NAME | DESCRIPTION | Thin Terms | Thin Usage | Thin Topics | SEE ALSO | COLOPHON

LVMTHIN(7)                                                        LVMTHIN(7)

NAME         top

       lvmthin — LVM thin provisioning

DESCRIPTION         top

       Blocks in a standard lvm(8) Logical Volume (LV) are allocated when
       the LV is created, but blocks in a thin provisioned LV are allocated
       as they are written.  Because of this, a thin provisioned LV is given
       a virtual size, and can then be much larger than physically available
       storage.  The amount of physical storage provided for thin
       provisioned LVs can be increased later as the need arises.

       Blocks in a standard LV are allocated (during creation) from the
       Volume Group (VG), but blocks in a thin LV are allocated (during use)
       from a special "thin pool LV".  The thin pool LV contains blocks of
       physical storage, and blocks in thin LVs just reference blocks in the
       thin pool LV.

       A thin pool LV must be created before thin LVs can be created within
       it.  A thin pool LV is created by combining two standard LVs: a large
       data LV that will hold blocks for thin LVs, and a metadata LV that
       will hold metadata.  The metadata tracks which data blocks belong to
       each thin LV.

       Snapshots of thin LVs are efficient because the data blocks common to
       a thin LV and any of its snapshots are shared.  Snapshots may be
       taken of thin LVs or of other thin snapshots.  Blocks common to
       recursive snapshots are also shared in the thin pool.  There is no
       limit to or degradation from sequences of snapshots.

       As thin LVs or snapshot LVs are written to, they consume data blocks
       in the thin pool.  As free data blocks in the pool decrease, more
       free blocks may need to be supplied.  This is done by extending the
       thin pool data LV with additional physical space from the VG.
       Removing thin LVs or snapshots from the thin pool can also free
       blocks in the thin pool.  However, removing LVs is not always an
       effective way of freeing space in a thin pool because the amount is
       limited to the number of blocks not shared with other LVs in the
       pool.

       Incremental block allocation from thin pools can cause thin LVs to
       become fragmented.  Standard LVs generally avoid this problem by
       allocating all the blocks at once during creation.

Thin Terms         top

       ThinDataLV
              thin data LV
              large LV created in a VG
              used by thin pool to store ThinLV blocks

       ThinMetaLV
              thin metadata LV
              small LV created in a VG
              used by thin pool to track data block usage

       ThinPoolLV
              thin pool LV
              combination of ThinDataLV and ThinMetaLV
              contains ThinLVs and SnapLVs

       ThinLV
              thin LV
              created from ThinPoolLV
              appears blank after creation

       SnapLV
              snapshot LV
              created from ThinPoolLV
              appears as a snapshot of another LV after creation

Thin Usage         top

       The primary method for using lvm thin provisioning:

   1. create ThinDataLV
       Create an LV that will hold thin pool data.

       lvcreate -n ThinDataLV -L LargeSize VG

       Example
       # lvcreate -n pool0 -L 10G vg

   2. create ThinMetaLV
       Create an LV that will hold thin pool metadata.

       lvcreate -n ThinMetaLV -L SmallSize VG

       Example
       # lvcreate -n pool0meta -L 1G vg

       # lvs
         LV        VG Attr       LSize
         pool0     vg -wi-a----- 10.00g
         pool0meta vg -wi-a----- 1.00g

   3. create ThinPoolLV
       Combine the data and metadata LVs into a thin pool LV.
       ThinDataLV is renamed to hidden ThinPoolLV_tdata.
       ThinMetaLV is renamed to hidden ThinPoolLV_tmeta.
       The new ThinPoolLV takes the previous name of ThinDataLV.

       lvconvert --type thin-pool --poolmetadata VG/ThinMetaLV VG/ThinDataLV

       Example
       # lvconvert --type thin-pool --poolmetadata vg/pool0meta vg/pool0

       # lvs vg/pool0
         LV    VG Attr       LSize  Pool Origin Data% Meta%
         pool0 vg twi-a-tz-- 10.00g      0.00   0.00

       # lvs -a
         LV            VG Attr       LSize
         pool0         vg twi-a-tz-- 10.00g
         [pool0_tdata] vg Twi-ao---- 10.00g
         [pool0_tmeta] vg ewi-ao---- 1.00g

   4. create ThinLV
       Create a new thin LV from the thin pool LV.
       The thin LV is created with a virtual size.
       Multiple new thin LVs may be created in the thin pool.
       Thin LV names must be unique in the VG.
       The '--type thin' option is inferred from the virtual size option.
       The --thinpool argument specifies which thin pool will
       contain the ThinLV.

       lvcreate -n ThinLV -V VirtualSize --thinpool ThinPoolLV VG

       Example
       Create a thin LV in a thin pool:
       # lvcreate -n thin1 -V 1T --thinpool pool0 vg

       Create another thin LV in the same thin pool:
       # lvcreate -n thin2 -V 1T --thinpool pool0 vg

