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man: add lvmthin man page
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David Teigland
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man/lvmthin.7.in
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man/lvmthin.7.in
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.TH "LVMTHIN" "7" "LVM TOOLS #VERSION#" "Red Hat, Inc" "\""
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.SH NAME
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lvmthin - LVM thin provisioning
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.SH DESCRIPTION
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Blocks in a standard logical volume are allocated when the LV is created,
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but blocks in a thin provisioned logical volume are allocated as they are
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written. Because of this, a thin provisioned LV is given a virtual size,
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and can then be much larger than physically available storage. The amount
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of physical storage provided for thin provisioned LVs can be increased
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later as the need arises.
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Blocks in a standard LV are allocated (during creation) from the VG, but
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blocks in a thin LV are allocated (during use) from a special "thin pool
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LV". The thin pool LV contains blocks of physical storage, and blocks in
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thin LVs just reference blocks in the thin pool LV.
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A thin pool LV must be created before thin LV's can be created within it.
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A thin pool LV is created by combining two standard LV's: a large data LV
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that will hold blocks for thin LVs, and a metadata LV that will hold
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metadata. The metadata tracks which data blocks belong to each thin LV.
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Snapshots of thin LVs are efficient because the data blocks common to a
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thin LV and its snapshot are shared. Snapshots may be taken of thin LV's
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or of other thin snapshots. Blocks common to recursive snapshots are also
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shared in the thin pool. There is no limit to or degradation from
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sequences of snapshots.
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As thin LV's or snapshot LV's are written to, they consume data blocks in
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the thin pool. As free data blocks in the pool decrease, more free blocks
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may need to be supplied. This is done by extending the thin pool data LV
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with additional physical space from the VG. Removing thin LVs or
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snapshots from the thin pool can also free blocks in the thin pool.
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However, removing LVs is not always an effective way of freeing space in a
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thin pool because the amount is limited to the number of blocks not shared
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with other LVs in the pool.
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Incremental block allocation from thin pools can cause thin LVs to become
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fragmented. Standard LVs generally avoid this problem by allocating all
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the blocks at once during creation.
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.SH Thin Terms
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.TP
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ThinDataLV
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.br
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thin data LV
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.br
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large LV created in a VG
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.br
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used by thin pool to store ThinLV blocks
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.TP
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ThinMetaLV
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.br
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thin metadata LV
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.br
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small LV created in a VG
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.br
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used by thin pool to track data block usage
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.TP
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ThinPoolLV
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.br
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thin pool LV
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.br
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combination of ThinDataLV and ThinMetaLV
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.br
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contains ThinLVs and SnapLVs
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.TP
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ThinLV
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.br
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thin LV
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.br
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created from ThinPoolLV
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.br
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appears blank after creation
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.TP
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SnapLV
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.br
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snapshot LV
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.br
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created from ThinPoolLV
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.br
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appears as a snapshot of another LV after creation
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.SH Thin Usage
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The primary method for using lvm thin provisioning:
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.nf
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1. create ThinDataLV
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Create an LV that will hold thin pool data.
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Command
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lvcreate -n ThinDataLV -L LargeSize VG
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Example
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# lvcreate -n pool0 -L 100G vg
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2. create ThinMetaLV
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Create an LV that will hold thin pool metadata.
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Command
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lvcreate -n ThinMetaLV -L SmallSize VG
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Example
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# lvcreate -n pool0meta -L 1G vg
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# lvs
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pool0 vg -wi-a----- 10.00g
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pool0meta vg -wi-a----- 1.00g
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3. create ThinPoolLV
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Combine the data and metadata LVs into a thin pool LV.
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ThinDataLV is renamed to hidden ThinPoolLV_tdata.
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ThinMetaLV is renamed to hidden ThinPoolLV_tmeta.
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The new ThinPoolLV takes the previous name of ThinDataLV.
