1LVMRAID(7)                                                          LVMRAID(7)
2
3
4

NAME

6       lvmraid — LVM RAID
7
8

DESCRIPTION

10       lvm(8) RAID is a way to create a Logical Volume (LV) that uses multiple
11       physical devices to improve performance or  tolerate  device  failures.
12       In  LVM,  the  physical  devices are Physical Volumes (PVs) in a single
13       Volume Group (VG).
14
15       How LV data blocks are placed onto PVs is determined by the RAID level.
16       RAID  levels  are  commonly referred to as 'raid' followed by a number,
17       e.g.  raid1, raid5 or raid6.  Selecting a RAID  level  involves  making
18       tradeoffs  among:  physical  device  requirements, fault tolerance, and
19       performance.  A description of the RAID levels can be found at
20       www.snia.org/sites/default/files/SNIA_DDF_Technical_Position_v2.0.pdf
21
22       LVM RAID uses both Device Mapper (DM) and Multiple Device (MD)  drivers
23       from  the  Linux  kernel.   DM is used to create and manage visible LVM
24       devices, and MD is used to place data on physical devices.
25
26       LVM creates hidden LVs (dm devices) layered between the visible LV  and
27       physical  devices.   LVs  in the middle layers are called sub LVs.  For
28       LVM raid, a sub LV pair to store data and metadata (raid superblock and
29       write  intent  bitmap)  is  created per raid image/leg (see lvs command
30       examples below).
31
32

Create a RAID LV

34       To create a RAID LV, use lvcreate and specify an LV type.  The LV  type
35       corresponds  to  a  RAID level.  The basic RAID levels that can be used
36       are: raid0, raid1, raid4, raid5, raid6, raid10.
37
38       lvcreate --type RaidLevel [OPTIONS] --name Name --size Size VG [PVs]
39
40       To display the LV type of an existing LV, run:
41
42       lvs -o name,segtype LV
43
44       (The LV type is also referred to as "segment type" or "segtype".)
45
46       LVs can be created with the following types:
47
48
49   raid0
50
51
52       Also called striping, raid0 spreads LV data across multiple devices  in
53       units  of  stripe size.  This is used to increase performance.  LV data
54       will be lost if any of the devices fail.
55
56       lvcreate --type raid0 [--stripes Number --stripesize Size] VG [PVs]
57
58
59       --stripes specifies the number of devices to spread the LV across.
60
61
62       --stripesize specifies the size of each stripe in kilobytes.   This  is
63              the  amount  of data that is written to one device before moving
64              to the next.
65
66       PVs specifies the devices to use.  If not specified,  lvm  will  choose
67       Number  devices,  one for each stripe based on the number of PVs avail‐
68       able or supplied.
69
70
71   raid1
72
73
74       Also called mirroring, raid1 uses  multiple  devices  to  duplicate  LV
75       data.   The  LV  data  remains  available if all but one of the devices
76       fail.  The minimum number of devices (i.e. sub LV pairs) required is 2.
77
78       lvcreate --type raid1 [--mirrors Number] VG [PVs]
79
80
81       --mirrors specifies the number of mirror  images  in  addition  to  the
82              original  LV  image, e.g. --mirrors 1 means there are two images
83              of the data, the original and one mirror image.
84
85       PVs specifies the devices to use.  If not specified,  lvm  will  choose
86       Number devices, one for each image.
87
88
89   raid4
90
91
92       raid4  is a form of striping that uses an extra, first device dedicated
93       to storing parity blocks.  The LV data remains available if one  device
94       fails.  The parity is used to recalculate data that is lost from a sin‐
95       gle device.  The minimum number of devices required is 3.
96
97       lvcreate --type raid4 [--stripes Number --stripesize Size] VG [PVs]
98
99
100       --stripes specifies the number of devices to use  for  LV  data.   This
101              does  not  include  the extra device lvm adds for storing parity
102              blocks.  A  raid4  LV  with  Number  stripes  requires  Number+1
103              devices.  Number must be 2 or more.
104
105
106       --stripesize  specifies  the size of each stripe in kilobytes.  This is
107              the amount of data that is written to one device  before  moving
108              to the next.
109
110       PVs  specifies  the  devices to use.  If not specified, lvm will choose
111       Number+1 separate devices.
112
113       raid4 is called non-rotating  parity  because  the  parity  blocks  are
114       always stored on the same device.
115
116
117   raid5
118
119
120       raid5  is a form of striping that uses an extra device for storing par‐
121       ity blocks.  LV data and parity blocks are stored on each device, typi‐
122       cally  in  a  rotating  pattern  for  performance reasons.  The LV data
123       remains available if one device fails.  The parity is used to  recalcu‐
124       late  data  that  is  lost from a single device.  The minimum number of
125       devices required is 3 (unless converting from 2 legged raid1 to reshape
126       to more stripes; see reshaping).
127
128       lvcreate --type raid5 [--stripes Number --stripesize Size] VG [PVs]
129
130
131       --stripes  specifies  the  number  of devices to use for LV data.  This
132              does not include the extra device lvm adds  for  storing  parity
133              blocks.   A  raid5  LV  with  Number  stripes  requires Number+1
134              devices.  Number must be 2 or more.
135
136
137       --stripesize specifies the size of each stripe in kilobytes.   This  is
138              the  amount  of data that is written to one device before moving
139              to the next.
140
141       PVs specifies the devices to use.  If not specified,  lvm  will  choose
142       Number+1 separate devices.
143
144       raid5 is called rotating parity because the parity blocks are placed on
145       different devices in a round-robin sequence.  There are  variations  of
146       raid5  with  different  algorithms  for placing the parity blocks.  The
147       default variant is raid5_ls (raid5 left symmetric, which is a  rotating
148       parity 0 with data restart.)  See RAID5 variants below.
149
150
151   raid6
152
153
154       raid6  is a form of striping like raid5, but uses two extra devices for
155       parity blocks.  LV data and parity blocks are stored  on  each  device,
156       typically  in  a rotating pattern for perfomramce reasons.  The LV data
157       remains available if up to two devices fail.  The  parity  is  used  to
158       recalculate  data  that  is  lost from one or two devices.  The minimum
159       number of devices required is 5.
160
161       lvcreate --type raid6 [--stripes Number --stripesize Size] VG [PVs]
162
163
164       --stripes specifies the number of devices to use  for  LV  data.   This
165              does not include the extra two devices lvm adds for storing par‐
166              ity blocks.  A raid6 LV with Number  stripes  requires  Number+2
167              devices.  Number must be 3 or more.
168
169
170       --stripesize  specifies  the size of each stripe in kilobytes.  This is
171              the amount of data that is written to one device  before  moving
172              to the next.
173
174       PVs  specifies  the  devices to use.  If not specified, lvm will choose
175       Number+2 separate devices.
176
177       Like raid5, there are variations of raid6 with different algorithms for
178       placing the parity blocks.  The default variant is raid6_zr (raid6 zero
179       restart, aka left symmetric, which is a rotating  parity  0  with  data
180       restart.)  See RAID6 variants below.
181
182
183   raid10
184
185
186       raid10  is  a combination of raid1 and raid0, striping data across mir‐
187       rored devices.  LV data  remains  available  if  one  or  more  devices
188       remains  in each mirror set.  The minimum number of devices required is
189       4.
190
191       lvcreate --type raid10
192              [--mirrors NumberMirrors]
193              [--stripes NumberStripes --stripesize Size]
194              VG [PVs]
195
196
197       --mirrors specifies the number of mirror  images  within  each  stripe.
198              e.g.   --mirrors  1  means there are two images of the data, the
199              original and one mirror image.
200
201
202       --stripes specifies the total number of devices to  use  in  all  raid1
203              images (not the number of raid1 devices to spread the LV across,
204              even though that  is  the  effective  result).   The  number  of
205              devices  in  each raid1 mirror will be NumberStripes/(NumberMir‐
206              rors+1), e.g. mirrors 1 and stripes 4 will  stripe  data  across
207              two raid1 mirrors, where each mirror is devices.
208
209
210       --stripesize  specifies  the size of each stripe in kilobytes.  This is
211              the amount of data that is written to one device  before  moving
212              to the next.
213
214       PVs  specifies  the  devices to use.  If not specified, lvm will choose
215       the necessary devices.  Devices are used to create mirrors in the order
216       listed,  e.g. for mirrors 1, stripes 2, listing PV1 PV2 PV3 PV4 results
217       in mirrors PV1/PV2 and PV3/PV4.
218
219       RAID10 is not mirroring on top of stripes, which would be RAID01, which
220       is less tolerant of device failures.
221
222
223

