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LVMTHIN(7)                                                          LVMTHIN(7)



NAME
       lvmthin -- LVM thin provisioning


DESCRIPTION
       Blocks in a standard logical volume are allocated when the LV is created, but blocks in a thin provisioned log-
       ical volume 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 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  combin-
       ing  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
       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
       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 VG/ThinPoolLV

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

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

       # 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 -s VG/ThinLV
       lvcreate -n SnapLV -s 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
       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




   Alternate syntax for specifying type thin-pool


       The fully specified syntax for creating a thin pool LV shown above is:

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

       An existing LV is converted to a thin pool by changing its type to thin-pool.  An alternate syntax may be  used
       for the same operation:

       lvconvert --thinpool VG/ThinDataLV --poolmetadata VG/ThinMetaLV

       The  thin-pool type is inferred by lvm; the --thinpool option is not an alias for --type thin-pool.  The use of
       the --thinpool option here is different from the use of the --thinpool option when creating a thin LV, where it
       specifies the pool in which the thin LV is created.



   Automatic pool metadata LV


       A  thin  data  LV can be converted to a thin pool LV without specifying a thin pool metadata LV.  LVM automati-
       cally 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  recom-
       mended 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  skip-
       ping behavior does not apply to deactivation commands.

       A  snapshot LV with the "k" attribute can be activated using the -K (or --ignoreactivationskip) option in addi-
       tion 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 activa-
       tion 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  snap-
       sots, 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 exhaus-
       tion" 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 "Automat-
       ically  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 collec-
       tion 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 extends to be overwrit-
       ten 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 manu-
       ally 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 --thin 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 -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
       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)




Red Hat, Inc       LVM TOOLS 2.02.143(2)-RHEL6 (2016-12-13)         LVMTHIN(7)