Commit | Line | Data |
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1da177e4 | 1 | Tools that manage md devices can be found at |
0ea6e611 | 2 | http://www.kernel.org/pub/linux/utils/raid/ |
1da177e4 LT |
3 | |
4 | ||
5 | Boot time assembly of RAID arrays | |
6 | --------------------------------- | |
7 | ||
8 | You can boot with your md device with the following kernel command | |
9 | lines: | |
10 | ||
11 | for old raid arrays without persistent superblocks: | |
12 | md=<md device no.>,<raid level>,<chunk size factor>,<fault level>,dev0,dev1,...,devn | |
13 | ||
14 | for raid arrays with persistent superblocks | |
15 | md=<md device no.>,dev0,dev1,...,devn | |
16 | or, to assemble a partitionable array: | |
17 | md=d<md device no.>,dev0,dev1,...,devn | |
18 | ||
19 | md device no. = the number of the md device ... | |
20 | 0 means md0, | |
21 | 1 md1, | |
22 | 2 md2, | |
23 | 3 md3, | |
24 | 4 md4 | |
25 | ||
26 | raid level = -1 linear mode | |
27 | 0 striped mode | |
28 | other modes are only supported with persistent super blocks | |
29 | ||
30 | chunk size factor = (raid-0 and raid-1 only) | |
31 | Set the chunk size as 4k << n. | |
32 | ||
33 | fault level = totally ignored | |
34 | ||
35 | dev0-devn: e.g. /dev/hda1,/dev/hdc1,/dev/sda1,/dev/sdb1 | |
36 | ||
37 | A possible loadlin line (Harald Hoyer <HarryH@Royal.Net>) looks like this: | |
38 | ||
39 | e:\loadlin\loadlin e:\zimage root=/dev/md0 md=0,0,4,0,/dev/hdb2,/dev/hdc3 ro | |
40 | ||
41 | ||
42 | Boot time autodetection of RAID arrays | |
43 | -------------------------------------- | |
44 | ||
45 | When md is compiled into the kernel (not as module), partitions of | |
46 | type 0xfd are scanned and automatically assembled into RAID arrays. | |
47 | This autodetection may be suppressed with the kernel parameter | |
48 | "raid=noautodetect". As of kernel 2.6.9, only drives with a type 0 | |
49 | superblock can be autodetected and run at boot time. | |
50 | ||
51 | The kernel parameter "raid=partitionable" (or "raid=part") means | |
52 | that all auto-detected arrays are assembled as partitionable. | |
53 | ||
6ff8d8ec N |
54 | Boot time assembly of degraded/dirty arrays |
55 | ------------------------------------------- | |
56 | ||
57 | If a raid5 or raid6 array is both dirty and degraded, it could have | |
58 | undetectable data corruption. This is because the fact that it is | |
59 | 'dirty' means that the parity cannot be trusted, and the fact that it | |
60 | is degraded means that some datablocks are missing and cannot reliably | |
61 | be reconstructed (due to no parity). | |
62 | ||
63 | For this reason, md will normally refuse to start such an array. This | |
64 | requires the sysadmin to take action to explicitly start the array | |
fff9289b | 65 | despite possible corruption. This is normally done with |
6ff8d8ec N |
66 | mdadm --assemble --force .... |
67 | ||
68 | This option is not really available if the array has the root | |
69 | filesystem on it. In order to support this booting from such an | |
70 | array, md supports a module parameter "start_dirty_degraded" which, | |
71 | when set to 1, bypassed the checks and will allows dirty degraded | |
72 | arrays to be started. | |
73 | ||
74 | So, to boot with a root filesystem of a dirty degraded raid[56], use | |
75 | ||
76 | md-mod.start_dirty_degraded=1 | |
77 | ||
1da177e4 LT |
78 | |
79 | Superblock formats | |
80 | ------------------ | |
81 | ||
82 | The md driver can support a variety of different superblock formats. | |
83 | Currently, it supports superblock formats "0.90.0" and the "md-1" format | |
84 | introduced in the 2.5 development series. | |
85 | ||
86 | The kernel will autodetect which format superblock is being used. | |
87 | ||
88 | Superblock format '0' is treated differently to others for legacy | |
89 | reasons - it is the original superblock format. | |
90 | ||
91 | ||
92 | General Rules - apply for all superblock formats | |
93 | ------------------------------------------------ | |
94 | ||
95 | An array is 'created' by writing appropriate superblocks to all | |
96 | devices. | |
97 | ||
98 | It is 'assembled' by associating each of these devices with an | |
99 | particular md virtual device. Once it is completely assembled, it can | |
100 | be accessed. | |
101 | ||
102 | An array should be created by a user-space tool. This will write | |