       # lvs vg/thin1 vg/thin2
         LV    VG Attr       LSize Pool  Origin Data%
         thin1 vg Vwi-a-tz-- 1.00t pool0        0.00
         thin2 vg Vwi-a-tz-- 1.00t pool0        0.00

   5. create SnapLV
       Create snapshots of an existing ThinLV or SnapLV.
       Do not specify -L, --size when creating a thin snapshot.
       A size argument will cause an old COW snapshot to be created.

       lvcreate -n SnapLV --snapshot VG/ThinLV
       lvcreate -n SnapLV --snapshot VG/PrevSnapLV

       Example
       Create first snapshot of an existing ThinLV:
       # lvcreate -n thin1s1 -s vg/thin1

       Create second snapshot of the same ThinLV:
       # lvcreate -n thin1s2 -s vg/thin1

       Create a snapshot of the first snapshot:
       # lvcreate -n thin1s1s1 -s vg/thin1s1

       # lvs vg/thin1s1 vg/thin1s2 vg/thin1s1s1
         LV        VG Attr       LSize Pool  Origin
         thin1s1   vg Vwi---tz-k 1.00t pool0 thin1
         thin1s2   vg Vwi---tz-k 1.00t pool0 thin1
         thin1s1s1 vg Vwi---tz-k 1.00t pool0 thin1s1

   6. activate SnapLV
       Thin snapshots are created with the persistent "activation skip"
       flag, indicated by the "k" attribute.  Use -K with lvchange or
       vgchange to activate thin snapshots with the "k" attribute.

       lvchange -ay -K VG/SnapLV

       Example
       # lvchange -ay -K vg/thin1s1

       # lvs vg/thin1s1
         LV      VG Attr       LSize Pool  Origin
         thin1s1 vg Vwi-a-tz-k 1.00t pool0 thin1

Thin Topics         top

       Alternate syntax for specifying type thin-pool
       Automatic pool metadata LV
       Specify devices for data and metadata LVs
       Tolerate device failures using raid
       Spare metadata LV
       Metadata check and repair
       Activation of thin snapshots
       Removing thin pool LVs, thin LVs and snapshots
       Manually manage free data space of thin pool LV
       Manually manage free metadata space of a thin pool LV
       Using fstrim to increase free space in a thin pool LV
       Automatically extend thin pool LV
       Data space exhaustion
       Metadata space exhaustion
       Automatic extend settings
       Zeroing
       Discard
       Chunk size
       Size of pool metadata LV
       Create a thin snapshot of an external, read only LV
       Convert a standard LV to a thin LV with an external origin
       Single step thin pool LV creation
       Single step thin pool LV and thin LV creation
       Merge thin snapshots
       XFS on snapshots

   Automatic pool metadata LV

       A thin data LV can be converted to a thin pool LV without specifying
       a thin pool metadata LV.  LVM automatically creates a metadata LV
       from the same VG.

       lvcreate -n ThinDataLV -L LargeSize VG
       lvconvert --type thin-pool VG/ThinDataLV

       Example
       # lvcreate -n pool0 -L 10G vg
       # lvconvert --type thin-pool vg/pool0

       # lvs -a
         pool0           vg          twi-a-tz--  10.00g
         [pool0_tdata]   vg          Twi-ao----  10.00g
         [pool0_tmeta]   vg          ewi-ao----  16.00m

   Specify devices for data and metadata LVs

       The data and metadata LVs in a thin pool are best created on separate
       physical devices.  To do that, specify the device name(s) at the end
       of the lvcreate line.  It can be especially helpful to use fast
       devices for the metadata LV.

       lvcreate -n ThinDataLV -L LargeSize VG LargePV
       lvcreate -n ThinMetaLV -L SmallSize VG SmallPV
       lvconvert --type thin-pool --poolmetadata VG/ThinMetaLV VG/ThinDataLV

       Example
       # lvcreate -n pool0 -L 10G vg /dev/sdA
       # lvcreate -n pool0meta -L 1G vg /dev/sdB
       # lvconvert --type thin-pool --poolmetadata vg/pool0meta vg/pool0

       lvm.conf(5) thin_pool_metadata_require_separate_pvs
       controls the default PV usage for thin pool creation.

   Tolerate device failures using raid

       To tolerate device failures, use raid for the pool data LV and pool
       metadata LV.  This is especially recommended for pool metadata LVs.

       lvcreate --type raid1 -m 1 -n ThinMetaLV -L SmallSize VG PVA PVB
       lvcreate --type raid1 -m 1 -n ThinDataLV -L LargeSize VG PVC PVD
       lvconvert --type thin-pool --poolmetadata VG/ThinMetaLV VG/ThinDataLV

       Example
       # lvcreate --type raid1 -m 1 -n pool0 -L 10G vg /dev/sdA /dev/sdB
       # lvcreate --type raid1 -m 1 -n pool0meta -L 1G vg /dev/sdC /dev/sdD
       # lvconvert --type thin-pool --poolmetadata vg/pool0meta vg/pool0

   Spare metadata LV

       The first time a thin pool LV is created, lvm will create a spare
       metadata LV in the VG.  This behavior can be controlled with the
       option --poolmetadataspare y|n.  (Future thin pool creations will
       also attempt to create the pmspare LV if none exists.)

