1LVMTHIN(7) LVMTHIN(7)
2
6 lvmthin — LVM thin provisioning
7
10 Blocks in a standard lvm(8) Logical Volume (LV) are allocated when the
11 LV is created, but blocks in a thin provisioned LV 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 Volume
18 Group (VG), but blocks in a thin LV are allocated (during use) from a
19 special "thin pool LV". The thin pool LV contains blocks of physical
20 storage, and blocks in thin LVs just reference blocks in the thin pool
21 LV.
22 A thin pool LV must be created before thin LVs can be created within
24 it. A thin pool LV is created by combining two standard LVs: a large
25 data LV that will hold blocks for thin LVs, and a metadata LV that will
26 hold metadata. The metadata tracks which data blocks belong to each
27 thin LV.
28 Snapshots of thin LVs are efficient because the data blocks common to a
30 thin LV and any of its snapshots are shared. Snapshots may be taken of
31 thin LVs or of other thin snapshots. Blocks common to recursive snap‐
32 shots are also shared in the thin pool. There is no limit to or degra‐
33 dation from sequences of snapshots.
34 As thin LVs or snapshot LVs are written to, they consume data blocks in
36 the thin pool. As free data blocks in the pool decrease, more free
37 blocks may need to be supplied. This is done by extending the thin
38 pool data LV with additional physical space from the VG. Removing thin
39 LVs or snapshots from the thin pool can also free blocks in the thin
40 pool. However, removing LVs is not always an effective way of freeing
41 space in a thin pool because the amount is limited to the number of
42 blocks not shared with other LVs in the pool.
43 Incremental block allocation from thin pools can cause thin LVs to
45 become fragmented. Standard LVs generally avoid this problem by allo‐
46 cating all the blocks at once during creation.
47
51 ThinDataLV
52 thin data LV
53 large LV created in a VG
54 used by thin pool to store ThinLV blocks
55 ThinMetaLV
58 thin metadata LV
59 small LV created in a VG
60 used by thin pool to track data block usage
61 ThinPoolLV
64 thin pool LV
65 combination of ThinDataLV and ThinMetaLV
66 contains ThinLVs and SnapLVs
67 ThinLV
70 thin LV
71 created from ThinPoolLV
72 appears blank after creation
73 SnapLV
76 snapshot LV
77 created from ThinPoolLV
78 appears as a snapshot of another LV after creation
79
84 The primary method for using lvm thin provisioning:
85 1. create ThinDataLV
88 Create an LV that will hold thin pool data.
89 lvcreate -n ThinDataLV -L LargeSize VG
91 Example
93 # lvcreate -n pool0 -L 10G vg
94 2. create ThinMetaLV
97 Create an LV that will hold thin pool metadata.
98 lvcreate -n ThinMetaLV -L SmallSize VG
100 Example
102 # lvcreate -n pool0meta -L 1G vg
103 # lvs
105 LV VG Attr LSize
106 pool0 vg -wi-a----- 10.00g
107 pool0meta vg -wi-a----- 1.00g
108 3. create ThinPoolLV
111 Combine the data and metadata LVs into a thin pool LV.
112 ThinDataLV is renamed to hidden ThinPoolLV_tdata.
113 ThinMetaLV is renamed to hidden ThinPoolLV_tmeta.
114 The new ThinPoolLV takes the previous name of ThinDataLV.
115 lvconvert --type thin-pool --poolmetadata VG/ThinMetaLV VG/ThinDataLV
117 Example
119 # lvconvert --type thin-pool --poolmetadata vg/pool0meta vg/pool0
120 # lvs vg/pool0
122 LV VG Attr LSize Pool Origin Data% Meta%
123 pool0 vg twi-a-tz-- 10.00g 0.00 0.00
124 # lvs -a
126 LV VG Attr LSize
127 pool0 vg twi-a-tz-- 10.00g
128 [pool0_tdata] vg Twi-ao---- 10.00g
129 [pool0_tmeta] vg ewi-ao---- 1.00g
130 4. create ThinLV
133 Create a new thin LV from the thin pool LV.
134 The thin LV is created with a virtual size.
135 Multiple new thin LVs may be created in the thin pool.
136 Thin LV names must be unique in the VG.
137 The '--type thin' option is inferred from the virtual size option.
138 The --thinpool argument specifies which thin pool will
139 contain the ThinLV.