Synchronization

225       Synchronization  is the process that makes all the devices in a RAID LV
226       consistent with each other.
227
228       In a RAID1 LV, all mirror images should have the same data.  When a new
229       mirror  image  is added, or a mirror image is missing data, then images
230       need to be synchronized.  Data blocks are copied from an existing image
231       to a new or outdated image to make them match.
232
233       In a RAID 4/5/6 LV, parity blocks and data blocks should match based on
234       the parity calculation.  When the devices in a RAID LV change, the data
235       and  parity blocks can become inconsistent and need to be synchronized.
236       Correct blocks are read, parity is calculated, and recalculated  blocks
237       are written.
238
239       The  RAID  implementation  keeps  track of which parts of a RAID LV are
240       synchronized.  When a RAID LV is first created and activated the  first
241       synchronization is called initialization.  A pointer stored in the raid
242       metadata keeps track of the initialization process thus allowing it  to
243       be restarted after a deactivation of the RaidLV or a crash.  Any writes
244       to the RaidLV dirties the respective region of the write intent  bitmap
245       which  allow  for  fast recovery of the regions after a crash.  Without
246       this, the entire LV would need to be synchronized  every  time  it  was
247       activated.
248
249       Automatic  synchronization  happens when a RAID LV is activated, but it
250       is usually partial because  the  bitmaps  reduce  the  areas  that  are
251       checked.  A full sync becomes necessary when devices in the RAID LV are
252       replaced.
253
254       The synchronization status of a RAID LV is reported  by  the  following
255       command, where "Cpy%Sync" = "100%" means sync is complete:
256
257       lvs -a -o name,sync_percent
258
259
260
261   Scrubbing
262       Scrubbing is a full scan of the RAID LV requested by a user.  Scrubbing
263       can find problems that are missed by partial synchronization.
264
265       Scrubbing assumes that RAID metadata and bitmaps may be inaccurate,  so
266       it  verifies  all RAID metadata, LV data, and parity blocks.  Scrubbing
267       can find inconsistencies caused  by  hardware  errors  or  degradation.
268       These  kinds of problems may be undetected by automatic synchronization
269       which excludes areas outside of the RAID write-intent bitmap.
270
271       The command to scrub a RAID LV can operate in two different modes:
272
273       lvchange --syncaction check|repair LV
274
275
276       check Check mode is read-only and only detects  inconsistent  areas  in
277              the RAID LV, it does not correct them.
278
279
280       repair  Repair  mode  checks and writes corrected blocks to synchronize
281              any inconsistent areas.
282
283
284       Scrubbing can consume a lot of bandwidth and slow down application  I/O
285       on the RAID LV.  To control the I/O rate used for scrubbing, use:
286
287
288       --maxrecoveryrate Size[k|UNIT]
289              Sets the maximum recovery rate for a RAID LV.  Size is specified
290              as an amount per second for each device in  the  array.   If  no
291              suffix  is  given,  then  KiB/sec/device  is  used.  Setting the
292              recovery rate to 0 means it will be unbounded.
293
294
295       --minrecoveryrate Size[k|UNIT]
296              Sets the minimum recovery rate for a RAID LV.  Size is specified
297              as  an  amount  per  second for each device in the array.  If no
298              suffix is given,  then  KiB/sec/device  is  used.   Setting  the
299              recovery rate to 0 means it will be unbounded.
300
301
302       To  display  the  current scrubbing in progress on an LV, including the
303       syncaction mode and percent complete, run:
304
305       lvs -a -o name,raid_sync_action,sync_percent
306
307       After scrubbing is complete, to  display  the  number  of  inconsistent
308       blocks found, run:
309
310       lvs -o name,raid_mismatch_count
311
312       Also,  if  mismatches  were  found, the lvs attr field will display the
313       letter "m" (mismatch) in the 9th position, e.g.
314
315       # lvs -o name,vgname,segtype,attr vg/lv
316         LV VG   Type  Attr
317         lv vg   raid1 Rwi-a-r-m-
318
319
320
321   Scrubbing Limitations
322       The check mode can only report the number of  inconsistent  blocks,  it
323       cannot  report which blocks are inconsistent.  This makes it impossible
324       to know which device has errors, or if the errors  affect  file  system
325       data, metadata or nothing at all.
326
327       The  repair  mode can make the RAID LV data consistent, but it does not
328       know which data is correct.  The result may be consistent but incorrect
329       data.   When  two  different blocks of data must be made consistent, it
330       chooses the block from the  device  that  would  be  used  during  RAID
331       intialization.   However,  if  the  PV  holding  corrupt data is known,
332       lvchange --rebuild can be used in place of scrubbing to reconstruct the
333       data on the bad device.
334
335       Future developments might include:
336
337       Allowing a user to choose the correct version of data during repair.
338
339       Using a majority of devices to determine the correct version of data to
340       use in a 3-way RAID1 or RAID6 LV.
341
342       Using a checksumming device  to  pin-point  when  and  where  an  error
343       occurs, allowing it to be rewritten.
344
345
346

