1LVMTHIN(7) LVMTHIN(7)
2
6 lvmthin — LVM thin provisioning
7
10 Blocks in a standard logical volume are allocated when the LV is cre‐
11 ated, but blocks in a thin provisioned logical volume are allocated as
12 they are written. Because of this, a thin provisioned LV is given a
13 virtual size, and can then be much larger than physically available
14 storage. The amount of physical storage provided for thin provisioned
15 LVs can be increased later as the need arises.
16 Blocks in a standard LV are allocated (during creation) from the VG,
18 but blocks in a thin LV are allocated (during use) from a special "thin
19 pool LV". The thin pool LV contains blocks of physical storage, and
20 blocks in thin LVs just reference blocks in the thin pool LV.
21 A thin pool LV must be created before thin LVs can be created within
23 it. A thin pool LV is created by combining two standard LVs: a large
24 data LV that will hold blocks for thin LVs, and a metadata LV that will
25 hold metadata. The metadata tracks which data blocks belong to each
26 thin LV.
27 Snapshots of thin LVs are efficient because the data blocks common to a
29 thin LV and any of its snapshots are shared. Snapshots may be taken of
30 thin LVs or of other thin snapshots. Blocks common to recursive snap‐
31 shots are also shared in the thin pool. There is no limit to or degra‐
32 dation from sequences of snapshots.
33 As thin LVs or snapshot LVs are written to, they consume data blocks in
35 the thin pool. As free data blocks in the pool decrease, more free
36 blocks may need to be supplied. This is done by extending the thin
37 pool data LV with additional physical space from the VG. Removing thin
38 LVs or snapshots from the thin pool can also free blocks in the thin
39 pool. However, removing LVs is not always an effective way of freeing
40 space in a thin pool because the amount is limited to the number of
41 blocks not shared with other LVs in the pool.
42 Incremental block allocation from thin pools can cause thin LVs to
44 become fragmented. Standard LVs generally avoid this problem by allo‐
45 cating all the blocks at once during creation.
46
50 ThinDataLV
51 thin data LV
52 large LV created in a VG
53 used by thin pool to store ThinLV blocks
54 ThinMetaLV
57 thin metadata LV
58 small LV created in a VG
59 used by thin pool to track data block usage
60 ThinPoolLV
63 thin pool LV
64 combination of ThinDataLV and ThinMetaLV
65 contains ThinLVs and SnapLVs
66 ThinLV
69 thin LV
70 created from ThinPoolLV
71 appears blank after creation
72 SnapLV
75 snapshot LV
76 created from ThinPoolLV
77 appears as a snapshot of another LV after creation
78
83 The primary method for using lvm thin provisioning:
84 1. create ThinDataLV
87 Create an LV that will hold thin pool data.
88 lvcreate -n ThinDataLV -L LargeSize VG
90 Example
92 # lvcreate -n pool0 -L 10G vg
93 2. create ThinMetaLV
96 Create an LV that will hold thin pool metadata.
97 lvcreate -n ThinMetaLV -L SmallSize VG
99 Example
101 # lvcreate -n pool0meta -L 1G vg
102 # lvs
104 LV VG Attr LSize
105 pool0 vg -wi-a----- 10.00g
106 pool0meta vg -wi-a----- 1.00g
107 3. create ThinPoolLV
110 Combine the data and metadata LVs into a thin pool LV.
111 ThinDataLV is renamed to hidden ThinPoolLV_tdata.
112 ThinMetaLV is renamed to hidden ThinPoolLV_tmeta.
113 The new ThinPoolLV takes the previous name of ThinDataLV.
114 lvconvert --type thin-pool --poolmetadata VG/ThinMetaLV VG/ThinDataLV
116 Example
118 # lvconvert --type thin-pool --poolmetadata vg/pool0meta vg/pool0
119 # lvs vg/pool0
121 LV VG Attr LSize Pool Origin Data% Meta%
122 pool0 vg twi-a-tz-- 10.00g 0.00 0.00
123 # lvs -a
125 LV VG Attr LSize
126 pool0 vg twi-a-tz-- 10.00g
127 [pool0_tdata] vg Twi-ao---- 10.00g
128 [pool0_tmeta] vg ewi-ao---- 1.00g
129 4. create ThinLV
132 Create a new thin LV from the thin pool LV.
133 The thin LV is created with a virtual size.
134 Multiple new thin LVs may be created in the thin pool.
135 Thin LV names must be unique in the VG.
136 The '--type thin' option is inferred from the virtual size option.
137 The --thinpool argument specifies which thin pool will
138 contain the ThinLV.