140 lvcreate -n ThinLV -V VirtualSize --thinpool ThinPoolLV VG
142 Example
144 Create a thin LV in a thin pool:
145 # lvcreate -n thin1 -V 1T --thinpool pool0 vg
146 Create another thin LV in the same thin pool:
148 # lvcreate -n thin2 -V 1T --thinpool pool0 vg
149 # lvs vg/thin1 vg/thin2
151 LV VG Attr LSize Pool Origin Data%
152 thin1 vg Vwi-a-tz-- 1.00t pool0 0.00
153 thin2 vg Vwi-a-tz-- 1.00t pool0 0.00
154 5. create SnapLV
157 Create snapshots of an existing ThinLV or SnapLV.
158 Do not specify -L, --size when creating a thin snapshot.
159 A size argument will cause an old COW snapshot to be created.
160 lvcreate -n SnapLV --snapshot VG/ThinLV
162 lvcreate -n SnapLV --snapshot VG/PrevSnapLV
163 Example
165 Create first snapshot of an existing ThinLV:
166 # lvcreate -n thin1s1 -s vg/thin1
167 Create second snapshot of the same ThinLV:
169 # lvcreate -n thin1s2 -s vg/thin1
170 Create a snapshot of the first snapshot:
172 # lvcreate -n thin1s1s1 -s vg/thin1s1
173 # lvs vg/thin1s1 vg/thin1s2 vg/thin1s1s1
175 LV VG Attr LSize Pool Origin
176 thin1s1 vg Vwi---tz-k 1.00t pool0 thin1
177 thin1s2 vg Vwi---tz-k 1.00t pool0 thin1
178 thin1s1s1 vg Vwi---tz-k 1.00t pool0 thin1s1
179 6. activate SnapLV
182 Thin snapshots are created with the persistent "activation skip" flag,
183 indicated by the "k" attribute. Use -K with lvchange or vgchange to
184 activate thin snapshots with the "k" attribute.
185 lvchange -ay -K VG/SnapLV
187 Example
189 # lvchange -ay -K vg/thin1s1
190 # lvs vg/thin1s1
192 LV VG Attr LSize Pool Origin
193 thin1s1 vg Vwi-a-tz-k 1.00t pool0 thin1
194
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 Automatic pool metadata LV
226 A thin data LV can be converted to a thin pool LV without specifying a
229 thin pool metadata LV. LVM automatically creates a metadata LV from
230 the same VG.
231 lvcreate -n ThinDataLV -L LargeSize VG
233 lvconvert --type thin-pool VG/ThinDataLV
234 Example
236 # lvcreate -n pool0 -L 10G vg
237 # lvconvert --type thin-pool vg/pool0
238 # lvs -a
240 pool0 vg twi-a-tz-- 10.00g
241 [pool0_tdata] vg Twi-ao---- 10.00g
242 [pool0_tmeta] vg ewi-ao---- 16.00m
243 Specify devices for data and metadata LVs
247 The data and metadata LVs in a thin pool are best created on separate
250 physical devices. To do that, specify the device name(s) at the end of
251 the lvcreate line. It can be especially helpful to use fast devices
252 for the metadata LV.
253 lvcreate -n ThinDataLV -L LargeSize VG LargePV
255 lvcreate -n ThinMetaLV -L SmallSize VG SmallPV
256 lvconvert --type thin-pool --poolmetadata VG/ThinMetaLV VG/ThinDataLV
257 Example
259 # lvcreate -n pool0 -L 10G vg /dev/sdA
260 # lvcreate -n pool0meta -L 1G vg /dev/sdB
261 # lvconvert --type thin-pool --poolmetadata vg/pool0meta vg/pool0
262 lvm.conf(5) thin_pool_metadata_require_separate_pvs
264 controls the default PV usage for thin pool creation.
265 Tolerate device failures using raid
270 To tolerate device failures, use raid for the pool data LV and pool
273 metadata LV. This is especially recommended for pool metadata LVs.
274 lvcreate --type raid1 -m 1 -n ThinMetaLV -L SmallSize VG PVA PVB
276 lvcreate --type raid1 -m 1 -n ThinDataLV -L LargeSize VG PVC PVD
277 lvconvert --type thin-pool --poolmetadata VG/ThinMetaLV VG/ThinDataLV
278 Example
280 # lvcreate --type raid1 -m 1 -n pool0 -L 10G vg /dev/sdA /dev/sdB
281 # lvcreate --type raid1 -m 1 -n pool0meta -L 1G vg /dev/sdC /dev/sdD
282 # lvconvert --type thin-pool --poolmetadata vg/pool0meta vg/pool0
283 Spare metadata LV
287 The first time a thin pool LV is created, lvm will create a spare meta‐
290 data LV in the VG. This behavior can be controlled with the option
291 --poolmetadataspare y|n. (Future thin pool creations will also attempt
292 to create the pmspare LV if none exists.)
293 To create the pmspare ("pool metadata spare") LV, lvm first creates an
295 LV with a default name, e.g. lvol0, and then converts this LV to a hid‐
296 den LV with the _pmspare suffix, e.g. lvol0_pmspare.
297 One pmspare LV is kept in a VG to be used for any thin pool.
299 The pmspare LV cannot be created explicitly, but may be removed explic‐
301 itly.
302 Example
304 # lvcreate -n pool0 -L 10G vg
305 # lvcreate -n pool0meta -L 1G vg
306 # lvconvert --type thin-pool --poolmetadata vg/pool0meta vg/pool0
307 # lvs -a
309 [lvol0_pmspare] vg ewi-------
310 pool0 vg twi---tz--
311 [pool0_tdata] vg Twi-------
312 [pool0_tmeta] vg ewi-------
313 The "Metadata check and repair" section describes the use of the pms‐
315 pare LV.
