0 to a RAID4, add the necessary disks and make
2854 the reshape happen, and then convert the RAID4 back to RAID0.
2856 When decreasing the number of devices, the size of the array will also
2857 decrease. If there was data in the array, it could get destroyed and
2858 this is not reversible, so you should firstly shrink the filesystem on
2859 the array to fit within the new size. To help prevent accidents,
2861 requires that the size of the array be decreased first with
2862 .BR "mdadm --grow --array-size" .
2863 This is a reversible change which simply makes the end of the array
2864 inaccessible. The integrity of any data can then be checked before
2865 the non-reversible reduction in the number of devices is request.
2867 When relocating the first few stripes on a RAID5 or RAID6, it is not
2868 possible to keep the data on disk completely consistent and
2869 crash-proof. To provide the required safety, mdadm disables writes to
2870 the array while this "critical section" is reshaped, and takes a
2871 backup of the data that is in that section. For grows, this backup may be
2872 stored in any spare devices that the array has, however it can also be
2873 stored in a separate file specified with the
2875 option, and is required to be specified for shrinks, RAID level
2876 changes and layout changes. If this option is used, and the system
2877 does crash during the critical period, the same file must be passed to
2879 to restore the backup and reassemble the array. When shrinking rather
2880 than growing the array, the reshape is done from the end towards the
2881 beginning, so the "critical section" is at the end of the reshape.
2885 Changing the RAID level of any array happens instantaneously. However
2886 in the RAID5 to RAID6 case this requires a non-standard layout of the
2887 RAID6 data, and in the RAID6 to RAID5 case that non-standard layout is
2888 required before the change can be accomplished. So while the level
2889 change is instant, the accompanying layout change can take quite a
2892 is required. If the array is not simultaneously being grown or
2893 shrunk, so that the array size will remain the same - for example,
2894 reshaping a 3-drive RAID5 into a 4-drive RAID6 - the backup file will
2895 be used not just for a "cricital section" but throughout the reshape
2896 operation, as described below under LAYOUT CHANGES.
2898 .SS CHUNK-SIZE AND LAYOUT CHANGES
2900 Changing the chunk-size or layout without also changing the number of
2901 devices as the same time will involve re-writing all blocks in-place.
2902 To ensure against data loss in the case of a crash, a
2904 must be provided for these changes. Small sections of the array will
2905 be copied to the backup file while they are being rearranged. This
2906 means that all the data is copied twice, once to the backup and once
2907 to the new layout on the array, so this type of reshape will go very
2910 If the reshape is interrupted for any reason, this backup file must be
2912 .B "mdadm --assemble"
2913 so the array can be reassembled. Consequently the file cannot be
2914 stored on the device being reshaped.
2919 A write-intent bitmap can be added to, or removed from, an active
2920 array. Either internal bitmaps, or bitmaps stored in a separate file,
2921 can be added. Note that if you add a bitmap stored in a file which is
2922 in a filesystem that is on the RAID array being affected, the system
2923 will deadlock. The bitmap must be on a separate filesystem.
2925 .SS CONSISTENCY POLICY CHANGES
2927 The consistency policy of an active array can be changed by using the
2928 .B \-\-consistency\-policy
2929 option in Grow mode. Currently this works only for the
2933 policies and allows to enable or disable the RAID5 Partial Parity Log (PPL).
2935 .SH INCREMENTAL MODE
2939 .B mdadm \-\-incremental
2943 .RI [ optional-aliases-for-device ]
2946 .B mdadm \-\-incremental \-\-fail
2950 .B mdadm \-\-incremental \-\-rebuild\-map
2953 .B mdadm \-\-incremental \-\-run \-\-scan
2956 This mode is designed to be used in conjunction with a device
2957 discovery system. As devices are found in a system, they can be
2959 .B "mdadm \-\-incremental"
2960 to be conditionally added to an appropriate array.
2962 Conversely, it can also be used with the
2964 flag to do just the opposite and find whatever array a particular device
2965 is part of and remove the device from that array.
