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, as well as adding or
129 removing a write-intent bitmap.
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
221 then the MANAGE mode is assumed.
222 Anything other than these will cause the
226 .SH Options that are not mode-specific are:
229 .BR \-h ", " \-\-help
230 Display general help message or, after one of the above options, a
231 mode-specific help message.
235 Display more detailed help about command line parsing and some commonly
239 .BR \-V ", " \-\-version
240 Print version information for mdadm.
243 .BR \-v ", " \-\-verbose
244 Be more verbose about what is happening. This can be used twice to be
246 The extra verbosity currently only affects
247 .B \-\-detail \-\-scan
249 .BR "\-\-examine \-\-scan" .
252 .BR \-q ", " \-\-quiet
253 Avoid printing purely informative messages. With this,
255 will be silent unless there is something really important to report.
259 Set first character of argv[0] to @ to indicate mdadm was launched
260 from initrd/initramfs and should not be shutdown by systemd as part of
261 the regular shutdown process. This option is normally only used by
262 the system's initscripts. Please see here for more details on how
263 systemd handled argv[0]:
265 .B http://www.freedesktop.org/wiki/Software/systemd/RootStorageDaemons
270 .BR \-f ", " \-\-force
271 Be more forceful about certain operations. See the various modes for
272 the exact meaning of this option in different contexts.
275 .BR \-c ", " \-\-config=
276 Specify the config file. Default is to use
277 .BR /etc/mdadm.conf ,
278 or if that is missing then
279 .BR /etc/mdadm/mdadm.conf .
280 If the config file given is
282 then nothing will be read, but
284 will act as though the config file contained exactly
285 .B "DEVICE partitions containers"
288 to find a list of devices to scan, and
290 to find a list of containers to examine.
293 is given for the config file, then
295 will act as though the config file were empty.
298 .BR \-s ", " \-\-scan
301 for missing information.
302 In general, this option gives
304 permission to get any missing information (like component devices,
305 array devices, array identities, and alert destination) from the
306 configuration file (see previous option);
307 one exception is MISC mode when using
313 says to get a list of array devices from
317 .BR \-e ", " \-\-metadata=
318 Declare the style of RAID metadata (superblock) to be used. The
319 default is {DEFAULT_METADATA} for
321 and to guess for other operations.
322 The default can be overridden by setting the
331 .ie '{DEFAULT_METADATA}'0.90'
332 .IP "0, 0.90, default"
336 Use the original 0.90 format superblock. This format limits arrays to
337 28 component devices and limits component devices of levels 1 and
338 greater to 2 terabytes. It is also possible for there to be confusion
339 about whether the superblock applies to a whole device or just the
340 last partition, if that partition starts on a 64K boundary.
341 .ie '{DEFAULT_METADATA}'0.90'
342 .IP "1, 1.0, 1.1, 1.2"
344 .IP "1, 1.0, 1.1, 1.2 default"
346 Use the new version-1 format superblock. This has fewer restrictions.
347 It can easily be moved between hosts with different endian-ness, and a
348 recovery operation can be checkpointed and restarted. The different
349 sub-versions store the superblock at different locations on the
350 device, either at the end (for 1.0), at the start (for 1.1) or 4K from
351 the start (for 1.2). "1" is equivalent to "1.2" (the commonly
352 preferred 1.x format).
353 'if '{DEFAULT_METADATA}'1.2' "default" is equivalent to "1.2".
355 Use the "Industry Standard" DDF (Disk Data Format) format defined by
357 When creating a DDF array a
359 will be created, and normal arrays can be created in that container.
361 Use the Intel(R) Matrix Storage Manager metadata format. This creates a
363 which is managed in a similar manner to DDF, and is supported by an
364 option-rom on some platforms:
366 .B http://www.intel.com/design/chipsets/matrixstorage_sb.htm
372 This will override any
374 setting in the config file and provides the identity of the host which
375 should be considered the home for any arrays.
377 When creating an array, the
379 will be recorded in the metadata. For version-1 superblocks, it will
380 be prefixed to the array name. For version-0.90 superblocks, part of
381 the SHA1 hash of the hostname will be stored in the later half of the
384 When reporting information about an array, any array which is tagged
385 for the given homehost will be reported as such.
387 When using Auto-Assemble, only arrays tagged for the given homehost
388 will be allowed to use 'local' names (i.e. not ending in '_' followed
389 by a digit string). See below under
390 .BR "Auto Assembly" .
396 needs to print the name for a device it normally finds the name in
398 which refers to the device and is shortest. When a path component is
402 will prefer a longer name if it contains that component. For example
403 .B \-\-prefer=by-uuid
404 will prefer a name in a subdirectory of
409 This functionality is currently only provided by
414 .SH For create, build, or grow:
417 .BR \-n ", " \-\-raid\-devices=
418 Specify the number of active devices in the array. This, plus the
419 number of spare devices (see below) must equal the number of
421 (including "\fBmissing\fP" devices)
422 that are listed on the command line for
424 Setting a value of 1 is probably
425 a mistake and so requires that
427 be specified first. A value of 1 will then be allowed for linear,
428 multipath, RAID0 and RAID1. It is never allowed for RAID4, RAID5 or RAID6.
430 This number can only be changed using
432 for RAID1, RAID4, RAID5 and RAID6 arrays, and only on kernels which provide
433 the necessary support.
436 .BR \-x ", " \-\-spare\-devices=
437 Specify the number of spare (eXtra) devices in the initial array.
438 Spares can also be added
439 and removed later. The number of component devices listed
440 on the command line must equal the number of RAID devices plus the
441 number of spare devices.
444 .BR \-z ", " \-\-size=
445 Amount (in Kibibytes) of space to use from each drive in RAID levels 1/4/5/6.
446 This must be a multiple of the chunk size, and must leave about 128Kb
447 of space at the end of the drive for the RAID superblock.
448 If this is not specified
449 (as it normally is not) the smallest drive (or partition) sets the
450 size, though if there is a variance among the drives of greater than 1%, a warning is
453 A suffix of 'M' or 'G' can be given to indicate Megabytes or
454 Gigabytes respectively.
456 Sometimes a replacement drive can be a little smaller than the
457 original drives though this should be minimised by IDEMA standards.
458 Such a replacement drive will be rejected by
460 To guard against this it can be useful to set the initial size
461 slightly smaller than the smaller device with the aim that it will
462 still be larger than any replacement.
464 This value can be set with
466 for RAID level 1/4/5/6 though
468 based arrays such as those with IMSM metadata may not be able to
470 If the array was created with a size smaller than the currently
471 active drives, the extra space can be accessed using
473 The size can be given as
475 which means to choose the largest size that fits on all current drives.
477 Before reducing the size of the array (with
478 .BR "\-\-grow \-\-size=" )
479 you should make sure that space isn't needed. If the device holds a
480 filesystem, you would need to resize the filesystem to use less space.
482 After reducing the array size you should check that the data stored in
483 the device is still available. If the device holds a filesystem, then
484 an 'fsck' of the filesystem is a minimum requirement. If there are
485 problems the array can be made bigger again with no loss with another
486 .B "\-\-grow \-\-size="
489 This value cannot be used when creating a
491 such as with DDF and IMSM metadata, though it perfectly valid when
492 creating an array inside a container.
495 .BR \-Z ", " \-\-array\-size=
496 This is only meaningful with
498 and its effect is not persistent: when the array is stopped and
499 restarted the default array size will be restored.
501 Setting the array-size causes the array to appear smaller to programs
502 that access the data. This is particularly needed before reshaping an
503 array so that it will be smaller. As the reshape is not reversible,
504 but setting the size with
506 is, it is required that the array size is reduced as appropriate
507 before the number of devices in the array is reduced.
509 Before reducing the size of the array you should make sure that space
510 isn't needed. If the device holds a filesystem, you would need to
511 resize the filesystem to use less space.
513 After reducing the array size you should check that the data stored in
514 the device is still available. If the device holds a filesystem, then
515 an 'fsck' of the filesystem is a minimum requirement. If there are
516 problems the array can be made bigger again with no loss with another
517 .B "\-\-grow \-\-array\-size="
520 A suffix of 'M' or 'G' can be given to indicate Megabytes or
521 Gigabytes respectively.
524 restores the apparent size of the array to be whatever the real
525 amount of available space is.
528 .BR \-c ", " \-\-chunk=
529 Specify chunk size of kibibytes. The default when creating an
530 array is 512KB. To ensure compatibility with earlier versions, the
531 default when Building and array with no persistent metadata is 64KB.