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Command
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lvconvert --thinpool VG/ThinDataLV --poolmetadata VG/ThinMetaLV
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Example
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# lvconvert --thinpool vg/pool0 --poolmetadata vg/pool0meta
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# lvs vg/pool0
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LV VG Attr LSize Pool Origin Data%
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pool0 vg twi-a-tz-- 10.00g 0.00
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# lvs -a
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pool0 vg twi-a-tz-- 10.00g
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[pool0_tdata] vg Twi-ao---- 10.00g
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[pool0_tmeta] vg ewi-ao---- 1.00g
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4. create ThinLV
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Create a new thin LV from the thin pool LV.
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The thin LV is created with a virtual size.
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Multiple new thin LV's may be created in the thin pool.
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Thin LV names must be unique in the VG.
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The thinpool argument specifies which thin pool will
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contain the ThinLV.
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Command
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lvcreate --type thin -n ThinLV -V VirtualSize --thinpool VG/ThinPoolLV
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Example
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Create a thin LV in a thin pool:
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# lvcreate --type thin -n thin1 -V 1T --thinpool vg/pool0
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Create another thin LV in the same thin pool:
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# lvcreate --type thin -n thin2 -V 1T --thinpool vg/pool0
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# lvs vg/thin1 vg/thin2
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LV VG Attr LSize Pool Origin Data%
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thin1 vg Vwi-a-tz-- 1.00t pool0 0.00
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thin2 vg Vwi-a-tz-- 1.00t pool0 0.00
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5. create SnapLV
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Create snapshots of an existing ThinLV or SnapLV.
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Command
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lvcreate --type thin -n SnapLV -s ThinLV --thinpool VG/ThinPoolLV
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lvcreate --type thin -n SnapLV -s PrevSnapLV --thinpool VG/ThinPoolLV
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Example
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Create first snapshot of an existing ThinLV:
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# lvcreate --type thin -n thin1s1 -s thin1 --thinpool vg/pool0
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Create second snapshot of the same ThinLV:
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# lvcreate --type thin -n thin1s2 -s thin1 --thinpool vg/pool0
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Create a snapshot of the first snapshot:
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# lvcreate --type thin -n thin1s1s1 -s thin1s1 --thinpool vg/pool0
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# lvs vg/thin1s1 vg/thin1s2 vg/thin1s1s1
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LV VG Attr LSize Pool Origin
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thin1s1 vg Vwi---tz-k 1.00t pool0 thin1
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thin1s2 vg Vwi---tz-k 1.00t pool0 thin1
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thin1s1s1 vg Vwi---tz-k 1.00t pool0 thin1s1
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6. activate SnapLV
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Thin snapshots are created with the persistent "activation skip"
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flag, indicated by the "k" attribute. Use -K with lvchange
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or vgchange to activate thin snapshots with the "k" attribute.
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Command
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lvchange -ay -K VG/SnapLV
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Example
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# lvchange -ay -K vg/thin1s1
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# lvs vg/thin1s1
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thin1s1 vg Vwi-a-tz-k 1.00t pool0 thin1
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.fi
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.SH Thin Topics
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Specify devices for data and metadata LVs
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.br
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Tolerate device failures using raid
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.br
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Spare metadata LV
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.br
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Metadata check and repair
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.br
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Automatic pool metadata LV
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.br
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Activation of thin snapshots
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.br
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Removing thin pool LV's, thin LV's and snapshots
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.br
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Manually manage free data space of thin pool LV
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.br
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Manually manage free metadata space of a thin pool LV
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.br
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Using fstrim to increase free space in a thin pool LV
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.br
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Automatically extend thin pool LV
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.br
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Zeroing
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.br
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Discard
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.br
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Chunk size
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.br
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Size of pool metadata LV
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.br
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Create a thin snapshot of an external, read only LV
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.br
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Convert a standard LV to a thin LV with an external origin
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.br
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Single step thin pool LV creation
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.br
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Single step thin pool LV and thin LV creation
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.br
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\&
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.SS Specify devices for data and metadata LVs
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\&
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The data and metadata LVs in a thin pool are best created on
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separate physical devices. To do that, specify the device name(s)
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at the end of the lvcreate line. It can be especially helpful
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to use fast devices for the metadata LV.