139 lvcreate -n ThinLV -V VirtualSize --thinpool VG/ThinPoolLV
141 Example
143 Create a thin LV in a thin pool:
144 # lvcreate -n thin1 -V 1T --thinpool vg/pool0
145 Create another thin LV in the same thin pool:
147 # lvcreate -n thin2 -V 1T --thinpool vg/pool0
148 # lvs vg/thin1 vg/thin2
150 LV VG Attr LSize Pool Origin Data%
151 thin1 vg Vwi-a-tz-- 1.00t pool0 0.00
152 thin2 vg Vwi-a-tz-- 1.00t pool0 0.00
153 5. create SnapLV
156 Create snapshots of an existing ThinLV or SnapLV.
157 Do not specify -L, --size when creating a thin snapshot.
158 A size argument will cause an old COW snapshot to be created.
159 lvcreate -n SnapLV -s VG/ThinLV
161 lvcreate -n SnapLV -s VG/PrevSnapLV
162 Example
164 Create first snapshot of an existing ThinLV:
165 # lvcreate -n thin1s1 -s vg/thin1
166 Create second snapshot of the same ThinLV:
168 # lvcreate -n thin1s2 -s vg/thin1
169 Create a snapshot of the first snapshot:
171 # lvcreate -n thin1s1s1 -s vg/thin1s1
172 # lvs vg/thin1s1 vg/thin1s2 vg/thin1s1s1
174 LV VG Attr LSize Pool Origin
175 thin1s1 vg Vwi---tz-k 1.00t pool0 thin1
176 thin1s2 vg Vwi---tz-k 1.00t pool0 thin1
177 thin1s1s1 vg Vwi---tz-k 1.00t pool0 thin1s1
178 6. activate SnapLV
181 Thin snapshots are created with the persistent "activation skip" flag,
182 indicated by the "k" attribute. Use -K with lvchange or vgchange to
183 activate thin snapshots with the "k" attribute.
184 lvchange -ay -K VG/SnapLV
186 Example
188 # lvchange -ay -K vg/thin1s1
189 # lvs vg/thin1s1
191 LV VG Attr LSize Pool Origin
192 thin1s1 vg Vwi-a-tz-k 1.00t pool0 thin1
193
196 Alternate syntax for specifying type thin-pool
197 Automatic pool metadata LV
198 Specify devices for data and metadata LVs
199 Tolerate device failures using raid
200 Spare metadata LV
201 Metadata check and repair
202 Activation of thin snapshots
203 Removing thin pool LVs, thin LVs and snapshots
204 Manually manage free data space of thin pool LV
205 Manually manage free metadata space of a thin pool LV
206 Using fstrim to increase free space in a thin pool LV
207 Automatically extend thin pool LV
208 Data space exhaustion
209 Metadata space exhaustion
210 Automatic extend settings
211 Zeroing
212 Discard
213 Chunk size
214 Size of pool metadata LV
215 Create a thin snapshot of an external, read only LV
216 Convert a standard LV to a thin LV with an external origin
217 Single step thin pool LV creation
218 Single step thin pool LV and thin LV creation
219 Merge thin snapshots
220 XFS on snapshots
221 Alternate syntax for specifying type thin-pool
226 The fully specified syntax for creating a thin pool LV shown above is:
229 lvconvert --type thin-pool --poolmetadata VG/ThinMetaLV VG/ThinDataLV
231 An existing LV is converted to a thin pool by changing its type to
233 thin-pool. An alternate syntax may be used for the same operation:
234 lvconvert --thinpool VG/ThinDataLV --poolmetadata VG/ThinMetaLV
236 The thin-pool type is inferred by lvm; the --thinpool option is not an
238 alias for --type thin-pool. The use of the --thinpool option here is
239 different from the use of the --thinpool option when creating a thin
240 LV, where it specifies the pool in which the thin LV is created.
241 Automatic pool metadata LV
245 A thin data LV can be converted to a thin pool LV without specifying a
248 thin pool metadata LV. LVM automatically creates a metadata LV from
249 the same VG.
250 lvcreate -n ThinDataLV -L LargeSize VG
252 lvconvert --type thin-pool VG/ThinDataLV
253 Example
255 # lvcreate -n pool0 -L 10G vg
256 # lvconvert --type thin-pool vg/pool0
257 # lvs -a
259 pool0 vg twi-a-tz-- 10.00g
260 [pool0_tdata] vg Twi-ao---- 10.00g
261 [pool0_tmeta] vg ewi-ao---- 16.00m
262 Specify devices for data and metadata LVs
266 The data and metadata LVs in a thin pool are best created on separate
269 physical devices. To do that, specify the device name(s) at the end of
270 the lvcreate line. It can be especially helpful to use fast devices
271 for the metadata LV.
272 lvcreate -n ThinDataLV -L LargeSize VG LargePV
274 lvcreate -n ThinMetaLV -L SmallSize VG SmallPV
275 lvconvert --type thin-pool --poolmetadata VG/ThinMetaLV VG/ThinDataLV
276 Example
278 # lvcreate -n pool0 -L 10G vg /dev/sdA
279 # lvcreate -n pool0meta -L 1G vg /dev/sdB
280 # lvconvert --type thin-pool --poolmetadata vg/pool0meta vg/pool0
281 lvm.conf(5) thin_pool_metadata_require_separate_pvs
283 controls the default PV usage for thin pool creation.
284 Tolerate device failures using raid
289 To tolerate device failures, use raid for the pool data LV and pool
292 metadata LV. This is especially recommended for pool metadata LVs.