532 This is only meaningful for RAID0, RAID4, RAID5, RAID6, and RAID10.
534 RAID4, RAID5, RAID6, and RAID10 require the chunk size to be a power
535 of 2. In any case it must be a multiple of 4KB.
537 A suffix of 'M' or 'G' can be given to indicate Megabytes or
538 Gigabytes respectively.
542 Specify rounding factor for a Linear array. The size of each
543 component will be rounded down to a multiple of this size.
544 This is a synonym for
546 but highlights the different meaning for Linear as compared to other
547 RAID levels. The default is 64K if a kernel earlier than 2.6.16 is in
548 use, and is 0K (i.e. no rounding) in later kernels.
551 .BR \-l ", " \-\-level=
552 Set RAID level. When used with
554 options are: linear, raid0, 0, stripe, raid1, 1, mirror, raid4, 4,
555 raid5, 5, raid6, 6, raid10, 10, multipath, mp, faulty, container.
556 Obviously some of these are synonymous.
560 metadata type is requested, only the
562 level is permitted, and it does not need to be explicitly given.
566 only linear, stripe, raid0, 0, raid1, multipath, mp, and faulty are valid.
570 to change the RAID level in some cases. See LEVEL CHANGES below.
573 .BR \-p ", " \-\-layout=
574 This option configures the fine details of data layout for RAID5, RAID6,
575 and RAID10 arrays, and controls the failure modes for
578 The layout of the RAID5 parity block can be one of
579 .BR left\-asymmetric ,
580 .BR left\-symmetric ,
581 .BR right\-asymmetric ,
582 .BR right\-symmetric ,
583 .BR la ", " ra ", " ls ", " rs .
585 .BR left\-symmetric .
587 It is also possible to cause RAID5 to use a RAID4-like layout by
593 Finally for RAID5 there are DDF\-compatible layouts,
594 .BR ddf\-zero\-restart ,
595 .BR ddf\-N\-restart ,
597 .BR ddf\-N\-continue .
599 These same layouts are available for RAID6. There are also 4 layouts
600 that will provide an intermediate stage for converting between RAID5
601 and RAID6. These provide a layout which is identical to the
602 corresponding RAID5 layout on the first N\-1 devices, and has the 'Q'
603 syndrome (the second 'parity' block used by RAID6) on the last device.
605 .BR left\-symmetric\-6 ,
606 .BR right\-symmetric\-6 ,
607 .BR left\-asymmetric\-6 ,
608 .BR right\-asymmetric\-6 ,
610 .BR parity\-first\-6 .
612 When setting the failure mode for level
615 .BR write\-transient ", " wt ,
616 .BR read\-transient ", " rt ,
617 .BR write\-persistent ", " wp ,
618 .BR read\-persistent ", " rp ,
620 .BR read\-fixable ", " rf ,
621 .BR clear ", " flush ", " none .
623 Each failure mode can be followed by a number, which is used as a period
624 between fault generation. Without a number, the fault is generated
625 once on the first relevant request. With a number, the fault will be
626 generated after that many requests, and will continue to be generated
627 every time the period elapses.
629 Multiple failure modes can be current simultaneously by using the
631 option to set subsequent failure modes.
633 "clear" or "none" will remove any pending or periodic failure modes,
634 and "flush" will clear any persistent faults.
636 Finally, the layout options for RAID10 are one of 'n', 'o' or 'f' followed
637 by a small number. The default is 'n2'. The supported options are:
640 signals 'near' copies. Multiple copies of one data block are at
641 similar offsets in different devices.
644 signals 'offset' copies. Rather than the chunks being duplicated
645 within a stripe, whole stripes are duplicated but are rotated by one
646 device so duplicate blocks are on different devices. Thus subsequent
647 copies of a block are in the next drive, and are one chunk further
652 (multiple copies have very different offsets).
653 See md(4) for more detail about 'near', 'offset', and 'far'.
655 The number is the number of copies of each datablock. 2 is normal, 3
656 can be useful. This number can be at most equal to the number of
657 devices in the array. It does not need to divide evenly into that
658 number (e.g. it is perfectly legal to have an 'n2' layout for an array
659 with an odd number of devices).
661 When an array is converted between RAID5 and RAID6 an intermediate
662 RAID6 layout is used in which the second parity block (Q) is always on
663 the last device. To convert a RAID5 to RAID6 and leave it in this new
664 layout (which does not require re-striping) use
665 .BR \-\-layout=preserve .
666 This will try to avoid any restriping.
668 The converse of this is
669 .B \-\-layout=normalise
670 which will change a non-standard RAID6 layout into a more standard
677 (thus explaining the p of
681 .BR \-b ", " \-\-bitmap=
682 Specify a file to store a write-intent bitmap in. The file should not
685 is also given. The same file should be provided
686 when assembling the array. If the word
688 is given, then the bitmap is stored with the metadata on the array,
689 and so is replicated on all devices. If the word
693 mode, then any bitmap that is present is removed.
695 To help catch typing errors, the filename must contain at least one
696 slash ('/') if it is a real file (not 'internal' or 'none').
698 Note: external bitmaps are only known to work on ext2 and ext3.
699 Storing bitmap files on other filesystems may result in serious problems.
702 .BR \-\-bitmap\-chunk=
703 Set the chunksize of the bitmap. Each bit corresponds to that many
704 Kilobytes of storage.
705 When using a file based bitmap, the default is to use the smallest
706 size that is at-least 4 and requires no more than 2^21 chunks.
709 bitmap, the chunksize defaults to 64Meg, or larger if necessary to
710 fit the bitmap into the available space.
712 A suffix of 'M' or 'G' can be given to indicate Megabytes or
713 Gigabytes respectively.
716 .BR \-W ", " \-\-write\-mostly
717 subsequent devices listed in a
722 command will be flagged as 'write-mostly'. This is valid for RAID1
723 only and means that the 'md' driver will avoid reading from these
724 devices if at all possible. This can be useful if mirroring over a
728 .BR \-\-write\-behind=
729 Specify that write-behind mode should be enabled (valid for RAID1
730 only). If an argument is specified, it will set the maximum number
731 of outstanding writes allowed. The default value is 256.
732 A write-intent bitmap is required in order to use write-behind
733 mode, and write-behind is only attempted on drives marked as
737 .BR \-\-assume\-clean
740 that the array pre-existed and is known to be clean. It can be useful
741 when trying to recover from a major failure as you can be sure that no
742 data will be affected unless you actually write to the array. It can
743 also be used when creating a RAID1 or RAID10 if you want to avoid the
744 initial resync, however this practice \(em while normally safe \(em is not
745 recommended. Use this only if you really know what you are doing.
747 When the devices that will be part of a new array were filled
748 with zeros before creation the operator knows the array is
749 actually clean. If that is the case, such as after running
750 badblocks, this argument can be used to tell mdadm the
751 facts the operator knows.
753 When an array is resized to a larger size with
754 .B "\-\-grow \-\-size="
755 the new space is normally resynced in that same way that the whole
756 array is resynced at creation. From Linux version 3.0,
758 can be used with that command to avoid the automatic resync.
761 .BR \-\-backup\-file=
764 is used to increase the number of raid-devices in a RAID5 or RAID6 if
765 there are no spare devices available, or to shrink, change RAID level
766 or layout. See the GROW MODE section below on RAID\-DEVICES CHANGES.
767 The file must be stored on a separate device, not on the RAID array
772 This option is complementary to the
773 .B \-\-freeze-reshape
774 option for assembly. It is needed when
776 operation is interrupted and it is not restarted automatically due to
777 .B \-\-freeze-reshape
778 usage during array assembly. This option is used together with
782 ) command and device for a pending reshape to be continued.
783 All parameters required for reshape continuation will be read from array metadata.
787 .BR \-\-backup\-file=
788 option to be set, continuation option will require to have exactly the same
789 backup file given as well.
791 Any other parameter passed together with
793 option will be ignored.
796 .BR \-N ", " \-\-name=
799 for the array. This is currently only effective when creating an
800 array with a version-1 superblock, or an array in a DDF container.
801 The name is a simple textual string that can be used to identify array
802 components when assembling. If name is needed but not specified, it
803 is taken from the basename of the device that is being created.
815 run the array, even if some of the components
816 appear to be active in another array or filesystem. Normally
818 will ask for confirmation before including such components in an
819 array. This option causes that question to be suppressed.