316 Metadata check and repair
320 If thin pool metadata is damaged, it may be repairable. Checking and
323 repairing thin pool metadata is analagous to running fsck/repair on a
324 file system.
325 When a thin pool LV is activated, lvm runs the thin_check command to
327 check the correctness of the metadata on the pool metadata LV.
328 lvm.conf(5) thin_check_executable
330 can be set to an empty string ("") to disable the thin_check step.
331 This is not recommended.
332 lvm.conf(5) thin_check_options
334 controls the command options used for the thin_check command.
335 If the thin_check command finds a problem with the metadata, the thin
337 pool LV is not activated, and the thin pool metadata needs to be
338 repaired.
339 Simple repair commands are not always successful. Advanced repair may
341 require editing thin pool metadata and lvm metadata. Newer versions of
342 the kernel and lvm tools may be more successful at repair. Report the
343 details of damaged thin metadata to get the best advice on recovery.
344 Command to repair a thin pool:
346 lvconvert --repair VG/ThinPoolLV
347 Repair performs the following steps:
349 1. Creates a new, repaired copy of the metadata.
351 lvconvert runs the thin_repair command to read damaged metadata from
352 the existing pool metadata LV, and writes a new repaired copy to the
353 VG's pmspare LV.
354 2. Replaces the thin pool metadata LV.
356 If step 1 is successful, the thin pool metadata LV is replaced with the
357 pmspare LV containing the corrected metadata. The previous thin pool
358 metadata LV, containing the damaged metadata, becomes visible with the
359 new name ThinPoolLV_tmetaN (where N is 0,1,...).
360 If the repair works, the thin pool LV and its thin LVs can be acti‐
362 vated, and the LV containing the damaged thin pool metadata can be
363 removed. It may be useful to move the new metadata LV (previously pms‐
364 pare) to a better PV.
365 If the repair does not work, the thin pool LV and its thin LVs are
367 lost.
368 If metadata is manually restored with thin_repair directly, the pool
370 metadata LV can be manually swapped with another LV containing new
371 metadata:
372 lvconvert --thinpool VG/ThinPoolLV --poolmetadata VG/NewThinMetaLV
374 Activation of thin snapshots
378 When a thin snapshot LV is created, it is by default given the "activa‐
381 tion skip" flag. This flag is indicated by the "k" attribute displayed
382 by lvs:
383 # lvs vg/thin1s1
385 LV VG Attr LSize Pool Origin
386 thin1s1 vg Vwi---tz-k 1.00t pool0 thin1
387 This flag causes the snapshot LV to be skipped, i.e. not activated, by
389 normal activation commands. The skipping behavior does not apply to
390 deactivation commands.
391 A snapshot LV with the "k" attribute can be activated using the -K (or
393 --ignoreactivationskip) option in addition to the standard -ay (or
394 --activate y) option.
395 Command to activate a thin snapshot LV:
397 lvchange -ay -K VG/SnapLV
398 The persistent "activation skip" flag can be turned off during lvcre‐
400 ate, or later with lvchange using the -kn (or --setactivationskip n)
401 option. It can be turned on again with -ky (or --setactivationskip y).
402 When the "activation skip" flag is removed, normal activation commands
404 will activate the LV, and the -K activation option is not needed.
405 Command to create snapshot LV without the activation skip flag:
407 lvcreate -kn -n SnapLV -s VG/ThinLV
408 Command to remove the activation skip flag from a snapshot LV:
410 lvchange -kn VG/SnapLV
411 lvm.conf(5) auto_set_activation_skip
413 controls the default activation skip setting used by lvcreate.
414 Removing thin pool LVs, thin LVs and snapshots
418 Removing a thin LV and its related snapshots returns the blocks it used
421 to the thin pool LV. These blocks will be reused for other thin LVs
422 and snapshots.
423 Removing a thin pool LV removes both the data LV and metadata LV and
425 returns the space to the VG.
426 lvremove of thin pool LVs, thin LVs and snapshots cannot be reversed
428 with vgcfgrestore.
429 vgcfgbackup does not back up thin pool metadata.
431 Manually manage free data space of thin pool LV
435 The available free space in a thin pool LV can be displayed with the
438 lvs command. Free space can be added by extending the thin pool LV.
439 Command to extend thin pool data space:
441 lvextend -L Size VG/ThinPoolLV
442 Example
444 1. A thin pool LV is using 26.96% of its data blocks.
445 # lvs
446 LV VG Attr LSize Pool Origin Data%
447 pool0 vg twi-a-tz-- 10.00g 26.96
448 2. Double the amount of physical space in the thin pool LV.
450 # lvextend -L+10G vg/pool0
451 3. The percentage of used data blocks is half the previous value.
453 # lvs
454 LV VG Attr LSize Pool Origin Data%
455 pool0 vg twi-a-tz-- 20.00g 13.48
456 Other methods of increasing free data space in a thin pool LV include
458 removing a thin LV and its related snapsots, or running fstrim on the
459 file system using a thin LV.