SubLVs

348       An  LV  is  often a combination of other hidden LVs called SubLVs.  The
349       SubLVs either use physical devices, or  are  built  from  other  SubLVs
350       themselves.   SubLVs  hold LV data blocks, RAID parity blocks, and RAID
351       metadata.  SubLVs are  generally  hidden,  so  the  lvs  -a  option  is
352       required to display them:
353
354       lvs -a -o name,segtype,devices
355
356       SubLV  names begin with the visible LV name, and have an automatic suf‐
357       fix indicating its role:
358
359
360       ·  SubLVs holding LV data or parity blocks have the  suffix  _rimage_#.
361          These SubLVs are sometimes referred to as DataLVs.
362
363
364       ·  SubLVs  holding  RAID metadata have the suffix _rmeta_#.  RAID meta‐
365          data includes superblock information, RAID type, bitmap, and  device
366          health  information.  These SubLVs are sometimes referred to as Met‐
367          aLVs.
368
369
370       SubLVs are an internal implementation detail of LVM.  The way they  are
371       used, constructed and named may change.
372
373       The following examples show the SubLV arrangement for each of the basic
374       RAID LV types, using the fewest number of devices allowed for each.
375
376
377   Examples
378       raid0
379       Each rimage SubLV holds a portion of LV data.  No parity is  used.   No
380       RAID metadata is used.
381
382       # lvcreate --type raid0 --stripes 2 --name lvr0 ...
383
384       # lvs -a -o name,segtype,devices
385         lvr0            raid0  lvr0_rimage_0(0),lvr0_rimage_1(0)
386         [lvr0_rimage_0] linear /dev/sda(...)
387         [lvr0_rimage_1] linear /dev/sdb(...)
388
389       raid1
390       Each rimage SubLV holds a complete copy of LV data.  No parity is used.
391       Each rmeta SubLV holds RAID metadata.
392
393       # lvcreate --type raid1 --mirrors 1 --name lvr1 ...
394
395       # lvs -a -o name,segtype,devices
396         lvr1            raid1  lvr1_rimage_0(0),lvr1_rimage_1(0)
397         [lvr1_rimage_0] linear /dev/sda(...)
398         [lvr1_rimage_1] linear /dev/sdb(...)
399         [lvr1_rmeta_0]  linear /dev/sda(...)
400         [lvr1_rmeta_1]  linear /dev/sdb(...)
401
402       raid4
403       At least three rimage SubLVs each hold a portion of  LV  data  and  one
404       rimage SubLV holds parity.  Each rmeta SubLV holds RAID metadata.
405
406       # lvcreate --type raid4 --stripes 2 --name lvr4 ...
407
408       # lvs -a -o name,segtype,devices
409         lvr4            raid4  lvr4_rimage_0(0),\
410                                lvr4_rimage_1(0),\
411                                lvr4_rimage_2(0)
412         [lvr4_rimage_0] linear /dev/sda(...)
413         [lvr4_rimage_1] linear /dev/sdb(...)
414         [lvr4_rimage_2] linear /dev/sdc(...)
415         [lvr4_rmeta_0]  linear /dev/sda(...)
416         [lvr4_rmeta_1]  linear /dev/sdb(...)
417         [lvr4_rmeta_2]  linear /dev/sdc(...)
418
419       raid5
420       At  least  three rimage SubLVs each typcially hold a portion of LV data
421       and parity (see section on raid5) Each rmeta SubLV holds RAID metadata.
422
423       # lvcreate --type raid5 --stripes 2 --name lvr5 ...
424
425       # lvs -a -o name,segtype,devices
426         lvr5            raid5  lvr5_rimage_0(0),\
427                                lvr5_rimage_1(0),\
428                                lvr5_rimage_2(0)
429         [lvr5_rimage_0] linear /dev/sda(...)
430         [lvr5_rimage_1] linear /dev/sdb(...)
431         [lvr5_rimage_2] linear /dev/sdc(...)
432         [lvr5_rmeta_0]  linear /dev/sda(...)
433         [lvr5_rmeta_1]  linear /dev/sdb(...)
434         [lvr5_rmeta_2]  linear /dev/sdc(...)
435
436       raid6
437       At least five rimage SubLVs each typically hold a portion  of  LV  data
438       and  parity.   (see section on raid6) Each rmeta SubLV holds RAID meta‐
439       data.
440
441       # lvcreate --type raid6 --stripes 3 --name lvr6
442
443       # lvs -a -o name,segtype,devices
444         lvr6            raid6  lvr6_rimage_0(0),\
445                                lvr6_rimage_1(0),\
446                                lvr6_rimage_2(0),\
447                                lvr6_rimage_3(0),\
448                                lvr6_rimage_4(0),\
449                                lvr6_rimage_5(0)
450         [lvr6_rimage_0] linear /dev/sda(...)
451         [lvr6_rimage_1] linear /dev/sdb(...)
452         [lvr6_rimage_2] linear /dev/sdc(...)
453         [lvr6_rimage_3] linear /dev/sdd(...)
454         [lvr6_rimage_4] linear /dev/sde(...)
455         [lvr6_rimage_5] linear /dev/sdf(...)
456         [lvr6_rmeta_0]  linear /dev/sda(...)
457         [lvr6_rmeta_1]  linear /dev/sdb(...)
458         [lvr6_rmeta_2]  linear /dev/sdc(...)
459         [lvr6_rmeta_3]  linear /dev/sdd(...)
460         [lvr6_rmeta_4]  linear /dev/sde(...)
461         [lvr6_rmeta_5]  linear /dev/sdf(...)
462
463       raid10
464       At least four rimage SubLVs each hold a portion of LV data.  No  parity
465       is used.  Each rmeta SubLV holds RAID metadata.
466
467       # lvcreate --type raid10 --stripes 2 --mirrors 1 --name lvr10
468
469       # lvs -a -o name,segtype,devices
470         lvr10            raid10 lvr10_rimage_0(0),\
471                                 lvr10_rimage_1(0),\
472                                 lvr10_rimage_2(0),\
473                                 lvr10_rimage_3(0)
474         [lvr10_rimage_0] linear /dev/sda(...)
475         [lvr10_rimage_1] linear /dev/sdb(...)
476         [lvr10_rimage_2] linear /dev/sdc(...)
477         [lvr10_rimage_3] linear /dev/sdd(...)
478         [lvr10_rmeta_0]  linear /dev/sda(...)
479         [lvr10_rmeta_1]  linear /dev/sdb(...)
480         [lvr10_rmeta_2]  linear /dev/sdc(...)
481         [lvr10_rmeta_3]  linear /dev/sdd(...)
482
483
484

Device Failure

486       Physical devices in a RAID LV can fail or be lost for multiple reasons.
487       A device could be disconnected, permanently failed, or temporarily dis‐
488       connected.   The  purpose  of RAID LVs (levels 1 and higher) is to con‐
489       tinue operating in a degraded mode, without losing LV data, even  after
490       a  device  fails.  The number of devices that can fail without the loss
491       of LV data depends on the RAID level:
492
493
494       ·  RAID0 (striped) LVs cannot tolerate losing  any  devices.   LV  data
495          will be lost if any devices fail.
496
497
498       ·  RAID1  LVs  can  tolerate  losing all but one device without LV data
499          loss.
500
501
502       ·  RAID4 and RAID5 LVs can tolerate losing one device without  LV  data
503          loss.
504
505
506       ·  RAID6 LVs can tolerate losing two devices without LV data loss.
507
508
509       ·  RAID10  is  variable,  and  depends  on  which devices are lost.  It
510          stripes across multiple mirror groups with raid1 layout thus it  can
511          tolerate  losing  all but one device in each of these groups without
512          LV data loss.
513
514
515       If a RAID LV is missing devices, or has other device-related  problems,
516       lvs reports this in the health_status (and attr) fields:
517
518       lvs -o name,lv_health_status
519
520       partial
521       Devices  are missing from the LV.  This is also indicated by the letter
522       "p" (partial) in the 9th position of the lvs attr field.
523
524       refresh needed
525       A device was temporarily missing but has returned.  The LV needs to  be
526       refreshed  to  use the device again (which will usually require partial
527       synchronization).  This is also indicated by the  letter  "r"  (refresh
528       needed)  in  the 9th position of the lvs attr field.  See Refreshing an
529       LV.  This could also indicate a problem with the device, in which  case
530       it should be be replaced, see Replacing Devices.
531
532       mismatches exist
533       See Scrubbing.
534
535       Most commands will also print a warning if a device is missing, e.g.
536       WARNING: Device for PV uItL3Z-wBME-DQy0-... not found or rejected ...
537
538       This  warning will go away if the device returns or is removed from the
539       VG (see vgreduce --removemissing).
540
541
542
543   Activating an LV with missing devices
544       A RAID LV that is missing devices may be activated or not, depending on
545       the "activation mode" used in lvchange:
546
547       lvchange -ay --activationmode complete|degraded|partial LV
548
549       complete
550       The LV is only activated if all devices are present.
551
552       degraded
553       The LV is activated with missing devices if the RAID level can tolerate
554       the number of missing devices without LV data loss.
555
556       partial
557       The LV is always activated, even if portions of the LV data are missing
558       because  of the missing device(s).  This should only be used to perform
559       extreme recovery or repair operations.
560
561       lvm.conf(5) activation/activation_mode
562       controls the activation mode when not specified by the command.
563
564       The default value is printed by:
565       lvmconfig --type default activation/activation_mode
566
567
568   Replacing Devices
569       Devices in a RAID LV can be replaced by other devices in the VG.   When
570       replacing  devices that are no longer visible on the system, use lvcon‐
571       vert --repair.  When replacing devices  that  are  still  visible,  use
572       lvconvert  --replace.   The  repair command will attempt to restore the
573       same number of data LVs that were previously in the  LV.   The  replace
574       option  can  be  repeated to replace multiple PVs.  Replacement devices
575       can be optionally listed with either option.
576
577       lvconvert --repair LV [NewPVs]
578
579       lvconvert --replace OldPV LV [NewPV]
580
581       lvconvert --replace OldPV1 --replace OldPV2 LV [NewPVs]
582
583       New devices require synchronization with existing devices, see Synchro‐
584       nization.
585
586
587   Refreshing an LV
588       Refreshing  a  RAID LV clears any transient device failures (device was
589       temporarily disconnected) and returns the LV  to  its  fully  redundant
590       mode.   Restoring  a  device will usually require at least partial syn‐
591       chronization (see Synchronization).  Failure to clear a transient fail‐
592       ure results in the RAID LV operating in degraded mode until it is reac‐
593       tivated.  Use the lvchange command to refresh an LV:
594
595       lvchange --refresh LV
596
597       # lvs -o name,vgname,segtype,attr,size vg
598         LV VG   Type  Attr       LSize
599         lv vg   raid1 Rwi-a-r-r- 100.00g
600
601       # lvchange --refresh vg/lv
602
603       # lvs -o name,vgname,segtype,attr,size vg
604         LV VG   Type  Attr       LSize
605         lv vg   raid1 Rwi-a-r--- 100.00g
606
607
608   Automatic repair
609       If a device in a RAID LV fails, device-mapper in  the  kernel  notifies
610       the  dmeventd(8)  monitoring process (see Monitoring).  dmeventd can be
611       configured to automatically respond using:
612
613       lvm.conf(5) activation/raid_fault_policy
614
615       Possible settings are:
616
617       warn
618       A warning is added to the system  log  indicating  that  a  device  has
619       failed  in  the RAID LV.  It is left to the user to repair the LV, e.g.
620       replace failed devices.
621
622       allocate
623       dmeventd automatically attempts to repair the LV using spare devices in
624       the  VG.   Note that even a transient failure is treated as a permanent
625       failure under this setting.  A new device is allocated  and  full  syn‐
626       chronization is started.
627
628       The specific command run by dmeventd to warn or repair is:
629       lvconvert --repair --use-policies LV
630
631
632
633   Corrupted Data
634       Data  on  a  device can be corrupted due to hardware errors without the
635       device ever being disconnected or there being any fault  in  the  soft‐
636       ware.  This should be rare, and can be detected (see Scrubbing).
637
638
639
640   Rebuild specific PVs
641       If  specific  PVs in a RAID LV are known to have corrupt data, the data
642       on those PVs can be reconstructed with:
643
644       lvchange --rebuild PV LV
645
646       The rebuild option can be repeated with different PVs  to  replace  the
647       data on multiple PVs.
648
649
650