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.nf
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lvcreate -n ThinDataLV -L LargeSize VG LargePV
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lvcreate -n ThinMetaLV -L SmallSize VG SmallPV
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lvconvert --thinpool VG/ThinDataLV --poolmetadata VG/ThinMetaLV
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Example
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# lvcreate -n pool0 -L 100G vg /dev/sdA
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# lvcreate -n pool0meta -L 1G vg /dev/sdB
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# lvconvert --thinpool vg/pool0 --poolmetadata vg/pool0meta
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.fi
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See lvm.conf thin_pool_metadata_require_separate_pvs to set
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default PV usage for thin pool creation.
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.SS Tolerate device failures using raid
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\&
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To tolerate device failures, use raid for the pool data LV and
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pool metadata LV. This is especially recommended for pool metadata LVs.
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.nf
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lvcreate --type raid1 -m 1 -n ThinMetaLV -L SmallSize VG PVA PVB
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lvcreate --type raid1 -m 1 -n ThinDataLV -L LargeSize VG PVC PVD
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lvconvert --thinpool VG/ThinDataLV --poolmetadata VG/ThinMetaLV
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Example
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# lvcreate --type raid1 -m 1 -n pool0 -L 100G vg /dev/sdA /dev/sdB
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# lvcreate --type raid1 -m 1 -n pool0meta -L 1G vg /dev/sdC /dev/sdD
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# lvconvert --thinpool vg/pool0 --poolmetadata vg/pool0meta
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.fi
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.SS Spare metadata LV
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\&
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The first time a thin pool LV is created, lvm will create a spare
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metadata LV in the VG. This behavior can be controlled with the
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option --poolmetadataspare y|n. (Future thin pool creations will
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also attempt to create the pmspare LV if none exists.)
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To create the pmspare ("pool metadata spare") LV, lvm first creates
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an LV with a default name, e.g. lvol0, and then converts this LV to
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a hidden LV with the _pmspare suffix, e.g. lvol0_pmspare.
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One pmspare LV is kept in a VG to be used for any thin pool.
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The pmspare LV cannot be created explicitly, but may be removed
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explicitly.
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.nf
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Example
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# lvcreate -n pool0 -L 10G vg
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# lvcreate -n pool0meta -L 10G vg
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# lvconvert --thinpool vg/pool0 --poolmetadata vg/pool0meta
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# lvs -a
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[lvol0_pmspare] vg ewi------- 10.00g
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pool0 vg twi---tz-- 10.00g
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[pool0_tdata] vg Twi------- 10.00g
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[pool0_tmeta] vg ewi------- 1.00g
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.fi
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The "Metadata check and repair" section describes the use of
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the pmspare LV.
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.SS Metadata check and repair
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\&
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If thin pool metadata is damaged, it may be repairable.
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Checking and repairing thin pool metadata is analagous to
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running fsck on a file system.
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When a thin pool LV is activated, lvm runs the thin_check command
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to check the correctness of the metadata on the pool metadata LV.
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To disable the thin_check step, set lvm.conf thin_check_executable to
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an empty string (""). This is not recommended.
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To set options for the thin_check command, set lvm.conf thin_check_options.
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If the thin_check command finds a problem with the metadata,
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the thin pool LV is not activated, and the thin pool metadata should
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be repaired.
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Command to repair a thin pool LV:
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.nf
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lvconvert --repair VG/ThinPoolLV
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.fi
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Repair performs the following steps:
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1. Creates a new, repaired copy of the metadata.
