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Correctly abort level change when reshape_array fails.
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1 .\" -*- nroff -*-
2 .\" Copyright Neil Brown and others.
3 .\" This program is free software; you can redistribute it and/or modify
4 .\" it under the terms of the GNU General Public License as published by
5 .\" the Free Software Foundation; either version 2 of the License, or
6 .\" (at your option) any later version.
7 .\" See file COPYING in distribution for details.
8 .TH MDADM 8 "" v3.1.4
9 .SH NAME
10 mdadm \- manage MD devices
11 .I aka
12 Linux Software RAID
13
14 .SH SYNOPSIS
15
16 .BI mdadm " [mode] <raiddevice> [options] <component-devices>"
17
18 .SH DESCRIPTION
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
24 device failure.
25
26 Linux Software RAID devices are implemented through the md (Multiple
27 Devices) device driver.
28
29 Currently, Linux supports
30 .B LINEAR
31 md devices,
32 .B RAID0
33 (striping),
34 .B RAID1
35 (mirroring),
36 .BR RAID4 ,
37 .BR RAID5 ,
38 .BR RAID6 ,
39 .BR RAID10 ,
40 .BR MULTIPATH ,
41 .BR FAULTY ,
42 and
43 .BR CONTAINER .
44
45 .B MULTIPATH
46 is not a Software RAID mechanism, but does involve
47 multiple devices:
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.
52
53 .B FAULTY
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.
56
57 .B CONTAINER
58 is different again. A
59 .B CONTAINER
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
67 second half.
68
69 With a
70 .BR CONTAINER ,
71 there is one set of metadata that describes all of
72 the arrays in the container. So when
73 .I mdadm
74 creates a
75 .B CONTAINER
76 device, the device just represents the metadata. Other normal arrays (RAID1
77 etc) can be created inside the container.
78
79 .SH MODES
80 mdadm has several major modes of operation:
81 .TP
82 .B Assemble
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.
86 .I mdadm
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.
90
91 .TP
92 .B Build
93 Build an array that doesn't have per-device metadata (superblocks). For these
94 sorts of arrays,
95 .I mdadm
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
99 .B Build
100 mode should only be used together with a complete understanding of
101 what you are doing.
102
103 .TP
104 .B Create
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
110 untouched.
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.
113
114 .TP
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.
120
121 .TP
122 .B "Grow"
123 Grow (or shrink) an array, or otherwise reshape it in some way.
124 Currently supported growth options including changing the active size
125 of component devices and changing the number of active devices in RAID
126 levels 1/4/5/6, changing the RAID level between 1, 5, and 6, changing
127 the chunk size and layout for RAID5 and RAID5, as well as adding or
128 removing a write-intent bitmap.
129
130 .TP
131 .B "Incremental Assembly"
132 Add a single device to an appropriate array. If the addition of the
133 device makes the array runnable, the array will be started.
134 This provides a convenient interface to a
135 .I hot-plug
136 system. As each device is detected,
137 .I mdadm
138 has a chance to include it in some array as appropriate.
139 Optionally, when the
140 .I \-\-fail
141 flag is passed in we will remove the device from any active array
142 instead of adding it.
143
144 If a
145 .B CONTAINER
146 is passed to
147 .I mdadm
148 in this mode, then any arrays within that container will be assembled
149 and started.
150
151 .TP
152 .B Manage
153 This is for doing things to specific components of an array such as
154 adding new spares and removing faulty devices.
155
156 .TP
157 .B Misc
158 This is an 'everything else' mode that supports operations on active
159 arrays, operations on component devices such as erasing old superblocks, and
160 information gathering operations.
161 .\"This mode allows operations on independent devices such as examine MD
162 .\"superblocks, erasing old superblocks and stopping active arrays.
163
164 .TP
165 .B Auto-detect
166 This mode does not act on a specific device or array, but rather it
167 requests the Linux Kernel to activate any auto-detected arrays.
168 .SH OPTIONS
169
170 .SH Options for selecting a mode are:
171
172 .TP
173 .BR \-A ", " \-\-assemble
174 Assemble a pre-existing array.
175
176 .TP
177 .BR \-B ", " \-\-build
178 Build a legacy array without superblocks.
179
180 .TP
181 .BR \-C ", " \-\-create
182 Create a new array.
183
184 .TP
185 .BR \-F ", " \-\-follow ", " \-\-monitor
186 Select
187 .B Monitor
188 mode.
189
190 .TP
191 .BR \-G ", " \-\-grow
192 Change the size or shape of an active array.
193
194 .TP
195 .BR \-I ", " \-\-incremental
196 Add/remove a single device to/from an appropriate array, and possibly start the array.
197
198 .TP
199 .B \-\-auto-detect
200 Request that the kernel starts any auto-detected arrays. This can only
201 work if
202 .I md
203 is compiled into the kernel \(em not if it is a module.
204 Arrays can be auto-detected by the kernel if all the components are in
205 primary MS-DOS partitions with partition type
206 .BR FD ,
207 and all use v0.90 metadata.
208 In-kernel autodetect is not recommended for new installations. Using
209 .I mdadm
210 to detect and assemble arrays \(em possibly in an
211 .I initrd
212 \(em is substantially more flexible and should be preferred.
213
214 .P
215 If a device is given before any options, or if the first option is
216 .BR \-\-add ,
217 .BR \-\-fail ,
218 or
219 .BR \-\-remove ,
220 then the MANAGE mode is assumed.
221 Anything other than these will cause the
222 .B Misc
223 mode to be assumed.
224
225 .SH Options that are not mode-specific are:
226
227 .TP
228 .BR \-h ", " \-\-help
229 Display general help message or, after one of the above options, a
230 mode-specific help message.
231
232 .TP
233 .B \-\-help\-options
234 Display more detailed help about command line parsing and some commonly
235 used options.
236
237 .TP
238 .BR \-V ", " \-\-version
239 Print version information for mdadm.
240
241 .TP
242 .BR \-v ", " \-\-verbose
243 Be more verbose about what is happening. This can be used twice to be
244 extra-verbose.
245 The extra verbosity currently only affects
246 .B \-\-detail \-\-scan
247 and
248 .BR "\-\-examine \-\-scan" .
249
250 .TP
251 .BR \-q ", " \-\-quiet
252 Avoid printing purely informative messages. With this,
253 .I mdadm
254 will be silent unless there is something really important to report.
255
256 .TP
257 .BR \-f ", " \-\-force
258 Be more forceful about certain operations. See the various modes for
259 the exact meaning of this option in different contexts.
260
261 .TP
262 .BR \-c ", " \-\-config=
263 Specify the config file. Default is to use
264 .BR /etc/mdadm.conf ,
265 or if that is missing then
266 .BR /etc/mdadm/mdadm.conf .
267 If the config file given is
268 .B "partitions"
269 then nothing will be read, but
270 .I mdadm
271 will act as though the config file contained exactly
272 .B "DEVICE partitions containers"
273 and will read
274 .B /proc/partitions
275 to find a list of devices to scan, and
276 .B /proc/mdstat
277 to find a list of containers to examine.
278 If the word
279 .B "none"
280 is given for the config file, then
281 .I mdadm
282 will act as though the config file were empty.
283
284 .TP
285 .BR \-s ", " \-\-scan
286 Scan config file or
287 .B /proc/mdstat
288 for missing information.
289 In general, this option gives
290 .I mdadm
291 permission to get any missing information (like component devices,
292 array devices, array identities, and alert destination) from the
293 configuration file (see previous option);
294 one exception is MISC mode when using
295 .B \-\-detail
296 or
297 .B \-\-stop,
298 in which case
299 .B \-\-scan
300 says to get a list of array devices from
301 .BR /proc/mdstat .
302
303 .TP
304 .BR \-e ", " \-\-metadata=
305 Declare the style of RAID metadata (superblock) to be used. The
306 default is {DEFAULT_METADATA} for
307 .BR \-\-create ,
308 and to guess for other operations.
309 The default can be overridden by setting the
310 .B metadata
311 value for the
312 .B CREATE
313 keyword in
314 .BR mdadm.conf .
315
316 Options are:
317 .RS
318 .ie '{DEFAULT_METADATA}'0.90'
319 .IP "0, 0.90, default"
320 .el
321 .IP "0, 0.90"
322 ..
323 Use the original 0.90 format superblock. This format limits arrays to
324 28 component devices and limits component devices of levels 1 and
325 greater to 2 terabytes. It is also possible for there to be confusion
326 about whether the superblock applies to a whole device or just the
327 last partition, if that partition starts on a 64K boundary.
328 .ie '{DEFAULT_METADATA}'0.90'
329 .IP "1, 1.0, 1.1, 1.2"
330 .el
331 .IP "1, 1.0, 1.1, 1.2 default"
332 ..
333 Use the new version-1 format superblock. This has fewer restrictions.
334 It can easily be moved between hosts with different endian-ness, and a
335 recovery operation can be checkpointed and restarted. The different
336 sub-versions store the superblock at different locations on the
337 device, either at the end (for 1.0), at the start (for 1.1) or 4K from
338 the start (for 1.2). "1" is equivalent to "1.0".
339 'if '{DEFAULT_METADATA}'1.2' "default" is equivalent to "1.2".
340 .IP ddf
341 Use the "Industry Standard" DDF (Disk Data Format) format defined by
342 SNIA.
343 When creating a DDF array a
344 .B CONTAINER
345 will be created, and normal arrays can be created in that container.
346 .IP imsm
347 Use the Intel(R) Matrix Storage Manager metadata format. This creates a
348 .B CONTAINER
349 which is managed in a similar manner to DDF, and is supported by an
350 option-rom on some platforms:
351 .IP
352 .B http://www.intel.com/design/chipsets/matrixstorage_sb.htm
353 .PP
354 .RE
355
356 .TP
357 .B \-\-homehost=
358 This will override any
359 .B HOMEHOST
360 setting in the config file and provides the identity of the host which
361 should be considered the home for any arrays.
362
363 When creating an array, the
364 .B homehost
365 will be recorded in the metadata. For version-1 superblocks, it will
366 be prefixed to the array name. For version-0.90 superblocks, part of
367 the SHA1 hash of the hostname will be stored in the later half of the
368 UUID.
369
370 When reporting information about an array, any array which is tagged
371 for the given homehost will be reported as such.
372
373 When using Auto-Assemble, only arrays tagged for the given homehost
374 will be allowed to use 'local' names (i.e. not ending in '_' followed
375 by a digit string). See below under
376 .BR "Auto Assembly" .
377
378 .SH For create, build, or grow:
379
380 .TP
381 .BR \-n ", " \-\-raid\-devices=
382 Specify the number of active devices in the array. This, plus the
383 number of spare devices (see below) must equal the number of
384 .I component-devices
385 (including "\fBmissing\fP" devices)
386 that are listed on the command line for
387 .BR \-\-create .
388 Setting a value of 1 is probably
389 a mistake and so requires that
390 .B \-\-force
391 be specified first. A value of 1 will then be allowed for linear,
392 multipath, RAID0 and RAID1. It is never allowed for RAID4, RAID5 or RAID6.
393 .br
394 This number can only be changed using
395 .B \-\-grow
396 for RAID1, RAID4, RAID5 and RAID6 arrays, and only on kernels which provide
397 the necessary support.