103 | superblocks to all devices. It will usually mark the array as | |
104 | 'unclean', or with some devices missing so that the kernel md driver | |
105 | can create appropriate redundancy (copying in raid1, parity | |
106 | calculation in raid4/5). | |
107 | ||
108 | When an array is assembled, it is first initialized with the | |
109 | SET_ARRAY_INFO ioctl. This contains, in particular, a major and minor | |
110 | version number. The major version number selects which superblock | |
111 | format is to be used. The minor number might be used to tune handling | |
112 | of the format, such as suggesting where on each device to look for the | |
113 | superblock. | |
114 | ||
115 | Then each device is added using the ADD_NEW_DISK ioctl. This | |
116 | provides, in particular, a major and minor number identifying the | |
117 | device to add. | |
118 | ||
119 | The array is started with the RUN_ARRAY ioctl. | |
120 | ||
121 | Once started, new devices can be added. They should have an | |
b6fec069 | 122 | appropriate superblock written to them, and then be passed in with |
1da177e4 LT |
123 | ADD_NEW_DISK. |
124 | ||
125 | Devices that have failed or are not yet active can be detached from an | |
126 | array using HOT_REMOVE_DISK. | |
127 | ||
128 | ||
129 | Specific Rules that apply to format-0 super block arrays, and | |
130 | arrays with no superblock (non-persistent). | |
131 | ------------------------------------------------------------- | |
132 | ||
133 | An array can be 'created' by describing the array (level, chunksize | |
b6fec069 | 134 | etc) in a SET_ARRAY_INFO ioctl. This must have major_version==0 and |
1da177e4 LT |
135 | raid_disks != 0. |
136 | ||
137 | Then uninitialized devices can be added with ADD_NEW_DISK. The | |
138 | structure passed to ADD_NEW_DISK must specify the state of the device | |
a33f3224 | 139 | and its role in the array. |
1da177e4 LT |
140 | |
141 | Once started with RUN_ARRAY, uninitialized spares can be added with | |
142 | HOT_ADD_DISK. | |
bb636547 N |
143 | |
144 | ||
145 | ||
146 | MD devices in sysfs | |
147 | ------------------- | |
148 | md devices appear in sysfs (/sys) as regular block devices, | |
149 | e.g. | |
150 | /sys/block/md0 | |
151 | ||
152 | Each 'md' device will contain a subdirectory called 'md' which | |
153 | contains further md-specific information about the device. | |
154 | ||
155 | All md devices contain: | |
156 | level | |
d33a56d3 N |
157 | a text file indicating the 'raid level'. e.g. raid0, raid1, |
158 | raid5, linear, multipath, faulty. | |
bb636547 | 159 | If no raid level has been set yet (array is still being |
d33a56d3 N |
160 | assembled), the value will reflect whatever has been written |
161 | to it, which may be a name like the above, or may be a number | |
162 | such as '0', '5', etc. | |
bb636547 N |
163 | |
164 | raid_disks | |
165 | a text file with a simple number indicating the number of devices | |
166 | in a fully functional array. If this is not yet known, the file | |
11373542 N |
167 | will be empty. If an array is being resized this will contain |
168 | the new number of devices. | |
169 | Some raid levels allow this value to be set while the array is | |
170 | active. This will reconfigure the array. Otherwise it can only | |
171 | be set while assembling an array. | |
172 | A change to this attribute will not be permitted if it would | |
173 | reduce the size of the array. To reduce the number of drives | |
174 | in an e.g. raid5, the array size must first be reduced by | |
175 | setting the 'array_size' attribute. | |
bb636547 | 176 | |
3b34380a | 177 | chunk_size |
11373542 N |
178 | This is the size in bytes for 'chunks' and is only relevant to |
179 | raid levels that involve striping (0,4,5,6,10). The address space | |
3b34380a N |
180 | of the array is conceptually divided into chunks and consecutive |
181 | chunks are striped onto neighbouring devices. | |
3f6dee9b | 182 | The size should be at least PAGE_SIZE (4k) and should be a power |
3b34380a N |
183 | of 2. This can only be set while assembling an array |
184 | ||
08a02ecd N |
185 | layout |
186 | The "layout" for the array for the particular level. This is | |
187 | simply a number that is interpretted differently by different | |
188 | levels. It can be written while assembling an array. | |
189 | ||
11373542 N |
190 | array_size |
191 | This can be used to artificially constrain the available space in | |