460 Manually manage free metadata space of a thin pool LV
464 The available metadata space in a thin pool LV can be displayed with
467 the lvs -o+metadata_percent command.
468 Command to extend thin pool metadata space:
470 lvextend --poolmetadatasize Size VG/ThinPoolLV
471 Example
473 1. A thin pool LV is using 12.40% of its metadata blocks.
474 # lvs -oname,size,data_percent,metadata_percent vg/pool0
475 LV LSize Data% Meta%
476 pool0 20.00g 13.48 12.40
477 2. Display a thin pool LV with its component thin data LV and thin
479 metadata LV.
480 # lvs -a -oname,attr,size vg
481 LV Attr LSize
482 pool0 twi-a-tz-- 20.00g
483 [pool0_tdata] Twi-ao---- 20.00g
484 [pool0_tmeta] ewi-ao---- 12.00m
485 3. Double the amount of physical space in the thin metadata LV.
487 # lvextend --poolmetadatasize +12M vg/pool0
488 4. The percentage of used metadata blocks is half the previous value.
490 # lvs -a -oname,size,data_percent,metadata_percent vg
491 LV LSize Data% Meta%
492 pool0 20.00g 13.48 6.20
493 [pool0_tdata] 20.00g
494 [pool0_tmeta] 24.00m
495 Using fstrim to increase free space in a thin pool LV
499 Removing files in a file system on top of a thin LV does not generally
502 add free space back to the thin pool. Manually running the fstrim com‐
503 mand can return space back to the thin pool that had been used by
504 removed files. fstrim uses discards and will not work if the thin pool
505 LV has discards mode set to ignore.
506 Example
508 A thin pool has 10G of physical data space, and a thin LV has a virtual
509 size of 100G. Writing a 1G file to the file system reduces the free
510 space in the thin pool by 10% and increases the virtual usage of the
511 file system by 1%. Removing the 1G file restores the virtual 1% to the
512 file system, but does not restore the physical 10% to the thin pool.
513 The fstrim command restores the physical space to the thin pool.
514 # lvs -a -oname,attr,size,pool_lv,origin,data_percent,metadata_percent vg
516 LV Attr LSize Pool Origin Data% Meta%
517 pool0 twi-a-tz-- 10.00g 47.01 21.03
518 thin1 Vwi-aotz-- 100.00g pool0 2.70
519 # df -h /mnt/X
521 Filesystem Size Used Avail Use% Mounted on
522 /dev/mapper/vg-thin1 99G 1.1G 93G 2% /mnt/X
523 # dd if=/dev/zero of=/mnt/X/1Gfile bs=4096 count=262144; sync
525 # lvs
527 pool0 vg twi-a-tz-- 10.00g 57.01 25.26
528 thin1 vg Vwi-aotz-- 100.00g pool0 3.70
529 # df -h /mnt/X
531 /dev/mapper/vg-thin1 99G 2.1G 92G 3% /mnt/X
532 # rm /mnt/X/1Gfile
534 # lvs
536 pool0 vg twi-a-tz-- 10.00g 57.01 25.26
537 thin1 vg Vwi-aotz-- 100.00g pool0 3.70
538 # df -h /mnt/X
540 /dev/mapper/vg-thin1 99G 1.1G 93G 2% /mnt/X
541 # fstrim -v /mnt/X
543 # lvs
545 pool0 vg twi-a-tz-- 10.00g 47.01 21.03
546 thin1 vg Vwi-aotz-- 100.00g pool0 2.70
547 The "Discard" section covers an option for automatically freeing data
549 space in a thin pool.
550 Automatically extend thin pool LV
554 The lvm daemon dmeventd (lvm2-monitor) monitors the data usage of thin
557 pool LVs and extends them when the usage reaches a certain level. The
558 necessary free space must exist in the VG to extend thin pool LVs.
559 Monitoring and extension of thin pool LVs are controlled independently.
560 monitoring
562 When a thin pool LV is activated, dmeventd will begin monitoring it by
564 default.
565 Command to start or stop dmeventd monitoring a thin pool LV:
567 lvchange --monitor {y|n} VG/ThinPoolLV
568 The current dmeventd monitoring status of a thin pool LV can be dis‐
570 played with the command lvs -o+seg_monitor.
571 autoextend
573 dmeventd should be configured to extend thin pool LVs before all data
575 space is used. Warnings are emitted through syslog when the use of a
576 thin pool reaches 80%, 85%, 90% and 95%. (See the section "Data space
577 exhaustion" for the effects of not extending a thin pool LV.) The
578 point at which dmeventd extends thin pool LVs, and the amount are con‐
579 trolled with two configuration settings:
580 lvm.conf(5) thin_pool_autoextend_threshold
582 is a percentage full value that defines when the thin pool LV should be
583 extended. Setting this to 100 disables automatic extention. The mini‐
584 mum value is 50.
585 lvm.conf(5) thin_pool_autoextend_percent
587 defines how much extra data space should be added to the thin pool LV
588 from the VG, in percent of its current size.