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.br
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lvconvert runs the thin_repair command to read damaged metadata
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from the existing pool metadata LV, and writes a new repaired
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copy to the VG's pmspare LV.
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2. Replaces the thin pool metadata LV.
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.br
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If step 1 is successful, the thin pool metadata LV is replaced
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with the pmspare LV containing the corrected metadata.
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The previous thin pool metadata LV, containing the damaged metadata,
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becomes visible with the new name ThinPoolLV_tmetaN (where N is 0,1,...).
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If the repair works, the thin pool LV and its thin LVs can be activated,
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and the LV containing the damaged thin pool metadata can be removed.
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It may be useful to move the new metadata LV (previously pmspare) to a
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better PV.
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If the repair does not work, the thin pool LV and its thin LVs are lost.
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If metadata is manually restored with thin_repair directly,
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the pool metadata LV can be manually swapped with another LV
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containing new metadata:
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.nf
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lvconvert --thinpool VG/ThinPoolLV --poolmetadata VG/NewThinMetaLV
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.fi
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The path to thin_check, thin_dump and thin_repair commands
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can be set in lvm.conf.
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.SS Automatic pool metadata LV
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\&
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A thin data LV can be converted to a thin pool LV without
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specifying a thin pool metadata LV. LVM will automatically
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create a metadata LV from the same VG.
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.nf
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lvcreate -n ThinDataLV -L LargeSize VG
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lvconvert --thinpool VG/ThinDataLV
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Example
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# lvcreate -n pool0 -L 10G vg
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# lvconvert --thinpool vg/pool0
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# lvs -a
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pool0 vg twi-a-tz-- 10.00g
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[pool0_tdata] vg Twi-ao---- 10.00g
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[pool0_tmeta] vg ewi-ao---- 16.00m
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.fi
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.SS Activation of thin snapshots
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\&
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When a thin snapshot LV is created, it is by default given the
|
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"activation skip" flag. This flag is indicated by the "k" attribute
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displayed by lvs:
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.nf
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# lvs vg/thin1s1
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LV VG Attr LSize Pool Origin
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thin1s1 vg Vwi---tz-k 1.00t pool0 thin1
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.fi
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This flag causes the snapshot LV to be skipped, i.e. not activated,
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by normal activation commands. The skipping behavior does not
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apply to deactivation commands.
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A snapshot LV with the "k" attribute can be activated using
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the -K (or --ignoreactivationskip) option in addition to the
|
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standard -ay (or --activate y) option.
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Command to activate a thin snapshot LV:
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.nf
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lvchange -ay -K VG/SnapLV
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.fi
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The persistent "activation skip" flag can be turned off during
|
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lvcreate, or later with lvchange using the -kn
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(or --setactivationskip n) option.
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It can be turned on again with -ky (or --setactivationskip y).
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When the "activation skip" flag is removed, normal activation
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commands will activate the LV, and the -K activation option is
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not needed.
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Command to create snapshot LV without the activation skip flag:
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.nf
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lvcreate --type thin -n SnapLV -kn -s ThinLV --thinpool VG/ThinPoolLV
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.fi
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Command to remove the activation skip flag from a snapshot LV:
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.nf
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lvchange -kn VG/SnapLV
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.fi
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See lvm.conf auto_set_activation_skip to set default usage of
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activation skip.
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.SS Removing thin pool LV's, thin LV's and snapshots
|
||||
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\&
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||||
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Removing a thin LV and its related snapshots returns the blocks it
|
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used to the thin pool LV. These blocks will be reused for other
|
||||
thin LVs and snapshots.
|
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||||
Removing a thin pool LV removes both the data LV and metadata LV
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and returns the space to the VG.
|
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lvremove of thin pool LV's, thin LV's and snapshots cannot be
|
||||
reversed with vgcfgrestore.