822 .BR \-f ", " \-\-force
825 accept the geometry and layout specified without question. Normally
827 will not allow creation of an array with only one device, and will try
828 to create a RAID5 array with one missing drive (as this makes the
829 initial resync work faster). With
832 will not try to be so clever.
835 .BR \-o ", " \-\-readonly
838 rather than read-write as normal. No writes will be allowed to the
839 array, and no resync, recovery, or reshape will be started.
842 .BR \-a ", " "\-\-auto{=yes,md,mdp,part,p}{NN}"
843 Instruct mdadm how to create the device file if needed, possibly allocating
844 an unused minor number. "md" causes a non-partitionable array
845 to be used (though since Linux 2.6.28, these array devices are in fact
846 partitionable). "mdp", "part" or "p" causes a partitionable array (2.6 and
847 later) to be used. "yes" requires the named md device to have
848 a 'standard' format, and the type and minor number will be determined
849 from this. With mdadm 3.0, device creation is normally left up to
851 so this option is unlikely to be needed.
852 See DEVICE NAMES below.
854 The argument can also come immediately after
859 is not given on the command line or in the config file, then
865 is also given, then any
867 entries in the config file will override the
869 instruction given on the command line.
871 For partitionable arrays,
873 will create the device file for the whole array and for the first 4
874 partitions. A different number of partitions can be specified at the
875 end of this option (e.g.
877 If the device name ends with a digit, the partition names add a 'p',
879 .IR /dev/md/home1p3 .
880 If there is no trailing digit, then the partition names just have a
882 .IR /dev/md/scratch3 .
884 If the md device name is in a 'standard' format as described in DEVICE
885 NAMES, then it will be created, if necessary, with the appropriate
886 device number based on that name. If the device name is not in one of these
887 formats, then a unused device number will be allocated. The device
888 number will be considered unused if there is no active array for that
889 number, and there is no entry in /dev for that number and with a
890 non-standard name. Names that are not in 'standard' format are only
891 allowed in "/dev/md/".
893 This is meaningful with
900 .\".BR \-\-symlink = no
905 .\"to create devices in
907 .\"it will also create symlinks from
909 .\"with names starting with
915 .\"to suppress this, or
916 .\".B \-\-symlink=yes
917 .\"to enforce this even if it is suppressing
923 .BR \-a ", " "\-\-add"
924 This option can be used in Grow mode in two cases.
926 If the target array is a Linear array, then
928 can be used to add one or more devices to the array. They
929 are simply catenated on to the end of the array. Once added, the
930 devices cannot be removed.
934 option is being used to increase the number of devices in an array,
937 can be used to add some extra devices to be included in the array.
938 In most cases this is not needed as the extra devices can be added as
939 spares first, and then the number of raid-disks can be changed.
940 However for RAID0, it is not possible to add spares. So to increase
941 the number of devices in a RAID0, it is necessary to set the new
942 number of devices, and to add the new devices, in the same command.
947 .BR \-u ", " \-\-uuid=
948 uuid of array to assemble. Devices which don't have this uuid are
952 .BR \-m ", " \-\-super\-minor=
953 Minor number of device that array was created for. Devices which
954 don't have this minor number are excluded. If you create an array as
955 /dev/md1, then all superblocks will contain the minor number 1, even if
956 the array is later assembled as /dev/md2.
958 Giving the literal word "dev" for
962 to use the minor number of the md device that is being assembled.
965 .B \-\-super\-minor=dev
966 will look for super blocks with a minor number of 0.
969 is only relevant for v0.90 metadata, and should not normally be used.
975 .BR \-N ", " \-\-name=
976 Specify the name of the array to assemble. This must be the name
977 that was specified when creating the array. It must either match
978 the name stored in the superblock exactly, or it must match
981 prefixed to the start of the given name.
984 .BR \-f ", " \-\-force
985 Assemble the array even if the metadata on some devices appears to be
988 cannot find enough working devices to start the array, but can find
989 some devices that are recorded as having failed, then it will mark
990 those devices as working so that the array can be started.
991 An array which requires
993 to be started may contain data corruption. Use it carefully.
997 Attempt to start the array even if fewer drives were given than were
998 present last time the array was active. Normally if not all the
999 expected drives are found and
1001 is not used, then the array will be assembled but not started.
1004 an attempt will be made to start it anyway.
1008 This is the reverse of
1010 in that it inhibits the startup of array unless all expected drives
1011 are present. This is only needed with
1013 and can be used if the physical connections to devices are
1014 not as reliable as you would like.
1017 .BR \-a ", " "\-\-auto{=no,yes,md,mdp,part}"
1018 See this option under Create and Build options.
1021 .BR \-b ", " \-\-bitmap=
1022 Specify the bitmap file that was given when the array was created. If
1025 bitmap, there is no need to specify this when assembling the array.
1028 .BR \-\-backup\-file=
1031 was used while reshaping an array (e.g. changing number of devices or
1032 chunk size) and the system crashed during the critical section, then the same
1034 must be presented to
1036 to allow possibly corrupted data to be restored, and the reshape
1040 .BR \-\-invalid\-backup
1041 If the file needed for the above option is not available for any
1042 reason an empty file can be given together with this option to
1043 indicate that the backup file is invalid. In this case the data that
1044 was being rearranged at the time of the crash could be irrecoverably
1045 lost, but the rest of the array may still be recoverable. This option
1046 should only be used as a last resort if there is no way to recover the
1051 .BR \-U ", " \-\-update=
1052 Update the superblock on each device while assembling the array. The
1053 argument given to this flag can be one of
1068 option will adjust the superblock of an array what was created on a Sparc
1069 machine running a patched 2.2 Linux kernel. This kernel got the
1070 alignment of part of the superblock wrong. You can use the
1071 .B "\-\-examine \-\-sparc2.2"
1074 to see what effect this would have.
1078 option will update the
1079 .B "preferred minor"
1080 field on each superblock to match the minor number of the array being
1082 This can be useful if
1084 reports a different "Preferred Minor" to
1086 In some cases this update will be performed automatically
1087 by the kernel driver. In particular the update happens automatically
1088 at the first write to an array with redundancy (RAID level 1 or
1089 greater) on a 2.6 (or later) kernel.
1093 option will change the uuid of the array. If a UUID is given with the
1095 option that UUID will be used as a new UUID and will
1097 be used to help identify the devices in the array.
1100 is given, a random UUID is chosen.
1104 option will change the
1106 of the array as stored in the superblock. This is only supported for
1107 version-1 superblocks.
1111 option will change the
1113 as recorded in the superblock. For version-0 superblocks, this is the
1114 same as updating the UUID.
1115 For version-1 superblocks, this involves updating the name.
1119 option will cause the array to be marked
1121 meaning that any redundancy in the array (e.g. parity for RAID5,
1122 copies for RAID1) may be incorrect. This will cause the RAID system
1123 to perform a "resync" pass to make sure that all redundant information
1128 option allows arrays to be moved between machines with different
1130 When assembling such an array for the first time after a move, giving
1131 .B "\-\-update=byteorder"
1134 to expect superblocks to have their byteorder reversed, and will
1135 correct that order before assembling the array. This is only valid
1136 with original (Version 0.90) superblocks.
1140 option will correct the summaries in the superblock. That is the
1141 counts of total, working, active, failed, and spare devices.
1145 option will rarely be of use. It applies to version 1.1 and 1.2 metadata
1146 only (where the metadata is at the start of the device) and is only
1147 useful when the component device has changed size (typically become
1148 larger). The version 1 metadata records the amount of the device that
1149 can be used to store data, so if a device in a version 1.1 or 1.2
1150 array becomes larger, the metadata will still be visible, but the
1151 extra space will not. In this case it might be useful to assemble the
1153 .BR \-\-update=devicesize .
1156 to determine the maximum usable amount of space on each device and
1157 update the relevant field in the metadata.
1161 option can be used when an array has an internal bitmap which is
1162 corrupt in some way so that assembling the array normally fails. It
1163 will cause any internal bitmap to be ignored.
1166 .BR \-\-freeze\-reshape
1167 Option is intended to be used in start-up scripts during initrd boot phase.
1168 When array under reshape is assembled during initrd phase, this option
1169 stops reshape after reshape critical section is being restored. This happens
1170 before file system pivot operation and avoids loss of file system context.
1171 Losing file system context would cause reshape to be broken.
1173 Reshape can be continued later using the
1175 option for the grow command.