Monitoring

652       When a RAID LV is activated the dmeventd(8) process is started to moni‐
653       tor the health of the LV.  Various events detected in  the  kernel  can
654       cause  a  notification  to be sent from device-mapper to the monitoring
655       process, including device failures and synchronization completion (e.g.
656       for initialization or scrubbing).
657
658       The  LVM  configuration file contains options that affect how the moni‐
659       toring process will respond to failure events (e.g. raid_fault_policy).
660       It  is  possible to turn on and off monitoring with lvchange, but it is
661       not recommended to turn this off unless you have a  thorough  knowledge
662       of the consequences.
663
664
665

Configuration Options

667       There are a number of options in the LVM configuration file that affect
668       the behavior of RAID LVs.  The tunable options  are  listed  below.   A
669       detailed description of each can be found in the LVM configuration file
670       itself.
671               mirror_segtype_default
672               raid10_segtype_default
673               raid_region_size
674               raid_fault_policy
675               activation_mode
676
677
678

RAID1 Tuning

680       A RAID1 LV can be tuned so that certain devices are avoided for reading
681       while all devices are still written to.
682
683       lvchange --[raid]writemostly PV[:y|n|t] LV
684
685       The specified device will be marked as "write mostly", which means that
686       reading from this device will be avoided, and  other  devices  will  be
687       preferred  for  reading  (unless no other devices are available.)  This
688       minimizes the I/O to the specified device.
689
690       If the PV name has no suffix, the write mostly attribute  is  set.   If
691       the  PV  name has the suffix :n, the write mostly attribute is cleared,
692       and the suffix :t toggles the current setting.
693
694       The write mostly option can be repeated on the command line  to  change
695       multiple devices at once.
696
697       To  report  the  current  write mostly setting, the lvs attr field will
698       show the letter "w" in the 9th position when write mostly is set:
699
700       lvs -a -o name,attr
701
702       When a device is marked write mostly, the maximum number of outstanding
703       writes  to that device can be configured.  Once the maximum is reached,
704       further writes become synchronous.  When synchronous, a write to the LV
705       will not complete until writes to all the mirror images are complete.
706
707       lvchange --[raid]writebehind Number LV
708
709       To report the current write behind setting, run:
710
711       lvs -o name,raid_write_behind
712
713       When  write  behind  is  not configured, or set to 0, all LV writes are
714       synchronous.
715
716
717

RAID Takeover

719       RAID takeover is converting a RAID LV from one RAID level  to  another,
720       e.g.   raid5  to  raid6.   Changing  the  RAID level is usually done to
721       increase or decrease resilience to device failures or to restripe  LVs.
722       This  is  done using lvconvert and specifying the new RAID level as the
723       LV type:
724
725       lvconvert --type RaidLevel LV [PVs]
726
727       The most common and recommended RAID takeover conversions are:
728
729
730       linear to raid1
731              Linear is a single image of LV data, and converting it to  raid1
732              adds  a mirror image which is a direct copy of the original lin‐
733              ear image.
734
735
736       striped/raid0 to raid4/5/6
737              Adding parity devices to a striped volume results in raid4/5/6.
738
739
740       Unnatural conversions  that  are  not  recommended  include  converting
741       between  striped  and  non-striped types.  This is because file systems
742       often optimize I/O patterns based on device striping values.  If  those
743       values change, it can decrease performance.
744
745       Converting  to  a  higher  RAID level requires allocating new SubLVs to
746       hold RAID metadata, and new SubLVs to hold parity blocks for  LV  data.
747       Converting  to a lower RAID level removes the SubLVs that are no longer
748       needed.
749
750       Conversion often requires full synchronization of the RAID LV (see Syn‐
751       chronization).  Converting to RAID1 requires copying all LV data blocks
752       to N new images on new devices.  Converting  to  a  parity  RAID  level
753       requires  reading  all  LV data blocks, calculating parity, and writing
754       the new parity blocks.  Synchronization can take a long time  depending
755       on  the throughpout of the devices used and the size of the RaidLV.  It
756       can degrade performance (rate controls also apply  to  conversion;  see
757       --minrecoveryrate and --maxrecoveryrate.)
758
759       Warning:  though  it  is possible to create striped LVs  with up to 128
760       stripes, a maximum of 64 stripes can  be  converted  to  raid0,  63  to
761       raid4/5  and 62 to raid6 because of the added parity SubLVs.  A striped
762       LV with a maximum of 32 stripes can be converted to raid10.
763
764
765       The following takeover conversions are currently possible:
766
767       ·  between striped and raid0.
768
769       ·  between linear and raid1.
770
771       ·  between mirror and raid1.
772
773       ·  between raid1 with two images and raid4/5.
774
775       ·  between striped/raid0 and raid4.
776
777       ·  between striped/raid0 and raid5.
778
779       ·  between striped/raid0 and raid6.
780
781       ·  between raid4 and raid5.
782
783       ·  between raid4/raid5 and raid6.
784
785       ·  between striped/raid0 and raid10.
786
787       ·  between striped and raid4.
788
789
790   Indirect conversions
791       Converting from one raid level to another may require  multiple  steps,
792       converting first to intermediate raid levels.
793
794       linear to raid6
795
796       To convert an LV from linear to raid6:
797       1. convert to raid1 with two images
798       2. convert to raid5 (internally raid5_ls) with two images
799       3. convert to raid5 with three or more stripes (reshape)
800       4. convert to raid6 (internally raid6_ls_6)
801       5. convert to raid6 (internally raid6_zr, reshape)
802
803       The commands to perform the steps above are:
804       1. lvconvert --type raid1 --mirrors 1 LV
805       2. lvconvert --type raid5 LV
806       3. lvconvert --stripes 3 LV
807       4. lvconvert --type raid6 LV
808       5. lvconvert --type raid6 LV
809
810       The  final  conversion from raid6_ls_6 to raid6_zr is done to avoid the
811       potential write/recovery performance reduction in raid6_ls_6 because of
812       the  dedicated  parity device.  raid6_zr rotates data and parity blocks
813       to avoid this.
814
815       linear to striped
816
817       To convert an LV from linear to striped:
818       1. convert to raid1 with two images
819       2. convert to raid5_n
820       3. convert to raid5_n with five 128k stripes (reshape)
821       4. convert raid5_n to striped
822
823       The commands to perform the steps above are:
824       1. lvconvert --type raid1 --mirrors 1 LV
825       2. lvconvert --type raid5_n LV
826       3. lvconvert --stripes 5 --stripesize 128k LV
827       4. lvconvert --type striped LV
828
829       The raid5_n type in step 2 is used because it has dedicated parity Sub‐
830       LVs  at  the end, and can be converted to striped directly.  The stripe
831       size is increased in step 3 to  add  extra  space  for  the  conversion
832       process.   This step grows the LV size by a factor of five.  After con‐
833       version, this extra space can be reduced (or used to grow the file sys‐
834       tem using the LV).
835
836       Reversing these steps will convert a striped LV to linear.
837
838       raid6 to striped
839
840       To convert an LV from raid6_nr to striped:
841       1. convert to raid6_n_6
842       2. convert to striped
843
844       The commands to perform the steps above are:
845       1. lvconvert --type raid6_n_6 LV
846       2. lvconvert --type striped LV
847
848
849
850   Examples
851       Converting an LV from linear to raid1.
852
853       # lvs -a -o name,segtype,size vg
854         LV   Type   LSize
855         lv   linear 300.00g
856
857       # lvconvert --type raid1 --mirrors 1 vg/lv
858
859       # lvs -a -o name,segtype,size vg
860         LV            Type   LSize
861         lv            raid1  300.00g
862         [lv_rimage_0] linear 300.00g
863         [lv_rimage_1] linear 300.00g
864         [lv_rmeta_0]  linear   3.00m
865         [lv_rmeta_1]  linear   3.00m
866
867       Converting an LV from mirror to raid1.
868
869       # lvs -a -o name,segtype,size vg
870         LV            Type   LSize
871         lv            mirror 100.00g
872         [lv_mimage_0] linear 100.00g
873         [lv_mimage_1] linear 100.00g
874         [lv_mlog]     linear   3.00m
875
876       # lvconvert --type raid1 vg/lv
877
878       # lvs -a -o name,segtype,size vg
879         LV            Type   LSize
880         lv            raid1  100.00g
881         [lv_rimage_0] linear 100.00g
882         [lv_rimage_1] linear 100.00g
883         [lv_rmeta_0]  linear   3.00m
884         [lv_rmeta_1]  linear   3.00m
885
886       Converting an LV from linear to raid1 (with 3 images).
887
888       # lvconvert --type raid1 --mirrors 2 vg/lv
889
890       Converting an LV from striped (with 4 stripes) to raid6_n_6.
891
892       # lvcreate --stripes 4 -L64M -n lv vg
893
894       # lvconvert --type raid6 vg/lv
895
896       # lvs -a -o lv_name,segtype,sync_percent,data_copies
897         LV            Type      Cpy%Sync #Cpy
898         lv            raid6_n_6 100.00      3
899         [lv_rimage_0] linear
900         [lv_rimage_1] linear
901         [lv_rimage_2] linear
902         [lv_rimage_3] linear
903         [lv_rimage_4] linear
904         [lv_rimage_5] linear
905         [lv_rmeta_0]  linear
906         [lv_rmeta_1]  linear
907         [lv_rmeta_2]  linear
908         [lv_rmeta_3]  linear
909         [lv_rmeta_4]  linear
910         [lv_rmeta_5]  linear
911
912       This  convert  begins  by  allocating MetaLVs (rmeta_#) for each of the
913       existing stripe devices.  It then creates  2  additional  MetaLV/DataLV
914       pairs (rmeta_#/rimage_#) for dedicated raid6 parity.
915
916       If  rotating data/parity is required, such as with raid6_nr, it must be
917       done by reshaping (see below).
918
919
920