       To create the pmspare ("pool metadata spare") LV, lvm first creates
       an LV with a default name, e.g. lvol0, and then converts this LV to a
       hidden LV with the _pmspare suffix, e.g. lvol0_pmspare.

       One pmspare LV is kept in a VG to be used for any thin pool.

       The pmspare LV cannot be created explicitly, but may be removed
       explicitly.

       Example
       # lvcreate -n pool0 -L 10G vg
       # lvcreate -n pool0meta -L 1G vg
       # lvconvert --type thin-pool --poolmetadata vg/pool0meta vg/pool0

       # lvs -a
         [lvol0_pmspare] vg          ewi-------
         pool0           vg          twi---tz--
         [pool0_tdata]   vg          Twi-------
         [pool0_tmeta]   vg          ewi-------

       The "Metadata check and repair" section describes the use of the
       pmspare LV.

   Metadata check and repair

       If thin pool metadata is damaged, it may be repairable.  Checking and
       repairing thin pool metadata is analagous to running fsck on a file
       system.

       When a thin pool LV is activated, lvm runs the thin_check command to
       check the correctness of the metadata on the pool metadata LV.

       lvm.conf(5) thin_check_executable
       can be set to an empty string ("") to disable the thin_check step.
       This is not recommended.

       lvm.conf(5) thin_check_options
       controls the command options used for the thin_check command.

       If the thin_check command finds a problem with the metadata, the thin
       pool LV is not activated, and the thin pool metadata needs to be
       repaired.

       Simple repair commands are not always successful.  Advanced repair
       may require editing thin pool metadata and lvm metadata.  Newer
       versions of the kernel and lvm tools may be more successful at
       repair.  Report the details of damaged thin metadata to get the best
       advice on recovery.

       Command to repair a thin pool:
       lvconvert --repair VG/ThinPoolLV

       Repair performs the following steps:

       1. Creates a new, repaired copy of the metadata.
       lvconvert runs the thin_repair command to read damaged metadata from
       the existing pool metadata LV, and writes a new repaired copy to the
       VG's pmspare LV.

       2. Replaces the thin pool metadata LV.
       If step 1 is successful, the thin pool metadata LV is replaced with
       the pmspare LV containing the corrected metadata.  The previous thin
       pool metadata LV, containing the damaged metadata, becomes visible
       with the new name ThinPoolLV_tmetaN (where N is 0,1,...).

       If the repair works, the thin pool LV and its thin LVs can be
       activated, and the LV containing the damaged thin pool metadata can
       be removed.  It may be useful to move the new metadata LV (previously
       pmspare) to a better PV.

       If the repair does not work, the thin pool LV and its thin LVs are
       lost.

       If metadata is manually restored with thin_repair directly, the pool
       metadata LV can be manually swapped with another LV containing new
       metadata:

       lvconvert --thinpool VG/ThinPoolLV --poolmetadata VG/NewThinMetaLV

   Activation of thin snapshots

       When a thin snapshot LV is created, it is by default given the
       "activation skip" flag.  This flag is indicated by the "k" attribute
       displayed by lvs:

       # lvs vg/thin1s1
         LV         VG  Attr       LSize Pool  Origin
         thin1s1    vg  Vwi---tz-k 1.00t pool0 thin1

       This flag causes the snapshot LV to be skipped, i.e. not activated,
       by normal activation commands.  The skipping behavior does not apply
       to deactivation commands.

       A snapshot LV with the "k" attribute can be activated using the -K
       (or --ignoreactivationskip) option in addition to the standard -ay
       (or --activate y) option.

       Command to activate a thin snapshot LV:
       lvchange -ay -K VG/SnapLV

       The persistent "activation skip" flag can be turned off during
       lvcreate, or later with lvchange using the -kn (or
       --setactivationskip n) option.  It can be turned on again with -ky
       (or --setactivationskip y).

       When the "activation skip" flag is removed, normal activation
       commands will activate the LV, and the -K activation option is not
       needed.

       Command to create snapshot LV without the activation skip flag:
       lvcreate -kn -n SnapLV -s VG/ThinLV

       Command to remove the activation skip flag from a snapshot LV:
       lvchange -kn VG/SnapLV

       lvm.conf(5) auto_set_activation_skip
       controls the default activation skip setting used by lvcreate.

   Removing thin pool LVs, thin LVs and snapshots

       Removing a thin LV and its related snapshots returns the blocks it
       used to the thin pool LV.  These blocks will be reused for other thin
       LVs and snapshots.

       Removing a thin pool LV removes both the data LV and metadata LV and
       returns the space to the VG.

       lvremove of thin pool LVs, thin LVs and snapshots cannot be reversed
       with vgcfgrestore.

       vgcfgbackup does not back up thin pool metadata.

   Manually manage free data space of thin pool LV

       The available free space in a thin pool LV can be displayed with the
       lvs command.  Free space can be added by extending the thin pool LV.