2967 If the device passed is a
2969 device created by a previous call to
2971 then rather than trying to add that device to an array, all the arrays
2972 described by the metadata of the container will be started.
2975 performs a number of tests to determine if the device is part of an
2976 array, and which array it should be part of. If an appropriate array
2977 is found, or can be created,
2979 adds the device to the array and conditionally starts the array.
2983 will normally only add devices to an array which were previously working
2984 (active or spare) parts of that array. The support for automatic
2985 inclusion of a new drive as a spare in some array requires
2986 a configuration through POLICY in config file.
2990 makes are as follow:
2992 Is the device permitted by
2994 That is, is it listed in a
2996 line in that file. If
2998 is absent then the default it to allow any device. Similarly if
3000 contains the special word
3002 then any device is allowed. Otherwise the device name given to
3004 or one of the aliases given, or an alias found in the filesystem,
3005 must match one of the names or patterns in a
3009 This is the only context where the aliases are used. They are
3010 usually provided by a
3013 .BR $env{DEVLINKS} .
3016 Does the device have a valid md superblock? If a specific metadata
3017 version is requested with
3021 then only that style of metadata is accepted, otherwise
3023 finds any known version of metadata. If no
3025 metadata is found, the device may be still added to an array
3026 as a spare if POLICY allows.
3030 Does the metadata match an expected array?
3031 The metadata can match in two ways. Either there is an array listed
3034 which identifies the array (either by UUID, by name, by device list,
3035 or by minor-number), or the array was created with a
3041 or on the command line.
3044 is not able to positively identify the array as belonging to the
3045 current host, the device will be rejected.
3050 keeps a list of arrays that it has partially assembled in
3052 If no array exists which matches
3053 the metadata on the new device,
3055 must choose a device name and unit number. It does this based on any
3058 or any name information stored in the metadata. If this name
3059 suggests a unit number, that number will be used, otherwise a free
3060 unit number will be chosen. Normally
3062 will prefer to create a partitionable array, however if the
3066 suggests that a non-partitionable array is preferred, that will be
3069 If the array is not found in the config file and its metadata does not
3070 identify it as belonging to the "homehost", then
3072 will choose a name for the array which is certain not to conflict with
3073 any array which does belong to this host. It does this be adding an
3074 underscore and a small number to the name preferred by the metadata.
3076 Once an appropriate array is found or created and the device is added,
3078 must decide if the array is ready to be started. It will
3079 normally compare the number of available (non-spare) devices to the
3080 number of devices that the metadata suggests need to be active. If
3081 there are at least that many, the array will be started. This means
3082 that if any devices are missing the array will not be restarted.
3088 in which case the array will be run as soon as there are enough
3089 devices present for the data to be accessible. For a RAID1, that
3090 means one device will start the array. For a clean RAID5, the array
3091 will be started as soon as all but one drive is present.
3093 Note that neither of these approaches is really ideal. If it can
3094 be known that all device discovery has completed, then
3098 can be run which will try to start all arrays that are being
3099 incrementally assembled. They are started in "read-auto" mode in
3100 which they are read-only until the first write request. This means
3101 that no metadata updates are made and no attempt at resync or recovery
3102 happens. Further devices that are found before the first write can
3103 still be added safely.
3106 This section describes environment variables that affect how mdadm
3111 Setting this value to 1 will prevent mdadm from automatically launching
3112 mdmon. This variable is intended primarily for debugging mdadm/mdmon.
3118 does not create any device nodes in /dev, but leaves that task to
3122 appears not to be configured, or if this environment variable is set
3125 will create and devices that are needed.
3128 .B MDADM_NO_SYSTEMCTL
3133 is in use it will normally request
3135 to start various background tasks (particularly
3137 rather than forking and running them in the background. This can be
3138 suppressed by setting
3139 .BR MDADM_NO_SYSTEMCTL=1 .
3143 A key value of IMSM metadata is that it allows interoperability with
3144 boot ROMs on Intel platforms, and with other major operating systems.