RAID Reshaping

922       RAID reshaping is changing attributes of a RAID LV  while  keeping  the
923       same  RAID  level.  This includes changing RAID layout, stripe size, or
924       number of stripes.
925
926       When changing the RAID layout or stripe size, no new SubLVs (MetaLVs or
927       DataLVs)  need  to  be  allocated,  but DataLVs are extended by a small
928       amount (typically 1 extent).  The extra space allows blocks in a stripe
929       to  be  updated  safely, and not be corrupted in case of a crash.  If a
930       crash occurs, reshaping can just be restarted.
931
932       (If blocks in a stripe were updated in place, a crash could leave  them
933       partially  updated  and corrupted.  Instead, an existing stripe is qui‐
934       esced, read, changed in layout, and the  new  stripe  written  to  free
935       space.  Once that is done, the new stripe is unquiesced and used.)
936
937
938   Examples
939       (Command output shown in examples may change.)
940
941       Converting raid6_n_6 to raid6_nr with rotating data/parity.
942
943       This   conversion   naturally   follows   a  previous  conversion  from
944       striped/raid0 to raid6_n_6 (shown above).  It completes the  transition
945       to a more traditional RAID6.
946
947       # lvs -o lv_name,segtype,sync_percent,data_copies
948         LV            Type      Cpy%Sync #Cpy
949         lv            raid6_n_6 100.00      3
950         [lv_rimage_0] linear
951         [lv_rimage_1] linear
952         [lv_rimage_2] linear
953         [lv_rimage_3] linear
954         [lv_rimage_4] linear
955         [lv_rimage_5] linear
956         [lv_rmeta_0]  linear
957         [lv_rmeta_1]  linear
958         [lv_rmeta_2]  linear
959         [lv_rmeta_3]  linear
960         [lv_rmeta_4]  linear
961         [lv_rmeta_5]  linear
962
963       # lvconvert --type raid6_nr vg/lv
964
965       # lvs -a -o lv_name,segtype,sync_percent,data_copies
966         LV            Type     Cpy%Sync #Cpy
967         lv            raid6_nr 100.00      3
968         [lv_rimage_0] linear
969         [lv_rimage_0] linear
970         [lv_rimage_1] linear
971         [lv_rimage_1] linear
972         [lv_rimage_2] linear
973         [lv_rimage_2] linear
974         [lv_rimage_3] linear
975         [lv_rimage_3] linear
976         [lv_rimage_4] linear
977         [lv_rimage_5] linear
978         [lv_rmeta_0]  linear
979         [lv_rmeta_1]  linear
980         [lv_rmeta_2]  linear
981         [lv_rmeta_3]  linear
982         [lv_rmeta_4]  linear
983         [lv_rmeta_5]  linear
984
985       The  DataLVs  are  larger  (additional  segment in each) which provides
986       space for out-of-place reshaping.  The result is:
987
988       # lvs -a -o lv_name,segtype,seg_pe_ranges,dataoffset
989         LV            Type     PE Ranges          DOff
990         lv            raid6_nr lv_rimage_0:0-32 \
991                                lv_rimage_1:0-32 \
992                                lv_rimage_2:0-32 \
993                                lv_rimage_3:0-32
994         [lv_rimage_0] linear   /dev/sda:0-31      2048
995         [lv_rimage_0] linear   /dev/sda:33-33
996         [lv_rimage_1] linear   /dev/sdaa:0-31     2048
997         [lv_rimage_1] linear   /dev/sdaa:33-33
998         [lv_rimage_2] linear   /dev/sdab:1-33     2048
999         [lv_rimage_3] linear   /dev/sdac:1-33     2048
1000         [lv_rmeta_0]  linear   /dev/sda:32-32
1001         [lv_rmeta_1]  linear   /dev/sdaa:32-32
1002         [lv_rmeta_2]  linear   /dev/sdab:0-0
1003         [lv_rmeta_3]  linear   /dev/sdac:0-0
1004
1005       All segments with PE ranges '33-33' provide  the  out-of-place  reshape
1006       space.   The  dataoffset column shows that the data was moved from ini‐
1007       tial offset 0 to 2048 sectors on each component DataLV.
1008
1009       For performance reasons the raid6_nr RaidLV can be restriped.   Convert
1010       it from 3-way striped to 5-way-striped.
1011
1012       # lvconvert --stripes 5 vg/lv
1013         Using default stripesize 64.00 KiB.
1014         WARNING: Adding stripes to active logical volume vg/lv will \
1015         grow it from 99 to 165 extents!
1016         Run "lvresize -l99 vg/lv" to shrink it or use the additional \
1017         capacity.
1018         Logical volume vg/lv successfully converted.
1019
1020       # lvs vg/lv
1021         LV   VG     Attr       LSize   Cpy%Sync
1022         lv   vg     rwi-a-r-s- 652.00m 52.94
1023
1024       # lvs -a -o lv_name,attr,segtype,seg_pe_ranges,dataoffset vg
1025         LV            Attr       Type     PE Ranges          DOff
1026         lv            rwi-a-r--- raid6_nr lv_rimage_0:0-33 \
1027                                           lv_rimage_1:0-33 \
1028                                           lv_rimage_2:0-33 ... \
1029                                           lv_rimage_5:0-33 \
1030                                           lv_rimage_6:0-33   0
1031         [lv_rimage_0] iwi-aor--- linear   /dev/sda:0-32      0
1032         [lv_rimage_0] iwi-aor--- linear   /dev/sda:34-34
1033         [lv_rimage_1] iwi-aor--- linear   /dev/sdaa:0-32     0
1034         [lv_rimage_1] iwi-aor--- linear   /dev/sdaa:34-34
1035         [lv_rimage_2] iwi-aor--- linear   /dev/sdab:0-32     0
1036         [lv_rimage_2] iwi-aor--- linear   /dev/sdab:34-34
1037         [lv_rimage_3] iwi-aor--- linear   /dev/sdac:1-34     0
1038         [lv_rimage_4] iwi-aor--- linear   /dev/sdad:1-34     0
1039         [lv_rimage_5] iwi-aor--- linear   /dev/sdae:1-34     0
1040         [lv_rimage_6] iwi-aor--- linear   /dev/sdaf:1-34     0
1041         [lv_rmeta_0]  ewi-aor--- linear   /dev/sda:33-33
1042         [lv_rmeta_1]  ewi-aor--- linear   /dev/sdaa:33-33
1043         [lv_rmeta_2]  ewi-aor--- linear   /dev/sdab:33-33
1044         [lv_rmeta_3]  ewi-aor--- linear   /dev/sdac:0-0
1045         [lv_rmeta_4]  ewi-aor--- linear   /dev/sdad:0-0
1046         [lv_rmeta_5]  ewi-aor--- linear   /dev/sdae:0-0
1047         [lv_rmeta_6]  ewi-aor--- linear   /dev/sdaf:0-0
1048
1049       Stripes  also  can  be  removed  from  raid5  and 6.  Convert the 5-way
1050       striped raid6_nr LV to 4-way-striped.  The force  option  needs  to  be
1051       used,  because  removing stripes (i.e. image SubLVs) from a RaidLV will
1052       shrink its size.
1053
1054       # lvconvert --stripes 4 vg/lv
1055         Using default stripesize 64.00 KiB.
1056         WARNING: Removing stripes from active logical volume vg/lv will \
1057         shrink it from 660.00 MiB to 528.00 MiB!
1058         THIS MAY DESTROY (PARTS OF) YOUR DATA!
1059         If that leaves the logical volume larger than 206 extents due \
1060         to stripe rounding,
1061         you may want to grow the content afterwards (filesystem etc.)
1062         WARNING: to remove freed stripes after the conversion has finished,\
1063         you have to run "lvconvert --stripes 4 vg/lv"
1064         Logical volume vg/lv successfully converted.
1065
1066       # lvs -a -o lv_name,attr,segtype,seg_pe_ranges,dataoffset vg
1067         LV            Attr       Type     PE Ranges          DOff
1068         lv            rwi-a-r-s- raid6_nr lv_rimage_0:0-33 \
1069                                           lv_rimage_1:0-33 \
1070                                           lv_rimage_2:0-33 ... \
1071                                           lv_rimage_5:0-33 \
1072                                           lv_rimage_6:0-33   0
1073         [lv_rimage_0] Iwi-aor--- linear   /dev/sda:0-32      0
1074         [lv_rimage_0] Iwi-aor--- linear   /dev/sda:34-34
1075         [lv_rimage_1] Iwi-aor--- linear   /dev/sdaa:0-32     0
1076         [lv_rimage_1] Iwi-aor--- linear   /dev/sdaa:34-34
1077         [lv_rimage_2] Iwi-aor--- linear   /dev/sdab:0-32     0
1078         [lv_rimage_2] Iwi-aor--- linear   /dev/sdab:34-34
1079         [lv_rimage_3] Iwi-aor--- linear   /dev/sdac:1-34     0
1080         [lv_rimage_4] Iwi-aor--- linear   /dev/sdad:1-34     0
1081         [lv_rimage_5] Iwi-aor--- linear   /dev/sdae:1-34     0
1082         [lv_rimage_6] Iwi-aor-R- linear   /dev/sdaf:1-34     0
1083         [lv_rmeta_0]  ewi-aor--- linear   /dev/sda:33-33
1084         [lv_rmeta_1]  ewi-aor--- linear   /dev/sdaa:33-33
1085         [lv_rmeta_2]  ewi-aor--- linear   /dev/sdab:33-33