293 lvcreate --type raid1 -m 1 -n ThinMetaLV -L SmallSize VG PVA PVB
295 lvcreate --type raid1 -m 1 -n ThinDataLV -L LargeSize VG PVC PVD
296 lvconvert --type thin-pool --poolmetadata VG/ThinMetaLV VG/ThinDataLV
297 Example
299 # lvcreate --type raid1 -m 1 -n pool0 -L 10G vg /dev/sdA /dev/sdB
300 # lvcreate --type raid1 -m 1 -n pool0meta -L 1G vg /dev/sdC /dev/sdD
301 # lvconvert --type thin-pool --poolmetadata vg/pool0meta vg/pool0
302 Spare metadata LV
306 The first time a thin pool LV is created, lvm will create a spare meta‐
309 data LV in the VG. This behavior can be controlled with the option
310 --poolmetadataspare y|n. (Future thin pool creations will also attempt
311 to create the pmspare LV if none exists.)
312 To create the pmspare ("pool metadata spare") LV, lvm first creates an
314 LV with a default name, e.g. lvol0, and then converts this LV to a hid‐
315 den LV with the _pmspare suffix, e.g. lvol0_pmspare.
316 One pmspare LV is kept in a VG to be used for any thin pool.
318 The pmspare LV cannot be created explicitly, but may be removed explic‐
320 itly.
321 Example
323 # lvcreate -n pool0 -L 10G vg
324 # lvcreate -n pool0meta -L 1G vg
325 # lvconvert --type thin-pool --poolmetadata vg/pool0meta vg/pool0
326 # lvs -a
328 [lvol0_pmspare] vg ewi-------
329 pool0 vg twi---tz--
330 [pool0_tdata] vg Twi-------
331 [pool0_tmeta] vg ewi-------
332 The "Metadata check and repair" section describes the use of the pms‐
334 pare LV.
335 Metadata check and repair
339 If thin pool metadata is damaged, it may be repairable. Checking and
342 repairing thin pool metadata is analagous to running fsck on a file
343 system.
344 When a thin pool LV is activated, lvm runs the thin_check command to
346 check the correctness of the metadata on the pool metadata LV.
347 lvm.conf(5) thin_check_executable
349 can be set to an empty string ("") to disable the thin_check step.
350 This is not recommended.
351 lvm.conf(5) thin_check_options
353 controls the command options used for the thin_check command.
354 If the thin_check command finds a problem with the metadata, the thin
356 pool LV is not activated, and the thin pool metadata needs to be
357 repaired.
358 Simple repair commands are not always successful. Advanced repair may
360 require editing thin pool metadata and lvm metadata. Newer versions of
361 the kernel and lvm tools may be more successful at repair. Report the
362 details of damaged thin metadata to get the best advice on recovery.
363 Command to repair a thin pool:
365 lvconvert --repair VG/ThinPoolLV
366 Repair performs the following steps:
368 1. Creates a new, repaired copy of the metadata.
370 lvconvert runs the thin_repair command to read damaged metadata from
371 the existing pool metadata LV, and writes a new repaired copy to the
372 VG's pmspare LV.
373 2. Replaces the thin pool metadata LV.
375 If step 1 is successful, the thin pool metadata LV is replaced with the
376 pmspare LV containing the corrected metadata. The previous thin pool
377 metadata LV, containing the damaged metadata, becomes visible with the
378 new name ThinPoolLV_tmetaN (where N is 0,1,...).
379 If the repair works, the thin pool LV and its thin LVs can be acti‐
381 vated, and the LV containing the damaged thin pool metadata can be
382 removed. It may be useful to move the new metadata LV (previously pms‐
383 pare) to a better PV.
384 If the repair does not work, the thin pool LV and its thin LVs are
386 lost.
387 If metadata is manually restored with thin_repair directly, the pool
389 metadata LV can be manually swapped with another LV containing new
390 metadata:
391 lvconvert --thinpool VG/ThinPoolLV --poolmetadata VG/NewThinMetaLV
393 Activation of thin snapshots
397 When a thin snapshot LV is created, it is by default given the "activa‐
400 tion skip" flag. This flag is indicated by the "k" attribute displayed
401 by lvs:
402 # lvs vg/thin1s1
404 LV VG Attr LSize Pool Origin
405 thin1s1 vg Vwi---tz-k 1.00t pool0 thin1
406 This flag causes the snapshot LV to be skipped, i.e. not activated, by
408 normal activation commands. The skipping behavior does not apply to
409 deactivation commands.
410 A snapshot LV with the "k" attribute can be activated using the -K (or
412 --ignoreactivationskip) option in addition to the standard -ay (or
413 --activate y) option.
414 Command to activate a thin snapshot LV:
416 lvchange -ay -K VG/SnapLV
417 The persistent "activation skip" flag can be turned off during lvcre‐
419 ate, or later with lvchange using the -kn (or --setactivationskip n)
420 option. It can be turned on again with -ky (or --setactivationskip y).
421 When the "activation skip" flag is removed, normal activation commands
423 will activate the LV, and the -K activation option is not needed.
424 Command to create snapshot LV without the activation skip flag:
426 lvcreate -kn -n SnapLV -s VG/ThinLV
427 Command to remove the activation skip flag from a snapshot LV:
429 lvchange -kn VG/SnapLV
430 lvm.conf(5) auto_set_activation_skip
432 controls the default activation skip setting used by lvcreate.
433 Removing thin pool LVs, thin LVs and snapshots
437 Removing a thin LV and its related snapshots returns the blocks it used
440 to the thin pool LV. These blocks will be reused for other thin LVs
441 and snapshots.