       Command to extend thin pool data space:
       lvextend -L Size VG/ThinPoolLV

       Example
       1. A thin pool LV is using 26.96% of its data blocks.
       # lvs
         LV    VG           Attr       LSize   Pool  Origin Data%
         pool0 vg           twi-a-tz--  10.00g               26.96

       2. Double the amount of physical space in the thin pool LV.
       # lvextend -L+10G vg/pool0

       3. The percentage of used data blocks is half the previous value.
       # lvs
         LV    VG           Attr       LSize   Pool  Origin Data%
         pool0 vg           twi-a-tz--  20.00g               13.48

       Other methods of increasing free data space in a thin pool LV include
       removing a thin LV and its related snapsots, or running fstrim on the
       file system using a thin LV.

   Manually manage free metadata space of a thin pool LV

       The available metadata space in a thin pool LV can be displayed with
       the lvs -o+metadata_percent command.

       Command to extend thin pool metadata space:
       lvextend --poolmetadatasize Size VG/ThinPoolLV

       Example
       1. A thin pool LV is using 12.40% of its metadata blocks.
       # lvs -oname,size,data_percent,metadata_percent vg/pool0
         LV    LSize   Data%  Meta%
         pool0  20.00g  13.48  12.40

       2. Display a thin pool LV with its component thin data LV and thin
       metadata LV.
       # lvs -a -oname,attr,size vg
         LV              Attr       LSize
         pool0           twi-a-tz--  20.00g
         [pool0_tdata]   Twi-ao----  20.00g
         [pool0_tmeta]   ewi-ao----  12.00m

       3. Double the amount of physical space in the thin metadata LV.
       # lvextend --poolmetadatasize +12M vg/pool0

       4. The percentage of used metadata blocks is half the previous value.
       # lvs -a -oname,size,data_percent,metadata_percent vg
         LV              LSize   Data%  Meta%
         pool0            20.00g  13.48   6.20
         [pool0_tdata]    20.00g
         [pool0_tmeta]    24.00m

   Using fstrim to increase free space in a thin pool LV

       Removing files in a file system on top of a thin LV does not
       generally add free space back to the thin pool.  Manually running the
       fstrim command can return space back to the thin pool that had been
       used by removed files.  fstrim uses discards and will not work if the
       thin pool LV has discards mode set to ignore.

       Example
       A thin pool has 10G of physical data space, and a thin LV has a
       virtual size of 100G.  Writing a 1G file to the file system reduces
       the free space in the thin pool by 10% and increases the virtual
       usage of the file system by 1%.  Removing the 1G file restores the
       virtual 1% to the file system, but does not restore the physical 10%
       to the thin pool.  The fstrim command restores the physical space to
       the thin pool.

       # lvs -a -oname,attr,size,pool_lv,origin,data_percent,metadata_percent vg
       LV              Attr       LSize   Pool  Origin Data%  Meta%
       pool0           twi-a-tz--  10.00g               47.01  21.03
       thin1           Vwi-aotz-- 100.00g pool0          2.70

       # df -h /mnt/X
       Filesystem            Size  Used Avail Use% Mounted on
       /dev/mapper/vg-thin1   99G  1.1G   93G   2% /mnt/X

       # dd if=/dev/zero of=/mnt/X/1Gfile bs=4096 count=262144; sync

       # lvs
       pool0           vg   twi-a-tz--  10.00g               57.01  25.26
       thin1           vg   Vwi-aotz-- 100.00g pool0          3.70

       # df -h /mnt/X
       /dev/mapper/vg-thin1   99G  2.1G   92G   3% /mnt/X

       # rm /mnt/X/1Gfile

       # lvs
       pool0           vg   twi-a-tz--  10.00g               57.01  25.26
       thin1           vg   Vwi-aotz-- 100.00g pool0          3.70

       # df -h /mnt/X
       /dev/mapper/vg-thin1   99G  1.1G   93G   2% /mnt/X

       # fstrim -v /mnt/X

       # lvs
       pool0           vg   twi-a-tz--  10.00g               47.01  21.03
       thin1           vg   Vwi-aotz-- 100.00g pool0          2.70

       The "Discard" section covers an option for automatically freeing data
       space in a thin pool.

   Automatically extend thin pool LV

       The lvm daemon dmeventd (lvm2-monitor) monitors the data usage of
       thin pool LVs and extends them when the usage reaches a certain
       level.  The necessary free space must exist in the VG to extend thin
       pool LVs.  Monitoring and extension of thin pool LVs are controlled
       independently.

       monitoring

       When a thin pool LV is activated, dmeventd will begin monitoring it
       by default.