1177 .SH For Manage mode:
1180 .BR \-t ", " \-\-test
1181 Unless a more serious error occurred,
1183 will exit with a status of 2 if no changes were made to the array and
1184 0 if at least one change was made.
1185 This can be useful when an indirect specifier such as
1190 is used in requesting an operation on the array.
1192 will report failure if these specifiers didn't find any match.
1195 .BR \-a ", " \-\-add
1196 hot-add listed devices.
1197 If a device appears to have recently been part of the array
1198 (possibly it failed or was removed) the device is re\-added as described
1200 If that fails or the device was never part of the array, the device is
1201 added as a hot-spare.
1202 If the array is degraded, it will immediately start to rebuild data
1205 Note that this and the following options are only meaningful on array
1206 with redundancy. They don't apply to RAID0 or Linear.
1210 re\-add a device that was previous removed from an array.
1211 If the metadata on the device reports that it is a member of the
1212 array, and the slot that it used is still vacant, then the device will
1213 be added back to the array in the same position. This will normally
1214 cause the data for that device to be recovered. However based on the
1215 event count on the device, the recovery may only require sections that
1216 are flagged a write-intent bitmap to be recovered or may not require
1217 any recovery at all.
1219 When used on an array that has no metadata (i.e. it was built with
1221 it will be assumed that bitmap-based recovery is enough to make the
1222 device fully consistent with the array.
1226 can be accompanied by
1227 .BR \-\-update=devicesize .
1228 See the description of this option when used in Assemble mode for an
1229 explanation of its use.
1231 If the device name given is
1233 then mdadm will try to find any device that looks like it should be
1234 part of the array but isn't and will try to re\-add all such devices.
1237 .BR \-r ", " \-\-remove
1238 remove listed devices. They must not be active. i.e. they should
1239 be failed or spare devices. As well as the name of a device file
1248 The first causes all failed device to be removed. The second causes
1249 any device which is no longer connected to the system (i.e an 'open'
1252 to be removed. This will only succeed for devices that are spares or
1253 have already been marked as failed.
1256 .BR \-f ", " \-\-fail
1257 mark listed devices as faulty.
1258 As well as the name of a device file, the word
1260 can be given. This will cause any device that has been detached from
1261 the system to be marked as failed. It can then be removed.
1269 .BR \-\-write\-mostly
1270 Subsequent devices that are added or re\-added will have the 'write-mostly'
1271 flag set. This is only valid for RAID1 and means that the 'md' driver
1272 will avoid reading from these devices if possible.
1275 Subsequent devices that are added or re\-added will have the 'write-mostly'
1279 Each of these options requires that the first device listed is the array
1280 to be acted upon, and the remainder are component devices to be added,
1281 removed, marked as faulty, etc. Several different operations can be
1282 specified for different devices, e.g.
1284 mdadm /dev/md0 \-\-add /dev/sda1 \-\-fail /dev/sdb1 \-\-remove /dev/sdb1
1286 Each operation applies to all devices listed until the next
1289 If an array is using a write-intent bitmap, then devices which have
1290 been removed can be re\-added in a way that avoids a full
1291 reconstruction but instead just updates the blocks that have changed
1292 since the device was removed. For arrays with persistent metadata
1293 (superblocks) this is done automatically. For arrays created with
1295 mdadm needs to be told that this device we removed recently with
1298 Devices can only be removed from an array if they are not in active
1299 use, i.e. that must be spares or failed devices. To remove an active
1300 device, it must first be marked as
1306 .BR \-Q ", " \-\-query
1307 Examine a device to see
1308 (1) if it is an md device and (2) if it is a component of an md
1310 Information about what is discovered is presented.
1313 .BR \-D ", " \-\-detail
1314 Print details of one or more md devices.
1317 .BR \-\-detail\-platform
1318 Print details of the platform's RAID capabilities (firmware / hardware
1319 topology) for a given metadata format.
1322 .BR \-Y ", " \-\-export
1324 .B \-\-detail , \-\-detail-platform
1327 output will be formatted as
1329 pairs for easy import into the environment.
1332 .BR \-E ", " \-\-examine
1333 Print contents of the metadata stored on the named device(s).
1334 Note the contrast between
1339 applies to devices which are components of an array, while
1341 applies to a whole array which is currently active.
1344 If an array was created on a SPARC machine with a 2.2 Linux kernel
1345 patched with RAID support, the superblock will have been created
1346 incorrectly, or at least incompatibly with 2.4 and later kernels.
1351 will fix the superblock before displaying it. If this appears to do
1352 the right thing, then the array can be successfully assembled using
1353 .BR "\-\-assemble \-\-update=sparc2.2" .
1356 .BR \-X ", " \-\-examine\-bitmap
1357 Report information about a bitmap file.
1358 The argument is either an external bitmap file or an array component
1359 in case of an internal bitmap. Note that running this on an array
1362 does not report the bitmap for that array.
1365 .BR \-R ", " \-\-run
1366 start a partially assembled array. If
1368 did not find enough devices to fully start the array, it might leaving
1369 it partially assembled. If you wish, you can then use
1371 to start the array in degraded mode.
1374 .BR \-S ", " \-\-stop
1375 deactivate array, releasing all resources.
1378 .BR \-o ", " \-\-readonly
1379 mark array as readonly.
1382 .BR \-w ", " \-\-readwrite
1383 mark array as readwrite.
1386 .B \-\-zero\-superblock
1387 If the device contains a valid md superblock, the block is
1388 overwritten with zeros. With
1390 the block where the superblock would be is overwritten even if it
1391 doesn't appear to be valid.
1394 .B \-\-kill\-subarray=
1395 If the device is a container and the argument to \-\-kill\-subarray
1396 specifies an inactive subarray in the container, then the subarray is
1397 deleted. Deleting all subarrays will leave an 'empty-container' or
1398 spare superblock on the drives. See \-\-zero\-superblock for completely
1399 removing a superblock. Note that some formats depend on the subarray
1400 index for generating a UUID, this command will fail if it would change
1401 the UUID of an active subarray.
1404 .B \-\-update\-subarray=
1405 If the device is a container and the argument to \-\-update\-subarray
1406 specifies a subarray in the container, then attempt to update the given
1407 superblock field in the subarray. See below in
1412 .BR \-t ", " \-\-test
1417 is set to reflect the status of the device. See below in
1422 .BR \-W ", " \-\-wait
1423 For each md device given, wait for any resync, recovery, or reshape
1424 activity to finish before returning.
1426 will return with success if it actually waited for every device
1427 listed, otherwise it will return failure.
1431 For each md device given, or each device in /proc/mdstat if
1433 is given, arrange for the array to be marked clean as soon as possible.
1435 will return with success if the array uses external metadata and we
1436 successfully waited. For native arrays this returns immediately as the
1437 kernel handles dirty-clean transitions at shutdown. No action is taken
1438 if safe-mode handling is disabled.
1440 .SH For Incremental Assembly mode:
1442 .BR \-\-rebuild\-map ", " \-r
1443 Rebuild the map file
1447 uses to help track which arrays are currently being assembled.
1450 .BR \-\-run ", " \-R
1451 Run any array assembled as soon as a minimal number of devices are
1452 available, rather than waiting until all expected devices are present.
1455 .BR \-\-scan ", " \-s
1456 Only meaningful with
1460 file for arrays that are being incrementally assembled and will try to
1461 start any that are not already started. If any such array is listed
1464 as requiring an external bitmap, that bitmap will be attached first.
1467 .BR \-\-fail ", " \-f
1468 This allows the hot-plug system to remove devices that have fully disappeared
1469 from the kernel. It will first fail and then remove the device from any
1470 array it belongs to.
1471 The device name given should be a kernel device name such as "sda",
1477 Only used with \-\-fail. The 'path' given will be recorded so that if
1478 a new device appears at the same location it can be automatically
1479 added to the same array. This allows the failed device to be
1480 automatically replaced by a new device without metadata if it appears
1481 at specified path. This option is normally only set by a
1485 .SH For Monitor mode:
1487 .BR \-m ", " \-\-mail
1488 Give a mail address to send alerts to.
1491 .BR \-p ", " \-\-program ", " \-\-alert
1492 Give a program to be run whenever an event is detected.
1495 .BR \-y ", " \-\-syslog
1496 Cause all events to be reported through 'syslog'. The messages have
1497 facility of 'daemon' and varying priorities.