442 Removing a thin pool LV removes both the data LV and metadata LV and
444 returns the space to the VG.
445 lvremove of thin pool LVs, thin LVs and snapshots cannot be reversed
447 with vgcfgrestore.
448 vgcfgbackup does not back up thin pool metadata.
450 Manually manage free data space of thin pool LV
454 The available free space in a thin pool LV can be displayed with the
457 lvs command. Free space can be added by extending the thin pool LV.
458 Command to extend thin pool data space:
460 lvextend -L Size VG/ThinPoolLV
461 Example
463 1. A thin pool LV is using 26.96% of its data blocks.
464 # lvs
465 LV VG Attr LSize Pool Origin Data%
466 pool0 vg twi-a-tz-- 10.00g 26.96
467 2. Double the amount of physical space in the thin pool LV.
469 # lvextend -L+10G vg/pool0
470 3. The percentage of used data blocks is half the previous value.
472 # lvs
473 LV VG Attr LSize Pool Origin Data%
474 pool0 vg twi-a-tz-- 20.00g 13.48
475 Other methods of increasing free data space in a thin pool LV include
477 removing a thin LV and its related snapsots, or running fstrim on the
478 file system using a thin LV.
479 Manually manage free metadata space of a thin pool LV
483 The available metadata space in a thin pool LV can be displayed with
486 the lvs -o+metadata_percent command.
487 Command to extend thin pool metadata space:
489 lvextend --poolmetadatasize Size VG/ThinPoolLV
490 Example
492 1. A thin pool LV is using 12.40% of its metadata blocks.
493 # lvs -oname,size,data_percent,metadata_percent vg/pool0
494 LV LSize Data% Meta%
495 pool0 20.00g 13.48 12.40
496 2. Display a thin pool LV with its component thin data LV and thin
498 metadata LV.
499 # lvs -a -oname,attr,size vg
500 LV Attr LSize
501 pool0 twi-a-tz-- 20.00g
502 [pool0_tdata] Twi-ao---- 20.00g
503 [pool0_tmeta] ewi-ao---- 12.00m
504 3. Double the amount of physical space in the thin metadata LV.
506 # lvextend --poolmetadatasize +12M vg/pool0
507 4. The percentage of used metadata blocks is half the previous value.
509 # lvs -a -oname,size,data_percent,metadata_percent vg
510 LV LSize Data% Meta%
511 pool0 20.00g 13.48 6.20
512 [pool0_tdata] 20.00g
513 [pool0_tmeta] 24.00m
514 Using fstrim to increase free space in a thin pool LV
518 Removing files in a file system on top of a thin LV does not generally
521 add free space back to the thin pool. Manually running the fstrim com‐
522 mand can return space back to the thin pool that had been used by
523 removed files. fstrim uses discards and will not work if the thin pool
524 LV has discards mode set to ignore.
525 Example
527 A thin pool has 10G of physical data space, and a thin LV has a virtual
528 size of 100G. Writing a 1G file to the file system reduces the free
529 space in the thin pool by 10% and increases the virtual usage of the
530 file system by 1%. Removing the 1G file restores the virtual 1% to the
531 file system, but does not restore the physical 10% to the thin pool.
532 The fstrim command restores the physical space to the thin pool.
533 # lvs -a -oname,attr,size,pool_lv,origin,data_percent,metadata_percent vg
535 LV Attr LSize Pool Origin Data% Meta%
536 pool0 twi-a-tz-- 10.00g 47.01 21.03
537 thin1 Vwi-aotz-- 100.00g pool0 2.70
538 # df -h /mnt/X
540 Filesystem Size Used Avail Use% Mounted on
541 /dev/mapper/vg-thin1 99G 1.1G 93G 2% /mnt/X
542 # dd if=/dev/zero of=/mnt/X/1Gfile bs=4096 count=262144; sync
544 # lvs
546 pool0 vg twi-a-tz-- 10.00g 57.01 25.26
547 thin1 vg Vwi-aotz-- 100.00g pool0 3.70
548 # df -h /mnt/X
550 /dev/mapper/vg-thin1 99G 2.1G 92G 3% /mnt/X
551 # rm /mnt/X/1Gfile
553 # lvs
555 pool0 vg twi-a-tz-- 10.00g 57.01 25.26
556 thin1 vg Vwi-aotz-- 100.00g pool0 3.70
557 # df -h /mnt/X
559 /dev/mapper/vg-thin1 99G 1.1G 93G 2% /mnt/X
560 # fstrim -v /mnt/X
562 # lvs
564 pool0 vg twi-a-tz-- 10.00g 47.01 21.03
565 thin1 vg Vwi-aotz-- 100.00g pool0 2.70
566 The "Discard" section covers an option for automatically freeing data
568 space in a thin pool.
569 Automatically extend thin pool LV
573 The lvm daemon dmeventd (lvm2-monitor) monitors the data usage of thin
576 pool LVs and extends them when the usage reaches a certain level. The
577 necessary free space must exist in the VG to extend thin pool LVs.
578 Monitoring and extension of thin pool LVs are controlled independently.
579 monitoring
581 When a thin pool LV is activated, dmeventd will begin monitoring it by
583 default.