1086         [lv_rmeta_3]  ewi-aor--- linear   /dev/sdac:0-0
1087         [lv_rmeta_4]  ewi-aor--- linear   /dev/sdad:0-0
1088         [lv_rmeta_5]  ewi-aor--- linear   /dev/sdae:0-0
1089         [lv_rmeta_6]  ewi-aor-R- linear   /dev/sdaf:0-0
1090
1091       The 's' in column 9 of the attribute field shows the  RaidLV  is  still
1092       reshaping.  The 'R' in the same column of the attribute field shows the
1093       freed image Sub LVs which will need removing once  the  reshaping  fin‐
1094       ished.
1095
1096       # lvs -o lv_name,attr,segtype,seg_pe_ranges,dataoffset vg
1097         LV   Attr       Type     PE Ranges          DOff
1098         lv   rwi-a-r-R- raid6_nr lv_rimage_0:0-33 \
1099                                  lv_rimage_1:0-33 \
1100                                  lv_rimage_2:0-33 ... \
1101                                  lv_rimage_5:0-33 \
1102                                  lv_rimage_6:0-33   8192
1103
1104       Now  that  the reshape is finished the 'R' atribute on the RaidLV shows
1105       images can be removed.
1106
1107       # lvs -o lv_name,attr,segtype,seg_pe_ranges,dataoffset vg
1108         LV   Attr       Type     PE Ranges          DOff
1109         lv   rwi-a-r-R- raid6_nr lv_rimage_0:0-33 \
1110                                  lv_rimage_1:0-33 \
1111                                  lv_rimage_2:0-33 ... \
1112                                  lv_rimage_5:0-33 \
1113                                  lv_rimage_6:0-33   8192
1114
1115       This is achieved by  repeating  the  command  ("lvconvert  --stripes  4
1116       vg/lv" would be sufficient).
1117
1118       # lvconvert --stripes 4 vg/lv
1119         Using default stripesize 64.00 KiB.
1120         Logical volume vg/lv successfully converted.
1121
1122       # lvs -a -o lv_name,attr,segtype,seg_pe_ranges,dataoffset vg
1123         LV            Attr       Type     PE Ranges          DOff
1124         lv            rwi-a-r--- raid6_nr lv_rimage_0:0-33 \
1125                                           lv_rimage_1:0-33 \
1126                                           lv_rimage_2:0-33 ... \
1127                                           lv_rimage_5:0-33   8192
1128         [lv_rimage_0] iwi-aor--- linear   /dev/sda:0-32      8192
1129         [lv_rimage_0] iwi-aor--- linear   /dev/sda:34-34
1130         [lv_rimage_1] iwi-aor--- linear   /dev/sdaa:0-32     8192
1131         [lv_rimage_1] iwi-aor--- linear   /dev/sdaa:34-34
1132         [lv_rimage_2] iwi-aor--- linear   /dev/sdab:0-32     8192
1133         [lv_rimage_2] iwi-aor--- linear   /dev/sdab:34-34
1134         [lv_rimage_3] iwi-aor--- linear   /dev/sdac:1-34     8192
1135         [lv_rimage_4] iwi-aor--- linear   /dev/sdad:1-34     8192
1136         [lv_rimage_5] iwi-aor--- linear   /dev/sdae:1-34     8192
1137         [lv_rmeta_0]  ewi-aor--- linear   /dev/sda:33-33
1138         [lv_rmeta_1]  ewi-aor--- linear   /dev/sdaa:33-33
1139         [lv_rmeta_2]  ewi-aor--- linear   /dev/sdab:33-33
1140         [lv_rmeta_3]  ewi-aor--- linear   /dev/sdac:0-0
1141         [lv_rmeta_4]  ewi-aor--- linear   /dev/sdad:0-0
1142         [lv_rmeta_5]  ewi-aor--- linear   /dev/sdae:0-0
1143
1144       # lvs -a -o lv_name,attr,segtype,reshapelen vg
1145         LV            Attr       Type     RSize
1146         lv            rwi-a-r--- raid6_nr 24.00m
1147         [lv_rimage_0] iwi-aor--- linear    4.00m
1148         [lv_rimage_0] iwi-aor--- linear
1149         [lv_rimage_1] iwi-aor--- linear    4.00m
1150         [lv_rimage_1] iwi-aor--- linear
1151         [lv_rimage_2] iwi-aor--- linear    4.00m
1152         [lv_rimage_2] iwi-aor--- linear
1153         [lv_rimage_3] iwi-aor--- linear    4.00m
1154         [lv_rimage_4] iwi-aor--- linear    4.00m
1155         [lv_rimage_5] iwi-aor--- linear    4.00m
1156         [lv_rmeta_0]  ewi-aor--- linear
1157         [lv_rmeta_1]  ewi-aor--- linear
1158         [lv_rmeta_2]  ewi-aor--- linear
1159         [lv_rmeta_3]  ewi-aor--- linear
1160         [lv_rmeta_4]  ewi-aor--- linear
1161         [lv_rmeta_5]  ewi-aor--- linear
1162
1163       Future  developments  might  include  automatic  removal  of  the freed
1164       images.
1165
1166       If the reshape space shall be removed any lvconvert command not  chang‐
1167       ing the layout can be used:
1168
1169       # lvconvert --stripes 4 vg/lv
1170         Using default stripesize 64.00 KiB.
1171         No change in RAID LV vg/lv layout, freeing reshape space.
1172         Logical volume vg/lv successfully converted.
1173
1174       # lvs -a -o lv_name,attr,segtype,reshapelen vg
1175         LV            Attr       Type     RSize
1176         lv            rwi-a-r--- raid6_nr    0
1177         [lv_rimage_0] iwi-aor--- linear      0
1178         [lv_rimage_0] iwi-aor--- linear
1179         [lv_rimage_1] iwi-aor--- linear      0
1180         [lv_rimage_1] iwi-aor--- linear
1181         [lv_rimage_2] iwi-aor--- linear      0
1182         [lv_rimage_2] iwi-aor--- linear
1183         [lv_rimage_3] iwi-aor--- linear      0
1184         [lv_rimage_4] iwi-aor--- linear      0
1185         [lv_rimage_5] iwi-aor--- linear      0
1186         [lv_rmeta_0]  ewi-aor--- linear
1187         [lv_rmeta_1]  ewi-aor--- linear
1188         [lv_rmeta_2]  ewi-aor--- linear
1189         [lv_rmeta_3]  ewi-aor--- linear
1190         [lv_rmeta_4]  ewi-aor--- linear
1191         [lv_rmeta_5]  ewi-aor--- linear
1192
1193       In case the RaidLV should be converted to striped:
1194
1195       # lvconvert --type striped vg/lv
1196         Unable to convert LV vg/lv from raid6_nr to striped.
1197         Converting vg/lv from raid6_nr is directly possible to the \
1198         following layouts:
1199           raid6_nc
1200           raid6_zr
1201           raid6_la_6
1202           raid6_ls_6
1203           raid6_ra_6
1204           raid6_rs_6
1205           raid6_n_6
1206
1207       A  direct conversion isn't possible thus the command informed about the
1208       possible ones.  raid6_n_6 is suitable to convert to striped so  convert
1209       to  it first (this is a reshape changing the raid6 layout from raid6_nr
1210       to raid6_n_6).
1211
1212       # lvconvert --type raid6_n_6
1213         Using default stripesize 64.00 KiB.
1214         Converting raid6_nr LV vg/lv to raid6_n_6.
1215       Are you sure you want to convert raid6_nr LV vg/lv? [y/n]: y
1216         Logical volume vg/lv successfully converted.
1217
1218       Wait for the reshape to finish.
1219
1220       # lvconvert --type striped vg/lv
1221         Logical volume vg/lv successfully converted.
1222
1223       # lvs -o lv_name,attr,segtype,seg_pe_ranges,dataoffset vg
1224         LV   Attr       Type    PE Ranges  DOff
1225         lv   -wi-a----- striped /dev/sda:2-32 \
1226                                 /dev/sdaa:2-32 \
1227                                 /dev/sdab:2-32 \
1228                                 /dev/sdac:3-33
1229         lv   -wi-a----- striped /dev/sda:34-35 \
1230                                 /dev/sdaa:34-35 \
1231                                 /dev/sdab:34-35 \
1232                                 /dev/sdac:34-35
1233
1234       From striped we can convert to raid10
1235
1236       # lvconvert --type raid10 vg/lv
1237         Using default stripesize 64.00 KiB.
1238         Logical volume vg/lv successfully converted.
1239
1240       # lvs -o lv_name,attr,segtype,seg_pe_ranges,dataoffset vg
1241         LV   Attr       Type   PE Ranges          DOff
1242         lv   rwi-a-r--- raid10 lv_rimage_0:0-32 \
1243                                lv_rimage_4:0-32 \
1244                                lv_rimage_1:0-32 ... \
1245                                lv_rimage_3:0-32 \
1246                                lv_rimage_7:0-32   0
1247
1248       # lvs -a -o lv_name,attr,segtype,seg_pe_ranges,dataoffset vg
1249         WARNING: Cannot find matching striped segment for vg/lv_rimage_3.
1250         LV            Attr       Type   PE Ranges          DOff
1251         lv            rwi-a-r--- raid10 lv_rimage_0:0-32 \
1252                                         lv_rimage_4:0-32 \
1253                                         lv_rimage_1:0-32 ... \
1254                                         lv_rimage_3:0-32 \
1255                                         lv_rimage_7:0-32   0