192 | the array to be less than is actually available on the combined | |
193 | devices. Writing a number (in Kilobytes) which is less than | |
194 | the available size will set the size. Any reconfiguration of the | |
195 | array (e.g. adding devices) will not cause the size to change. | |
196 | Writing the word 'default' will cause the effective size of the | |
197 | array to be whatever size is actually available based on | |
198 | 'level', 'chunk_size' and 'component_size'. | |
199 | ||
200 | This can be used to reduce the size of the array before reducing | |
201 | the number of devices in a raid4/5/6, or to support external | |
202 | metadata formats which mandate such clipping. | |
203 | ||
08a02ecd N |
204 | reshape_position |
205 | This is either "none" or a sector number within the devices of | |
206 | the array where "reshape" is up to. If this is set, the three | |
207 | attributes mentioned above (raid_disks, chunk_size, layout) can | |
208 | potentially have 2 values, an old and a new value. If these | |
209 | values differ, reading the attribute returns | |
210 | new (old) | |
211 | and writing will effect the 'new' value, leaving the 'old' | |
212 | unchanged. | |
213 | ||
a35b0d69 N |
214 | component_size |
215 | For arrays with data redundancy (i.e. not raid0, linear, faulty, | |
216 | multipath), all components must be the same size - or at least | |
217 | there must a size that they all provide space for. This is a key | |
218 | part or the geometry of the array. It is measured in sectors | |
219 | and can be read from here. Writing to this value may resize | |
220 | the array if the personality supports it (raid1, raid5, raid6), | |
221 | and if the component drives are large enough. | |
222 | ||
8bb93aac N |
223 | metadata_version |
224 | This indicates the format that is being used to record metadata | |
225 | about the array. It can be 0.90 (traditional format), 1.0, 1.1, | |
226 | 1.2 (newer format in varying locations) or "none" indicating that | |
227 | the kernel isn't managing metadata at all. | |
11373542 N |
228 | Alternately it can be "external:" followed by a string which |
229 | is set by user-space. This indicates that metadata is managed | |
230 | by a user-space program. Any device failure or other event that | |
231 | requires a metadata update will cause array activity to be | |
232 | suspended until the event is acknowledged. | |
8bb93aac | 233 | |
a94213b1 N |
234 | resync_start |
235 | The point at which resync should start. If no resync is needed, | |
06e3c817 DW |
236 | this will be a very large number (or 'none' since 2.6.30-rc1). At |
237 | array creation it will default to 0, though starting the array as | |
238 | 'clean' will set it much larger. | |
a94213b1 | 239 | |
6d7ff738 N |
240 | new_dev |
241 | This file can be written but not read. The value written should | |
242 | be a block device number as major:minor. e.g. 8:0 | |
243 | This will cause that device to be attached to the array, if it is | |
244 | available. It will then appear at md/dev-XXX (depending on the | |
245 | name of the device) and further configuration is then possible. | |
246 | ||
16f17b39 N |
247 | safe_mode_delay |
248 | When an md array has seen no write requests for a certain period | |
249 | of time, it will be marked as 'clean'. When another write | |
fff9289b ML |
250 | request arrives, the array is marked as 'dirty' before the write |
251 | commences. This is known as 'safe_mode'. | |
16f17b39 N |
252 | The 'certain period' is controlled by this file which stores the |
253 | period as a number of seconds. The default is 200msec (0.200). | |
254 | Writing a value of 0 disables safemode. | |
255 | ||
9e653b63 N |
256 | array_state |
257 | This file contains a single word which describes the current | |
258 | state of the array. In many cases, the state can be set by | |
259 | writing the word for the desired state, however some states | |
260 | cannot be explicitly set, and some transitions are not allowed. | |
261 | ||
0fd62b86 NB |
262 | Select/poll works on this file. All changes except between |
263 | active_idle and active (which can be frequent and are not | |
264 | very interesting) are notified. active->active_idle is | |
265 | reported if the metadata is externally managed. | |
266 | ||
9e653b63 N |
267 | clear |
268 | No devices, no size, no level | |
269 | Writing is equivalent to STOP_ARRAY ioctl | |