       Command to start or stop dmeventd monitoring a thin pool LV:
       lvchange --monitor {y|n} VG/ThinPoolLV

       The current dmeventd monitoring status of a thin pool LV can be
       displayed with the command lvs -o+seg_monitor.

       autoextend

       dmeventd should be configured to extend thin pool LVs before all data
       space is used.  Warnings are emitted through syslog when the use of a
       thin pool reaches 80%, 85%, 90% and 95%.  (See the section "Data
       space exhaustion" for the effects of not extending a thin pool LV.)
       The point at which dmeventd extends thin pool LVs, and the amount are
       controlled with two configuration settings:

       lvm.conf(5) thin_pool_autoextend_threshold
       is a percentage full value that defines when the thin pool LV should
       be extended.  Setting this to 100 disables automatic extention.  The
       minimum value is 50.

       lvm.conf(5) thin_pool_autoextend_percent
       defines how much extra data space should be added to the thin pool LV
       from the VG, in percent of its current size.

       disabling

       There are multiple ways that extension of thin pools could be
       prevented:

       · If the dmeventd daemon is not running, no monitoring or automatic
         extension will occur.

       · Even when dmeventd is running, all monitoring can be disabled with
         the lvm.conf monitoring setting.

       · To activate or create a thin pool LV without interacting with
         dmeventd, the --ignoremonitoring option can be used.  With this
         option, the command will not ask dmeventd to monitor the thin pool
         LV.

       · Setting thin_pool_autoextend_threshould to 100 disables automatic
         extension of thin pool LVs, even if they are being monitored by
         dmeventd.

       Example
       If thin_pool_autoextend_threshold is 70 and
       thin_pool_autoextend_percent is 20, whenever a pool exceeds 70%
       usage, it will be extended by another 20%.  For a 1G pool, using 700M
       will trigger a resize to 1.2G. When the usage exceeds 840M, the pool
       will be extended to 1.44G, and so on.

   Data space exhaustion

       When properly managed, thin pool data space should be extended before
       it is all used (see the section "Automatically extend thin pool LV").
       If thin pool data space is already exhausted, it can still be
       extended (see the section "Manually manage free data space of thin
       pool LV".)

       The behavior of a full thin pool is configurable with the
       --errorwhenfull y|n option to lvcreate or lvchange.  The
       errorwhenfull setting applies only to writes; reading thin LVs can
       continue even when data space is exhausted.

       Command to change the handling of a full thin pool:
       lvchange --errorwhenfull {y|n} VG/ThinPoolLV

       lvm.conf(5) error_when_full
       controls the default error when full behavior.

       The current setting of a thin pool LV can be displayed with the
       command: lvs -o+lv_when_full.

       The errorwhenfull setting does not effect the monitoring and
       autoextend settings, and the monitoring/autoextend settings do not
       effect the errorwhenfull setting.  It is only when
       monitoring/autoextend are not effective that the thin pool becomes
       full and the errorwhenfull setting is applied.

       errorwhenfull n

       This is the default.  Writes to thin LVs are accepted and queued,
       with the expectation that pool data space will be extended soon.
       Once data space is extended, the queued writes will be processed, and
       the thin pool will return to normal operation.

       While waiting to be extended, the thin pool will queue writes for up
       to 60 seconds (the default).  If data space has not been extended
       after this time, the queued writes will return an error to the
       caller, e.g. the file system.  This can result in file system
       corruption for non-journaled file systems that may require fsck.
       When a thin pool returns errors for writes to a thin LV, any file
       system is subject to losing unsynced user data.

       The 60 second timeout can be changed or disabled with the dm-
       thin-pool kernel module option no_space_timeout.  This option sets
       the number of seconds that thin pools will queue writes.  If set to
       0, writes will not time out.  Disabling timeouts can result in the
       system running out of resources, memory exhaustion, hung tasks, and
       deadlocks.  (The timeout applies to all thin pools on the system.)

       errorwhenfull y

       Writes to thin LVs immediately return an error, and no writes are
       queued.  In the case of a file system, this can result in corruption
       that may require fsck (the specific consequences depend on the thin
       LV user.)

       data percent

       When data space is exhausted, the lvs command displays 100 under
       Data% for the thin pool LV:

       # lvs vg/pool0
         LV     VG           Attr       LSize   Pool  Origin Data%
         pool0  vg           twi-a-tz-- 512.00m              100.00

       causes

       A thin pool may run out of data space for any of the following
       reasons:

       · Automatic extension of the thin pool is disabled, and the thin pool
         is not manually extended.  (Disabling automatic extension is not
         recommended.)

       · The dmeventd daemon is not running and the thin pool is not
         manually extended.  (Disabling dmeventd is not recommended.)

       · Automatic extension of the thin pool is too slow given the rate of
         writes to thin LVs in the pool.  (This can be addressed by tuning
         the thin_pool_autoextend_threshold and
         thin_pool_autoextend_percent.  See "Automatic extend settings".)

       · The VG does not have enough free blocks to extend the thin pool.

   Metadata space exhaustion

       If thin pool metadata space is exhausted (or a thin pool metadata
       operation fails), errors will be returned for IO operations on thin
       LVs.

       When metadata space is exhausted, the lvs command displays 100 under
       Meta% for the thin pool LV:

       # lvs -o lv_name,size,data_percent,metadata_percent vg/pool0
         LV    LSize Data%  Meta%
         pool0              100.00

       The same reasons for thin pool data space exhaustion apply to thin
       pool metadata space.