1500 .BR \-d ", " \-\-delay
1501 Give a delay in seconds.
1503 polls the md arrays and then waits this many seconds before polling
1504 again. The default is 60 seconds. Since 2.6.16, there is no need to
1505 reduce this as the kernel alerts
1507 immediately when there is any change.
1510 .BR \-r ", " \-\-increment
1511 Give a percentage increment.
1513 will generate RebuildNN events with the given percentage increment.
1516 .BR \-f ", " \-\-daemonise
1519 to run as a background daemon if it decides to monitor anything. This
1520 causes it to fork and run in the child, and to disconnect from the
1521 terminal. The process id of the child is written to stdout.
1524 which will only continue monitoring if a mail address or alert program
1525 is found in the config file.
1528 .BR \-i ", " \-\-pid\-file
1531 is running in daemon mode, write the pid of the daemon process to
1532 the specified file, instead of printing it on standard output.
1535 .BR \-1 ", " \-\-oneshot
1536 Check arrays only once. This will generate
1538 events and more significantly
1544 .B " mdadm \-\-monitor \-\-scan \-1"
1546 from a cron script will ensure regular notification of any degraded arrays.
1549 .BR \-t ", " \-\-test
1552 alert for every array found at startup. This alert gets mailed and
1553 passed to the alert program. This can be used for testing that alert
1554 message do get through successfully.
1558 This inhibits the functionality for moving spares between arrays.
1559 Only one monitoring process started with
1561 but without this flag is allowed, otherwise the two could interfere
1568 .B mdadm \-\-assemble
1569 .I md-device options-and-component-devices...
1572 .B mdadm \-\-assemble \-\-scan
1573 .I md-devices-and-options...
1576 .B mdadm \-\-assemble \-\-scan
1580 This usage assembles one or more RAID arrays from pre-existing components.
1581 For each array, mdadm needs to know the md device, the identity of the
1582 array, and a number of component-devices. These can be found in a number of ways.
1584 In the first usage example (without the
1586 the first device given is the md device.
1587 In the second usage example, all devices listed are treated as md
1588 devices and assembly is attempted.
1589 In the third (where no devices are listed) all md devices that are
1590 listed in the configuration file are assembled. If no arrays are
1591 described by the configuration file, then any arrays that
1592 can be found on unused devices will be assembled.
1594 If precisely one device is listed, but
1600 was given and identity information is extracted from the configuration file.
1602 The identity can be given with the
1608 option, will be taken from the md-device record in the config file, or
1609 will be taken from the super block of the first component-device
1610 listed on the command line.
1612 Devices can be given on the
1614 command line or in the config file. Only devices which have an md
1615 superblock which contains the right identity will be considered for
1618 The config file is only used if explicitly named with
1620 or requested with (a possibly implicit)
1625 .B /etc/mdadm/mdadm.conf
1630 is not given, then the config file will only be used to find the
1631 identity of md arrays.
1633 Normally the array will be started after it is assembled. However if
1635 is not given and not all expected drives were listed, then the array
1636 is not started (to guard against usage errors). To insist that the
1637 array be started in this case (as may work for RAID1, 4, 5, 6, or 10),
1646 does not create any entries in
1650 It does record information in
1654 to choose the correct name.
1658 detects that udev is not configured, it will create the devices in
1662 In Linux kernels prior to version 2.6.28 there were two distinctly
1663 different types of md devices that could be created: one that could be
1664 partitioned using standard partitioning tools and one that could not.
1665 Since 2.6.28 that distinction is no longer relevant as both type of
1666 devices can be partitioned.
1668 will normally create the type that originally could not be partitioned
1669 as it has a well defined major number (9).
1671 Prior to 2.6.28, it is important that mdadm chooses the correct type
1672 of array device to use. This can be controlled with the
1674 option. In particular, a value of "mdp" or "part" or "p" tells mdadm
1675 to use a partitionable device rather than the default.
1677 In the no-udev case, the value given to
1679 can be suffixed by a number. This tells
1681 to create that number of partition devices rather than the default of 4.
1685 can also be given in the configuration file as a word starting
1687 on the ARRAY line for the relevant array.
1694 and no devices are listed,
1696 will first attempt to assemble all the arrays listed in the config
1699 If no arrays are listed in the config (other than those marked
1701 it will look through the available devices for possible arrays and
1702 will try to assemble anything that it finds. Arrays which are tagged
1703 as belonging to the given homehost will be assembled and started
1704 normally. Arrays which do not obviously belong to this host are given
1705 names that are expected not to conflict with anything local, and are
1706 started "read-auto" so that nothing is written to any device until the
1707 array is written to. i.e. automatic resync etc is delayed.
1711 finds a consistent set of devices that look like they should comprise
1712 an array, and if the superblock is tagged as belonging to the given
1713 home host, it will automatically choose a device name and try to
1714 assemble the array. If the array uses version-0.90 metadata, then the
1716 number as recorded in the superblock is used to create a name in
1720 If the array uses version-1 metadata, then the
1722 from the superblock is used to similarly create a name in
1724 (the name will have any 'host' prefix stripped first).
1726 This behaviour can be modified by the
1730 configuration file. This line can indicate that specific metadata
1731 type should, or should not, be automatically assembled. If an array
1732 is found which is not listed in
1734 and has a metadata format that is denied by the
1736 line, then it will not be assembled.
1739 line can also request that all arrays identified as being for this
1740 homehost should be assembled regardless of their metadata type.
1743 for further details.
1745 Note: Auto assembly cannot be used for assembling and activating some
1746 arrays which are undergoing reshape. In particular as the
1748 cannot be given, any reshape which requires a backup-file to continue
1749 cannot be started by auto assembly. An array which is growing to more
1750 devices and has passed the critical section can be assembled using
1761 .BI \-\-raid\-devices= Z
1765 This usage is similar to
1767 The difference is that it creates an array without a superblock. With
1768 these arrays there is no difference between initially creating the array and
1769 subsequently assembling the array, except that hopefully there is useful
1770 data there in the second case.
1772 The level may raid0, linear, raid1, raid10, multipath, or faulty, or
1773 one of their synonyms. All devices must be listed and the array will
1774 be started once complete. It will often be appropriate to use
1775 .B \-\-assume\-clean
1776 with levels raid1 or raid10.
1787 .BI \-\-raid\-devices= Z
1791 This usage will initialise a new md array, associate some devices with
1792 it, and activate the array.
1794 The named device will normally not exist when
1795 .I "mdadm \-\-create"
1796 is run, but will be created by
1798 once the array becomes active.
1800 As devices are added, they are checked to see if they contain RAID
1801 superblocks or filesystems. They are also checked to see if the variance in
1802 device size exceeds 1%.
1804 If any discrepancy is found, the array will not automatically be run, though
1807 can override this caution.
1809 To create a "degraded" array in which some devices are missing, simply
1810 give the word "\fBmissing\fP"
1811 in place of a device name. This will cause
1813 to leave the corresponding slot in the array empty.
1814 For a RAID4 or RAID5 array at most one slot can be
1815 "\fBmissing\fP"; for a RAID6 array at most two slots.
1816 For a RAID1 array, only one real device needs to be given. All of the
1820 When creating a RAID5 array,
1822 will automatically create a degraded array with an extra spare drive.
1823 This is because building the spare into a degraded array is in general
1824 faster than resyncing the parity on a non-degraded, but not clean,
1825 array. This feature can be overridden with the
1829 When creating an array with version-1 metadata a name for the array is
1831 If this is not given with the
1835 will choose a name based on the last component of the name of the
1836 device being created. So if
1838 is being created, then the name
1843 is being created, then the name
1847 When creating a partition based array, using
1849 with version-1.x metadata, the partition type should be set to
1851 (non fs-data). This type selection allows for greater precision since
1852 using any other [RAID auto-detect (0xFD) or a GNU/Linux partition (0x83)],
1853 might create problems in the event of array recovery through a live cdrom.
1855 A new array will normally get a randomly assigned 128bit UUID which is
1856 very likely to be unique. If you have a specific need, you can choose
1857 a UUID for the array by giving the
1859 option. Be warned that creating two arrays with the same UUID is a
1860 recipe for disaster. Also, using
1862 when creating a v0.90 array will silently override any
1867 .\"option is given, it is not necessary to list any component-devices in this command.
1868 .\"They can be added later, before a
1872 .\"is given, the apparent size of the smallest drive given is used.
1874 If the metadata type supports it (currently only 1.x metadata), space
1875 will be allocated to store a bad block list. This allows a modest
1876 number of bad blocks to be recorded, allowing the drive to remain in
1877 service while only partially functional.