398
399 .TP
400 .BR \-x ", " \-\-spare\-devices=
401 Specify the number of spare (eXtra) devices in the initial array.
402 Spares can also be added
403 and removed later. The number of component devices listed
404 on the command line must equal the number of RAID devices plus the
405 number of spare devices.
406
407 .TP
408 .BR \-z ", " \-\-size=
409 Amount (in Kibibytes) of space to use from each drive in RAID levels 1/4/5/6.
410 This must be a multiple of the chunk size, and must leave about 128Kb
411 of space at the end of the drive for the RAID superblock.
412 If this is not specified
413 (as it normally is not) the smallest drive (or partition) sets the
414 size, though if there is a variance among the drives of greater than 1%, a warning is
415 issued.
416
417 A suffix of 'M' or 'G' can be given to indicate Megabytes or
418 Gigabytes respectively.
419
420 This value can be set with
421 .B \-\-grow
422 for RAID level 1/4/5/6. If the array was created with a size smaller
423 than the currently active drives, the extra space can be accessed
424 using
425 .BR \-\-grow .
426 The size can be given as
427 .B max
428 which means to choose the largest size that fits on all current drives.
429
430 This value can not be used with
431 .B CONTAINER
432 metadata such as DDF and IMSM.
433
434 .TP
435 .BR \-Z ", " \-\-array-size=
436 This is only meaningful with
437 .B \-\-grow
438 and its effect is not persistent: when the array is stopped and
439 restarted the default array size will be restored.
440
441 Setting the array-size causes the array to appear smaller to programs
442 that access the data. This is particularly needed before reshaping an
443 array so that it will be smaller. As the reshape is not reversible,
444 but setting the size with
445 .B \-\-array-size
446 is, it is required that the array size is reduced as appropriate
447 before the number of devices in the array is reduced.
448
449 A suffix of 'M' or 'G' can be given to indicate Megabytes or
450 Gigabytes respectively.
451 A value of
452 .B max
453 restores the apparent size of the array to be whatever the real
454 amount of available space is.
455
456 .TP
457 .BR \-c ", " \-\-chunk=
458 Specify chunk size of kibibytes. The default when creating an
459 array is 512KB. To ensure compatibility with earlier versions, the
460 default when Building and array with no persistent metadata is 64KB.
461 This is only meaningful for RAID0, RAID4, RAID5, RAID6, and RAID10.
462
463 A suffix of 'M' or 'G' can be given to indicate Megabytes or
464 Gigabytes respectively.
465
466 .TP
467 .BR \-\-rounding=
468 Specify rounding factor for a Linear array. The size of each
469 component will be rounded down to a multiple of this size.
470 This is a synonym for
471 .B \-\-chunk
472 but highlights the different meaning for Linear as compared to other
473 RAID levels. The default is 64K if a kernel earlier than 2.6.16 is in
474 use, and is 0K (i.e. no rounding) in later kernels.
475
476 .TP
477 .BR \-l ", " \-\-level=
478 Set RAID level. When used with
479 .BR \-\-create ,
480 options are: linear, raid0, 0, stripe, raid1, 1, mirror, raid4, 4,
481 raid5, 5, raid6, 6, raid10, 10, multipath, mp, faulty, container.
482 Obviously some of these are synonymous.
483
484 When a
485 .B CONTAINER
486 metadata type is requested, only the
487 .B container
488 level is permitted, and it does not need to be explicitly given.
489
490 When used with
491 .BR \-\-build ,
492 only linear, stripe, raid0, 0, raid1, multipath, mp, and faulty are valid.
493
494 Can be used with
495 .B \-\-grow
496 to change the RAID level in some cases. See LEVEL CHANGES below.
497
498 .TP
499 .BR \-p ", " \-\-layout=
500 This option configures the fine details of data layout for RAID5, RAID6,
501 and RAID10 arrays, and controls the failure modes for
502 .IR faulty .
503
504 The layout of the RAID5 parity block can be one of
505 .BR left\-asymmetric ,
506 .BR left\-symmetric ,
507 .BR right\-asymmetric ,
508 .BR right\-symmetric ,
509 .BR la ", " ra ", " ls ", " rs .
510 The default is
511 .BR left\-symmetric .
512
513 It is also possible to cause RAID5 to use a RAID4-like layout by
514 choosing
515 .BR parity\-first ,
516 or
517 .BR parity\-last .
518
519 Finally for RAID5 there are DDF\-compatible layouts,
520 .BR ddf\-zero\-restart ,
521 .BR ddf\-N\-restart ,
522 and
523 .BR ddf\-N\-continue .
524
525 These same layouts are available for RAID6. There are also 4 layouts
526 that will provide an intermediate stage for converting between RAID5
527 and RAID6. These provide a layout which is identical to the
528 corresponding RAID5 layout on the first N\-1 devices, and has the 'Q'
529 syndrome (the second 'parity' block used by RAID6) on the last device.
530 These layouts are:
531 .BR left\-symmetric\-6 ,
532 .BR right\-symmetric\-6 ,
533 .BR left\-asymmetric\-6 ,
534 .BR right\-asymmetric\-6 ,
535 and
536 .BR parity\-first\-6 .
537
538 When setting the failure mode for level
539 .I faulty,
540 the options are:
541 .BR write\-transient ", " wt ,
542 .BR read\-transient ", " rt ,
543 .BR write\-persistent ", " wp ,
544 .BR read\-persistent ", " rp ,
545 .BR write\-all ,
546 .BR read\-fixable ", " rf ,
547 .BR clear ", " flush ", " none .
548
549 Each failure mode can be followed by a number, which is used as a period
550 between fault generation. Without a number, the fault is generated
551 once on the first relevant request. With a number, the fault will be
552 generated after that many requests, and will continue to be generated
553 every time the period elapses.
554
555 Multiple failure modes can be current simultaneously by using the
556 .B \-\-grow
557 option to set subsequent failure modes.
558
559 "clear" or "none" will remove any pending or periodic failure modes,
560 and "flush" will clear any persistent faults.
561
562 Finally, the layout options for RAID10 are one of 'n', 'o' or 'f' followed
563 by a small number. The default is 'n2'. The supported options are:
564
565 .I 'n'
566 signals 'near' copies. Multiple copies of one data block are at
567 similar offsets in different devices.
568
569 .I 'o'
570 signals 'offset' copies. Rather than the chunks being duplicated
571 within a stripe, whole stripes are duplicated but are rotated by one
572 device so duplicate blocks are on different devices. Thus subsequent
573 copies of a block are in the next drive, and are one chunk further
574 down.
575
576 .I 'f'
577 signals 'far' copies
578 (multiple copies have very different offsets).
579 See md(4) for more detail about 'near', 'offset', and 'far'.
580
581 The number is the number of copies of each datablock. 2 is normal, 3
582 can be useful. This number can be at most equal to the number of
583 devices in the array. It does not need to divide evenly into that
584 number (e.g. it is perfectly legal to have an 'n2' layout for an array
585 with an odd number of devices).
586
587 When an array is converted between RAID5 and RAID6 an intermediate
588 RAID6 layout is used in which the second parity block (Q) is always on
589 the last device. To convert a RAID5 to RAID6 and leave it in this new
590 layout (which does not require re-striping) use
591 .BR \-\-layout=preserve .
592 This will try to avoid any restriping.
593
594 The converse of this is
595 .B \-\-layout=normalise
596 which will change a non-standard RAID6 layout into a more standard
597 arrangement.
598
599 .TP
600 .BR \-\-parity=
601 same as
602 .B \-\-layout
603 (thus explaining the p of
604 .BR \-p ).
605
606 .TP
607 .BR \-b ", " \-\-bitmap=
608 Specify a file to store a write-intent bitmap in. The file should not
609 exist unless
610 .B \-\-force
611 is also given. The same file should be provided
612 when assembling the array. If the word
613 .B "internal"
614 is given, then the bitmap is stored with the metadata on the array,
615 and so is replicated on all devices. If the word
616 .B "none"
617 is given with
618 .B \-\-grow
619 mode, then any bitmap that is present is removed.
620
621 To help catch typing errors, the filename must contain at least one
622 slash ('/') if it is a real file (not 'internal' or 'none').
623
624 Note: external bitmaps are only known to work on ext2 and ext3.
625 Storing bitmap files on other filesystems may result in serious problems.
626
627 .TP
628 .BR \-\-bitmap\-chunk=
629 Set the chunksize of the bitmap. Each bit corresponds to that many
630 Kilobytes of storage.
631 When using a file based bitmap, the default is to use the smallest
632 size that is at-least 4 and requires no more than 2^21 chunks.
633 When using an
634 .B internal
635 bitmap, the chunksize defaults to 64Meg, or larger if necessary to
636 fit the bitmap into the available space.
637
638 A suffix of 'M' or 'G' can be given to indicate Megabytes or
639 Gigabytes respectively.
640
641 .TP
642 .BR \-W ", " \-\-write\-mostly
643 subsequent devices listed in a
644 .BR \-\-build ,
645 .BR \-\-create ,
646 or
647 .B \-\-add
648 command will be flagged as 'write-mostly'. This is valid for RAID1
649 only and means that the 'md' driver will avoid reading from these
650 devices if at all possible. This can be useful if mirroring over a
651 slow link.
652
653 .TP
654 .BR \-\-write\-behind=
655 Specify that write-behind mode should be enabled (valid for RAID1
656 only). If an argument is specified, it will set the maximum number
657 of outstanding writes allowed. The default value is 256.
658 A write-intent bitmap is required in order to use write-behind
659 mode, and write-behind is only attempted on drives marked as
660 .IR write-mostly .
661
662 .TP
663 .BR \-\-assume\-clean
664 Tell
665 .I mdadm
666 that the array pre-existed and is known to be clean. It can be useful
667 when trying to recover from a major failure as you can be sure that no
668 data will be affected unless you actually write to the array. It can
669 also be used when creating a RAID1 or RAID10 if you want to avoid the
670 initial resync, however this practice \(em while normally safe \(em is not
671 recommended. Use this only if you really know what you are doing.
672 .IP
673 When the devices that will be part of a new array were filled
674 with zeros before creation the operator knows the array is
675 actually clean. If that is the case, such as after running
676 badblocks, this argument can be used to tell mdadm the
677 facts the operator knows.
678
679 .TP
680 .BR \-\-backup\-file=
681 This is needed when
682 .B \-\-grow
683 is used to increase the number of raid-devices in a RAID5 or RAID6 if
684 there are no spare devices available, or to shrink, change RAID level
685 or layout. See the GROW MODE section below on RAID\-DEVICES CHANGES.
686 The file must be stored on a separate device, not on the RAID array
687 being reshaped.
688
689 .TP
690 .BR \-N ", " \-\-name=
691 Set a
692 .B name
693 for the array. This is currently only effective when creating an
694 array with a version-1 superblock, or an array in a DDF container.
695 The name is a simple textual string that can be used to identify array
696 components when assembling. If name is needed but not specified, it
697 is taken from the basename of the device that is being created.
698 e.g. when creating
699 .I /dev/md/home
700 the
701 .B name
702 will default to
703 .IR home .
704
705 .TP
706 .BR \-R ", " \-\-run
707 Insist that
708 .I mdadm
709 run the array, even if some of the components
710 appear to be active in another array or filesystem. Normally
711 .I mdadm
712 will ask for confirmation before including such components in an
713 array. This option causes that question to be suppressed.