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||||
|
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vgcfgbackup does not back up thin pool metadata.
|
||||
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||||
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||||
.SS Manually manage free data space of thin pool LV
|
||||
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\&
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|
||||
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.
|
||||
|
||||
.nf
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Example
|
||||
|
||||
1. A thin pool LV is using 26.96% of its data blocks.
|
||||
# lvs
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||||
LV VG Attr LSize Pool Origin Data%
|
||||
pool0 vg twi-a-tz-- 10.00g 26.96
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||||
|
||||
2. Double the amount of physical space in the thin pool LV.
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||||
# lvextend -L+10G vg/pool0
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||||
|
||||
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
|
||||
.fi
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||||
|
||||
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.
|
||||
|
||||
|
||||
.SS 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.
|
||||
|
||||
Example
|
||||
|
||||
1. A thin pool LV is using 12.40% of its metadata blocks.
|
||||
.nf
|
||||
# lvs -oname,size,data_percent,metadata_percent vg/pool0
|
||||
LV LSize Data% Meta%
|
||||
pool0 20.00g 13.48 12.40
|
||||
.fi
|
||||
|
||||
2. Display a thin pool LV with its component thin data LV and thin metadata LV.
|
||||
.nf
|
||||
# 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
|
||||
.fi
|
||||
|
||||
3. Double the amount of physical space in the thin metadata LV.
|
||||
.nf
|
||||
# lvextend -L+12M vg/pool0_tmeta
|
||||
.fi
|
||||
|
||||
4. The percentage of used metadata blocks is half the previous value.
|
||||
.nf
|
||||
# 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
|
||||
.fi
|
||||
|
||||
|
||||
.SS 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.
|
||||
|
||||
.nf
|
||||
# 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
|
||||
.fi
|
||||
|
||||
|
||||
.SS Automatically extend thin pool LV
|
||||
|
||||
\&
|
||||
|
||||
An lvm daemon (dmeventd) will by default monitor the data usage of
|
||||
thin pool LVs and extend them when the usage reaches a certain level.
|
||||
The necessary free space must exist in the VG to extend the thin pool
|
||||
LVs.
|
||||
|
||||
Command to enable or disable the monitoring and automatic extension
|
||||
of an existing thin pool LV:
|
||||
|
||||
.nf
|
||||
lvchange --monitor {y|n} VG/ThinPoolLV
|
||||
.fi
|
||||
|
||||
The lvm.conf thin_pool_autoextend_threshold and thin_pool_autoextend_percent
|
||||
options define the autoextend behavior.
|
||||
|
||||
thin_pool_autoextend_threshold is a percentage value that defines when
|
||||
the thin pool LV should be extended. Setting this to 100 disables
|
||||
automatic extention. The minimum value is 50.
|
||||
|
||||
thin_pool_autoextend_percent defines how much extra data space should
|
||||
be added to the thin pool, in percent of its current size.
|
||||
|
||||
Warnings are emitted through syslog when the use of a pool reaches 80%,
|
||||
85%, 90% and 95%.
|
||||
|
||||
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.
|
||||
|
||||
|
||||
.SS 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:
|
||||
.nf
|
||||
lvconvert -Z{y|n} --thinpool VG/ThinDataLV --poolmetadata VG/ThinMetaLV
|
||||
.fi
|
||||
|
||||
Command to change the zeroing mode of an existing thin pool LV:
|
||||
.nf
|
||||
lvchange -Z{y|n} VG/ThinPoolLV
|
||||
.fi
|
||||
|
||||
If zeroing mode is changed from "n" to "y", previously provisioned
|
||||
blocks are not zeroed.
|
||||
|
||||
Provisioning of large zeroed chunks impacts performance.
|
||||
|
||||
See lvm.conf thin_pool_zero to set default zeroing mode.