270 | inactive | |
271 | May have some settings, but array is not active | |
272 | all IO results in error | |
273 | When written, doesn't tear down array, but just stops it | |
274 | suspended (not supported yet) | |
275 | All IO requests will block. The array can be reconfigured. | |
276 | Writing this, if accepted, will block until array is quiessent | |
277 | readonly | |
278 | no resync can happen. no superblocks get written. | |
279 | write requests fail | |
280 | read-auto | |
281 | like readonly, but behaves like 'clean' on a write request. | |
282 | ||
283 | clean - no pending writes, but otherwise active. | |
284 | When written to inactive array, starts without resync | |
285 | If a write request arrives then | |
286 | if metadata is known, mark 'dirty' and switch to 'active'. | |
287 | if not known, block and switch to write-pending | |
288 | If written to an active array that has pending writes, then fails. | |
289 | active | |
290 | fully active: IO and resync can be happening. | |
291 | When written to inactive array, starts with resync | |
292 | ||
293 | write-pending | |
294 | clean, but writes are blocked waiting for 'active' to be written. | |
295 | ||
296 | active-idle | |
297 | like active, but no writes have been seen for a while (safe_mode_delay). | |
298 | ||
43a70507 N |
299 | bitmap/location |
300 | This indicates where the write-intent bitmap for the array is | |
301 | stored. | |
302 | It can be one of "none", "file" or "[+-]N". | |
303 | "file" may later be extended to "file:/file/name" | |
304 | "[+-]N" means that many sectors from the start of the metadata. | |
305 | This is replicated on all devices. For arrays with externally | |
306 | managed metadata, the offset is from the beginning of the | |
307 | device. | |
308 | bitmap/chunksize | |
309 | The size, in bytes, of the chunk which will be represented by a | |
310 | single bit. For RAID456, it is a portion of an individual | |
311 | device. For RAID10, it is a portion of the array. For RAID1, it | |
312 | is both (they come to the same thing). | |
313 | bitmap/time_base | |
314 | The time, in seconds, between looking for bits in the bitmap to | |
315 | be cleared. In the current implementation, a bit will be cleared | |
316 | between 2 and 3 times "time_base" after all the covered blocks | |
317 | are known to be in-sync. | |
318 | bitmap/backlog | |
319 | When write-mostly devices are active in a RAID1, write requests | |
320 | to those devices proceed in the background - the filesystem (or | |
321 | other user of the device) does not have to wait for them. | |
322 | 'backlog' sets a limit on the number of concurrent background | |
323 | writes. If there are more than this, new writes will by | |
324 | synchronous. | |
ece5cff0 N |
325 | bitmap/metadata |
326 | This can be either 'internal' or 'external'. | |
327 | 'internal' is the default and means the metadata for the bitmap | |
328 | is stored in the first 256 bytes of the allocated space and is | |
329 | managed by the md module. | |
330 | 'external' means that bitmap metadata is managed externally to | |
331 | the kernel (i.e. by some userspace program) | |
332 | bitmap/can_clear | |
333 | This is either 'true' or 'false'. If 'true', then bits in the | |
334 | bitmap will be cleared when the corresponding blocks are thought | |
335 | to be in-sync. If 'false', bits will never be cleared. | |
336 | This is automatically set to 'false' if a write happens on a | |
337 | degraded array, or if the array becomes degraded during a write. | |
338 | When metadata is managed externally, it should be set to true | |
339 | once the array becomes non-degraded, and this fact has been | |
340 | recorded in the metadata. | |
43a70507 N |
341 | |
342 | ||
343 | ||
9e653b63 | 344 | |
bb636547 N |
345 | As component devices are added to an md array, they appear in the 'md' |
346 | directory as new directories named | |
347 | dev-XXX | |
348 | where XXX is a name that the kernel knows for the device, e.g. hdb1. | |
349 | Each directory contains: | |
350 | ||
351 | block | |
352 | a symlink to the block device in /sys/block, e.g. | |
353 | /sys/block/md0/md/dev-hdb1/block -> ../../../../block/hdb/hdb1 | |
354 | ||
355 | super | |
356 | A file containing an image of the superblock read from, or | |
357 | written to, that device. | |
358 | ||
359 | state | |