714
715 .TP
716 .BR \-f ", " \-\-force
717 Insist that
718 .I mdadm
719 accept the geometry and layout specified without question. Normally
720 .I mdadm
721 will not allow creation of an array with only one device, and will try
722 to create a RAID5 array with one missing drive (as this makes the
723 initial resync work faster). With
724 .BR \-\-force ,
725 .I mdadm
726 will not try to be so clever.
727
728 .TP
729 .BR \-a ", " "\-\-auto{=yes,md,mdp,part,p}{NN}"
730 Instruct mdadm how to create the device file if needed, possibly allocating
731 an unused minor number. "md" causes a non-partitionable array
732 to be used (though since Linux 2.6.28, these array devices are in fact
733 partitionable). "mdp", "part" or "p" causes a partitionable array (2.6 and
734 later) to be used. "yes" requires the named md device to have
735 a 'standard' format, and the type and minor number will be determined
736 from this. With mdadm 3.0, device creation is normally left up to
737 .I udev
738 so this option is unlikely to be needed.
739 See DEVICE NAMES below.
740
741 The argument can also come immediately after
742 "\-a". e.g. "\-ap".
743
744 If
745 .B \-\-auto
746 is not given on the command line or in the config file, then
747 the default will be
748 .BR \-\-auto=yes .
749
750 If
751 .B \-\-scan
752 is also given, then any
753 .I auto=
754 entries in the config file will override the
755 .B \-\-auto
756 instruction given on the command line.
757
758 For partitionable arrays,
759 .I mdadm
760 will create the device file for the whole array and for the first 4
761 partitions. A different number of partitions can be specified at the
762 end of this option (e.g.
763 .BR \-\-auto=p7 ).
764 If the device name ends with a digit, the partition names add a 'p',
765 and a number, e.g.
766 .IR /dev/md/home1p3 .
767 If there is no trailing digit, then the partition names just have a
768 number added, e.g.
769 .IR /dev/md/scratch3 .
770
771 If the md device name is in a 'standard' format as described in DEVICE
772 NAMES, then it will be created, if necessary, with the appropriate
773 device number based on that name. If the device name is not in one of these
774 formats, then a unused device number will be allocated. The device
775 number will be considered unused if there is no active array for that
776 number, and there is no entry in /dev for that number and with a
777 non-standard name. Names that are not in 'standard' format are only
778 allowed in "/dev/md/".
779
780 .ig XX
781 .\".TP
782 .\".BR \-\-symlink = no
783 .\"Normally when
784 .\".B \-\-auto
785 .\"causes
786 .\".I mdadm
787 .\"to create devices in
788 .\".B /dev/md/
789 .\"it will also create symlinks from
790 .\".B /dev/
791 .\"with names starting with
792 .\".B md
793 .\"or
794 .\".BR md_ .
795 .\"Use
796 .\".B \-\-symlink=no
797 .\"to suppress this, or
798 .\".B \-\-symlink=yes
799 .\"to enforce this even if it is suppressing
800 .\".IR mdadm.conf .
801 .\"
802 .XX
803
804 .SH For assemble:
805
806 .TP
807 .BR \-u ", " \-\-uuid=
808 uuid of array to assemble. Devices which don't have this uuid are
809 excluded
810
811 .TP
812 .BR \-m ", " \-\-super\-minor=
813 Minor number of device that array was created for. Devices which
814 don't have this minor number are excluded. If you create an array as
815 /dev/md1, then all superblocks will contain the minor number 1, even if
816 the array is later assembled as /dev/md2.
817
818 Giving the literal word "dev" for
819 .B \-\-super\-minor
820 will cause
821 .I mdadm
822 to use the minor number of the md device that is being assembled.
823 e.g. when assembling
824 .BR /dev/md0 ,
825 .B \-\-super\-minor=dev
826 will look for super blocks with a minor number of 0.
827
828 .B \-\-super\-minor
829 is only relevant for v0.90 metadata, and should not normally be used.
830 Using
831 .B \-\-uuid
832 is much safer.
833
834 .TP
835 .BR \-N ", " \-\-name=
836 Specify the name of the array to assemble. This must be the name
837 that was specified when creating the array. It must either match
838 the name stored in the superblock exactly, or it must match
839 with the current
840 .I homehost
841 prefixed to the start of the given name.
842
843 .TP
844 .BR \-f ", " \-\-force
845 Assemble the array even if the metadata on some devices appears to be
846 out-of-date. If
847 .I mdadm
848 cannot find enough working devices to start the array, but can find
849 some devices that are recorded as having failed, then it will mark
850 those devices as working so that the array can be started.
851 An array which requires
852 .B \-\-force
853 to be started may contain data corruption. Use it carefully.
854
855 .TP
856 .BR \-R ", " \-\-run
857 Attempt to start the array even if fewer drives were given than were
858 present last time the array was active. Normally if not all the
859 expected drives are found and
860 .B \-\-scan
861 is not used, then the array will be assembled but not started.
862 With
863 .B \-\-run
864 an attempt will be made to start it anyway.
865
866 .TP
867 .B \-\-no\-degraded
868 This is the reverse of
869 .B \-\-run
870 in that it inhibits the startup of array unless all expected drives
871 are present. This is only needed with
872 .B \-\-scan,
873 and can be used if the physical connections to devices are
874 not as reliable as you would like.
875
876 .TP
877 .BR \-a ", " "\-\-auto{=no,yes,md,mdp,part}"
878 See this option under Create and Build options.
879
880 .TP
881 .BR \-b ", " \-\-bitmap=
882 Specify the bitmap file that was given when the array was created. If
883 an array has an
884 .B internal
885 bitmap, there is no need to specify this when assembling the array.
886
887 .TP
888 .BR \-\-backup\-file=
889 If
890 .B \-\-backup\-file
891 was used while reshaping an array (e.g. changing number of devices or
892 chunk size) and the system crashed during the critical section, then the same
893 .B \-\-backup\-file
894 must be presented to
895 .B \-\-assemble
896 to allow possibly corrupted data to be restored, and the reshape
897 to be completed.
898
899 .TP
900 .BR \-\-invalid\-backup
901 If the file needed for the above option is not available for any
902 reason an empty file can be given together with this option to
903 indicate that the backup file is invalid. In this case the data that
904 was being rearranged at the time of the crash could be irrecoverably
905 lost, but the rest of the array may still be recoverable. This option
906 should only be used as a last resort if there is no way to recover the
907 backup file.
908
909
910 .TP
911 .BR \-U ", " \-\-update=
912 Update the superblock on each device while assembling the array. The
913 argument given to this flag can be one of
914 .BR sparc2.2 ,
915 .BR summaries ,
916 .BR uuid ,
917 .BR name ,
918 .BR homehost ,
919 .BR resync ,
920 .BR byteorder ,
921 .BR devicesize ,
922 .BR no\-bitmap ,
923 or
924 .BR super\-minor .
925
926 The
927 .B sparc2.2
928 option will adjust the superblock of an array what was created on a Sparc
929 machine running a patched 2.2 Linux kernel. This kernel got the
930 alignment of part of the superblock wrong. You can use the
931 .B "\-\-examine \-\-sparc2.2"
932 option to
933 .I mdadm
934 to see what effect this would have.
935
936 The
937 .B super\-minor
938 option will update the
939 .B "preferred minor"
940 field on each superblock to match the minor number of the array being
941 assembled.
942 This can be useful if
943 .B \-\-examine
944 reports a different "Preferred Minor" to
945 .BR \-\-detail .
946 In some cases this update will be performed automatically
947 by the kernel driver. In particular the update happens automatically
948 at the first write to an array with redundancy (RAID level 1 or
949 greater) on a 2.6 (or later) kernel.
950
951 The
952 .B uuid
953 option will change the uuid of the array. If a UUID is given with the
954 .B \-\-uuid
955 option that UUID will be used as a new UUID and will
956 .B NOT
957 be used to help identify the devices in the array.
958 If no
959 .B \-\-uuid
960 is given, a random UUID is chosen.
961
962 The
963 .B name
964 option will change the
965 .I name
966 of the array as stored in the superblock. This is only supported for
967 version-1 superblocks.
968
969 The
970 .B homehost
971 option will change the
972 .I homehost
973 as recorded in the superblock. For version-0 superblocks, this is the
974 same as updating the UUID.
975 For version-1 superblocks, this involves updating the name.
976
977 The
978 .B resync
979 option will cause the array to be marked
980 .I dirty
981 meaning that any redundancy in the array (e.g. parity for RAID5,
982 copies for RAID1) may be incorrect. This will cause the RAID system
983 to perform a "resync" pass to make sure that all redundant information
984 is correct.
985
986 The
987 .B byteorder
988 option allows arrays to be moved between machines with different
989 byte-order.
990 When assembling such an array for the first time after a move, giving
991 .B "\-\-update=byteorder"
992 will cause
993 .I mdadm
994 to expect superblocks to have their byteorder reversed, and will
995 correct that order before assembling the array. This is only valid
996 with original (Version 0.90) superblocks.
997
998 The
999 .B summaries
1000 option will correct the summaries in the superblock. That is the
1001 counts of total, working, active, failed, and spare devices.
1002
1003 The
1004 .B devicesize
1005 option will rarely be of use. It applies to version 1.1 and 1.2 metadata
1006 only (where the metadata is at the start of the device) and is only
1007 useful when the component device has changed size (typically become
1008 larger). The version 1 metadata records the amount of the device that
1009 can be used to store data, so if a device in a version 1.1 or 1.2
1010 array becomes larger, the metadata will still be visible, but the
1011 extra space will not. In this case it might be useful to assemble the
1012 array with
1013 .BR \-\-update=devicesize .
1014 This will cause
1015 .I mdadm
1016 to determine the maximum usable amount of space on each device and
1017 update the relevant field in the metadata.
1018
1019 The
1020 .B no\-bitmap
1021 option can be used when an array has an internal bitmap which is
1022 corrupt in some way so that assembling the array normally fails. It
1023 will cause any internal bitmap to be ignored.
1024
1025 .ig
1026 .TP
1027 .B \-\-auto\-update\-homehost
1028 This flag is only meaningful with auto-assembly (see discussion below).
1029 In that situation, if no suitable arrays are found for this homehost,
1030 .I mdadm
1031 will rescan for any arrays at all and will assemble them and update the
1032 homehost to match the current host.
1033 ..
1034
1035 .SH For Manage mode:
1036
1037 .TP
1038 .BR \-t ", " \-\-test
1039 Unless a more serious error occurred,
1040 .I mdadm
1041 will exit with a status of 2 if no changes were made to the array and
1042 0 if at least one change was made.
1043 This can be useful when an indirect specifier such as
1044 .BR missing ,
1045 .B detached
1046 or
1047 .B faulty
1048 is used in requesting an operation on the array.
1049 .B \-\-test
1050 will report failure if these specifiers didn't find any match.
1051
1052 .TP
1053 .BR \-a ", " \-\-add
1054 hot-add listed devices.
1055 If a device appears to have recently been part of the array
1056 (possibly it failed or was removed) the device is re\-added as describe
1057 in the next point.
1058 If that fails or the device was never part of the array, the device is
1059 added as a hot-spare.
1060 If the array is degraded, it will immediately start to rebuild data
1061 onto that spare.
1062
1063 Note that this and the following options are only meaningful on array
1064 with redundancy. They don't apply to RAID0 or Linear.