3147 will only allow an IMSM array to be created or modified if detects
3148 that it is running on an Intel platform which supports IMSM, and
3149 supports the particular configuration of IMSM that is being requested
3150 (some functionality requires newer OROM support).
3152 These checks can be suppressed by setting IMSM_NO_PLATFORM=1 in the
3153 environment. This can be useful for testing or for disaster
3154 recovery. You should be aware that interoperability may be
3155 compromised by setting this value.
3158 .B MDADM_GROW_ALLOW_OLD
3159 If an array is stopped while it is performing a reshape and that
3160 reshape was making use of a backup file, then when the array is
3163 will sometimes complain that the backup file is too old. If this
3164 happens and you are certain it is the right backup file, you can
3165 over-ride this check by setting
3166 .B MDADM_GROW_ALLOW_OLD=1
3171 Any string given in this variable is added to the start of the
3173 line in the config file, or treated as the whole
3175 line if none is given. It can be used to disable certain metadata
3178 is called from a boot script. For example
3180 .B " export MDADM_CONF_AUTO='-ddf -imsm'
3184 does not automatically assemble any DDF or
3185 IMSM arrays that are found. This can be useful on systems configured
3186 to manage such arrays with
3192 .B " mdadm \-\-query /dev/name-of-device"
3194 This will find out if a given device is a RAID array, or is part of
3195 one, and will provide brief information about the device.
3197 .B " mdadm \-\-assemble \-\-scan"
3199 This will assemble and start all arrays listed in the standard config
3200 file. This command will typically go in a system startup file.
3202 .B " mdadm \-\-stop \-\-scan"
3204 This will shut down all arrays that can be shut down (i.e. are not
3205 currently in use). This will typically go in a system shutdown script.
3207 .B " mdadm \-\-follow \-\-scan \-\-delay=120"
3209 If (and only if) there is an Email address or program given in the
3210 standard config file, then
3211 monitor the status of all arrays listed in that file by
3212 polling them ever 2 minutes.
3214 .B " mdadm \-\-create /dev/md0 \-\-level=1 \-\-raid\-devices=2 /dev/hd[ac]1"
3216 Create /dev/md0 as a RAID1 array consisting of /dev/hda1 and /dev/hdc1.
3219 .B " echo 'DEVICE /dev/hd*[0\-9] /dev/sd*[0\-9]' > mdadm.conf"
3221 .B " mdadm \-\-detail \-\-scan >> mdadm.conf"
3223 This will create a prototype config file that describes currently
3224 active arrays that are known to be made from partitions of IDE or SCSI drives.
3225 This file should be reviewed before being used as it may
3226 contain unwanted detail.
3228 .B " echo 'DEVICE /dev/hd[a\-z] /dev/sd*[a\-z]' > mdadm.conf"
3230 .B " mdadm \-\-examine \-\-scan \-\-config=mdadm.conf >> mdadm.conf"
3232 This will find arrays which could be assembled from existing IDE and
3233 SCSI whole drives (not partitions), and store the information in the
3234 format of a config file.
3235 This file is very likely to contain unwanted detail, particularly
3238 entries. It should be reviewed and edited before being used as an
3241 .B " mdadm \-\-examine \-\-brief \-\-scan \-\-config=partitions"
3243 .B " mdadm \-Ebsc partitions"
3245 Create a list of devices by reading
3246 .BR /proc/partitions ,
3247 scan these for RAID superblocks, and printout a brief listing of all
3250 .B " mdadm \-Ac partitions \-m 0 /dev/md0"
3252 Scan all partitions and devices listed in
3253 .BR /proc/partitions
3256 out of all such devices with a RAID superblock with a minor number of 0.
3258 .B " mdadm \-\-monitor \-\-scan \-\-daemonise > /run/mdadm/mon.pid"
3260 If config file contains a mail address or alert program, run mdadm in
3261 the background in monitor mode monitoring all md devices. Also write
3262 pid of mdadm daemon to
3263 .BR /run/mdadm/mon.pid .