       Metadata space exhaustion can lead to inconsistent thin pool metadata
       and inconsistent file systems, so the response requires offline
       checking and repair.

       1. Deactivate the thin pool LV, or reboot the system if this is not
       possible.

       2. Repair thin pool with lvconvert --repair.
          See "Metadata check and repair".

       3. Extend pool metadata space with lvextend --poolmetadatasize.
          See "Manually manage free metadata space of a thin pool LV".

       4. Check and repair file system with fsck.

   Automatic extend settings

       Thin pool LVs can be extended according to preset values.  The
       presets determine if the LV should be extended based on how full it
       is, and if so by how much.  When dmeventd monitors thin pool LVs, it
       uses lvextend with these presets.  (See "Automatically extend thin
       pool LV".)

       Command to extend a thin pool data LV using presets:
       lvextend --use-policies VG/ThinPoolLV

       The command uses these settings:

       lvm.conf(5) thin_pool_autoextend_threshold
       autoextend the LV when its usage exceeds this percent.

       lvm.conf(5) thin_pool_autoextend_percent
       autoextend the LV by this much additional space.

       To see the default values of these settings, run:

       lvmconfig --type default --withcomment
              activation/thin_pool_autoextend_threshold

       lvmconfig --type default --withcomment
              activation/thin_pool_autoextend_percent

       To change these values globally, edit lvm.conf(5).

       To change these values on a per-VG or per-LV basis, attach a
       "profile" to the VG or LV.  A profile is a collection of config
       settings, saved in a local text file (using the lvm.conf format).
       lvm looks for profiles in the profile_dir directory, e.g.
       /etc/lvm/profile/.  Once attached to a VG or LV, lvm will process the
       VG or LV using the settings from the attached profile.  A profile is
       named and referenced by its file name.

       To use a profile to customize the lvextend settings for an LV:

       · Create a file containing settings, saved in profile_dir.  For the
         profile_dir location, run:
         lvmconfig config/profile_dir

       · Attach the profile to an LV, using the command:
         lvchange --metadataprofile ProfileName VG/ThinPoolLV

       · Extend the LV using the profile settings:
         lvextend --use-policies VG/ThinPoolLV

       Example
       # lvmconfig config/profile_dir
       profile_dir="/etc/lvm/profile"

       # cat /etc/lvm/profile/pool0extend.profile
       activation {
               thin_pool_autoextend_threshold=50
               thin_pool_autoextend_percent=10
       }

       # lvchange --metadataprofile pool0extend vg/pool0

       # lvextend --use-policies vg/pool0

       Notes

       · A profile is attached to a VG or LV by name, where the name
         references a local file in profile_dir.  If the VG is moved to
         another machine, the file with the profile also needs to be moved.

       · Only certain settings can be used in a VG or LV profile, see:
         lvmconfig --type profilable-metadata.

       · An LV without a profile of its own will inherit the VG profile.

       · Remove a profile from an LV using the command:
         lvchange --detachprofile VG/ThinPoolLV.

       · Commands can also have profiles applied to them.  The settings that
         can be applied to a command are different than the settings that
         can be applied to a VG or LV.  See lvmconfig --type profilable-
         command.  To apply a profile to a command, write a profile, save it
         in the profile directory, and run the command using the option:
         --commandprofile ProfileName.

   Zeroing

       When a thin pool provisions a new data block for a thin LV, the new
       block is first overwritten with zeros.  The zeroing mode is indicated
       by the "z" attribute displayed by lvs.  The option -Z (or --zero) can
       be added to commands to specify the zeroing mode.

       Command to set the zeroing mode when creating a thin pool LV:
       lvconvert --type thin-pool -Z{y|n}
              --poolmetadata VG/ThinMetaLV VG/ThinDataLV

       Command to change the zeroing mode of an existing thin pool LV:
       lvchange -Z{y|n} VG/ThinPoolLV

       If zeroing mode is changed from "n" to "y", previously provisioned
       blocks are not zeroed.

       Provisioning of large zeroed chunks impacts performance.

       lvm.conf(5) thin_pool_zero
       controls the default zeroing mode used when creating a thin pool.

   Discard

       The discard behavior of a thin pool LV determines how discard
       requests are handled.  Enabling discard under a file system may
       adversely affect the file system performance (see the section on
       fstrim for an alternative.)  Possible discard behaviors:

       ignore: Ignore any discards that are received.

       nopassdown: Process any discards in the thin pool itself and allow
       the no longer needed extents to be overwritten by new data.

       passdown: Process discards in the thin pool (as with nopassdown), and
       pass the discards down the the underlying device.  This is the
       default mode.

       Command to display the current discard mode of a thin pool LV:
       lvs -o+discards VG/ThinPoolLV

       Command to set the discard mode when creating a thin pool LV:
       lvconvert --discards {ignore|nopassdown|passdown}
              --type thin-pool --poolmetadata VG/ThinMetaLV VG/ThinDataLV

       Command to change the discard mode of an existing thin pool LV:
       lvchange --discards {ignore|nopassdown|passdown} VG/ThinPoolLV

       Example
       # lvs -o name,discards vg/pool0
       pool0 passdown

       # lvchange --discards ignore vg/pool0

       lvm.conf(5) thin_pool_discards
       controls the default discards mode used when creating a thin pool.