1065
1066 .TP
1067 .BR \-\-re\-add
1068 re\-add a device that was previous removed from an array.
1069 If the metadata on the device reports that it is a member of the
1070 array, and the slot that it used is still vacant, then the device will
1071 be added back to the array in the same position. This will normally
1072 cause the data for that device to be recovered. However based on the
1073 event count on the device, the recovery may only require sections that
1074 are flagged a write-intent bitmap to be recovered or may not require
1075 any recovery at all.
1076
1077 When used on an array that has no metadata (i.e. it was built with
1078 .BR \-\-build)
1079 it will be assumed that bitmap-based recovery is enough to make the
1080 device fully consistent with the array.
1081
1082 When
1083 .B \-\-re\-add
1084 can be accompanied by
1085 .BR \-\-update=devicesize .
1086 See the description of this option when used in Assemble mode for an
1087 explanation of its use.
1088
1089 If the device name given is
1090 .B missing
1091 then mdadm will try to find any device that looks like it should be
1092 part of the array but isn't and will try to re\-add all such devices.
1093
1094 .TP
1095 .BR \-r ", " \-\-remove
1096 remove listed devices. They must not be active. i.e. they should
1097 be failed or spare devices. As well as the name of a device file
1098 (e.g.
1099 .BR /dev/sda1 )
1100 the words
1101 .B failed
1102 and
1103 .B detached
1104 can be given to
1105 .BR \-\-remove .
1106 The first causes all failed device to be removed. The second causes
1107 any device which is no longer connected to the system (i.e an 'open'
1108 returns
1109 .BR ENXIO )
1110 to be removed. This will only succeed for devices that are spares or
1111 have already been marked as failed.
1112
1113 .TP
1114 .BR \-f ", " \-\-fail
1115 mark listed devices as faulty.
1116 As well as the name of a device file, the word
1117 .B detached
1118 can be given. This will cause any device that has been detached from
1119 the system to be marked as failed. It can then be removed.
1120
1121 .TP
1122 .BR \-\-set\-faulty
1123 same as
1124 .BR \-\-fail .
1125
1126 .TP
1127 .BR \-\-write\-mostly
1128 Subsequent devices that are added or re\-added will have the 'write-mostly'
1129 flag set. This is only valid for RAID1 and means that the 'md' driver
1130 will avoid reading from these devices if possible.
1131 .TP
1132 .BR \-\-readwrite
1133 Subsequent devices that are added or re\-added will have the 'write-mostly'
1134 flag cleared.
1135
1136 .P
1137 Each of these options requires that the first device listed is the array
1138 to be acted upon, and the remainder are component devices to be added,
1139 removed, marked as faulty, etc. Several different operations can be
1140 specified for different devices, e.g.
1141 .in +5
1142 mdadm /dev/md0 \-\-add /dev/sda1 \-\-fail /dev/sdb1 \-\-remove /dev/sdb1
1143 .in -5
1144 Each operation applies to all devices listed until the next
1145 operation.
1146
1147 If an array is using a write-intent bitmap, then devices which have
1148 been removed can be re\-added in a way that avoids a full
1149 reconstruction but instead just updates the blocks that have changed
1150 since the device was removed. For arrays with persistent metadata
1151 (superblocks) this is done automatically. For arrays created with
1152 .B \-\-build
1153 mdadm needs to be told that this device we removed recently with
1154 .BR \-\-re\-add .
1155
1156 Devices can only be removed from an array if they are not in active
1157 use, i.e. that must be spares or failed devices. To remove an active
1158 device, it must first be marked as
1159 .B faulty.
1160
1161 .SH For Misc mode:
1162
1163 .TP
1164 .BR \-Q ", " \-\-query
1165 Examine a device to see
1166 (1) if it is an md device and (2) if it is a component of an md
1167 array.
1168 Information about what is discovered is presented.
1169
1170 .TP
1171 .BR \-D ", " \-\-detail
1172 Print details of one or more md devices.
1173
1174 .TP
1175 .BR \-\-detail\-platform
1176 Print details of the platform's RAID capabilities (firmware / hardware
1177 topology) for a given metadata format.
1178
1179 .TP
1180 .BR \-Y ", " \-\-export
1181 When used with
1182 .B \-\-detail
1183 or
1184 .BR \-\-examine ,
1185 output will be formatted as
1186 .B key=value
1187 pairs for easy import into the environment.
1188
1189 .TP
1190 .BR \-E ", " \-\-examine
1191 Print contents of the metadata stored on the named device(s).
1192 Note the contrast between
1193 .B \-\-examine
1194 and
1195 .BR \-\-detail .
1196 .B \-\-examine
1197 applies to devices which are components of an array, while
1198 .B \-\-detail
1199 applies to a whole array which is currently active.
1200 .TP
1201 .B \-\-sparc2.2
1202 If an array was created on a SPARC machine with a 2.2 Linux kernel
1203 patched with RAID support, the superblock will have been created
1204 incorrectly, or at least incompatibly with 2.4 and later kernels.
1205 Using the
1206 .B \-\-sparc2.2
1207 flag with
1208 .B \-\-examine
1209 will fix the superblock before displaying it. If this appears to do
1210 the right thing, then the array can be successfully assembled using
1211 .BR "\-\-assemble \-\-update=sparc2.2" .
1212
1213 .TP
1214 .BR \-X ", " \-\-examine\-bitmap
1215 Report information about a bitmap file.
1216 The argument is either an external bitmap file or an array component
1217 in case of an internal bitmap. Note that running this on an array
1218 device (e.g.
1219 .BR /dev/md0 )
1220 does not report the bitmap for that array.
1221
1222 .TP
1223 .BR \-R ", " \-\-run
1224 start a partially assembled array. If
1225 .B \-\-assemble
1226 did not find enough devices to fully start the array, it might leaving
1227 it partially assembled. If you wish, you can then use
1228 .B \-\-run
1229 to start the array in degraded mode.
1230
1231 .TP
1232 .BR \-S ", " \-\-stop
1233 deactivate array, releasing all resources.
1234
1235 .TP
1236 .BR \-o ", " \-\-readonly
1237 mark array as readonly.
1238
1239 .TP
1240 .BR \-w ", " \-\-readwrite
1241 mark array as readwrite.
1242
1243 .TP
1244 .B \-\-zero\-superblock
1245 If the device contains a valid md superblock, the block is
1246 overwritten with zeros. With
1247 .B \-\-force
1248 the block where the superblock would be is overwritten even if it
1249 doesn't appear to be valid.
1250
1251 .TP
1252 .B \-\-kill\-subarray=
1253 If the device is a container and the argument to \-\-kill\-subarray
1254 specifies an inactive subarray in the container, then the subarray is
1255 deleted. Deleting all subarrays will leave an 'empty-container' or
1256 spare superblock on the drives. See \-\-zero\-superblock for completely
1257 removing a superblock. Note that some formats depend on the subarray
1258 index for generating a UUID, this command will fail if it would change
1259 the UUID of an active subarray.
1260
1261 .TP
1262 .B \-\-update\-subarray=
1263 If the device is a container and the argument to \-\-update\-subarray
1264 specifies a subarray in the container, then attempt to update the given
1265 superblock field in the subarray. See below in
1266 .B MISC MODE
1267 for details.
1268
1269 .TP
1270 .BR \-t ", " \-\-test
1271 When used with
1272 .BR \-\-detail ,
1273 the exit status of
1274 .I mdadm
1275 is set to reflect the status of the device. See below in
1276 .B MISC MODE
1277 for details.
1278
1279 .TP
1280 .BR \-W ", " \-\-wait
1281 For each md device given, wait for any resync, recovery, or reshape
1282 activity to finish before returning.
1283 .I mdadm
1284 will return with success if it actually waited for every device
1285 listed, otherwise it will return failure.
1286
1287 .TP
1288 .BR \-\-wait\-clean
1289 For each md device given, or each device in /proc/mdstat if
1290 .B \-\-scan
1291 is given, arrange for the array to be marked clean as soon as possible.
1292 .I mdadm
1293 will return with success if the array uses external metadata and we
1294 successfully waited. For native arrays this returns immediately as the
1295 kernel handles dirty-clean transitions at shutdown. No action is taken
1296 if safe-mode handling is disabled.
1297
1298 .SH For Incremental Assembly mode:
1299 .TP
1300 .BR \-\-rebuild\-map ", " \-r
1301 Rebuild the map file
1302 .RB ( /var/run/mdadm/map )
1303 that
1304 .I mdadm
1305 uses to help track which arrays are currently being assembled.
1306
1307 .TP
1308 .BR \-\-run ", " \-R
1309 Run any array assembled as soon as a minimal number of devices are
1310 available, rather than waiting until all expected devices are present.
1311
1312 .TP
1313 .BR \-\-scan ", " \-s
1314 Only meaningful with
1315 .B \-R
1316 this will scan the
1317 .B map
1318 file for arrays that are being incrementally assembled and will try to
1319 start any that are not already started. If any such array is listed
1320 in
1321 .B mdadm.conf
1322 as requiring an external bitmap, that bitmap will be attached first.
1323
1324 .TP
1325 .BR \-\-fail ", " \-f
1326 This allows the hot-plug system to remove devices that have fully disappeared
1327 from the kernel. It will first fail and then remove the device from any
1328 array it belongs to.
1329 The device name given should be a kernel device name such as "sda",
1330 not a name in
1331 .IR /dev .
1332
1333 .SH For Monitor mode:
1334 .TP
1335 .BR \-m ", " \-\-mail
1336 Give a mail address to send alerts to.
1337
1338 .TP
1339 .BR \-p ", " \-\-program ", " \-\-alert
1340 Give a program to be run whenever an event is detected.
1341
1342 .TP
1343 .BR \-y ", " \-\-syslog
1344 Cause all events to be reported through 'syslog'. The messages have
1345 facility of 'daemon' and varying priorities.
1346
1347 .TP
1348 .BR \-d ", " \-\-delay
1349 Give a delay in seconds.
1350 .I mdadm
1351 polls the md arrays and then waits this many seconds before polling
1352 again. The default is 60 seconds. Since 2.6.16, there is no need to
1353 reduce this as the kernel alerts
1354 .I mdadm
1355 immediately when there is any change.
1356
1357 .TP
1358 .BR \-r ", " \-\-increment
1359 Give a percentage increment.
1360 .I mdadm
1361 will generate RebuildNN events with the given percentage increment.
1362
1363 .TP
1364 .BR \-f ", " \-\-daemonise
1365 Tell
1366 .I mdadm
1367 to run as a background daemon if it decides to monitor anything. This
1368 causes it to fork and run in the child, and to disconnect from the
1369 terminal. The process id of the child is written to stdout.
1370 This is useful with
1371 .B \-\-scan
1372 which will only continue monitoring if a mail address or alert program
1373 is found in the config file.
1374
1375 .TP
1376 .BR \-i ", " \-\-pid\-file
1377 When
1378 .I mdadm
1379 is running in daemon mode, write the pid of the daemon process to
1380 the specified file, instead of printing it on standard output.
1381
1382 .TP
1383 .BR \-1 ", " \-\-oneshot
1384 Check arrays only once. This will generate
1385 .B NewArray
1386 events and more significantly
1387 .B DegradedArray
1388 and
1389 .B SparesMissing
1390 events. Running
1391 .in +5
1392 .B " mdadm \-\-monitor \-\-scan \-1"
1393 .in -5
1394 from a cron script will ensure regular notification of any degraded arrays.