2d78f8c4 | 360 | A file recording the current state of the device in the array |
bb636547 N |
361 | which can be a comma separated list of |
362 | faulty - device has been kicked from active use due to | |
2d78f8c4 N |
363 | a detected fault, or it has unacknowledged bad |
364 | blocks | |
bb636547 | 365 | in_sync - device is a fully in-sync member of the array |
f655675b | 366 | writemostly - device will only be subject to read |
2d78f8c4 | 367 | requests if there are no other options. |
f655675b | 368 | This applies only to raid1 arrays. |
0b7d8386 NK |
369 | blocked - device has failed, and the failure hasn't been |
370 | acknowledged yet by the metadata handler. | |
52664732 NB |
371 | Writes that would write to this device if |
372 | it were not faulty are blocked. | |
bb636547 N |
373 | spare - device is working, but not a full member. |
374 | This includes spares that are in the process | |
d6bc8ac9 | 375 | of being recovered to |
0b7d8386 | 376 | write_error - device has ever seen a write error. |
2d78f8c4 N |
377 | want_replacement - device is (mostly) working but probably |
378 | should be replaced, either due to errors or | |
379 | due to user request. | |
380 | replacement - device is a replacement for another active | |
381 | device with same raid_disk. | |
382 | ||
383 | ||
d6bc8ac9 | 384 | This list may grow in future. |
45dc2de1 N |
385 | This can be written to. |
386 | Writing "faulty" simulates a failure on the device. | |
387 | Writing "remove" removes the device from the array. | |
f655675b N |
388 | Writing "writemostly" sets the writemostly flag. |
389 | Writing "-writemostly" clears the writemostly flag. | |
52664732 | 390 | Writing "blocked" sets the "blocked" flag. |
0b7d8386 NK |
391 | Writing "-blocked" clears the "blocked" flags and allows writes |
392 | to complete and possibly simulates an error. | |
06e3c817 | 393 | Writing "in_sync" sets the in_sync flag. |
0b7d8386 NK |
394 | Writing "write_error" sets writeerrorseen flag. |
395 | Writing "-write_error" clears writeerrorseen flag. | |
2d78f8c4 N |
396 | Writing "want_replacement" is allowed at any time except to a |
397 | replacement device or a spare. It sets the flag. | |
398 | Writing "-want_replacement" is allowed at any time. It clears | |
399 | the flag. | |
400 | Writing "replacement" or "-replacement" is only allowed before | |
401 | starting the array. It sets or clears the flag. | |
402 | ||
52664732 NB |
403 | |
404 | This file responds to select/poll. Any change to 'faulty' | |
405 | or 'blocked' causes an event. | |
bb636547 | 406 | |
4dbcdc75 N |
407 | errors |
408 | An approximate count of read errors that have been detected on | |
409 | this device but have not caused the device to be evicted from | |
410 | the array (either because they were corrected or because they | |
411 | happened while the array was read-only). When using version-1 | |
412 | metadata, this value persists across restarts of the array. | |
413 | ||
414 | This value can be written while assembling an array thus | |
415 | providing an ongoing count for arrays with metadata managed by | |
416 | userspace. | |
417 | ||
014236d2 N |
418 | slot |
419 | This gives the role that the device has in the array. It will | |
420 | either be 'none' if the device is not active in the array | |
421 | (i.e. is a spare or has failed) or an integer less than the | |
992caacf | 422 | 'raid_disks' number for the array indicating which position |
014236d2 N |
423 | it currently fills. This can only be set while assembling an |
424 | array. A device for which this is set is assumed to be working. | |
425 | ||
93c8cad0 N |
426 | offset |
427 | This gives the location in the device (in sectors from the | |
428 | start) where data from the array will be stored. Any part of | |
b6fec069 | 429 | the device before this offset is not touched, unless it is |
93c8cad0 N |
430 | used for storing metadata (Formats 1.1 and 1.2). |
431 | ||
83303b61 N |
432 | size |
433 | The amount of the device, after the offset, that can be used | |
434 | for storage of data. This will normally be the same as the | |
435 | component_size. This can be written while assembling an | |
436 | array. If a value less than the current component_size is | |
d7027458 | 437 | written, it will be rejected. |
83303b61 | 438 | |
06e3c817 | 439 | recovery_start |
06e3c817 DW |
440 | When the device is not 'in_sync', this records the number of |