584 Command to start or stop dmeventd monitoring a thin pool LV:
586 lvchange --monitor {y|n} VG/ThinPoolLV
587 The current dmeventd monitoring status of a thin pool LV can be dis‐
589 played with the command lvs -o+seg_monitor.
590 autoextend
592 dmeventd should be configured to extend thin pool LVs before all data
594 space is used. Warnings are emitted through syslog when the use of a
595 thin pool reaches 80%, 85%, 90% and 95%. (See the section "Data space
596 exhaustion" for the effects of not extending a thin pool LV.) The
597 point at which dmeventd extends thin pool LVs, and the amount are con‐
598 trolled with two configuration settings:
599 lvm.conf(5) thin_pool_autoextend_threshold
601 is a percentage full value that defines when the thin pool LV should be
602 extended. Setting this to 100 disables automatic extention. The mini‐
603 mum value is 50.
604 lvm.conf(5) thin_pool_autoextend_percent
606 defines how much extra data space should be added to the thin pool LV
607 from the VG, in percent of its current size.
608 disabling
610 There are multiple ways that extension of thin pools could be pre‐
612 vented:
613 · If the dmeventd daemon is not running, no monitoring or automatic
616 extension will occur.
617 · Even when dmeventd is running, all monitoring can be disabled with
620 the lvm.conf monitoring setting.
621 · To activate or create a thin pool LV without interacting with
624 dmeventd, the --ignoremonitoring option can be used. With this
625 option, the command will not ask dmeventd to monitor the thin pool
626 LV.
627 · Setting thin_pool_autoextend_threshould to 100 disables automatic
630 extension of thin pool LVs, even if they are being monitored by
631 dmeventd.
632 Example
635 If thin_pool_autoextend_threshold is 70 and thin_pool_autoextend_per‐
636 cent is 20, whenever a pool exceeds 70% usage, it will be extended by
637 another 20%. For a 1G pool, using 700M will trigger a resize to 1.2G.
638 When the usage exceeds 840M, the pool will be extended to 1.44G, and so
639 on.
640 Data space exhaustion
644 When properly managed, thin pool data space should be extended before
647 it is all used (see the section "Automatically extend thin pool LV").
648 If thin pool data space is already exhausted, it can still be extended
649 (see the section "Manually manage free data space of thin pool LV".)
650 The behavior of a full thin pool is configurable with the --errorwhen‐
652 full y|n option to lvcreate or lvchange. The errorwhenfull setting
653 applies only to writes; reading thin LVs can continue even when data
654 space is exhausted.
655 Command to change the handling of a full thin pool:
657 lvchange --errorwhenfull {y|n} VG/ThinPoolLV
658 lvm.conf(5) error_when_full
660 controls the default error when full behavior.
661 The current setting of a thin pool LV can be displayed with the com‐
663 mand: lvs -o+lv_when_full.
664 The errorwhenfull setting does not effect the monitoring and autoextend
666 settings, and the monitoring/autoextend settings do not effect the
667 errorwhenfull setting. It is only when monitoring/autoextend are not
668 effective that the thin pool becomes full and the errorwhenfull setting
669 is applied.
670 errorwhenfull n
672 This is the default. Writes to thin LVs are accepted and queued, with
674 the expectation that pool data space will be extended soon. Once data
675 space is extended, the queued writes will be processed, and the thin
676 pool will return to normal operation.
677 While waiting to be extended, the thin pool will queue writes for up to
679 60 seconds (the default). If data space has not been extended after
680 this time, the queued writes will return an error to the caller, e.g.
681 the file system. This can result in file system corruption for non-
682 journaled file systems that may require fsck. When a thin pool returns
683 errors for writes to a thin LV, any file system is subject to losing
684 unsynced user data.
685 The 60 second timeout can be changed or disabled with the dm-thin-pool
687 kernel module option no_space_timeout. This option sets the number of
688 seconds that thin pools will queue writes. If set to 0, writes will
689 not time out. Disabling timeouts can result in the system running out
690 of resources, memory exhaustion, hung tasks, and deadlocks. (The time‐
691 out applies to all thin pools on the system.)
692 errorwhenfull y
694 Writes to thin LVs immediately return an error, and no writes are
696 queued. In the case of a file system, this can result in corruption
697 that may require fsck (the specific consequences depend on the thin LV
698 user.)
699 data percent
701 When data space is exhausted, the lvs command displays 100 under Data%
703 for the thin pool LV:
704 # lvs vg/pool0
706 LV VG Attr LSize Pool Origin Data%
707 pool0 vg twi-a-tz-- 512.00m 100.00
708 causes
710 A thin pool may run out of data space for any of the following reasons:
712 · Automatic extension of the thin pool is disabled, and the thin pool
715 is not manually extended. (Disabling automatic extension is not rec‐
716 ommended.)
717 · The dmeventd daemon is not running and the thin pool is not manually
720 extended. (Disabling dmeventd is not recommended.)
721 · Automatic extension of the thin pool is too slow given the rate of
724 writes to thin LVs in the pool. (This can be addressed by tuning the
725 thin_pool_autoextend_threshold and thin_pool_autoextend_percent. See
726 "Automatic extend settings".)
727 · The VG does not have enough free blocks to extend the thin pool.