1395
1396 .TP
1397 .BR \-t ", " \-\-test
1398 Generate a
1399 .B TestMessage
1400 alert for every array found at startup. This alert gets mailed and
1401 passed to the alert program. This can be used for testing that alert
1402 message do get through successfully.
1403
1404 .SH ASSEMBLE MODE
1405
1406 .HP 12
1407 Usage:
1408 .B mdadm \-\-assemble
1409 .I md-device options-and-component-devices...
1410 .HP 12
1411 Usage:
1412 .B mdadm \-\-assemble \-\-scan
1413 .I md-devices-and-options...
1414 .HP 12
1415 Usage:
1416 .B mdadm \-\-assemble \-\-scan
1417 .I options...
1418
1419 .PP
1420 This usage assembles one or more RAID arrays from pre-existing components.
1421 For each array, mdadm needs to know the md device, the identity of the
1422 array, and a number of component-devices. These can be found in a number of ways.
1423
1424 In the first usage example (without the
1425 .BR \-\-scan )
1426 the first device given is the md device.
1427 In the second usage example, all devices listed are treated as md
1428 devices and assembly is attempted.
1429 In the third (where no devices are listed) all md devices that are
1430 listed in the configuration file are assembled. If not arrays are
1431 described by the configuration file, then any arrays that
1432 can be found on unused devices will be assembled.
1433
1434 If precisely one device is listed, but
1435 .B \-\-scan
1436 is not given, then
1437 .I mdadm
1438 acts as though
1439 .B \-\-scan
1440 was given and identity information is extracted from the configuration file.
1441
1442 The identity can be given with the
1443 .B \-\-uuid
1444 option, the
1445 .B \-\-name
1446 option, or the
1447 .B \-\-super\-minor
1448 option, will be taken from the md-device record in the config file, or
1449 will be taken from the super block of the first component-device
1450 listed on the command line.
1451
1452 Devices can be given on the
1453 .B \-\-assemble
1454 command line or in the config file. Only devices which have an md
1455 superblock which contains the right identity will be considered for
1456 any array.
1457
1458 The config file is only used if explicitly named with
1459 .B \-\-config
1460 or requested with (a possibly implicit)
1461 .BR \-\-scan .
1462 In the later case,
1463 .B /etc/mdadm.conf
1464 or
1465 .B /etc/mdadm/mdadm.conf
1466 is used.
1467
1468 If
1469 .B \-\-scan
1470 is not given, then the config file will only be used to find the
1471 identity of md arrays.
1472
1473 Normally the array will be started after it is assembled. However if
1474 .B \-\-scan
1475 is not given and not all expected drives were listed, then the array
1476 is not started (to guard against usage errors). To insist that the
1477 array be started in this case (as may work for RAID1, 4, 5, 6, or 10),
1478 give the
1479 .B \-\-run
1480 flag.
1481
1482 If
1483 .I udev
1484 is active,
1485 .I mdadm
1486 does not create any entries in
1487 .B /dev
1488 but leaves that to
1489 .IR udev .
1490 It does record information in
1491 .B /var/run/mdadm/map
1492 which will allow
1493 .I udev
1494 to choose the correct name.
1495
1496 If
1497 .I mdadm
1498 detects that udev is not configured, it will create the devices in
1499 .B /dev
1500 itself.
1501
1502 In Linux kernels prior to version 2.6.28 there were two distinctly
1503 different types of md devices that could be created: one that could be
1504 partitioned using standard partitioning tools and one that could not.
1505 Since 2.6.28 that distinction is no longer relevant as both type of
1506 devices can be partitioned.
1507 .I mdadm
1508 will normally create the type that originally could not be partitioned
1509 as it has a well defined major number (9).
1510
1511 Prior to 2.6.28, it is important that mdadm chooses the correct type
1512 of array device to use. This can be controlled with the
1513 .B \-\-auto
1514 option. In particular, a value of "mdp" or "part" or "p" tells mdadm
1515 to use a partitionable device rather than the default.
1516
1517 In the no-udev case, the value given to
1518 .B \-\-auto
1519 can be suffixed by a number. This tells
1520 .I mdadm
1521 to create that number of partition devices rather than the default of 4.
1522
1523 The value given to
1524 .B \-\-auto
1525 can also be given in the configuration file as a word starting
1526 .B auto=
1527 on the ARRAY line for the relevant array.
1528
1529 .SS Auto Assembly
1530 When
1531 .B \-\-assemble
1532 is used with
1533 .B \-\-scan
1534 and no devices are listed,
1535 .I mdadm
1536 will first attempt to assemble all the arrays listed in the config
1537 file.
1538
1539 In no array at listed in the config (other than those marked
1540 .BR <ignore> )
1541 it will look through the available devices for possible arrays and
1542 will try to assemble anything that it finds. Arrays which are tagged
1543 as belonging to the given homehost will be assembled and started
1544 normally. Arrays which do not obviously belong to this host are given
1545 names that are expected not to conflict with anything local, and are
1546 started "read-auto" so that nothing is written to any device until the
1547 array is written to. i.e. automatic resync etc is delayed.
1548
1549 If
1550 .I mdadm
1551 finds a consistent set of devices that look like they should comprise
1552 an array, and if the superblock is tagged as belonging to the given
1553 home host, it will automatically choose a device name and try to
1554 assemble the array. If the array uses version-0.90 metadata, then the
1555 .B minor
1556 number as recorded in the superblock is used to create a name in
1557 .B /dev/md/
1558 so for example
1559 .BR /dev/md/3 .
1560 If the array uses version-1 metadata, then the
1561 .B name
1562 from the superblock is used to similarly create a name in
1563 .B /dev/md/
1564 (the name will have any 'host' prefix stripped first).
1565
1566 This behaviour can be modified by the
1567 .I AUTO
1568 line in the
1569 .I mdadm.conf
1570 configuration file. This line can indicate that specific metadata
1571 type should, or should not, be automatically assembled. If an array
1572 is found which is not listed in
1573 .I mdadm.conf
1574 and has a metadata format that is denied by the
1575 .I AUTO
1576 line, then it will not be assembled.
1577 The
1578 .I AUTO
1579 line can also request that all arrays identified as being for this
1580 homehost should be assembled regardless of their metadata type.
1581 See
1582 .IR mdadm.conf (5)
1583 for further details.
1584
1585 .ig
1586 If
1587 .I mdadm
1588 cannot find any array for the given host at all, and if
1589 .B \-\-auto\-update\-homehost
1590 is given, then
1591 .I mdadm
1592 will search again for any array (not just an array created for this
1593 host) and will assemble each assuming
1594 .BR \-\-update=homehost .
1595 This will change the host tag in the superblock so that on the next run,
1596 these arrays will be found without the second pass. The intention of
1597 this feature is to support transitioning a set of md arrays to using
1598 homehost tagging.
1599
1600 The reason for requiring arrays to be tagged with the homehost for
1601 auto assembly is to guard against problems that can arise when moving
1602 devices from one host to another.
1603 ..
1604
1605 .SH BUILD MODE
1606
1607 .HP 12
1608 Usage:
1609 .B mdadm \-\-build
1610 .I md-device
1611 .BI \-\-chunk= X
1612 .BI \-\-level= Y
1613 .BI \-\-raid\-devices= Z
1614 .I devices
1615
1616 .PP
1617 This usage is similar to
1618 .BR \-\-create .
1619 The difference is that it creates an array without a superblock. With
1620 these arrays there is no difference between initially creating the array and
1621 subsequently assembling the array, except that hopefully there is useful
1622 data there in the second case.
1623
1624 The level may raid0, linear, raid1, raid10, multipath, or faulty, or
1625 one of their synonyms. All devices must be listed and the array will
1626 be started once complete. It will often be appropriate to use
1627 .B \-\-assume\-clean
1628 with levels raid1 or raid10.
1629
1630 .SH CREATE MODE
1631
1632 .HP 12
1633 Usage:
1634 .B mdadm \-\-create
1635 .I md-device
1636 .BI \-\-chunk= X
1637 .BI \-\-level= Y
1638 .br
1639 .BI \-\-raid\-devices= Z
1640 .I devices
1641
1642 .PP
1643 This usage will initialise a new md array, associate some devices with
1644 it, and activate the array.
1645
1646 The named device will normally not exist when
1647 .I "mdadm \-\-create"
1648 is run, but will be created by
1649 .I udev
1650 once the array becomes active.
1651
1652 As devices are added, they are checked to see if they contain RAID
1653 superblocks or filesystems. They are also checked to see if the variance in
1654 device size exceeds 1%.
1655
1656 If any discrepancy is found, the array will not automatically be run, though
1657 the presence of a
1658 .B \-\-run
1659 can override this caution.
1660
1661 To create a "degraded" array in which some devices are missing, simply
1662 give the word "\fBmissing\fP"
1663 in place of a device name. This will cause
1664 .I mdadm
1665 to leave the corresponding slot in the array empty.
1666 For a RAID4 or RAID5 array at most one slot can be
1667 "\fBmissing\fP"; for a RAID6 array at most two slots.
1668 For a RAID1 array, only one real device needs to be given. All of the
1669 others can be
1670 "\fBmissing\fP".
1671
1672 When creating a RAID5 array,
1673 .I mdadm
1674 will automatically create a degraded array with an extra spare drive.
1675 This is because building the spare into a degraded array is in general
1676 faster than resyncing the parity on a non-degraded, but not clean,
1677 array. This feature can be overridden with the
1678 .B \-\-force
1679 option.
1680
1681 When creating an array with version-1 metadata a name for the array is
1682 required.
1683 If this is not given with the
1684 .B \-\-name
1685 option,
1686 .I mdadm
1687 will choose a name based on the last component of the name of the
1688 device being created. So if
1689 .B /dev/md3
1690 is being created, then the name
1691 .B 3
1692 will be chosen.
1693 If
1694 .B /dev/md/home
1695 is being created, then the name
1696 .B home
1697 will be used.
1698
1699 When creating a partition based array, using
1700 .I mdadm
1701 with version-1.x metadata, the partition type should be set to
1702 .B 0xDA
1703 (non fs-data). This type selection allows for greater precision since
1704 using any other [RAID auto-detect (0xFD) or a GNU/Linux partition (0x83)],
1705 might create problems in the event of array recovery through a live cdrom.
1706
1707 A new array will normally get a randomly assigned 128bit UUID which is
1708 very likely to be unique. If you have a specific need, you can choose
1709 a UUID for the array by giving the
1710 .B \-\-uuid=
1711 option. Be warned that creating two arrays with the same UUID is a
1712 recipe for disaster. Also, using
1713 .B \-\-uuid=
1714 when creating a v0.90 array will silently override any
1715 .B \-\-homehost=
1716 setting.
1717 .\"If the
1718 .\".B \-\-size
1719 .\"option is given, it is not necessary to list any component-devices in this command.
1720 .\"They can be added later, before a
1721 .\".B \-\-run.
1722 .\"If no
1723 .\".B \-\-size
1724 .\"is given, the apparent size of the smallest drive given is used.