   Chunk size

       The size of data blocks managed by a thin pool can be specified with
       the --chunksize option when the thin pool LV is created.  The default
       unit is KiB. The value must be a multiple of 64KiB between 64KiB and
       1GiB.

       When a thin pool is used primarily for the thin provisioning feature,
       a larger value is optimal.  To optimize for many snapshots, a smaller
       value reduces copying time and consumes less space.

       Command to display the thin pool LV chunk size:
       lvs -o+chunksize VG/ThinPoolLV

       Example
       # lvs -o name,chunksize
         pool0 64.00k

       lvm.conf(5) thin_pool_chunk_size
       controls the default chunk size used when creating a thin pool.

       The default value is shown by:
       lvmconfig --type default allocation/thin_pool_chunk_size

   Size of pool metadata LV

       The amount of thin metadata depends on how many blocks are shared
       between thin LVs (i.e. through snapshots).  A thin pool with many
       snapshots may need a larger metadata LV.  Thin pool metadata LV sizes
       can be from 2MiB to 16GiB.

       When using lvcreate to create what will become a thin metadata LV,
       the size is specified with the -L--size option.

       When an LVM command automatically creates a thin metadata LV, the
       size is specified with the --poolmetadatasize option.  When this
       option is not given, LVM automatically chooses a size based on the
       data size and chunk size.

       It can be hard to predict the amount of metadata space that will be
       needed, so it is recommended to start with a size of 1GiB which
       should be enough for all practical purposes.  A thin pool metadata LV
       can later be manually or automatically extended if needed.

   Create a thin snapshot of an external, read only LV

       Thin snapshots are typically taken of other thin LVs or other thin
       snapshot LVs within the same thin pool.  It is also possible to take
       thin snapshots of external, read only LVs.  Writes to the snapshot
       are stored in the thin pool, and the external LV is used to read
       unwritten parts of the thin snapshot.

       lvcreate -n SnapLV -s VG/ExternalOriginLV --thinpool VG/ThinPoolLV

       Example
       # lvchange -an vg/lve
       # lvchange --permission r vg/lve
       # lvcreate -n snaplve -s vg/lve --thinpool vg/pool0

       # lvs vg/lve vg/snaplve
         LV      VG  Attr       LSize  Pool  Origin Data%
         lve     vg  ori------- 10.00g
         snaplve vg  Vwi-a-tz-- 10.00g pool0 lve      0.00

   Convert a standard LV to a thin LV with an external origin

       A new thin LV can be created and given the name of an existing
       standard LV.  At the same time, the existing LV is converted to a
       read only external LV with a new name.  Unwritten portions of the
       thin LV are read from the external LV.  The new name given to the
       existing LV can be specified with --originname, otherwise the
       existing LV will be given a default name, e.g. lvol#.

       Convert ExampleLV into a read only external LV with the new name
       NewExternalOriginLV, and create a new thin LV that is given the
       previous name of ExampleLV.

       lvconvert --type thin --thinpool VG/ThinPoolLV
              --originname NewExternalOriginLV VG/ExampleLV

       Example
       # lvcreate -n lv_example -L 10G vg

       # lvs
         lv_example      vg          -wi-a-----  10.00g

       # lvconvert --type thin --thinpool vg/pool0
                 --originname lv_external --thin vg/lv_example

       # lvs
         LV              VG          Attr       LSize   Pool  Origin
         lv_example      vg          Vwi-a-tz--  10.00g pool0 lv_external
         lv_external     vg          ori-------  10.00g

   Single step thin pool LV creation

       A thin pool LV can be created with a single lvcreate command, rather
       than using lvconvert on existing LVs.  This one command creates a
       thin data LV, a thin metadata LV, and combines the two into a thin
       pool LV.

       lvcreate --type thin-pool -L LargeSize -n ThinPoolLV VG

       Example
       # lvcreate --type thin-pool -L8M -n pool0 vg

       # lvs vg/pool0
         LV    VG  Attr       LSize Pool Origin Data%
         pool0 vg  twi-a-tz-- 8.00m               0.00

       # lvs -a
         pool0           vg          twi-a-tz--   8.00m
         [pool0_tdata]   vg          Twi-ao----   8.00m
         [pool0_tmeta]   vg          ewi-ao----   8.00m

   Single step thin pool LV and thin LV creation

       A thin pool LV and a thin LV can be created with a single lvcreate
       command.  This one command creates a thin data LV, a thin metadata
       LV, combines the two into a thin pool LV, and creates a thin LV in
       the new pool.
       -L LargeSize specifies the physical size of the thin pool LV.
       -V VirtualSize specifies the virtual size of the thin LV.

       lvcreate --type thin -V VirtualSize -L LargeSize
              -n ThinLV --thinpool VG/ThinPoolLV

