lvmthin(glossar.html) - phpMan

LVMTHIN(7)                                                          LVMTHIN(7)

NAME
       lvmthin -- LVM thin provisioning

DESCRIPTION
       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  snap-
       shots are also shared in the thin pool.  There is no limit to or degra-
       dation 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  allo-
       cating 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 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
       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 meta-
       data 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 hid-
       den 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 explic-
       itly.
       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 pms-
       pare 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/repair 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  acti-
       vated,  and  the  LV  containing  the damaged thin pool metadata can be
       removed.  It may be useful to move the new metadata LV (previously pms-
       pare) 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 "activa-
       tion 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  lvcre-
       ate,  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 com-
       mand 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  dis-
       played 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 con-
       trolled 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 mini-
       mum 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 pre-
       vented:

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

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

       o 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.

       o 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_per-
       cent 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  --errorwhen-
       full  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 com-
       mand: 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  repair.  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 time-
       out 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 fs repair (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:

       o Automatic extension of the thin pool is disabled, and the  thin  pool
         is not manually extended.  (Disabling automatic extension is not rec-
         ommended.)

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

       o 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".)

       o 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 oper-
       ation 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  check-
       ing 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.

   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 pro-
       files 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 set-
       tings 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:

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

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

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

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

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

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

       o 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 pro-
         file directory, and run the command using the  option:  --commandpro-
         file 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 alterna-
       tive.)  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 snap-
       shots 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 NewEx-
       ternalOriginLV, 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 com-
       mand.  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  lvcon-
       vert  --merge command.  The result of a snapshot merge is that the ori-
       gin 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 2.02.187(2)-RHEL7 (2020-03-24)         LVMTHIN(7)