1725
1726 When creating an array within a
1727 .B CONTAINER
1728 .I mdadm
1729 can be given either the list of devices to use, or simply the name of
1730 the container. The former case gives control over which devices in
1731 the container will be used for the array. The latter case allows
1732 .I mdadm
1733 to automatically choose which devices to use based on how much spare
1734 space is available.
1735
1736 The General Management options that are valid with
1737 .B \-\-create
1738 are:
1739 .TP
1740 .B \-\-run
1741 insist on running the array even if some devices look like they might
1742 be in use.
1743
1744 .TP
1745 .B \-\-readonly
1746 start the array readonly \(em not supported yet.
1747
1748 .SH MANAGE MODE
1749 .HP 12
1750 Usage:
1751 .B mdadm
1752 .I device
1753 .I options... devices...
1754 .PP
1755
1756 This usage will allow individual devices in an array to be failed,
1757 removed or added. It is possible to perform multiple operations with
1758 on command. For example:
1759 .br
1760 .B " mdadm /dev/md0 \-f /dev/hda1 \-r /dev/hda1 \-a /dev/hda1"
1761 .br
1762 will firstly mark
1763 .B /dev/hda1
1764 as faulty in
1765 .B /dev/md0
1766 and will then remove it from the array and finally add it back
1767 in as a spare. However only one md array can be affected by a single
1768 command.
1769
1770 When a device is added to an active array, mdadm checks to see if it
1771 has metadata on it which suggests that it was recently a member of the
1772 array. If it does, it tries to "re\-add" the device. If there have
1773 been no changes since the device was removed, or if the array has a
1774 write-intent bitmap which has recorded whatever changes there were,
1775 then the device will immediately become a full member of the array and
1776 those differences recorded in the bitmap will be resolved.
1777
1778 .SH MISC MODE
1779 .HP 12
1780 Usage:
1781 .B mdadm
1782 .I options ...
1783 .I devices ...
1784 .PP
1785
1786 MISC mode includes a number of distinct operations that
1787 operate on distinct devices. The operations are:
1788 .TP
1789 .B \-\-query
1790 The device is examined to see if it is
1791 (1) an active md array, or
1792 (2) a component of an md array.
1793 The information discovered is reported.
1794
1795 .TP
1796 .B \-\-detail
1797 The device should be an active md device.
1798 .B mdadm
1799 will display a detailed description of the array.
1800 .B \-\-brief
1801 or
1802 .B \-\-scan
1803 will cause the output to be less detailed and the format to be
1804 suitable for inclusion in
1805 .BR /etc/mdadm.conf .
1806 The exit status of
1807 .I mdadm
1808 will normally be 0 unless
1809 .I mdadm
1810 failed to get useful information about the device(s); however, if the
1811 .B \-\-test
1812 option is given, then the exit status will be:
1813 .RS
1814 .TP
1815 0
1816 The array is functioning normally.
1817 .TP
1818 1
1819 The array has at least one failed device.
1820 .TP
1821 2
1822 The array has multiple failed devices such that it is unusable.
1823 .TP
1824 4
1825 There was an error while trying to get information about the device.
1826 .RE
1827
1828 .TP
1829 .B \-\-detail\-platform
1830 Print detail of the platform's RAID capabilities (firmware / hardware
1831 topology). If the metadata is specified with
1832 .B \-e
1833 or
1834 .B \-\-metadata=
1835 then the return status will be:
1836 .RS
1837 .TP
1838 0
1839 metadata successfully enumerated its platform components on this system
1840 .TP
1841 1
1842 metadata is platform independent
1843 .TP
1844 2
1845 metadata failed to find its platform components on this system
1846 .RE
1847
1848 .TP
1849 .B \-\-update\-subarray=
1850 If the device is a container and the argument to \-\-update\-subarray
1851 specifies a subarray in the container, then attempt to update the given
1852 superblock field in the subarray. Similar to updating an array in
1853 "assemble" mode, the field to update is selected by
1854 .B \-U
1855 or
1856 .B \-\-update=
1857 option. Currently only
1858 .B name
1859 is supported.
1860
1861 The
1862 .B name
1863 option updates the subarray name in the metadata, it may not affect the
1864 device node name or the device node symlink until the subarray is
1865 re\-assembled. If updating
1866 .B name
1867 would change the UUID of an active subarray this operation is blocked,
1868 and the command will end in an error.
1869
1870 .TP
1871 .B \-\-examine
1872 The device should be a component of an md array.
1873 .I mdadm
1874 will read the md superblock of the device and display the contents.
1875 If
1876 .B \-\-brief
1877 or
1878 .B \-\-scan
1879 is given, then multiple devices that are components of the one array
1880 are grouped together and reported in a single entry suitable
1881 for inclusion in
1882 .BR /etc/mdadm.conf .
1883
1884 Having
1885 .B \-\-scan
1886 without listing any devices will cause all devices listed in the
1887 config file to be examined.
1888
1889 .TP
1890 .B \-\-stop
1891 The devices should be active md arrays which will be deactivated, as
1892 long as they are not currently in use.
1893
1894 .TP
1895 .B \-\-run
1896 This will fully activate a partially assembled md array.
1897
1898 .TP
1899 .B \-\-readonly
1900 This will mark an active array as read-only, providing that it is
1901 not currently being used.
1902
1903 .TP
1904 .B \-\-readwrite
1905 This will change a
1906 .B readonly
1907 array back to being read/write.
1908
1909 .TP
1910 .B \-\-scan
1911 For all operations except
1912 .BR \-\-examine ,
1913 .B \-\-scan
1914 will cause the operation to be applied to all arrays listed in
1915 .BR /proc/mdstat .
1916 For
1917 .BR \-\-examine,
1918 .B \-\-scan
1919 causes all devices listed in the config file to be examined.
1920
1921 .TP
1922 .BR \-b ", " \-\-brief
1923 Be less verbose. This is used with
1924 .B \-\-detail
1925 and
1926 .BR \-\-examine .
1927 Using
1928 .B \-\-brief
1929 with
1930 .B \-\-verbose
1931 gives an intermediate level of verbosity.
1932
1933 .SH MONITOR MODE
1934
1935 .HP 12
1936 Usage:
1937 .B mdadm \-\-monitor
1938 .I options... devices...
1939
1940 .PP
1941 This usage causes
1942 .I mdadm
1943 to periodically poll a number of md arrays and to report on any events
1944 noticed.
1945 .I mdadm
1946 will never exit once it decides that there are arrays to be checked,
1947 so it should normally be run in the background.
1948
1949 As well as reporting events,
1950 .I mdadm
1951 may move a spare drive from one array to another if they are in the
1952 same
1953 .B spare-group
1954 and if the destination array has a failed drive but no spares.
1955
1956 If any devices are listed on the command line,
1957 .I mdadm
1958 will only monitor those devices. Otherwise all arrays listed in the
1959 configuration file will be monitored. Further, if
1960 .B \-\-scan
1961 is given, then any other md devices that appear in
1962 .B /proc/mdstat
1963 will also be monitored.
1964
1965 The result of monitoring the arrays is the generation of events.
1966 These events are passed to a separate program (if specified) and may
1967 be mailed to a given E-mail address.
1968
1969 When passing events to a program, the program is run once for each event,
1970 and is given 2 or 3 command-line arguments: the first is the
1971 name of the event (see below), the second is the name of the
1972 md device which is affected, and the third is the name of a related
1973 device if relevant (such as a component device that has failed).
1974
1975 If
1976 .B \-\-scan
1977 is given, then a program or an E-mail address must be specified on the
1978 command line or in the config file. If neither are available, then
1979 .I mdadm
1980 will not monitor anything.
1981 Without
1982 .B \-\-scan,
1983 .I mdadm
1984 will continue monitoring as long as something was found to monitor. If
1985 no program or email is given, then each event is reported to
1986 .BR stdout .
1987
1988 The different events are:
1989
1990 .RS 4
1991 .TP
1992 .B DeviceDisappeared
1993 An md array which previously was configured appears to no longer be
1994 configured. (syslog priority: Critical)
1995
1996 If
1997 .I mdadm
1998 was told to monitor an array which is RAID0 or Linear, then it will
1999 report
2000 .B DeviceDisappeared
2001 with the extra information
2002 .BR Wrong-Level .
2003 This is because RAID0 and Linear do not support the device-failed,
2004 hot-spare and resync operations which are monitored.
2005
2006 .TP
2007 .B RebuildStarted
2008 An md array started reconstruction. (syslog priority: Warning)
2009
2010 .TP
2011 .BI Rebuild NN
2012 Where
2013 .I NN
2014 is a two-digit number (ie. 05, 48). This indicates that rebuild
2015 has passed that many percent of the total. The events are generated
2016 with fixed increment since 0. Increment size may be specified with
2017 a commandline option (default is 20). (syslog priority: Warning)
2018
2019 .TP
2020 .B RebuildFinished
2021 An md array that was rebuilding, isn't any more, either because it
2022 finished normally or was aborted. (syslog priority: Warning)
2023
2024 .TP
2025 .B Fail
2026 An active component device of an array has been marked as
2027 faulty. (syslog priority: Critical)
2028
2029 .TP
2030 .B FailSpare
2031 A spare component device which was being rebuilt to replace a faulty
2032 device has failed. (syslog priority: Critical)
2033
2034 .TP
2035 .B SpareActive
2036 A spare component device which was being rebuilt to replace a faulty
2037 device has been successfully rebuilt and has been made active.
2038 (syslog priority: Info)
2039
2040 .TP
2041 .B NewArray
2042 A new md array has been detected in the
2043 .B /proc/mdstat
2044 file. (syslog priority: Info)
2045
2046 .TP
2047 .B DegradedArray
2048 A newly noticed array appears to be degraded. This message is not
2049 generated when
2050 .I mdadm
2051 notices a drive failure which causes degradation, but only when
2052 .I mdadm
2053 notices that an array is degraded when it first sees the array.
2054 (syslog priority: Critical)
2055
2056 .TP
2057 .B MoveSpare
2058 A spare drive has been moved from one array in a
2059 .B spare-group
2060 to another to allow a failed drive to be replaced.
2061 (syslog priority: Info)
2062
2063 .TP
2064 .B SparesMissing
2065 If
2066 .I mdadm
2067 has been told, via the config file, that an array should have a certain
2068 number of spare devices, and
2069 .I mdadm
2070 detects that it has fewer than this number when it first sees the
2071 array, it will report a
2072 .B SparesMissing
2073 message.
2074 (syslog priority: Warning)
2075
2076 .TP
2077 .B TestMessage
2078 An array was found at startup, and the
2079 .B \-\-test
2080 flag was given.
2081 (syslog priority: Info)
2082 .RE
2083
2084 Only
2085 .B Fail,
2086 .B FailSpare,
2087 .B DegradedArray,
2088 .B SparesMissing
2089 and
2090 .B TestMessage
2091 cause Email to be sent. All events cause the program to be run.
2092 The program is run with two or three arguments: the event
2093 name, the array device and possibly a second device.
2094
2095 Each event has an associated array device (e.g.
2096 .BR /dev/md1 )
2097 and possibly a second device. For
2098 .BR Fail ,
2099 .BR FailSpare ,
2100 and
2101 .B SpareActive
2102 the second device is the relevant component device.
2103 For
2104 .B MoveSpare
2105 the second device is the array that the spare was moved from.