3265 .B " mdadm \-Iq /dev/somedevice"
3267 Try to incorporate newly discovered device into some array as
3270 .B " mdadm \-\-incremental \-\-rebuild\-map \-\-run \-\-scan"
3272 Rebuild the array map from any current arrays, and then start any that
3275 .B " mdadm /dev/md4 --fail detached --remove detached"
3277 Any devices which are components of /dev/md4 will be marked as faulty
3278 and then remove from the array.
3280 .B " mdadm --grow /dev/md4 --level=6 --backup-file=/root/backup-md4"
3284 which is currently a RAID5 array will be converted to RAID6. There
3285 should normally already be a spare drive attached to the array as a
3286 RAID6 needs one more drive than a matching RAID5.
3288 .B " mdadm --create /dev/md/ddf --metadata=ddf --raid-disks 6 /dev/sd[a-f]"
3290 Create a DDF array over 6 devices.
3292 .B " mdadm --create /dev/md/home -n3 -l5 -z 30000000 /dev/md/ddf"
3294 Create a RAID5 array over any 3 devices in the given DDF set. Use
3295 only 30 gigabytes of each device.
3297 .B " mdadm -A /dev/md/ddf1 /dev/sd[a-f]"
3299 Assemble a pre-exist ddf array.
3301 .B " mdadm -I /dev/md/ddf1"
3303 Assemble all arrays contained in the ddf array, assigning names as
3306 .B " mdadm \-\-create \-\-help"
3308 Provide help about the Create mode.
3310 .B " mdadm \-\-config \-\-help"
3312 Provide help about the format of the config file.
3314 .B " mdadm \-\-help"
3316 Provide general help.
3326 lists all active md devices with information about them.
3328 uses this to find arrays when
3330 is given in Misc mode, and to monitor array reconstruction
3333 .SS {CONFFILE} (or {CONFFILE2})
3335 Default config file. See
3339 .SS {CONFFILE}.d (or {CONFFILE2}.d)
3341 Default directory containing configuration files. See
3348 mode is used, this file gets a list of arrays currently being created.
3353 understand two sorts of names for array devices.
3355 The first is the so-called 'standard' format name, which matches the
3356 names used by the kernel and which appear in
3359 The second sort can be freely chosen, but must reside in
3361 When giving a device name to
3363 to create or assemble an array, either full path name such as
3367 can be given, or just the suffix of the second sort of name, such as
3373 chooses device names during auto-assembly or incremental assembly, it
3374 will sometimes add a small sequence number to the end of the name to
3375 avoid conflicted between multiple arrays that have the same name. If
3377 can reasonably determine that the array really is meant for this host,
3378 either by a hostname in the metadata, or by the presence of the array
3381 then it will leave off the suffix if possible.
3382 Also if the homehost is specified as
3385 will only use a suffix if a different array of the same name already
3386 exists or is listed in the config file.
3388 The standard names for non-partitioned arrays (the only sort of md
3389 array available in 2.4 and earlier) are of the form
3393 where NN is a number.
3394 The standard names for partitionable arrays (as available from 2.6
3395 onwards) are of the form:
3399 Partition numbers should be indicated by adding "pMM" to these, thus "/dev/md/d1p2".
3401 From kernel version 2.6.28 the "non-partitioned array" can actually
3402 be partitioned. So the "md_d\fBNN\fP"
3403 names are no longer needed, and
3404 partitions such as "/dev/md\fBNN\fPp\fBXX\fP"
3407 From kernel version 2.6.29 standard names can be non-numeric following
3414 is any string. These names are supported by
3416 since version 3.3 provided they are enabled in
3421 was previously known as
3425 For further information on mdadm usage, MD and the various levels of
3428 .B https://raid.wiki.kernel.org/
3430 (based upon Jakob \(/Ostergaard's Software\-RAID.HOWTO)
3432 The latest version of
3434 should always be available from
3436 .B https://www.kernel.org/pub/linux/utils/raid/mdadm/
projects / thirdparty / mdadm.git / blob