441 | sectors from the start of the device which are known to be | |
442 | correct. This is normally zero, but during a recovery | |
b6fec069 | 443 | operation it will steadily increase, and if the recovery is |
06e3c817 DW |
444 | interrupted, restoring this value can cause recovery to |
445 | avoid repeating the earlier blocks. With v1.x metadata, this | |
446 | value is saved and restored automatically. | |
447 | ||
448 | This can be set whenever the device is not an active member of | |
449 | the array, either before the array is activated, or before | |
450 | the 'slot' is set. | |
451 | ||
452 | Setting this to 'none' is equivalent to setting 'in_sync'. | |
453 | Setting to any other value also clears the 'in_sync' flag. | |
454 | ||
6e0d2d03 NK |
455 | bad_blocks |
456 | This gives the list of all known bad blocks in the form of | |
457 | start address and length (in sectors respectively). If output | |
458 | is too big to fit in a page, it will be truncated. Writing | |
459 | "sector length" to this file adds new acknowledged (i.e. | |
460 | recorded to disk safely) bad blocks. | |
461 | ||
462 | unacknowledged_bad_blocks | |
463 | This gives the list of known-but-not-yet-saved-to-disk bad | |
464 | blocks in the same form of 'bad_blocks'. If output is too big | |
465 | to fit in a page, it will be truncated. Writing to this file | |
466 | adds bad blocks without acknowledging them. This is largely | |
467 | for testing. | |
468 | ||
06e3c817 | 469 | |
bb636547 | 470 | |
b6fec069 | 471 | An active md device will also contain an entry for each active device |
bb636547 N |
472 | in the array. These are named |
473 | ||
474 | rdNN | |
475 | ||
992caacf | 476 | where 'NN' is the position in the array, starting from 0. |
bb636547 N |
477 | So for a 3 drive array there will be rd0, rd1, rd2. |
478 | These are symbolic links to the appropriate 'dev-XXX' entry. | |
479 | Thus, for example, | |
480 | cat /sys/block/md*/md/rd*/state | |
481 | will show 'in_sync' on every line. | |
482 | ||
483 | ||
484 | ||
b6fec069 | 485 | Active md devices for levels that support data redundancy (1,4,5,6,10) |
bb636547 N |
486 | also have |
487 | ||
488 | sync_action | |
489 | a text file that can be used to monitor and control the rebuild | |
490 | process. It contains one word which can be one of: | |
491 | resync - redundancy is being recalculated after unclean | |
492 | shutdown or creation | |
493 | recover - a hot spare is being built to replace a | |
494 | failed/missing device | |
495 | idle - nothing is happening | |
496 | check - A full check of redundancy was requested and is | |
b6fec069 | 497 | happening. This reads all blocks and checks |
bb636547 N |
498 | them. A repair may also happen for some raid |
499 | levels. | |
500 | repair - A full check and repair is happening. This is | |
501 | similar to 'resync', but was requested by the | |
502 | user, and the write-intent bitmap is NOT used to | |
503 | optimise the process. | |
504 | ||
505 | This file is writable, and each of the strings that could be | |
506 | read are meaningful for writing. | |
507 | ||
508 | 'idle' will stop an active resync/recovery etc. There is no | |
509 | guarantee that another resync/recovery may not be automatically | |
510 | started again, though some event will be needed to trigger | |
511 | this. | |
512 | 'resync' or 'recovery' can be used to restart the | |
513 | corresponding operation if it was stopped with 'idle'. | |
514 | 'check' and 'repair' will start the appropriate process | |
515 | providing the current state is 'idle'. | |
516 | ||
72a23c21 NB |
517 | This file responds to select/poll. Any important change in the value |
518 | triggers a poll event. Sometimes the value will briefly be | |
519 | "recover" if a recovery seems to be needed, but cannot be | |
520 | achieved. In that case, the transition to "recover" isn't | |
521 | notified, but the transition away is. | |
522 | ||
a99ac971 NB |
523 | degraded |
524 | This contains a count of the number of devices by which the | |
b6fec069 | 525 | arrays is degraded. So an optimal array will show '0'. A |
a99ac971 NB |
526 | single failed/missing drive will show '1', etc. |
527 | This file responds to select/poll, any increase or decrease | |
528 | in the count of missing devices will trigger an event. | |
529 | ||
bb636547 N |
530 | mismatch_count |
531 | When performing 'check' and 'repair', and possibly when | |