       Equivalent to:
       lvcreate --type thin-pool -L LargeSize VG/ThinPoolLV
       lvcreate -n ThinLV -V VirtualSize --thinpool VG/ThinPoolLV

       Example
       # lvcreate -L8M -V2G -n thin1 --thinpool vg/pool0

       # lvs -a
         pool0           vg          twi-a-tz--   8.00m
         [pool0_tdata]   vg          Twi-ao----   8.00m
         [pool0_tmeta]   vg          ewi-ao----   8.00m
         thin1           vg          Vwi-a-tz--   2.00g pool0

   Merge thin snapshots

       A thin snapshot can be merged into its origin thin LV using the
       lvconvert --merge command.  The result of a snapshot merge is that
       the origin thin LV takes the content of the snapshot LV, and the
       snapshot LV is removed.  Any content that was unique to the origin
       thin LV is lost after the merge.

       Because a merge changes the content of an LV, it cannot be done while
       the LVs are open, e.g. mounted.  If a merge is initiated while the
       LVs are open, the effect of the merge is delayed until the origin
       thin LV is next activated.

       lvconvert --merge VG/SnapLV

       Example
       # lvs vg
         LV      VG Attr       LSize   Pool  Origin
         pool0   vg twi-a-tz--  10.00g
         thin1   vg Vwi-a-tz-- 100.00g pool0
         thin1s1 vg Vwi-a-tz-k 100.00g pool0 thin1

       # lvconvert --merge vg/thin1s1

       # lvs vg
         LV      VG Attr       LSize   Pool  Origin
         pool0   vg twi-a-tz--  10.00g
         thin1   vg Vwi-a-tz-- 100.00g pool0

       Example
       Delayed merging of open LVs.

       # lvs vg
         LV      VG Attr       LSize   Pool  Origin
         pool0   vg twi-a-tz--  10.00g
         thin1   vg Vwi-aotz-- 100.00g pool0
         thin1s1 vg Vwi-aotz-k 100.00g pool0 thin1

       # df
       /dev/mapper/vg-thin1            100G   33M  100G   1% /mnt/X
       /dev/mapper/vg-thin1s1          100G   33M  100G   1% /mnt/Xs

       # ls /mnt/X
       file1 file2 file3
       # ls /mnt/Xs
       file3 file4 file5

       # lvconvert --merge vg/thin1s1
       Logical volume vg/thin1s1 contains a filesystem in use.
       Delaying merge since snapshot is open.
       Merging of thin snapshot thin1s1 will occur on next activation.

       # umount /mnt/X
       # umount /mnt/Xs

       # lvs -a vg
         LV              VG   Attr       LSize   Pool  Origin
         pool0           vg   twi-a-tz--  10.00g
         [pool0_tdata]   vg   Twi-ao----  10.00g
         [pool0_tmeta]   vg   ewi-ao----   1.00g
         thin1           vg   Owi-a-tz-- 100.00g pool0
         [thin1s1]       vg   Swi-a-tz-k 100.00g pool0 thin1

       # lvchange -an vg/thin1
       # lvchange -ay vg/thin1

       # mount /dev/vg/thin1 /mnt/X

       # ls /mnt/X
       file3 file4 file5

   XFS on snapshots

       Mounting an XFS file system on a new snapshot LV requires attention
       to the file system's log state and uuid.  On the snapshot LV, the xfs
       log will contain a dummy transaction, and the xfs uuid will match the
       uuid from the file system on the origin LV.

       If the snapshot LV is writable, mounting will recover the log to
       clear the dummy transaction, but will require skipping the uuid
       check:

       mount /dev/VG/SnapLV /mnt -o nouuid

       Or, the uuid can be changed on disk before mounting:

       xfs_admin -U generate /dev/VG/SnapLV
       mount /dev/VG/SnapLV /mnt

       If the snapshot LV is readonly, the log recovery and uuid check need
       to be skipped while mounting readonly:

       mount /dev/VG/SnapLV /mnt -o ro,nouuid,norecovery

SEE ALSO         top

       lvm(8), lvm.conf(5), lvmconfig(8), lvcreate(8), lvconvert(8),
       lvchange(8), lvextend(8), lvremove(8), lvs(8), thin_dump(8),
       thin_repair(8) thin_restore(8)

COLOPHON         top

       This page is part of the lvm2 (Logical Volume Manager 2) project.
       Information about the project can be found at 
       ⟨http://www.sourceware.org/lvm2/⟩.  If you have a bug report for this
       manual page, send it to linux-lvm@redhat.com.  This page was obtained
       from the project's upstream Git repository 
       ⟨git://sourceware.org/git/lvm2.git⟩ on 2017-05-03.  If you discover
       any rendering problems in this HTML version of the page, or you
       believe there is a better or more up-to-date source for the page, or
       you have corrections or improvements to the information in this
       COLOPHON (which is not part of the original manual page), send a mail
       to man-pages@man7.org

Red Hat, Inc       LVM TOOLS 2.02.171(2)-git (2017-04-13)         LVMTHIN(7)

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