2106
2107 For
2108 .I mdadm
2109 to move spares from one array to another, the different arrays need to
2110 be labeled with the same
2111 .B spare-group
2112 in the configuration file. The
2113 .B spare-group
2114 name can be any string; it is only necessary that different spare
2115 groups use different names.
2116
2117 When
2118 .I mdadm
2119 detects that an array in a spare group has fewer active
2120 devices than necessary for the complete array, and has no spare
2121 devices, it will look for another array in the same spare group that
2122 has a full complement of working drive and a spare. It will then
2123 attempt to remove the spare from the second drive and add it to the
2124 first.
2125 If the removal succeeds but the adding fails, then it is added back to
2126 the original array.
2127
2128 .SH GROW MODE
2129 The GROW mode is used for changing the size or shape of an active
2130 array.
2131 For this to work, the kernel must support the necessary change.
2132 Various types of growth are being added during 2.6 development,
2133 including restructuring a RAID5 array to have more active devices.
2134
2135 Currently the only support available is to
2136 .IP \(bu 4
2137 change the "size" attribute
2138 for RAID1, RAID5 and RAID6.
2139 .IP \(bu 4
2140 increase or decrease the "raid\-devices" attribute of RAID1, RAID5,
2141 and RAID6.
2142 .IP \bu 4
2143 change the chunk-size and layout of RAID5 and RAID6.
2144 .IP \bu 4
2145 convert between RAID1 and RAID5, and between RAID5 and RAID6.
2146 .IP \(bu 4
2147 add a write-intent bitmap to any array which supports these bitmaps, or
2148 remove a write-intent bitmap from such an array.
2149 .PP
2150
2151 GROW mode is not currently supported for
2152 .B CONTAINERS
2153 or arrays inside containers.
2154
2155 .SS SIZE CHANGES
2156 Normally when an array is built the "size" it taken from the smallest
2157 of the drives. If all the small drives in an arrays are, one at a
2158 time, removed and replaced with larger drives, then you could have an
2159 array of large drives with only a small amount used. In this
2160 situation, changing the "size" with "GROW" mode will allow the extra
2161 space to start being used. If the size is increased in this way, a
2162 "resync" process will start to make sure the new parts of the array
2163 are synchronised.
2164
2165 Note that when an array changes size, any filesystem that may be
2166 stored in the array will not automatically grow to use the space. The
2167 filesystem will need to be explicitly told to use the extra space.
2168
2169 Also the size of an array cannot be changed while it has an active
2170 bitmap. If an array has a bitmap, it must be removed before the size
2171 can be changed. Once the change it complete a new bitmap can be created.
2172
2173 .SS RAID\-DEVICES CHANGES
2174
2175 A RAID1 array can work with any number of devices from 1 upwards
2176 (though 1 is not very useful). There may be times which you want to
2177 increase or decrease the number of active devices. Note that this is
2178 different to hot-add or hot-remove which changes the number of
2179 inactive devices.
2180
2181 When reducing the number of devices in a RAID1 array, the slots which
2182 are to be removed from the array must already be vacant. That is, the
2183 devices which were in those slots must be failed and removed.
2184
2185 When the number of devices is increased, any hot spares that are
2186 present will be activated immediately.
2187
2188 Changing the number of active devices in a RAID5 or RAID6 is much more
2189 effort. Every block in the array will need to be read and written
2190 back to a new location. From 2.6.17, the Linux Kernel is able to
2191 increase the number of devices in a RAID5 safely, including restarting
2192 an interrupted "reshape". From 2.6.31, the Linux Kernel is able to
2193 increase or decrease the number of devices in a RAID5 or RAID6.
2194
2195 When decreasing the number of devices, the size of the array will also
2196 decrease. If there was data in the array, it could get destroyed and
2197 this is not reversible. To help prevent accidents,
2198 .I mdadm
2199 requires that the size of the array be decreased first with
2200 .BR "mdadm --grow --array-size" .
2201 This is a reversible change which simply makes the end of the array
2202 inaccessible. The integrity of any data can then be checked before
2203 the non-reversible reduction in the number of devices is request.
2204
2205 When relocating the first few stripes on a RAID5 or RAID6, it is not
2206 possible to keep the data on disk completely consistent and
2207 crash-proof. To provide the required safety, mdadm disables writes to
2208 the array while this "critical section" is reshaped, and takes a
2209 backup of the data that is in that section. For grows, this backup may be
2210 stored in any spare devices that the array has, however it can also be
2211 stored in a separate file specified with the
2212 .B \-\-backup\-file
2213 option, and is required to be specified for shrinks, RAID level
2214 changes and layout changes. If this option is used, and the system
2215 does crash during the critical period, the same file must be passed to
2216 .B \-\-assemble
2217 to restore the backup and reassemble the array. When shrinking rather
2218 than growing the array, the reshape is done from the end towards the
2219 beginning, so the "critical section" is at the end of the reshape.
2220
2221 .SS LEVEL CHANGES
2222
2223 Changing the RAID level of any array happens instantaneously. However
2224 in the RAID5 to RAID6 case this requires a non-standard layout of the
2225 RAID6 data, and in the RAID6 to RAID5 case that non-standard layout is
2226 required before the change can be accomplished. So while the level
2227 change is instant, the accompanying layout change can take quite a
2228 long time. A
2229 .B \-\-backup\-file
2230 is required. If the array is not simultaneously being grown or
2231 shrunk, so that the array size will remain the same - for example,
2232 reshaping a 3-drive RAID5 into a 4-drive RAID6 - the backup file will
2233 be used not just for a "cricital section" but throughout the reshape
2234 operation, as described below under LAYOUT CHANGES.
2235
2236 .SS CHUNK-SIZE AND LAYOUT CHANGES
2237
2238 Changing the chunk-size of layout without also changing the number of
2239 devices as the same time will involve re-writing all blocks in-place.
2240 To ensure against data loss in the case of a crash, a
2241 .B --backup-file
2242 must be provided for these changes. Small sections of the array will
2243 be copied to the backup file while they are being rearranged. This
2244 means that all the data is copied twice, once to the backup and once
2245 to the new layout on the array, so this type of reshape will go very
2246 slowly.
2247
2248 If the reshape is interrupted for any reason, this backup file must be
2249 made available to
2250 .B "mdadm --assemble"
2251 so the array can be reassembled. Consequently the file cannot be
2252 stored on the device being reshaped.
2253
2254
2255 .SS BITMAP CHANGES
2256
2257 A write-intent bitmap can be added to, or removed from, an active
2258 array. Either internal bitmaps, or bitmaps stored in a separate file,
2259 can be added. Note that if you add a bitmap stored in a file which is
2260 in a filesystem that is on the RAID array being affected, the system
2261 will deadlock. The bitmap must be on a separate filesystem.
2262
2263 .SH INCREMENTAL MODE
2264
2265 .HP 12
2266 Usage:
2267 .B mdadm \-\-incremental
2268 .RB [ \-\-run ]
2269 .RB [ \-\-quiet ]
2270 .I component-device
2271 .HP 12
2272 Usage:
2273 .B mdadm \-\-incremental \-\-fail
2274 .I component-device
2275 .HP 12
2276 Usage:
2277 .B mdadm \-\-incremental \-\-rebuild\-map
2278 .HP 12
2279 Usage:
2280 .B mdadm \-\-incremental \-\-run \-\-scan
2281
2282 .PP
2283 This mode is designed to be used in conjunction with a device
2284 discovery system. As devices are found in a system, they can be
2285 passed to
2286 .B "mdadm \-\-incremental"
2287 to be conditionally added to an appropriate array.
2288
2289 Conversely, it can also be used with the
2290 .B \-\-fail
2291 flag to do just the opposite and find whatever array a particular device
2292 is part of and remove the device from that array.
2293
2294 If the device passed is a
2295 .B CONTAINER
2296 device created by a previous call to
2297 .IR mdadm ,
2298 then rather than trying to add that device to an array, all the arrays
2299 described by the metadata of the container will be started.
2300
2301 .I mdadm
2302 performs a number of tests to determine if the device is part of an
2303 array, and which array it should be part of. If an appropriate array
2304 is found, or can be created,
2305 .I mdadm
2306 adds the device to the array and conditionally starts the array.
2307
2308 Note that
2309 .I mdadm
2310 will only add devices to an array which were previously working
2311 (active or spare) parts of that array. It does not currently support
2312 automatic inclusion of a new drive as a spare in some array.
2313
2314 The tests that
2315 .I mdadm
2316 makes are as follow:
2317 .IP +
2318 Is the device permitted by
2319 .BR mdadm.conf ?
2320 That is, is it listed in a
2321 .B DEVICES
2322 line in that file. If
2323 .B DEVICES
2324 is absent then the default it to allow any device. Similar if
2325 .B DEVICES
2326 contains the special word
2327 .B partitions
2328 then any device is allowed. Otherwise the device name given to
2329 .I mdadm
2330 must match one of the names or patterns in a
2331 .B DEVICES
2332 line.
2333
2334 .IP +
2335 Does the device have a valid md superblock. If a specific metadata
2336 version is request with
2337 .B \-\-metadata
2338 or
2339 .B \-e
2340 then only that style of metadata is accepted, otherwise
2341 .I mdadm
2342 finds any known version of metadata. If no
2343 .I md
2344 metadata is found, the device is rejected.
2345
2346 .ig
2347 .IP +
2348 Does the metadata match an expected array?
2349 The metadata can match in two ways. Either there is an array listed
2350 in
2351 .B mdadm.conf
2352 which identifies the array (either by UUID, by name, by device list,
2353 or by minor-number), or the array was created with a
2354 .B homehost
2355 specified and that
2356 .B homehost
2357 matches the one in
2358 .B mdadm.conf
2359 or on the command line.
2360 If
2361 .I mdadm
2362 is not able to positively identify the array as belonging to the
2363 current host, the device will be rejected.
2364 ..
2365
2366 .I mdadm
2367 keeps a list of arrays that it has partially assembled in
2368 .B /var/run/mdadm/map
2369 (or
2370 .B /var/run/mdadm.map
2371 if the directory doesn't exist. Or maybe even
2372 .BR /dev/.mdadm.map ).
2373 If no array exists which matches
2374 the metadata on the new device,
2375 .I mdadm
2376 must choose a device name and unit number. It does this based on any
2377 name given in
2378 .B mdadm.conf
2379 or any name information stored in the metadata. If this name
2380 suggests a unit number, that number will be used, otherwise a free
2381 unit number will be chosen. Normally
2382 .I mdadm
2383 will prefer to create a partitionable array, however if the
2384 .B CREATE
2385 line in
2386 .B mdadm.conf
2387 suggests that a non-partitionable array is preferred, that will be
2388 honoured.
2389
2390 If the array is not found in the config file and its metadata does not
2391 identify it as belonging to the "homehost", then
2392 .I mdadm
2393 will choose a name for the array which is certain not to conflict with
2394 any array which does belong to this host. It does this be adding an
2395 underscore and a small number to the name preferred by the metadata.
2396
2397 Once an appropriate array is found or created and the device is added,
2398 .I mdadm
2399 must decide if the array is ready to be started. It will
2400 normally compare the number of available (non-spare) devices to the
2401 number of devices that the metadata suggests need to be active. If
2402 there are at least that many, the array will be started. This means
2403 that if any devices are missing the array will not be restarted.