589 disabling
591 There are multiple ways that extension of thin pools could be pre‐
593 vented:
594 · If the dmeventd daemon is not running, no monitoring or automatic
597 extension will occur.
598 · Even when dmeventd is running, all monitoring can be disabled with
601 the lvm.conf monitoring setting.
602 · To activate or create a thin pool LV without interacting with
605 dmeventd, the --ignoremonitoring option can be used. With this
606 option, the command will not ask dmeventd to monitor the thin pool
607 LV.
608 · Setting thin_pool_autoextend_threshould to 100 disables automatic
611 extension of thin pool LVs, even if they are being monitored by
612 dmeventd.
613 Example
616 If thin_pool_autoextend_threshold is 70 and thin_pool_autoextend_per‐
617 cent is 20, whenever a pool exceeds 70% usage, it will be extended by
618 another 20%. For a 1G pool, using 700M will trigger a resize to 1.2G.
619 When the usage exceeds 840M, the pool will be extended to 1.44G, and so
620 on.
621 Data space exhaustion
625 When properly managed, thin pool data space should be extended before
628 it is all used (see the section "Automatically extend thin pool LV").
629 If thin pool data space is already exhausted, it can still be extended
630 (see the section "Manually manage free data space of thin pool LV".)
631 The behavior of a full thin pool is configurable with the --errorwhen‐
633 full y|n option to lvcreate or lvchange. The errorwhenfull setting
634 applies only to writes; reading thin LVs can continue even when data
635 space is exhausted.
636 Command to change the handling of a full thin pool:
638 lvchange --errorwhenfull {y|n} VG/ThinPoolLV
639 lvm.conf(5) error_when_full
641 controls the default error when full behavior.
642 The current setting of a thin pool LV can be displayed with the com‐
644 mand: lvs -o+lv_when_full.
645 The errorwhenfull setting does not effect the monitoring and autoextend
647 settings, and the monitoring/autoextend settings do not effect the
648 errorwhenfull setting. It is only when monitoring/autoextend are not
649 effective that the thin pool becomes full and the errorwhenfull setting
650 is applied.
651 errorwhenfull n
653 This is the default. Writes to thin LVs are accepted and queued, with
655 the expectation that pool data space will be extended soon. Once data
656 space is extended, the queued writes will be processed, and the thin
657 pool will return to normal operation.
658 While waiting to be extended, the thin pool will queue writes for up to
660 60 seconds (the default). If data space has not been extended after
661 this time, the queued writes will return an error to the caller, e.g.
662 the file system. This can result in file system corruption for non-
663 journaled file systems that may require repair. When a thin pool
664 returns errors for writes to a thin LV, any file system is subject to
665 losing unsynced user data.
666 The 60 second timeout can be changed or disabled with the dm-thin-pool
668 kernel module option no_space_timeout. This option sets the number of
669 seconds that thin pools will queue writes. If set to 0, writes will
670 not time out. Disabling timeouts can result in the system running out
671 of resources, memory exhaustion, hung tasks, and deadlocks. (The time‐
672 out applies to all thin pools on the system.)
673 errorwhenfull y
675 Writes to thin LVs immediately return an error, and no writes are
677 queued. In the case of a file system, this can result in corruption
678 that may require fs repair (the specific consequences depend on the
679 thin LV user.)
680 data percent
682 When data space is exhausted, the lvs command displays 100 under Data%
684 for the thin pool LV:
685 # lvs vg/pool0
687 LV VG Attr LSize Pool Origin Data%
688 pool0 vg twi-a-tz-- 512.00m 100.00
689 causes
691 A thin pool may run out of data space for any of the following reasons:
693 · Automatic extension of the thin pool is disabled, and the thin pool
696 is not manually extended. (Disabling automatic extension is not rec‐
697 ommended.)
698 · The dmeventd daemon is not running and the thin pool is not manually
701 extended. (Disabling dmeventd is not recommended.)
702 · Automatic extension of the thin pool is too slow given the rate of
705 writes to thin LVs in the pool. (This can be addressed by tuning the
706 thin_pool_autoextend_threshold and thin_pool_autoextend_percent. See
707 "Automatic extend settings".)
708 · The VG does not have enough free blocks to extend the thin pool.
711 Metadata space exhaustion
714 If thin pool metadata space is exhausted (or a thin pool metadata oper‐
717 ation fails), errors will be returned for IO operations on thin LVs.
718 When metadata space is exhausted, the lvs command displays 100 under
720 Meta% for the thin pool LV:
721 # lvs -o lv_name,size,data_percent,metadata_percent vg/pool0
723 LV LSize Data% Meta%
724 pool0 100.00
725 The same reasons for thin pool data space exhaustion apply to thin pool
727 metadata space.
728 Metadata space exhaustion can lead to inconsistent thin pool metadata
730 and inconsistent file systems, so the response requires offline check‐
731 ing and repair.
732 1. Deactivate the thin pool LV, or reboot the system if this is not
734 possible.