730 Metadata space exhaustion
733 If thin pool metadata space is exhausted (or a thin pool metadata oper‐
736 ation fails), errors will be returned for IO operations on thin LVs.
737 When metadata space is exhausted, the lvs command displays 100 under
739 Meta% for the thin pool LV:
740 # lvs -o lv_name,size,data_percent,metadata_percent vg/pool0
742 LV LSize Data% Meta%
743 pool0 100.00
744 The same reasons for thin pool data space exhaustion apply to thin pool
746 metadata space.
747 Metadata space exhaustion can lead to inconsistent thin pool metadata
749 and inconsistent file systems, so the response requires offline check‐
750 ing and repair.
751 1. Deactivate the thin pool LV, or reboot the system if this is not
753 possible.
754 2. Repair thin pool with lvconvert --repair.
756 See "Metadata check and repair".
757 3. Extend pool metadata space with lvextend --poolmetadatasize.
759 See "Manually manage free metadata space of a thin pool LV".
760 4. Check and repair file system with fsck.
762 Automatic extend settings
766 Thin pool LVs can be extended according to preset values. The presets
769 determine if the LV should be extended based on how full it is, and if
770 so by how much. When dmeventd monitors thin pool LVs, it uses lvextend
771 with these presets. (See "Automatically extend thin pool LV".)
772 Command to extend a thin pool data LV using presets:
774 lvextend --use-policies VG/ThinPoolLV
775 The command uses these settings:
777 lvm.conf(5) thin_pool_autoextend_threshold
779 autoextend the LV when its usage exceeds this percent.
780 lvm.conf(5) thin_pool_autoextend_percent
782 autoextend the LV by this much additional space.
783 To see the default values of these settings, run:
785 lvmconfig --type default --withcomment
787 activation/thin_pool_autoextend_threshold
788 lvmconfig --type default --withcomment
790 activation/thin_pool_autoextend_percent
791 To change these values globally, edit lvm.conf(5).
793 To change these values on a per-VG or per-LV basis, attach a "profile"
795 to the VG or LV. A profile is a collection of config settings, saved
796 in a local text file (using the lvm.conf format). lvm looks for pro‐
797 files in the profile_dir directory, e.g. /etc/lvm/profile/. Once
798 attached to a VG or LV, lvm will process the VG or LV using the set‐
799 tings from the attached profile. A profile is named and referenced by
800 its file name.
801 To use a profile to customize the lvextend settings for an LV:
803 · Create a file containing settings, saved in profile_dir. For the
806 profile_dir location, run:
807 lvmconfig config/profile_dir
808 · Attach the profile to an LV, using the command:
811 lvchange --metadataprofile ProfileName VG/ThinPoolLV
812 · Extend the LV using the profile settings:
815 lvextend --use-policies VG/ThinPoolLV
816 Example
819 # lvmconfig config/profile_dir
820 profile_dir="/etc/lvm/profile"
821 # cat /etc/lvm/profile/pool0extend.profile
823 activation {
824 thin_pool_autoextend_threshold=50
825 thin_pool_autoextend_percent=10
826 }
827 # lvchange --metadataprofile pool0extend vg/pool0
829 # lvextend --use-policies vg/pool0
831 Notes
833 · A profile is attached to a VG or LV by name, where the name refer‐
835 ences a local file in profile_dir. If the VG is moved to another
836 machine, the file with the profile also needs to be moved.
837 · Only certain settings can be used in a VG or LV profile, see:
840 lvmconfig --type profilable-metadata.
841 · An LV without a profile of its own will inherit the VG profile.
844 · Remove a profile from an LV using the command:
847 lvchange --detachprofile VG/ThinPoolLV.
848 · Commands can also have profiles applied to them. The settings that
851 can be applied to a command are different than the settings that can
852 be applied to a VG or LV. See lvmconfig --type profilable-command.
853 To apply a profile to a command, write a profile, save it in the pro‐
854 file directory, and run the command using the option: --commandpro‐
855 file ProfileName.
856 Zeroing
860 When a thin pool provisions a new data block for a thin LV, the new
863 block is first overwritten with zeros. The zeroing mode is indicated
864 by the "z" attribute displayed by lvs. The option -Z (or --zero) can
865 be added to commands to specify the zeroing mode.
866 Command to set the zeroing mode when creating a thin pool LV:
868 lvconvert --type thin-pool -Z{y|n}
869 --poolmetadata VG/ThinMetaLV VG/ThinDataLV
870 Command to change the zeroing mode of an existing thin pool LV:
872 lvchange -Z{y|n} VG/ThinPoolLV
873 If zeroing mode is changed from "n" to "y", previously provisioned
875 blocks are not zeroed.
876 Provisioning of large zeroed chunks impacts performance.
878 lvm.conf(5) thin_pool_zero
880 controls the default zeroing mode used when creating a thin pool.
881 Discard
885 The discard behavior of a thin pool LV determines how discard requests
888 are handled. Enabling discard under a file system may adversely affect
889 the file system performance (see the section on fstrim for an alterna‐
890 tive.) Possible discard behaviors:
891 ignore: Ignore any discards that are received.
893 nopassdown: Process any discards in the thin pool itself and allow the
895 no longer needed extends to be overwritten by new data.
896 passdown: Process discards in the thin pool (as with nopassdown), and
898 pass the discards down the the underlying device. This is the default
899 mode.