2404
2405 As an alternative,
2406 .B \-\-run
2407 may be passed to
2408 .I mdadm
2409 in which case the array will be run as soon as there are enough
2410 devices present for the data to be accessible. For a RAID1, that
2411 means one device will start the array. For a clean RAID5, the array
2412 will be started as soon as all but one drive is present.
2413
2414 Note that neither of these approaches is really ideal. If it can
2415 be known that all device discovery has completed, then
2416 .br
2417 .B " mdadm \-IRs"
2418 .br
2419 can be run which will try to start all arrays that are being
2420 incrementally assembled. They are started in "read-auto" mode in
2421 which they are read-only until the first write request. This means
2422 that no metadata updates are made and no attempt at resync or recovery
2423 happens. Further devices that are found before the first write can
2424 still be added safely.
2425
2426 .SH ENVIRONMENT
2427 This section describes environment variables that affect how mdadm
2428 operates.
2429
2430 .TP
2431 .B MDADM_NO_MDMON
2432 Setting this value to 1 will prevent mdadm from automatically launching
2433 mdmon. This variable is intended primarily for debugging mdadm/mdmon.
2434
2435 .TP
2436 .B MDADM_NO_UDEV
2437 Normally,
2438 .I mdadm
2439 does not create any device nodes in /dev, but leaves that task to
2440 .IR udev .
2441 If
2442 .I udev
2443 appears not to be configured, or if this environment variable is set
2444 to '1', the
2445 .I mdadm
2446 will create and devices that are needed.
2447
2448 .SH EXAMPLES
2449
2450 .B " mdadm \-\-query /dev/name-of-device"
2451 .br
2452 This will find out if a given device is a RAID array, or is part of
2453 one, and will provide brief information about the device.
2454
2455 .B " mdadm \-\-assemble \-\-scan"
2456 .br
2457 This will assemble and start all arrays listed in the standard config
2458 file. This command will typically go in a system startup file.
2459
2460 .B " mdadm \-\-stop \-\-scan"
2461 .br
2462 This will shut down all arrays that can be shut down (i.e. are not
2463 currently in use). This will typically go in a system shutdown script.
2464
2465 .B " mdadm \-\-follow \-\-scan \-\-delay=120"
2466 .br
2467 If (and only if) there is an Email address or program given in the
2468 standard config file, then
2469 monitor the status of all arrays listed in that file by
2470 polling them ever 2 minutes.
2471
2472 .B " mdadm \-\-create /dev/md0 \-\-level=1 \-\-raid\-devices=2 /dev/hd[ac]1"
2473 .br
2474 Create /dev/md0 as a RAID1 array consisting of /dev/hda1 and /dev/hdc1.
2475
2476 .br
2477 .B " echo 'DEVICE /dev/hd*[0\-9] /dev/sd*[0\-9]' > mdadm.conf"
2478 .br
2479 .B " mdadm \-\-detail \-\-scan >> mdadm.conf"
2480 .br
2481 This will create a prototype config file that describes currently
2482 active arrays that are known to be made from partitions of IDE or SCSI drives.
2483 This file should be reviewed before being used as it may
2484 contain unwanted detail.
2485
2486 .B " echo 'DEVICE /dev/hd[a\-z] /dev/sd*[a\-z]' > mdadm.conf"
2487 .br
2488 .B " mdadm \-\-examine \-\-scan \-\-config=mdadm.conf >> mdadm.conf"
2489 .br
2490 This will find arrays which could be assembled from existing IDE and
2491 SCSI whole drives (not partitions), and store the information in the
2492 format of a config file.
2493 This file is very likely to contain unwanted detail, particularly
2494 the
2495 .B devices=
2496 entries. It should be reviewed and edited before being used as an
2497 actual config file.
2498
2499 .B " mdadm \-\-examine \-\-brief \-\-scan \-\-config=partitions"
2500 .br
2501 .B " mdadm \-Ebsc partitions"
2502 .br
2503 Create a list of devices by reading
2504 .BR /proc/partitions ,
2505 scan these for RAID superblocks, and printout a brief listing of all
2506 that were found.
2507
2508 .B " mdadm \-Ac partitions \-m 0 /dev/md0"
2509 .br
2510 Scan all partitions and devices listed in
2511 .BR /proc/partitions
2512 and assemble
2513 .B /dev/md0
2514 out of all such devices with a RAID superblock with a minor number of 0.
2515
2516 .B " mdadm \-\-monitor \-\-scan \-\-daemonise > /var/run/mdadm"
2517 .br
2518 If config file contains a mail address or alert program, run mdadm in
2519 the background in monitor mode monitoring all md devices. Also write
2520 pid of mdadm daemon to
2521 .BR /var/run/mdadm .
2522
2523 .B " mdadm \-Iq /dev/somedevice"
2524 .br
2525 Try to incorporate newly discovered device into some array as
2526 appropriate.
2527
2528 .B " mdadm \-\-incremental \-\-rebuild\-map \-\-run \-\-scan"
2529 .br
2530 Rebuild the array map from any current arrays, and then start any that
2531 can be started.
2532
2533 .B " mdadm /dev/md4 --fail detached --remove detached"
2534 .br
2535 Any devices which are components of /dev/md4 will be marked as faulty
2536 and then remove from the array.
2537
2538 .B " mdadm --grow /dev/md4 --level=6 --backup-file=/root/backup-md4
2539 .br
2540 The array
2541 .B /dev/md4
2542 which is currently a RAID5 array will be converted to RAID6. There
2543 should normally already be a spare drive attached to the array as a
2544 RAID6 needs one more drive than a matching RAID5.
2545
2546 .B " mdadm --create /dev/md/ddf --metadata=ddf --raid-disks 6 /dev/sd[a-f]"
2547 .br
2548 Create a DDF array over 6 devices.
2549
2550 .B " mdadm --create /dev/md/home -n3 -l5 -z 30000000 /dev/md/ddf"
2551 .br
2552 Create a RAID5 array over any 3 devices in the given DDF set. Use
2553 only 30 gigabytes of each device.
2554
2555 .B " mdadm -A /dev/md/ddf1 /dev/sd[a-f]"
2556 .br
2557 Assemble a pre-exist ddf array.
2558
2559 .B " mdadm -I /dev/md/ddf1"
2560 .br
2561 Assemble all arrays contained in the ddf array, assigning names as
2562 appropriate.
2563
2564 .B " mdadm \-\-create \-\-help"
2565 .br
2566 Provide help about the Create mode.
2567
2568 .B " mdadm \-\-config \-\-help"
2569 .br
2570 Provide help about the format of the config file.
2571
2572 .B " mdadm \-\-help"
2573 .br
2574 Provide general help.
2575
2576 .SH FILES
2577
2578 .SS /proc/mdstat
2579
2580 If you're using the
2581 .B /proc
2582 filesystem,
2583 .B /proc/mdstat
2584 lists all active md devices with information about them.
2585 .I mdadm
2586 uses this to find arrays when
2587 .B \-\-scan
2588 is given in Misc mode, and to monitor array reconstruction
2589 on Monitor mode.
2590
2591 .SS /etc/mdadm.conf
2592
2593 The config file lists which devices may be scanned to see if
2594 they contain MD super block, and gives identifying information
2595 (e.g. UUID) about known MD arrays. See
2596 .BR mdadm.conf (5)
2597 for more details.
2598
2599 .SS /var/run/mdadm/map
2600 When
2601 .B \-\-incremental
2602 mode is used, this file gets a list of arrays currently being created.
2603 If
2604 .B /var/run/mdadm
2605 does not exist as a directory, then
2606 .B /var/run/mdadm.map
2607 is used instead. If
2608 .B /var/run
2609 is not available (as may be the case during early boot),
2610 .B /dev/.mdadm.map
2611 is used on the basis that
2612 .B /dev
2613 is usually available very early in boot.
2614
2615 .SH DEVICE NAMES
2616
2617 .I mdadm
2618 understand two sorts of names for array devices.
2619
2620 The first is the so-called 'standard' format name, which matches the
2621 names used by the kernel and which appear in
2622 .IR /proc/mdstat .
2623
2624 The second sort can be freely chosen, but must reside in
2625 .IR /dev/md/ .
2626 When giving a device name to
2627 .I mdadm
2628 to create or assemble an array, either full path name such as
2629 .I /dev/md0
2630 or
2631 .I /dev/md/home
2632 can be given, or just the suffix of the second sort of name, such as
2633 .I home
2634 can be given.
2635
2636 When
2637 .I mdadm
2638 chooses device names during auto-assembly or incremental assembly, it
2639 will sometimes add a small sequence number to the end of the name to
2640 avoid conflicted between multiple arrays that have the same name. If
2641 .I mdadm
2642 can reasonably determine that the array really is meant for this host,
2643 either by a hostname in the metadata, or by the presence of the array
2644 in /etc/mdadm.conf, then it will leave off the suffix if possible.
2645 Also if the homehost is specified as
2646 .B <ignore>
2647 .I mdadm
2648 will only use a suffix if a different array of the same name already
2649 exists or is listed in the config file.
2650
2651 The standard names for non-partitioned arrays (the only sort of md
2652 array available in 2.4 and earlier) are of the form
2653 .IP
2654 /dev/mdNN
2655 .PP
2656 where NN is a number.
2657 The standard names for partitionable arrays (as available from 2.6
2658 onwards) are of the form
2659 .IP
2660 /dev/md_dNN
2661 .PP
2662 Partition numbers should be indicated by added "pMM" to these, thus "/dev/md/d1p2".
2663 .PP
2664 From kernel version, 2.6.28 the "non-partitioned array" can actually
2665 be partitioned. So the "md_dNN" names are no longer needed, and
2666 partitions such as "/dev/mdNNpXX" are possible.
2667
2668 .SH NOTE
2669 .I mdadm
2670 was previously known as
2671 .IR mdctl .
2672 .P
2673 .I mdadm
2674 is completely separate from the
2675 .I raidtools
2676 package, and does not use the
2677 .I /etc/raidtab
2678 configuration file at all.
2679
2680 .SH SEE ALSO
2681 For further information on mdadm usage, MD and the various levels of
2682 RAID, see:
2683 .IP
2684 .B http://linux\-raid.osdl.org/
2685 .PP
2686 (based upon Jakob \(/Ostergaard's Software\-RAID.HOWTO)
2687 .\".PP
2688 .\"for new releases of the RAID driver check out:
2689 .\"
2690 .\".IP
2691 .\".UR ftp://ftp.kernel.org/pub/linux/kernel/people/mingo/raid-patches
2692 .\"ftp://ftp.kernel.org/pub/linux/kernel/people/mingo/raid-patches
2693 .\".UE
2694 .\".PP
2695 .\"or
2696 .\".IP
2697 .\".UR http://www.cse.unsw.edu.au/~neilb/patches/linux-stable/
2698 .\"http://www.cse.unsw.edu.au/~neilb/patches/linux-stable/
2699 .\".UE
2700 .PP
2701 The latest version of
2702 .I mdadm
2703 should always be available from
2704 .IP
2705 .B http://www.kernel.org/pub/linux/utils/raid/mdadm/
2706 .PP
2707 Related man pages:
2708 .PP
2709 .IR mdmon (8),
2710 .IR mdadm.conf (5),
2711 .IR md (4).
2712 .PP
2713 .IR raidtab (5),
2714 .IR raid0run (8),
2715 .IR raidstop (8),
2716 .IR mkraid (8).