1879 When creating an array within a
1882 can be given either the list of devices to use, or simply the name of
1883 the container. The former case gives control over which devices in
1884 the container will be used for the array. The latter case allows
1886 to automatically choose which devices to use based on how much spare
1889 The General Management options that are valid with
1894 insist on running the array even if some devices look like they might
1899 start the array readonly \(em not supported yet.
1906 .I options... devices...
1909 This usage will allow individual devices in an array to be failed,
1910 removed or added. It is possible to perform multiple operations with
1911 on command. For example:
1913 .B " mdadm /dev/md0 \-f /dev/hda1 \-r /dev/hda1 \-a /dev/hda1"
1919 and will then remove it from the array and finally add it back
1920 in as a spare. However only one md array can be affected by a single
1923 When a device is added to an active array, mdadm checks to see if it
1924 has metadata on it which suggests that it was recently a member of the
1925 array. If it does, it tries to "re\-add" the device. If there have
1926 been no changes since the device was removed, or if the array has a
1927 write-intent bitmap which has recorded whatever changes there were,
1928 then the device will immediately become a full member of the array and
1929 those differences recorded in the bitmap will be resolved.
1939 MISC mode includes a number of distinct operations that
1940 operate on distinct devices. The operations are:
1943 The device is examined to see if it is
1944 (1) an active md array, or
1945 (2) a component of an md array.
1946 The information discovered is reported.
1950 The device should be an active md device.
1952 will display a detailed description of the array.
1956 will cause the output to be less detailed and the format to be
1957 suitable for inclusion in
1961 will normally be 0 unless
1963 failed to get useful information about the device(s); however, if the
1965 option is given, then the exit status will be:
1969 The array is functioning normally.
1972 The array has at least one failed device.
1975 The array has multiple failed devices such that it is unusable.
1978 There was an error while trying to get information about the device.
1982 .B \-\-detail\-platform
1983 Print detail of the platform's RAID capabilities (firmware / hardware
1984 topology). If the metadata is specified with
1988 then the return status will be:
1992 metadata successfully enumerated its platform components on this system
1995 metadata is platform independent
1998 metadata failed to find its platform components on this system
2002 .B \-\-update\-subarray=
2003 If the device is a container and the argument to \-\-update\-subarray
2004 specifies a subarray in the container, then attempt to update the given
2005 superblock field in the subarray. Similar to updating an array in
2006 "assemble" mode, the field to update is selected by
2010 option. Currently only
2016 option updates the subarray name in the metadata, it may not affect the
2017 device node name or the device node symlink until the subarray is
2018 re\-assembled. If updating
2020 would change the UUID of an active subarray this operation is blocked,
2021 and the command will end in an error.
2025 The device should be a component of an md array.
2027 will read the md superblock of the device and display the contents.
2032 is given, then multiple devices that are components of the one array
2033 are grouped together and reported in a single entry suitable
2039 without listing any devices will cause all devices listed in the
2040 config file to be examined.
2044 The devices should be active md arrays which will be deactivated, as
2045 long as they are not currently in use.
2049 This will fully activate a partially assembled md array.
2053 This will mark an active array as read-only, providing that it is
2054 not currently being used.
2060 array back to being read/write.
2064 For all operations except
2067 will cause the operation to be applied to all arrays listed in
2072 causes all devices listed in the config file to be examined.
2075 .BR \-b ", " \-\-brief
2076 Be less verbose. This is used with
2084 gives an intermediate level of verbosity.
2090 .B mdadm \-\-monitor
2091 .I options... devices...
2096 to periodically poll a number of md arrays and to report on any events
2099 will never exit once it decides that there are arrays to be checked,
2100 so it should normally be run in the background.
2102 As well as reporting events,
2104 may move a spare drive from one array to another if they are in the
2109 and if the destination array has a failed drive but no spares.
2111 If any devices are listed on the command line,
2113 will only monitor those devices. Otherwise all arrays listed in the
2114 configuration file will be monitored. Further, if
2116 is given, then any other md devices that appear in
2118 will also be monitored.
2120 The result of monitoring the arrays is the generation of events.
2121 These events are passed to a separate program (if specified) and may
2122 be mailed to a given E-mail address.
2124 When passing events to a program, the program is run once for each event,
2125 and is given 2 or 3 command-line arguments: the first is the
2126 name of the event (see below), the second is the name of the
2127 md device which is affected, and the third is the name of a related
2128 device if relevant (such as a component device that has failed).
2132 is given, then a program or an E-mail address must be specified on the
2133 command line or in the config file. If neither are available, then
2135 will not monitor anything.
2139 will continue monitoring as long as something was found to monitor. If
2140 no program or email is given, then each event is reported to
2143 The different events are:
2147 .B DeviceDisappeared
2148 An md array which previously was configured appears to no longer be
2149 configured. (syslog priority: Critical)
2153 was told to monitor an array which is RAID0 or Linear, then it will
2155 .B DeviceDisappeared
2156 with the extra information
2158 This is because RAID0 and Linear do not support the device-failed,
2159 hot-spare and resync operations which are monitored.
2163 An md array started reconstruction. (syslog priority: Warning)
2169 is a two-digit number (ie. 05, 48). This indicates that rebuild
2170 has passed that many percent of the total. The events are generated
2171 with fixed increment since 0. Increment size may be specified with
2172 a commandline option (default is 20). (syslog priority: Warning)
2176 An md array that was rebuilding, isn't any more, either because it
2177 finished normally or was aborted. (syslog priority: Warning)
2181 An active component device of an array has been marked as
2182 faulty. (syslog priority: Critical)
2186 A spare component device which was being rebuilt to replace a faulty
2187 device has failed. (syslog priority: Critical)
2191 A spare component device which was being rebuilt to replace a faulty
2192 device has been successfully rebuilt and has been made active.
2193 (syslog priority: Info)
2197 A new md array has been detected in the
2199 file. (syslog priority: Info)
2203 A newly noticed array appears to be degraded. This message is not
2206 notices a drive failure which causes degradation, but only when
2208 notices that an array is degraded when it first sees the array.
2209 (syslog priority: Critical)
2213 A spare drive has been moved from one array in a
2217 to another to allow a failed drive to be replaced.
2218 (syslog priority: Info)
2224 has been told, via the config file, that an array should have a certain
2225 number of spare devices, and
2227 detects that it has fewer than this number when it first sees the
2228 array, it will report a
2231 (syslog priority: Warning)
2235 An array was found at startup, and the
2238 (syslog priority: Info)
2248 cause Email to be sent. All events cause the program to be run.
2249 The program is run with two or three arguments: the event
2250 name, the array device and possibly a second device.
2252 Each event has an associated array device (e.g.
2254 and possibly a second device. For
2259 the second device is the relevant component device.
2262 the second device is the array that the spare was moved from.
2266 to move spares from one array to another, the different arrays need to
2267 be labeled with the same
2269 or the spares must be allowed to migrate through matching POLICY domains
2270 in the configuration file. The
2272 name can be any string; it is only necessary that different spare
2273 groups use different names.
2277 detects that an array in a spare group has fewer active
2278 devices than necessary for the complete array, and has no spare
2279 devices, it will look for another array in the same spare group that
2280 has a full complement of working drive and a spare. It will then
2281 attempt to remove the spare from the second drive and add it to the
2283 If the removal succeeds but the adding fails, then it is added back to
2286 If the spare group for a degraded array is not defined,
2288 will look at the rules of spare migration specified by POLICY lines in
2290 and then follow similar steps as above if a matching spare is found.
2293 The GROW mode is used for changing the size or shape of an active
2295 For this to work, the kernel must support the necessary change.
2296 Various types of growth are being added during 2.6 development.
2298 Currently the supported changes include
2300 change the "size" attribute for RAID1, RAID4, RAID5 and RAID6.
2302 increase or decrease the "raid\-devices" attribute of RAID0, RAID1, RAID4,
2305 change the chunk-size and layout of RAID0, RAID4, RAID5 and RAID6.
2307 convert between RAID1 and RAID5, between RAID5 and RAID6, between
2308 RAID0, RAID4, and RAID5, and between RAID0 and RAID10 (in the near-2 mode).
2310 add a write-intent bitmap to any array which supports these bitmaps, or
2311 remove a write-intent bitmap from such an array.