900 Command to display the current discard mode of a thin pool LV:
902 lvs -o+discards VG/ThinPoolLV
903 Command to set the discard mode when creating a thin pool LV:
905 lvconvert --discards {ignore|nopassdown|passdown}
906 --type thin-pool --poolmetadata VG/ThinMetaLV VG/ThinDataLV
907 Command to change the discard mode of an existing thin pool LV:
909 lvchange --discards {ignore|nopassdown|passdown} VG/ThinPoolLV
910 Example
912 # lvs -o name,discards vg/pool0
913 pool0 passdown
914 # lvchange --discards ignore vg/pool0
916 lvm.conf(5) thin_pool_discards
918 controls the default discards mode used when creating a thin pool.
919 Chunk size
923 The size of data blocks managed by a thin pool can be specified with
926 the --chunksize option when the thin pool LV is created. The default
927 unit is KiB. The value must be a multiple of 64KiB between 64KiB and
928 1GiB.
929 When a thin pool is used primarily for the thin provisioning feature, a
931 larger value is optimal. To optimize for many snapshots, a smaller
932 value reduces copying time and consumes less space.
933 Command to display the thin pool LV chunk size:
935 lvs -o+chunksize VG/ThinPoolLV
936 Example
938 # lvs -o name,chunksize
939 pool0 64.00k
940 lvm.conf(5) thin_pool_chunk_size
942 controls the default chunk size used when creating a thin pool.
943 The default value is shown by:
945 lvmconfig --type default allocation/thin_pool_chunk_size
946 Size of pool metadata LV
950 The amount of thin metadata depends on how many blocks are shared
953 between thin LVs (i.e. through snapshots). A thin pool with many snap‐
954 shots may need a larger metadata LV. Thin pool metadata LV sizes can
955 be from 2MiB to 16GiB.
956 When using lvcreate to create what will become a thin metadata LV, the
958 size is specified with the -L|--size option.
959 When an LVM command automatically creates a thin metadata LV, the size
961 is specified with the --poolmetadatasize option. When this option is
962 not given, LVM automatically chooses a size based on the data size and
963 chunk size.
964 It can be hard to predict the amount of metadata space that will be
966 needed, so it is recommended to start with a size of 1GiB which should
967 be enough for all practical purposes. A thin pool metadata LV can
968 later be manually or automatically extended if needed.
969 Create a thin snapshot of an external, read only LV
973 Thin snapshots are typically taken of other thin LVs or other thin
976 snapshot LVs within the same thin pool. It is also possible to take
977 thin snapshots of external, read only LVs. Writes to the snapshot are
978 stored in the thin pool, and the external LV is used to read unwritten
979 parts of the thin snapshot.
980 lvcreate -n SnapLV -s VG/ExternalOriginLV --thinpool VG/ThinPoolLV
982 Example
984 # lvchange -an vg/lve
985 # lvchange --permission r vg/lve
986 # lvcreate -n snaplve -s vg/lve --thinpool vg/pool0
987 # lvs vg/lve vg/snaplve
989 LV VG Attr LSize Pool Origin Data%
990 lve vg ori------- 10.00g
991 snaplve vg Vwi-a-tz-- 10.00g pool0 lve 0.00
992 Convert a standard LV to a thin LV with an external origin
996 A new thin LV can be created and given the name of an existing standard
999 LV. At the same time, the existing LV is converted to a read only
1000 external LV with a new name. Unwritten portions of the thin LV are
1001 read from the external LV. The new name given to the existing LV can
1002 be specified with --originname, otherwise the existing LV will be given
1003 a default name, e.g. lvol#.
1004 Convert ExampleLV into a read only external LV with the new name NewEx‐
1006 ternalOriginLV, and create a new thin LV that is given the previous
1007 name of ExampleLV.
1008 lvconvert --type thin --thinpool VG/ThinPoolLV
1010 --originname NewExternalOriginLV --thin VG/ExampleLV
1011 Example
1013 # lvcreate -n lv_example -L 10G vg
1014 # lvs
1016 lv_example vg -wi-a----- 10.00g
1017 # lvconvert --type thin --thinpool vg/pool0
1019 --originname lv_external --thin vg/lv_example
1020 # lvs
1022 LV VG Attr LSize Pool Origin
1023 lv_example vg Vwi-a-tz-- 10.00g pool0 lv_external
1024 lv_external vg ori------- 10.00g
1025 Single step thin pool LV creation
1029 A thin pool LV can be created with a single lvcreate command, rather
1032 than using lvconvert on existing LVs. This one command creates a thin
1033 data LV, a thin metadata LV, and combines the two into a thin pool LV.
1034 lvcreate --type thin-pool -L LargeSize -n ThinPoolLV VG
1036 Example
1038 # lvcreate --type thin-pool -L8M -n pool0 vg
1039 # lvs vg/pool0
1041 LV VG Attr LSize Pool Origin Data%
1042 pool0 vg twi-a-tz-- 8.00m 0.00
1043 # lvs -a
1045 pool0 vg twi-a-tz-- 8.00m
1046 [pool0_tdata] vg Twi-ao---- 8.00m
1047 [pool0_tmeta] vg ewi-ao---- 8.00m
1048 Single step thin pool LV and thin LV creation
1052 A thin pool LV and a thin LV can be created with a single lvcreate com‐
1055 mand. This one command creates a thin data LV, a thin metadata LV,
1056 combines the two into a thin pool LV, and creates a thin LV in the new
1057 pool.