735 2. Repair thin pool with lvconvert --repair.
737 See "Metadata check and repair".
738 3. Extend pool metadata space with lvextend --poolmetadatasize.
740 See "Manually manage free metadata space of a thin pool LV".
741 4. Check and repair file system.
743 Automatic extend settings
747 Thin pool LVs can be extended according to preset values. The presets
750 determine if the LV should be extended based on how full it is, and if
751 so by how much. When dmeventd monitors thin pool LVs, it uses lvextend
752 with these presets. (See "Automatically extend thin pool LV".)
753 Command to extend a thin pool data LV using presets:
755 lvextend --use-policies VG/ThinPoolLV
756 The command uses these settings:
758 lvm.conf(5) thin_pool_autoextend_threshold
760 autoextend the LV when its usage exceeds this percent.
761 lvm.conf(5) thin_pool_autoextend_percent
763 autoextend the LV by this much additional space.
764 To see the default values of these settings, run:
766 lvmconfig --type default --withcomment
768 activation/thin_pool_autoextend_threshold
769 lvmconfig --type default --withcomment
771 activation/thin_pool_autoextend_percent
772 To change these values globally, edit lvm.conf(5).
774 To change these values on a per-VG or per-LV basis, attach a "profile"
776 to the VG or LV. A profile is a collection of config settings, saved
777 in a local text file (using the lvm.conf format). lvm looks for pro‐
778 files in the profile_dir directory, e.g. /etc/lvm/profile/. Once
779 attached to a VG or LV, lvm will process the VG or LV using the set‐
780 tings from the attached profile. A profile is named and referenced by
781 its file name.
782 To use a profile to customize the lvextend settings for an LV:
784 · Create a file containing settings, saved in profile_dir. For the
787 profile_dir location, run:
788 lvmconfig config/profile_dir
789 · Attach the profile to an LV, using the command:
792 lvchange --metadataprofile ProfileName VG/ThinPoolLV
793 · Extend the LV using the profile settings:
796 lvextend --use-policies VG/ThinPoolLV
797 Example
800 # lvmconfig config/profile_dir
801 profile_dir="/etc/lvm/profile"
802 # cat /etc/lvm/profile/pool0extend.profile
804 activation {
805 thin_pool_autoextend_threshold=50
806 thin_pool_autoextend_percent=10
807 }
808 # lvchange --metadataprofile pool0extend vg/pool0
810 # lvextend --use-policies vg/pool0
812 Notes
814 · A profile is attached to a VG or LV by name, where the name refer‐
816 ences a local file in profile_dir. If the VG is moved to another
817 machine, the file with the profile also needs to be moved.
818 · Only certain settings can be used in a VG or LV profile, see:
821 lvmconfig --type profilable-metadata.
822 · An LV without a profile of its own will inherit the VG profile.
825 · Remove a profile from an LV using the command:
828 lvchange --detachprofile VG/ThinPoolLV.
829 · Commands can also have profiles applied to them. The settings that
832 can be applied to a command are different than the settings that can
833 be applied to a VG or LV. See lvmconfig --type profilable-command.
834 To apply a profile to a command, write a profile, save it in the pro‐
835 file directory, and run the command using the option: --commandpro‐
836 file ProfileName.
837 Zeroing
841 When a thin pool provisions a new data block for a thin LV, the new
844 block is first overwritten with zeros. The zeroing mode is indicated
845 by the "z" attribute displayed by lvs. The option -Z (or --zero) can
846 be added to commands to specify the zeroing mode.
847 Command to set the zeroing mode when creating a thin pool LV:
849 lvconvert --type thin-pool -Z{y|n}
850 --poolmetadata VG/ThinMetaLV VG/ThinDataLV
851 Command to change the zeroing mode of an existing thin pool LV:
853 lvchange -Z{y|n} VG/ThinPoolLV
854 If zeroing mode is changed from "n" to "y", previously provisioned
856 blocks are not zeroed.
857 Provisioning of large zeroed chunks impacts performance.
859 lvm.conf(5) thin_pool_zero
861 controls the default zeroing mode used when creating a thin pool.
862 Discard
866 The discard behavior of a thin pool LV determines how discard requests
869 are handled. Enabling discard under a file system may adversely affect
870 the file system performance (see the section on fstrim for an alterna‐
871 tive.) Possible discard behaviors:
872 ignore: Ignore any discards that are received.
874 nopassdown: Process any discards in the thin pool itself and allow the
876 no longer needed extents to be overwritten by new data.
877 passdown: Process discards in the thin pool (as with nopassdown), and
879 pass the discards down the the underlying device. This is the default
880 mode.
881 Command to display the current discard mode of a thin pool LV:
883 lvs -o+discards VG/ThinPoolLV
884 Command to set the discard mode when creating a thin pool LV:
886 lvconvert --discards {ignore|nopassdown|passdown}
887 --type thin-pool --poolmetadata VG/ThinMetaLV VG/ThinDataLV
888 Command to change the discard mode of an existing thin pool LV:
890 lvchange --discards {ignore|nopassdown|passdown} VG/ThinPoolLV
891 Example
893 # lvs -o name,discards vg/pool0
894 pool0 passdown
895 # lvchange --discards ignore vg/pool0
897 lvm.conf(5) thin_pool_discards
899 controls the default discards mode used when creating a thin pool.