2314 Using GROW on containers is currently supported only for Intel's IMSM
2315 container format. The number of devices in a container can be
2316 increased - which affects all arrays in the container - or an array
2317 in a container can be converted between levels where those levels are
2318 supported by the container, and the conversion is on of those listed
2319 above. Resizing arrays in an IMSM container with
2321 is not yet supported.
2323 Grow functionality (e.g. expand a number of raid devices) for Intel's
2324 IMSM container format has an experimental status. It is guarded by the
2325 .B MDADM_EXPERIMENTAL
2326 environment variable which must be set to '1' for a GROW command to
2328 This is for the following reasons:
2331 Intel's native IMSM check-pointing is not fully tested yet.
2332 This can causes IMSM incompatibility during the grow process: an array
2333 which is growing cannot roam between Microsoft Windows(R) and Linux
2337 Interrupting a grow operation is not recommended, because it
2338 has not been fully tested for Intel's IMSM container format yet.
2341 Note: Intel's native checkpointing doesn't use
2343 option and it is transparent for assembly feature.
2346 Normally when an array is built the "size" is taken from the smallest
2347 of the drives. If all the small drives in an arrays are, one at a
2348 time, removed and replaced with larger drives, then you could have an
2349 array of large drives with only a small amount used. In this
2350 situation, changing the "size" with "GROW" mode will allow the extra
2351 space to start being used. If the size is increased in this way, a
2352 "resync" process will start to make sure the new parts of the array
2355 Note that when an array changes size, any filesystem that may be
2356 stored in the array will not automatically grow or shrink to use or
2357 vacate the space. The
2358 filesystem will need to be explicitly told to use the extra space
2359 after growing, or to reduce its size
2361 to shrinking the array.
2363 Also the size of an array cannot be changed while it has an active
2364 bitmap. If an array has a bitmap, it must be removed before the size
2365 can be changed. Once the change is complete a new bitmap can be created.
2367 .SS RAID\-DEVICES CHANGES
2369 A RAID1 array can work with any number of devices from 1 upwards
2370 (though 1 is not very useful). There may be times which you want to
2371 increase or decrease the number of active devices. Note that this is
2372 different to hot-add or hot-remove which changes the number of
2375 When reducing the number of devices in a RAID1 array, the slots which
2376 are to be removed from the array must already be vacant. That is, the
2377 devices which were in those slots must be failed and removed.
2379 When the number of devices is increased, any hot spares that are
2380 present will be activated immediately.
2382 Changing the number of active devices in a RAID5 or RAID6 is much more
2383 effort. Every block in the array will need to be read and written
2384 back to a new location. From 2.6.17, the Linux Kernel is able to
2385 increase the number of devices in a RAID5 safely, including restarting
2386 an interrupted "reshape". From 2.6.31, the Linux Kernel is able to
2387 increase or decrease the number of devices in a RAID5 or RAID6.
2389 From 2.6.35, the Linux Kernel is able to convert a RAID0 in to a RAID4
2392 uses this functionality and the ability to add
2393 devices to a RAID4 to allow devices to be added to a RAID0. When
2394 requested to do this,
2396 will convert the RAID0 to a RAID4, add the necessary disks and make
2397 the reshape happen, and then convert the RAID4 back to RAID0.
2399 When decreasing the number of devices, the size of the array will also
2400 decrease. If there was data in the array, it could get destroyed and
2401 this is not reversible, so you should firstly shrink the filesystem on
2402 the array to fit within the new size. To help prevent accidents,
2404 requires that the size of the array be decreased first with
2405 .BR "mdadm --grow --array-size" .
2406 This is a reversible change which simply makes the end of the array
2407 inaccessible. The integrity of any data can then be checked before
2408 the non-reversible reduction in the number of devices is request.
2410 When relocating the first few stripes on a RAID5 or RAID6, it is not
2411 possible to keep the data on disk completely consistent and
2412 crash-proof. To provide the required safety, mdadm disables writes to
2413 the array while this "critical section" is reshaped, and takes a
2414 backup of the data that is in that section. For grows, this backup may be
2415 stored in any spare devices that the array has, however it can also be
2416 stored in a separate file specified with the
2418 option, and is required to be specified for shrinks, RAID level
2419 changes and layout changes. If this option is used, and the system
2420 does crash during the critical period, the same file must be passed to
2422 to restore the backup and reassemble the array. When shrinking rather
2423 than growing the array, the reshape is done from the end towards the
2424 beginning, so the "critical section" is at the end of the reshape.
2428 Changing the RAID level of any array happens instantaneously. However
2429 in the RAID5 to RAID6 case this requires a non-standard layout of the
2430 RAID6 data, and in the RAID6 to RAID5 case that non-standard layout is
2431 required before the change can be accomplished. So while the level
2432 change is instant, the accompanying layout change can take quite a
2435 is required. If the array is not simultaneously being grown or
2436 shrunk, so that the array size will remain the same - for example,
2437 reshaping a 3-drive RAID5 into a 4-drive RAID6 - the backup file will
2438 be used not just for a "cricital section" but throughout the reshape
2439 operation, as described below under LAYOUT CHANGES.
2441 .SS CHUNK-SIZE AND LAYOUT CHANGES
2443 Changing the chunk-size of layout without also changing the number of
2444 devices as the same time will involve re-writing all blocks in-place.
2445 To ensure against data loss in the case of a crash, a
2447 must be provided for these changes. Small sections of the array will
2448 be copied to the backup file while they are being rearranged. This
2449 means that all the data is copied twice, once to the backup and once
2450 to the new layout on the array, so this type of reshape will go very
2453 If the reshape is interrupted for any reason, this backup file must be
2455 .B "mdadm --assemble"
2456 so the array can be reassembled. Consequently the file cannot be
2457 stored on the device being reshaped.
2462 A write-intent bitmap can be added to, or removed from, an active
2463 array. Either internal bitmaps, or bitmaps stored in a separate file,
2464 can be added. Note that if you add a bitmap stored in a file which is
2465 in a filesystem that is on the RAID array being affected, the system
2466 will deadlock. The bitmap must be on a separate filesystem.
2468 .SH INCREMENTAL MODE
2472 .B mdadm \-\-incremental
2478 .B mdadm \-\-incremental \-\-fail
2482 .B mdadm \-\-incremental \-\-rebuild\-map
2485 .B mdadm \-\-incremental \-\-run \-\-scan
2488 This mode is designed to be used in conjunction with a device
2489 discovery system. As devices are found in a system, they can be
2491 .B "mdadm \-\-incremental"
2492 to be conditionally added to an appropriate array.
2494 Conversely, it can also be used with the
2496 flag to do just the opposite and find whatever array a particular device
2497 is part of and remove the device from that array.
2499 If the device passed is a
2501 device created by a previous call to
2503 then rather than trying to add that device to an array, all the arrays
2504 described by the metadata of the container will be started.
2507 performs a number of tests to determine if the device is part of an
2508 array, and which array it should be part of. If an appropriate array
2509 is found, or can be created,
2511 adds the device to the array and conditionally starts the array.
2515 will normally only add devices to an array which were previously working
2516 (active or spare) parts of that array. The support for automatic
2517 inclusion of a new drive as a spare in some array requires
2518 a configuration through POLICY in config file.
2522 makes are as follow:
2524 Is the device permitted by
2526 That is, is it listed in a
2528 line in that file. If
2530 is absent then the default it to allow any device. Similar if
2532 contains the special word
2534 then any device is allowed. Otherwise the device name given to
2536 must match one of the names or patterns in a
2541 Does the device have a valid md superblock? If a specific metadata
2542 version is requested with
2546 then only that style of metadata is accepted, otherwise
2548 finds any known version of metadata. If no
2550 metadata is found, the device may be still added to an array
2551 as a spare if POLICY allows.
2555 Does the metadata match an expected array?
2556 The metadata can match in two ways. Either there is an array listed
2559 which identifies the array (either by UUID, by name, by device list,
2560 or by minor-number), or the array was created with a
2566 or on the command line.
2569 is not able to positively identify the array as belonging to the
2570 current host, the device will be rejected.
2575 keeps a list of arrays that it has partially assembled in
2577 If no array exists which matches
2578 the metadata on the new device,
2580 must choose a device name and unit number. It does this based on any
2583 or any name information stored in the metadata. If this name
2584 suggests a unit number, that number will be used, otherwise a free
2585 unit number will be chosen. Normally
2587 will prefer to create a partitionable array, however if the
2591 suggests that a non-partitionable array is preferred, that will be
2594 If the array is not found in the config file and its metadata does not
2595 identify it as belonging to the "homehost", then
2597 will choose a name for the array which is certain not to conflict with
2598 any array which does belong to this host. It does this be adding an
2599 underscore and a small number to the name preferred by the metadata.