1256         [lv_rimage_0] iwi-aor--- linear /dev/sda:2-32      0
1257         [lv_rimage_0] iwi-aor--- linear /dev/sda:34-35
1258         [lv_rimage_1] iwi-aor--- linear /dev/sdaa:2-32     0
1259         [lv_rimage_1] iwi-aor--- linear /dev/sdaa:34-35
1260         [lv_rimage_2] iwi-aor--- linear /dev/sdab:2-32     0
1261         [lv_rimage_2] iwi-aor--- linear /dev/sdab:34-35
1262         [lv_rimage_3] iwi-XXr--- linear /dev/sdac:3-35     0
1263         [lv_rimage_4] iwi-aor--- linear /dev/sdad:1-33     0
1264         [lv_rimage_5] iwi-aor--- linear /dev/sdae:1-33     0
1265         [lv_rimage_6] iwi-aor--- linear /dev/sdaf:1-33     0
1266         [lv_rimage_7] iwi-aor--- linear /dev/sdag:1-33     0
1267         [lv_rmeta_0]  ewi-aor--- linear /dev/sda:0-0
1268         [lv_rmeta_1]  ewi-aor--- linear /dev/sdaa:0-0
1269         [lv_rmeta_2]  ewi-aor--- linear /dev/sdab:0-0
1270         [lv_rmeta_3]  ewi-aor--- linear /dev/sdac:0-0
1271         [lv_rmeta_4]  ewi-aor--- linear /dev/sdad:0-0
1272         [lv_rmeta_5]  ewi-aor--- linear /dev/sdae:0-0
1273         [lv_rmeta_6]  ewi-aor--- linear /dev/sdaf:0-0
1274         [lv_rmeta_7]  ewi-aor--- linear /dev/sdag:0-0
1275
1276       raid10 allows to add stripes but can't remove them.
1277
1278
1279       A more elaborate example to convert from linear to striped with interim
1280       conversions to raid1 then raid5 followed by restripe (4 steps).
1281
1282       We start with the linear LV.
1283
1284       # lvs -a -o name,size,segtype,syncpercent,datastripes,\
1285                   stripesize,reshapelenle,devices vg
1286         LV   LSize   Type   Cpy%Sync #DStr Stripe RSize Devices
1287         lv   128.00m linear              1     0        /dev/sda(0)
1288
1289       Then convert it to a 2-way raid1.
1290
1291       # lvconvert --mirrors 1 vg/lv
1292         Logical volume vg/lv successfully converted.
1293
1294       # lvs -a -o name,size,segtype,datastripes,\
1295                   stripesize,reshapelenle,devices vg
1296         LV            LSize   Type   #DStr Stripe RSize Devices
1297         lv            128.00m raid1      2     0        lv_rimage_0(0),\
1298                                                         lv_rimage_1(0)
1299         [lv_rimage_0] 128.00m linear     1     0        /dev/sda(0)
1300         [lv_rimage_1] 128.00m linear     1     0        /dev/sdhx(1)
1301         [lv_rmeta_0]    4.00m linear     1     0        /dev/sda(32)
1302         [lv_rmeta_1]    4.00m linear     1     0        /dev/sdhx(0)
1303
1304       Once  the raid1 LV is fully synchronized we convert it to raid5_n (only
1305       2-way raid1 LVs can be converted to raid5).   We  select  raid5_n  here
1306       because  it has dedicated parity SubLVs at the end and can be converted
1307       to striped directly without any additional conversion.
1308
1309       # lvconvert --type raid5_n vg/lv
1310         Using default stripesize 64.00 KiB.
1311         Logical volume vg/lv successfully converted.
1312
1313       # lvs -a -o name,size,segtype,syncpercent,datastripes,\
1314                   stripesize,reshapelenle,devices vg
1315         LV            LSize   Type    #DStr Stripe RSize Devices
1316         lv            128.00m raid5_n     1 64.00k     0 lv_rimage_0(0),\
1317                                                          lv_rimage_1(0)
1318         [lv_rimage_0] 128.00m linear      1     0      0 /dev/sda(0)
1319         [lv_rimage_1] 128.00m linear      1     0      0 /dev/sdhx(1)
1320         [lv_rmeta_0]    4.00m linear      1     0        /dev/sda(32)
1321         [lv_rmeta_1]    4.00m linear      1     0        /dev/sdhx(0)
1322
1323       Now we'll change the number of data stripes from 1  to  5  and  request
1324       128K  stripe size in one command.  This will grow the size of the LV by
1325       a factor of 5 (we add 4 data stripes to the one given).  That additonal
1326       space  can  be  used by e.g. growing any contained filesystem or the LV
1327       can be reduced in size after the reshaping conversion has finished.
1328
1329       # lvconvert --stripesize 128k --stripes 5 vg/lv
1330         Converting stripesize 64.00 KiB of raid5_n LV vg/lv to 128.00 KiB.
1331         WARNING: Adding stripes to active logical volume vg/lv will grow \
1332         it from 32 to 160 extents!
1333         Run "lvresize -l32 vg/lv" to shrink it or use the additional capacity.
1334         Logical volume vg/lv successfully converted.
1335
1336       # lvs -a -o name,size,segtype,datastripes,\
1337                   stripesize,reshapelenle,devices
1338         LV            LSize   Type    #DStr Stripe  RSize Devices
1339         lv            640.00m raid5_n     5 128.00k     6 lv_rimage_0(0),\
1340                                                           lv_rimage_1(0),\
1341                                                           lv_rimage_2(0),\
1342                                                           lv_rimage_3(0),\
1343                                                           lv_rimage_4(0),\
1344                                                           lv_rimage_5(0)
1345         [lv_rimage_0] 132.00m linear      1      0      1 /dev/sda(33)
1346         [lv_rimage_0] 132.00m linear      1      0        /dev/sda(0)
1347         [lv_rimage_1] 132.00m linear      1      0      1 /dev/sdhx(33)
1348         [lv_rimage_1] 132.00m linear      1      0        /dev/sdhx(1)
1349         [lv_rimage_2] 132.00m linear      1      0      1 /dev/sdhw(33)
1350         [lv_rimage_2] 132.00m linear      1      0        /dev/sdhw(1)
1351         [lv_rimage_3] 132.00m linear      1      0      1 /dev/sdhv(33)
1352         [lv_rimage_3] 132.00m linear      1      0        /dev/sdhv(1)
1353         [lv_rimage_4] 132.00m linear      1      0      1 /dev/sdhu(33)
1354         [lv_rimage_4] 132.00m linear      1      0        /dev/sdhu(1)
1355         [lv_rimage_5] 132.00m linear      1      0      1 /dev/sdht(33)
1356         [lv_rimage_5] 132.00m linear      1      0        /dev/sdht(1)
1357         [lv_rmeta_0]    4.00m linear      1      0        /dev/sda(32)
1358         [lv_rmeta_1]    4.00m linear      1      0        /dev/sdhx(0)
1359         [lv_rmeta_2]    4.00m linear      1      0        /dev/sdhw(0)
1360         [lv_rmeta_3]    4.00m linear      1      0        /dev/sdhv(0)
1361         [lv_rmeta_4]    4.00m linear      1      0        /dev/sdhu(0)
1362         [lv_rmeta_5]    4.00m linear      1      0        /dev/sdht(0)
1363
1364       Once the conversion has finished we can can convert to striped.
1365
1366       # lvconvert --type striped vg/lv
1367         Logical volume vg/lv successfully converted.
1368
1369       # lvs -a -o name,size,segtype,datastripes,\
1370                   stripesize,reshapelenle,devices vg
1371         LV   LSize   Type    #DStr Stripe  RSize Devices
1372         lv   640.00m striped     5 128.00k       /dev/sda(33),\
1373                                                  /dev/sdhx(33),\
1374                                                  /dev/sdhw(33),\
1375                                                  /dev/sdhv(33),\
1376                                                  /dev/sdhu(33)
1377         lv   640.00m striped     5 128.00k       /dev/sda(0),\
1378                                                  /dev/sdhx(1),\
1379                                                  /dev/sdhw(1),\
1380                                                  /dev/sdhv(1),\
1381                                                  /dev/sdhu(1)
1382
1383       Reversing these steps will convert a given striped LV to linear.
1384
1385       Mind the facts that stripes are removed thus the capacity of the RaidLV
1386       will shrink and that changing the RaidLV layout will influence its per‐
1387       formance.
1388
1389       "lvconvert --stripes 1 vg/lv" for converting to 1  stripe  will  inform
1390       upfront  about  the  reduced  size to allow for resizing the content or
1391       growing the RaidLV before actually converting to 1 stripe.  The --force
1392       option  is  needed to allow stripe removing conversions to prevent data
1393       loss.
1394
1395       Of course any interim step can be the intended last one (e.g. striped->
1396       raid1).
1397
1398