900 Chunk size
904 The size of data blocks managed by a thin pool can be specified with
907 the --chunksize option when the thin pool LV is created. The default
908 unit is KiB. The value must be a multiple of 64KiB between 64KiB and
909 1GiB.
910 When a thin pool is used primarily for the thin provisioning feature, a
912 larger value is optimal. To optimize for many snapshots, a smaller
913 value reduces copying time and consumes less space.
914 Command to display the thin pool LV chunk size:
916 lvs -o+chunksize VG/ThinPoolLV
917 Example
919 # lvs -o name,chunksize
920 pool0 64.00k
921 lvm.conf(5) thin_pool_chunk_size
923 controls the default chunk size used when creating a thin pool.
924 The default value is shown by:
926 lvmconfig --type default allocation/thin_pool_chunk_size
927 Size of pool metadata LV
931 The amount of thin metadata depends on how many blocks are shared
934 between thin LVs (i.e. through snapshots). A thin pool with many snap‐
935 shots may need a larger metadata LV. Thin pool metadata LV sizes can
936 be from 2MiB to 16GiB.
937 When using lvcreate to create what will become a thin metadata LV, the
939 size is specified with the -L--size option.
940 When an LVM command automatically creates a thin metadata LV, the size
942 is specified with the --poolmetadatasize option. When this option is
943 not given, LVM automatically chooses a size based on the data size and
944 chunk size.
945 It can be hard to predict the amount of metadata space that will be
947 needed, so it is recommended to start with a size of 1GiB which should
948 be enough for all practical purposes. A thin pool metadata LV can
949 later be manually or automatically extended if needed.
950 Create a thin snapshot of an external, read only LV
954 Thin snapshots are typically taken of other thin LVs or other thin
957 snapshot LVs within the same thin pool. It is also possible to take
958 thin snapshots of external, read only LVs. Writes to the snapshot are
959 stored in the thin pool, and the external LV is used to read unwritten
960 parts of the thin snapshot.
961 lvcreate -n SnapLV -s VG/ExternalOriginLV --thinpool VG/ThinPoolLV
963 Example
965 # lvchange -an vg/lve
966 # lvchange --permission r vg/lve
967 # lvcreate -n snaplve -s vg/lve --thinpool vg/pool0
968 # lvs vg/lve vg/snaplve
970 LV VG Attr LSize Pool Origin Data%
971 lve vg ori------- 10.00g
972 snaplve vg Vwi-a-tz-- 10.00g pool0 lve 0.00
973 Convert a standard LV to a thin LV with an external origin
977 A new thin LV can be created and given the name of an existing standard
980 LV. At the same time, the existing LV is converted to a read only
981 external LV with a new name. Unwritten portions of the thin LV are
982 read from the external LV. The new name given to the existing LV can
983 be specified with --originname, otherwise the existing LV will be given
984 a default name, e.g. lvol#.
985 Convert ExampleLV into a read only external LV with the new name NewEx‐
987 ternalOriginLV, and create a new thin LV that is given the previous
988 name of ExampleLV.
989 lvconvert --type thin --thinpool VG/ThinPoolLV
991 --originname NewExternalOriginLV VG/ExampleLV
992 Example
994 # lvcreate -n lv_example -L 10G vg
995 # lvs
997 lv_example vg -wi-a----- 10.00g
998 # lvconvert --type thin --thinpool vg/pool0
1000 --originname lv_external --thin vg/lv_example
1001 # lvs
1003 LV VG Attr LSize Pool Origin
1004 lv_example vg Vwi-a-tz-- 10.00g pool0 lv_external
1005 lv_external vg ori------- 10.00g
1006 Single step thin pool LV creation
1010 A thin pool LV can be created with a single lvcreate command, rather
1013 than using lvconvert on existing LVs. This one command creates a thin
1014 data LV, a thin metadata LV, and combines the two into a thin pool LV.
1015 lvcreate --type thin-pool -L LargeSize -n ThinPoolLV VG
1017 Example
1019 # lvcreate --type thin-pool -L8M -n pool0 vg
1020 # lvs vg/pool0
1022 LV VG Attr LSize Pool Origin Data%
1023 pool0 vg twi-a-tz-- 8.00m 0.00
1024 # lvs -a
1026 pool0 vg twi-a-tz-- 8.00m
1027 [pool0_tdata] vg Twi-ao---- 8.00m
1028 [pool0_tmeta] vg ewi-ao---- 8.00m
1029 Single step thin pool LV and thin LV creation
1033 A thin pool LV and a thin LV can be created with a single lvcreate com‐
1036 mand. This one command creates a thin data LV, a thin metadata LV,
1037 combines the two into a thin pool LV, and creates a thin LV in the new
1038 pool.