|
||||
|
||||
|
||||
.SS Discard
|
||||
|
||||
\&
|
||||
|
||||
The discard behavior of a thin pool LV determines how discard requests
|
||||
are handled. 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 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:
|
||||
.nf
|
||||
lvs -o+discards VG/ThinPoolLV
|
||||
.fi
|
||||
|
||||
Command to set the discard mode when creating a thin pool LV:
|
||||
.nf
|
||||
lvconvert --discards {ignore|nopassdown|passdown}
|
||||
--thinpool VG/ThinDataLV --poolmetadata VG/ThinMetaLV
|
||||
.fi
|
||||
|
||||
Command to change the discard mode of an existing thin pool LV:
|
||||
.nf
|
||||
lvchange --discards {ignore|nopassdown|passdown} VG/ThinPoolLV
|
||||
.fi
|
||||
|
||||
.nf
|
||||
Example
|
||||
# lvs -o name,discards vg/pool0
|
||||
pool0 passdown
|
||||
|
||||
# lvchange --discards ignore vg/pool0
|
||||
.fi
|
||||
|
||||
See lvm.conf thin_pool_discards to set the default discards mode.
|
||||
|
||||
|
||||
.SS 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 kilobytes and the default value is 64KiB. The value must be a
|
||||
power of two between 4KiB and 1GiB.
|
||||
|
||||
When a thin pool is used primarily for the thin provisioning feature,
|
||||
a larger value is optimal. To optimize for a lot of snapshotting,
|
||||
a smaller value reduces copying time and consumes less space.
|
||||
|
||||
Command to display the thin pool LV chunk size:
|
||||
.nf
|
||||
lvs -o+chunksize VG/ThinPoolLV
|
||||
|
||||
Example
|
||||
# lvs -o name,chunksize
|
||||
pool0 64.00k
|
||||
.fi
|
||||
|
||||
See lvm.conf thin_pool_chunk_size to set the default chunk size.
|
||||
|
||||
|
||||
.SS 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.
|
||||
|
||||
The range of supported metadata LV sizes is 2MiB to 16GiB.
|
||||
.br
|
||||
The default size is estimated with the formula:
|
||||
.br
|
||||
ThinPoolLVSize / ThinPoolLVChunkSize * 64b.
|
||||
|
||||
When creating a thin metadata LV explicitly, the size is specified
|
||||
in the lvcreate command. When a command automatically creates a
|
||||
thin metadata LV, the --poolmetadatasize option can be used specify
|
||||
a non-default size. The default unit is megabytes.
|
||||
|
||||
|
||||
.SS 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.
|
||||
|
||||
.nf
|
||||
lvcreate --type thin -n SnapLV -s VG/ExternalOriginLV
|
||||
--thinpool VG/ThinPoolLV
|
||||
|
||||
Example
|
||||
# lvchange -an vg/lve
|
||||
# lvchange --permission r vg/lve
|
||||
# lvcreate --type thin -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
|
||||
.fi
|
||||
|
||||
|
||||
.SS 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.
|
||||
|
||||
.nf
|
||||
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
|
||||
.fi
|
||||
|
||||
|
||||
.SS 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.
|
||||
|
||||
.nf
|
||||
lvcreate -L LargeSize --thinpool VG/ThinPoolLV
|
||||
|
||||
Example
|
||||
# lvcreate -l1 --thinpool vg/pool0
|
||||
|
||||
# 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
|
||||
.fi
|
||||
|
||||
|
||||
.SS 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.
|
||||
.br
|
||||
-L LargeSize specifies the physical size of the thin pool LV.
|
||||
.br
|
||||
-V VirtualSize specifies the virtual size of the thin LV.
|
||||
|
||||
.nf
|
||||
lvcreate -L LargeSize -V VirtualSize -n ThinLV --thinpool VG/ThinPoolLV
|
||||
|
||||
Equivalent to:
|
||||
lvcreate -L LargeSize --thinpool VG/ThinPoolLV
|
||||
lvcreate --type thin -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
|
||||
.fi
|
||||
|
||||
Loading…
x
Reference in New Issue
Block a user