1058 -L LargeSize specifies the physical size of the thin pool LV.
1059 -V VirtualSize specifies the virtual size of the thin LV.
1060 lvcreate -V VirtualSize -L LargeSize
1062 -n ThinLV --thinpool VG/ThinPoolLV
1063 Equivalent to:
1065 lvcreate --type thin-pool -L LargeSize VG/ThinPoolLV
1066 lvcreate -n ThinLV -V VirtualSize --thinpool VG/ThinPoolLV
1067 Example
1069 # lvcreate -L8M -V2G -n thin1 --thinpool vg/pool0
1070 # lvs -a
1072 pool0 vg twi-a-tz-- 8.00m
1073 [pool0_tdata] vg Twi-ao---- 8.00m
1074 [pool0_tmeta] vg ewi-ao---- 8.00m
1075 thin1 vg Vwi-a-tz-- 2.00g pool0
1076 Merge thin snapshots
1080 A thin snapshot can be merged into its origin thin LV using the lvcon‐
1083 vert --merge command. The result of a snapshot merge is that the ori‐
1084 gin thin LV takes the content of the snapshot LV, and the snapshot LV
1085 is removed. Any content that was unique to the origin thin LV is lost
1086 after the merge.
1087 Because a merge changes the content of an LV, it cannot be done while
1089 the LVs are open, e.g. mounted. If a merge is initiated while the LVs
1090 are open, the effect of the merge is delayed until the origin thin LV
1091 is next activated.
1092 lvconvert --merge VG/SnapLV
1094 Example
1096 # lvs vg
1097 LV VG Attr LSize Pool Origin
1098 pool0 vg twi-a-tz-- 10.00g
1099 thin1 vg Vwi-a-tz-- 100.00g pool0
1100 thin1s1 vg Vwi-a-tz-k 100.00g pool0 thin1
1101 # lvconvert --merge vg/thin1s1
1103 # lvs vg
1105 LV VG Attr LSize Pool Origin
1106 pool0 vg twi-a-tz-- 10.00g
1107 thin1 vg Vwi-a-tz-- 100.00g pool0
1108 Example
1110 Delayed merging of open LVs.
1111 # lvs vg
1113 LV VG Attr LSize Pool Origin
1114 pool0 vg twi-a-tz-- 10.00g
1115 thin1 vg Vwi-aotz-- 100.00g pool0
1116 thin1s1 vg Vwi-aotz-k 100.00g pool0 thin1
1117 # df
1119 /dev/mapper/vg-thin1 100G 33M 100G 1% /mnt/X
1120 /dev/mapper/vg-thin1s1 100G 33M 100G 1% /mnt/Xs
1121 # ls /mnt/X
1123 file1 file2 file3
1124 # ls /mnt/Xs
1125 file3 file4 file5
1126 # lvconvert --merge vg/thin1s1
1128 Logical volume vg/thin1s1 contains a filesystem in use.
1129 Delaying merge since snapshot is open.
1130 Merging of thin snapshot thin1s1 will occur on next activation.
1131 # umount /mnt/X
1133 # umount /mnt/Xs
1134 # lvs -a vg
1136 LV VG Attr LSize Pool Origin
1137 pool0 vg twi-a-tz-- 10.00g
1138 [pool0_tdata] vg Twi-ao---- 10.00g
1139 [pool0_tmeta] vg ewi-ao---- 1.00g
1140 thin1 vg Owi-a-tz-- 100.00g pool0
1141 [thin1s1] vg Swi-a-tz-k 100.00g pool0 thin1
1142 # lvchange -an vg/thin1
1144 # lvchange -ay vg/thin1
1145 # mount /dev/vg/thin1 /mnt/X
1147 # ls /mnt/X
1149 file3 file4 file5
1150 XFS on snapshots
1154 Mounting an XFS file system on a new snapshot LV requires attention to
1157 the file system's log state and uuid. On the snapshot LV, the xfs log
1158 will contain a dummy transaction, and the xfs uuid will match the uuid
1159 from the file system on the origin LV.
1160 If the snapshot LV is writable, mounting will recover the log to clear
1162 the dummy transaction, but will require skipping the uuid check:
1163 mount /dev/VG/SnapLV /mnt -o nouuid
1165 Or, the uuid can be changed on disk before mounting:
1167 xfs_admin -U generate /dev/VG/SnapLV
1169 mount /dev/VG/SnapLV /mnt
1170 If the snapshot LV is readonly, the log recovery and uuid check need to
1172 be skipped while mounting readonly:
1173 mount /dev/VG/SnapLV /mnt -o ro,nouuid,norecovery
1175
1178 lvm(8), lvm.conf(5), lvmconfig(8), lvcreate(8), lvconvert(8),
1179 lvchange(8), lvextend(8), lvremove(8), lvs(8), thin_dump(8),
1180 thin_repair(8) thin_restore(8)
1181Red Hat, Inc LVM TOOLS 2.02.143(2)-RHEL6 (2016-12-13) LVMTHIN(7)