1039 -L LargeSize specifies the physical size of the thin pool LV.
1040 -V VirtualSize specifies the virtual size of the thin LV.
1041 lvcreate --type thin -V VirtualSize -L LargeSize
1043 -n ThinLV --thinpool VG/ThinPoolLV
1044 Equivalent to:
1046 lvcreate --type thin-pool -L LargeSize VG/ThinPoolLV
1047 lvcreate -n ThinLV -V VirtualSize --thinpool VG/ThinPoolLV
1048 Example
1050 # lvcreate -L8M -V2G -n thin1 --thinpool vg/pool0
1051 # lvs -a
1053 pool0 vg twi-a-tz-- 8.00m
1054 [pool0_tdata] vg Twi-ao---- 8.00m
1055 [pool0_tmeta] vg ewi-ao---- 8.00m
1056 thin1 vg Vwi-a-tz-- 2.00g pool0
1057 Merge thin snapshots
1061 A thin snapshot can be merged into its origin thin LV using the lvcon‐
1064 vert --merge command. The result of a snapshot merge is that the ori‐
1065 gin thin LV takes the content of the snapshot LV, and the snapshot LV
1066 is removed. Any content that was unique to the origin thin LV is lost
1067 after the merge.
1068 Because a merge changes the content of an LV, it cannot be done while
1070 the LVs are open, e.g. mounted. If a merge is initiated while the LVs
1071 are open, the effect of the merge is delayed until the origin thin LV
1072 is next activated.
1073 lvconvert --merge VG/SnapLV
1075 Example
1077 # lvs vg
1078 LV VG Attr LSize Pool Origin
1079 pool0 vg twi-a-tz-- 10.00g
1080 thin1 vg Vwi-a-tz-- 100.00g pool0
1081 thin1s1 vg Vwi-a-tz-k 100.00g pool0 thin1
1082 # lvconvert --merge vg/thin1s1
1084 # lvs vg
1086 LV VG Attr LSize Pool Origin
1087 pool0 vg twi-a-tz-- 10.00g
1088 thin1 vg Vwi-a-tz-- 100.00g pool0
1089 Example
1091 Delayed merging of open LVs.
1092 # lvs vg
1094 LV VG Attr LSize Pool Origin
1095 pool0 vg twi-a-tz-- 10.00g
1096 thin1 vg Vwi-aotz-- 100.00g pool0
1097 thin1s1 vg Vwi-aotz-k 100.00g pool0 thin1
1098 # df
1100 /dev/mapper/vg-thin1 100G 33M 100G 1% /mnt/X
1101 /dev/mapper/vg-thin1s1 100G 33M 100G 1% /mnt/Xs
1102 # ls /mnt/X
1104 file1 file2 file3
1105 # ls /mnt/Xs
1106 file3 file4 file5
1107 # lvconvert --merge vg/thin1s1
1109 Logical volume vg/thin1s1 contains a filesystem in use.
1110 Delaying merge since snapshot is open.
1111 Merging of thin snapshot thin1s1 will occur on next activation.
1112 # umount /mnt/X
1114 # umount /mnt/Xs
1115 # lvs -a vg
1117 LV VG Attr LSize Pool Origin
1118 pool0 vg twi-a-tz-- 10.00g
1119 [pool0_tdata] vg Twi-ao---- 10.00g
1120 [pool0_tmeta] vg ewi-ao---- 1.00g
1121 thin1 vg Owi-a-tz-- 100.00g pool0
1122 [thin1s1] vg Swi-a-tz-k 100.00g pool0 thin1
1123 # lvchange -an vg/thin1
1125 # lvchange -ay vg/thin1
1126 # mount /dev/vg/thin1 /mnt/X
1128 # ls /mnt/X
1130 file3 file4 file5
1131 XFS on snapshots
1135 Mounting an XFS file system on a new snapshot LV requires attention to
1138 the file system's log state and uuid. On the snapshot LV, the xfs log
1139 will contain a dummy transaction, and the xfs uuid will match the uuid
1140 from the file system on the origin LV.
1141 If the snapshot LV is writable, mounting will recover the log to clear
1143 the dummy transaction, but will require skipping the uuid check:
1144 mount /dev/VG/SnapLV /mnt -o nouuid
1146 Or, the uuid can be changed on disk before mounting:
1148 xfs_admin -U generate /dev/VG/SnapLV
1150 mount /dev/VG/SnapLV /mnt
1151 If the snapshot LV is readonly, the log recovery and uuid check need to
1153 be skipped while mounting readonly:
1154 mount /dev/VG/SnapLV /mnt -o ro,nouuid,norecovery
1156
1159 lvm(8), lvm.conf(5), lvmconfig(8), lvcreate(8), lvconvert(8),
1160 lvchange(8), lvextend(8), lvremove(8), lvs(8), thin_dump(8),
1161 thin_repair(8) thin_restore(8)
1162Red Hat, Inc LVM TOOLS 2.03.06(2) (2019-10-23) LVMTHIN(7)