2601 Once an appropriate array is found or created and the device is added,
2603 must decide if the array is ready to be started. It will
2604 normally compare the number of available (non-spare) devices to the
2605 number of devices that the metadata suggests need to be active. If
2606 there are at least that many, the array will be started. This means
2607 that if any devices are missing the array will not be restarted.
2613 in which case the array will be run as soon as there are enough
2614 devices present for the data to be accessible. For a RAID1, that
2615 means one device will start the array. For a clean RAID5, the array
2616 will be started as soon as all but one drive is present.
2618 Note that neither of these approaches is really ideal. If it can
2619 be known that all device discovery has completed, then
2623 can be run which will try to start all arrays that are being
2624 incrementally assembled. They are started in "read-auto" mode in
2625 which they are read-only until the first write request. This means
2626 that no metadata updates are made and no attempt at resync or recovery
2627 happens. Further devices that are found before the first write can
2628 still be added safely.
2631 This section describes environment variables that affect how mdadm
2636 Setting this value to 1 will prevent mdadm from automatically launching
2637 mdmon. This variable is intended primarily for debugging mdadm/mdmon.
2643 does not create any device nodes in /dev, but leaves that task to
2647 appears not to be configured, or if this environment variable is set
2650 will create and devices that are needed.
2654 .B " mdadm \-\-query /dev/name-of-device"
2656 This will find out if a given device is a RAID array, or is part of
2657 one, and will provide brief information about the device.
2659 .B " mdadm \-\-assemble \-\-scan"
2661 This will assemble and start all arrays listed in the standard config
2662 file. This command will typically go in a system startup file.
2664 .B " mdadm \-\-stop \-\-scan"
2666 This will shut down all arrays that can be shut down (i.e. are not
2667 currently in use). This will typically go in a system shutdown script.
2669 .B " mdadm \-\-follow \-\-scan \-\-delay=120"
2671 If (and only if) there is an Email address or program given in the
2672 standard config file, then
2673 monitor the status of all arrays listed in that file by
2674 polling them ever 2 minutes.
2676 .B " mdadm \-\-create /dev/md0 \-\-level=1 \-\-raid\-devices=2 /dev/hd[ac]1"
2678 Create /dev/md0 as a RAID1 array consisting of /dev/hda1 and /dev/hdc1.
2681 .B " echo 'DEVICE /dev/hd*[0\-9] /dev/sd*[0\-9]' > mdadm.conf"
2683 .B " mdadm \-\-detail \-\-scan >> mdadm.conf"
2685 This will create a prototype config file that describes currently
2686 active arrays that are known to be made from partitions of IDE or SCSI drives.
2687 This file should be reviewed before being used as it may
2688 contain unwanted detail.
2690 .B " echo 'DEVICE /dev/hd[a\-z] /dev/sd*[a\-z]' > mdadm.conf"
2692 .B " mdadm \-\-examine \-\-scan \-\-config=mdadm.conf >> mdadm.conf"
2694 This will find arrays which could be assembled from existing IDE and
2695 SCSI whole drives (not partitions), and store the information in the
2696 format of a config file.
2697 This file is very likely to contain unwanted detail, particularly
2700 entries. It should be reviewed and edited before being used as an
2703 .B " mdadm \-\-examine \-\-brief \-\-scan \-\-config=partitions"
2705 .B " mdadm \-Ebsc partitions"
2707 Create a list of devices by reading
2708 .BR /proc/partitions ,
2709 scan these for RAID superblocks, and printout a brief listing of all
2712 .B " mdadm \-Ac partitions \-m 0 /dev/md0"
2714 Scan all partitions and devices listed in
2715 .BR /proc/partitions
2718 out of all such devices with a RAID superblock with a minor number of 0.
2720 .B " mdadm \-\-monitor \-\-scan \-\-daemonise > /run/mdadm/mon.pid"
2722 If config file contains a mail address or alert program, run mdadm in
2723 the background in monitor mode monitoring all md devices. Also write
2724 pid of mdadm daemon to
2725 .BR /run/mdadm/mon.pid .
2727 .B " mdadm \-Iq /dev/somedevice"
2729 Try to incorporate newly discovered device into some array as
2732 .B " mdadm \-\-incremental \-\-rebuild\-map \-\-run \-\-scan"
2734 Rebuild the array map from any current arrays, and then start any that
2737 .B " mdadm /dev/md4 --fail detached --remove detached"
2739 Any devices which are components of /dev/md4 will be marked as faulty
2740 and then remove from the array.
2742 .B " mdadm --grow /dev/md4 --level=6 --backup-file=/root/backup-md4"
2746 which is currently a RAID5 array will be converted to RAID6. There
2747 should normally already be a spare drive attached to the array as a
2748 RAID6 needs one more drive than a matching RAID5.
2750 .B " mdadm --create /dev/md/ddf --metadata=ddf --raid-disks 6 /dev/sd[a-f]"
2752 Create a DDF array over 6 devices.
2754 .B " mdadm --create /dev/md/home -n3 -l5 -z 30000000 /dev/md/ddf"
2756 Create a RAID5 array over any 3 devices in the given DDF set. Use
2757 only 30 gigabytes of each device.
2759 .B " mdadm -A /dev/md/ddf1 /dev/sd[a-f]"
2761 Assemble a pre-exist ddf array.
2763 .B " mdadm -I /dev/md/ddf1"
2765 Assemble all arrays contained in the ddf array, assigning names as
2768 .B " mdadm \-\-create \-\-help"
2770 Provide help about the Create mode.
2772 .B " mdadm \-\-config \-\-help"
2774 Provide help about the format of the config file.
2776 .B " mdadm \-\-help"
2778 Provide general help.
2788 lists all active md devices with information about them.
2790 uses this to find arrays when
2792 is given in Misc mode, and to monitor array reconstruction
2797 The config file lists which devices may be scanned to see if
2798 they contain MD super block, and gives identifying information
2799 (e.g. UUID) about known MD arrays. See
2806 mode is used, this file gets a list of arrays currently being created.
2811 understand two sorts of names for array devices.
2813 The first is the so-called 'standard' format name, which matches the
2814 names used by the kernel and which appear in
2817 The second sort can be freely chosen, but must reside in
2819 When giving a device name to
2821 to create or assemble an array, either full path name such as
2825 can be given, or just the suffix of the second sort of name, such as
2831 chooses device names during auto-assembly or incremental assembly, it
2832 will sometimes add a small sequence number to the end of the name to
2833 avoid conflicted between multiple arrays that have the same name. If
2835 can reasonably determine that the array really is meant for this host,
2836 either by a hostname in the metadata, or by the presence of the array
2839 then it will leave off the suffix if possible.
2840 Also if the homehost is specified as
2843 will only use a suffix if a different array of the same name already
2844 exists or is listed in the config file.
2846 The standard names for non-partitioned arrays (the only sort of md
2847 array available in 2.4 and earlier) are of the form
2851 where NN is a number.
2852 The standard names for partitionable arrays (as available from 2.6
2853 onwards) are of the form
2857 Partition numbers should be indicated by added "pMM" to these, thus "/dev/md/d1p2".
2859 From kernel version, 2.6.28 the "non-partitioned array" can actually
2860 be partitioned. So the "md_dNN" names are no longer needed, and
2861 partitions such as "/dev/mdNNpXX" are possible.
2865 was previously known as
2869 is completely separate from the
2871 package, and does not use the
2873 configuration file at all.
2876 For further information on mdadm usage, MD and the various levels of
2879 .B http://raid.wiki.kernel.org/
2881 (based upon Jakob \(/Ostergaard's Software\-RAID.HOWTO)
2883 .\"for new releases of the RAID driver check out:
2886 .\".UR ftp://ftp.kernel.org/pub/linux/kernel/people/mingo/raid-patches
2887 .\"ftp://ftp.kernel.org/pub/linux/kernel/people/mingo/raid-patches
2892 .\".UR http://www.cse.unsw.edu.au/~neilb/patches/linux-stable/
2893 .\"http://www.cse.unsw.edu.au/~neilb/patches/linux-stable/
2896 The latest version of
2898 should always be available from
2900 .B http://www.kernel.org/pub/linux/utils/raid/mdadm/
projects / thirdparty / mdadm.git / blob