532 | performing 'resync', md will count the number of errors that are | |
533 | found. The count in 'mismatch_cnt' is the number of sectors | |
534 | that were re-written, or (for 'check') would have been | |
535 | re-written. As most raid levels work in units of pages rather | |
c79a8d85 | 536 | than sectors, this may be larger than the number of actual errors |
bb636547 N |
537 | by a factor of the number of sectors in a page. |
538 | ||
9b1d1dac PC |
539 | bitmap_set_bits |
540 | If the array has a write-intent bitmap, then writing to this | |
541 | attribute can set bits in the bitmap, indicating that a resync | |
542 | would need to check the corresponding blocks. Either individual | |
543 | numbers or start-end pairs can be written. Multiple numbers | |
544 | can be separated by a space. | |
545 | Note that the numbers are 'bit' numbers, not 'block' numbers. | |
546 | They should be scaled by the bitmap_chunksize. | |
547 | ||
08a02ecd N |
548 | sync_speed_min |
549 | sync_speed_max | |
550 | This are similar to /proc/sys/dev/raid/speed_limit_{min,max} | |
551 | however they only apply to the particular array. | |
36f95a0b | 552 | If no value has been written to these, or if the word 'system' |
08a02ecd N |
553 | is written, then the system-wide value is used. If a value, |
554 | in kibibytes-per-second is written, then it is used. | |
555 | When the files are read, they show the currently active value | |
556 | followed by "(local)" or "(system)" depending on whether it is | |
557 | a locally set or system-wide value. | |
558 | ||
559 | sync_completed | |
560 | This shows the number of sectors that have been completed of | |
561 | whatever the current sync_action is, followed by the number of | |
562 | sectors in total that could need to be processed. The two | |
563 | numbers are separated by a '/' thus effectively showing one | |
564 | value, a fraction of the process that is complete. | |
c6207277 N |
565 | A 'select' on this attribute will return when resync completes, |
566 | when it reaches the current sync_max (below) and possibly at | |
567 | other times. | |
568 | ||
08a02ecd N |
569 | sync_speed |
570 | This shows the current actual speed, in K/sec, of the current | |
571 | sync_action. It is averaged over the last 30 seconds. | |
572 | ||
573 | suspend_lo | |
574 | suspend_hi | |
575 | The two values, given as numbers of sectors, indicate a range | |
576 | within the array where IO will be blocked. This is currently | |
577 | only supported for raid4/5/6. | |
578 | ||
28a83978 C |
579 | sync_min |
580 | sync_max | |
581 | The two values, given as numbers of sectors, indicate a range | |
f699bf23 | 582 | within the array where 'check'/'repair' will operate. Must be |
28a83978 C |
583 | a multiple of chunk_size. When it reaches "sync_max" it will |
584 | pause, rather than complete. | |
585 | You can use 'select' or 'poll' on "sync_completed" to wait for | |
586 | that number to reach sync_max. Then you can either increase | |
587 | "sync_max", or can write 'idle' to "sync_action". | |
588 | ||
0baac4db C |
589 | The value of 'max' for "sync_max" effectively disables the limit. |
590 | When a resync is active, the value can only ever be increased, | |
591 | never decreased. | |
592 | The value of '0' is the minimum for "sync_min". | |
593 | ||
594 | ||
08a02ecd | 595 | |
bb636547 N |
596 | Each active md device may also have attributes specific to the |
597 | personality module that manages it. | |
598 | These are specific to the implementation of the module and could | |
599 | change substantially if the implementation changes. | |
600 | ||
601 | These currently include | |
602 | ||
603 | stripe_cache_size (currently raid5 only) | |
604 | number of entries in the stripe cache. This is writable, but | |
605 | there are upper and lower limits (32768, 16). Default is 128. | |
606 | strip_cache_active (currently raid5 only) | |
607 | number of active entries in the stripe cache | |
8b3e6cdc DW |
608 | preread_bypass_threshold (currently raid5 only) |
609 | number of times a stripe requiring preread will be bypassed by | |
610 | a stripe that does not require preread. For fairness defaults | |
611 | to 1. Setting this to 0 disables bypass accounting and | |
612 | requires preread stripes to wait until all full-width stripe- | |
613 | writes are complete. Valid values are 0 to stripe_cache_size. |