RAID5 Variants

1400       raid5_ls
1401       · RAID5 left symmetric
1402       · Rotating parity N with data restart
1403
1404       raid5_la
1405       · RAID5 left symmetric
1406       · Rotating parity N with data continuation
1407
1408       raid5_rs
1409       · RAID5 right symmetric
1410       · Rotating parity 0 with data restart
1411
1412       raid5_ra
1413       · RAID5 right asymmetric
1414       · Rotating parity 0 with data continuation
1415
1416       raid5_n
1417       · RAID5 parity n
1418       · Dedicated parity device n used for striped/raid0 conversions
1419       · Used for RAID Takeover
1420
1421

RAID6 Variants

1423       raid6
1424       · RAID6 zero restart (aka left symmetric)
1425       · Rotating parity 0 with data restart
1426       · Same as raid6_zr
1427
1428       raid6_zr
1429       · RAID6 zero restart (aka left symmetric)
1430       · Rotating parity 0 with data restart
1431
1432       raid6_nr
1433       · RAID6 N restart (aka right symmetric)
1434       · Rotating parity N with data restart
1435
1436       raid6_nc
1437       · RAID6 N continue
1438       · Rotating parity N with data continuation
1439
1440       raid6_n_6
1441       · RAID6 last parity devices
1442       · Fixed dedicated last devices (P-Syndrome N-1 and Q-Syndrome N)
1443         with striped data used for striped/raid0 conversions
1444       · Used for RAID Takeover
1445
1446       raid6_{ls,rs,la,ra}_6
1447       · RAID6 last parity device
1448       · Dedicated last parity device used for conversions from/to
1449         raid5_{ls,rs,la,ra}
1450
1451       raid6_ls_6
1452       · RAID6 N continue
1453       · Same as raid5_ls for N-1 devices with fixed Q-Syndrome N
1454       · Used for RAID Takeover
1455
1456       raid6_la_6
1457       · RAID6 N continue
1458       · Same as raid5_la for N-1 devices with fixed Q-Syndrome N
1459       · Used forRAID Takeover
1460
1461       raid6_rs_6
1462       · RAID6 N continue
1463       · Same as raid5_rs for N-1 devices with fixed Q-Syndrome N
1464       · Used for RAID Takeover
1465
1466       raid6_ra_6
1467       · RAID6 N continue
1468       · ame as raid5_ra for N-1 devices with fixed Q-Syndrome N
1469       · Used for RAID Takeover
1470
1471
1472
1473

History

1475       The  2.6.38-rc1  version of the Linux kernel introduced a device-mapper
1476       target to interface with the software RAID  (MD)  personalities.   This
1477       provided device-mapper with RAID 4/5/6 capabilities and a larger devel‐
1478       opment community.  Later, support for RAID1, RAID10, and  RAID1E  (RAID
1479       10 variants) were added.  Support for these new kernel RAID targets was
1480       added to LVM version 2.02.87.  The capabilities of the LVM  raid1  type
1481       have  surpassed  the old mirror type.  raid1 is now recommended instead
1482       of mirror.  raid1 became the  default  for  mirroring  in  LVM  version
1483       2.02.100.
1484
1485
1486
1487
1488Red Hat, Inc           LVM TOOLS 2.03.09(2) (2020-03-26)            LVMRAID(7)
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