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1129 lines
30 KiB
Groff
1129 lines
30 KiB
Groff
.TH "LVMTHIN" "7" "LVM TOOLS #VERSION#" "Red Hat, Inc" "\""
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.SH NAME
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lvmthin \(em 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 LVs can be created within it.
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A thin pool LV is created by combining two standard LVs: 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 any of its snapshots are shared. Snapshots may be taken of
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thin LVs or of other thin snapshots. Blocks common to recursive snapshots
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are also shared in the thin pool. There is no limit to or degradation
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from sequences of snapshots.
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As thin LVs or snapshot LVs 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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.SS 1. create ThinDataLV
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Create an LV that will hold thin pool data.
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.B lvcreate \-n ThinDataLV \-L LargeSize VG
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.I Example
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.br
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# lvcreate \-n pool0 \-L 10G vg
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.SS 2. create ThinMetaLV
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Create an LV that will hold thin pool metadata.
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.B lvcreate \-n ThinMetaLV \-L SmallSize VG
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.I Example
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.br
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# lvcreate \-n pool0meta \-L 1G vg
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# lvs
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LV VG Attr LSize
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pool0 vg -wi-a----- 10.00g
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pool0meta vg -wi-a----- 1.00g
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.SS 3. create ThinPoolLV
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.nf
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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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.fi
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.B lvconvert \-\-thinpool VG/ThinDataLV \-\-poolmetadata VG/ThinMetaLV
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.I Example
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.br
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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% Meta%
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pool0 vg twi-a-tz-- 10.00g 0.00 0.00
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# lvs \-a
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LV VG Attr LSize
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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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.SS 4. create ThinLV
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.nf
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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 LVs 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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.fi
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.B lvcreate \-n ThinLV \-V VirtualSize \-\-thinpool VG/ThinPoolLV
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.I Example
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.br
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Create a thin LV in a thin pool:
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.br
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# lvcreate \-n thin1 \-V 1T \-\-thinpool vg/pool0
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Create another thin LV in the same thin pool:
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.br
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# lvcreate \-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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.SS 5. create SnapLV
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Create snapshots of an existing ThinLV or SnapLV.
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.br
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Do not specify
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.BR \-L ", " \-\-size
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when creating a thin snapshot.
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.br
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A size argument will cause an old COW snapshot to be created.
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.B lvcreate \-n SnapLV \-s VG/ThinLV
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.br
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.B lvcreate \-n SnapLV \-s VG/PrevSnapLV
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.I Example
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.br
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Create first snapshot of an existing ThinLV:
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.br
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# lvcreate \-n thin1s1 \-s vg/thin1
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Create second snapshot of the same ThinLV:
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.br
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# lvcreate \-n thin1s2 \-s vg/thin1
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Create a snapshot of the first snapshot:
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.br
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# lvcreate \-n thin1s1s1 \-s vg/thin1s1
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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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.SS 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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.B lvchange \-ay \-K VG/SnapLV
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.I Example
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.br
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# lvchange \-ay \-K vg/thin1s1
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# lvs vg/thin1s1
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LV VG Attr LSize Pool Origin
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thin1s1 vg Vwi-a-tz-k 1.00t pool0 thin1
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.SH Thin Topics
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.B Specify devices for data and metadata LVs
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.br
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.B Tolerate device failures using raid
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.br
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.B Spare metadata LV
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.br
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.B Metadata check and repair
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.br
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.B Automatic pool metadata LV
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.br
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.B Activation of thin snapshots
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.br
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.B Removing thin pool LVs, thin LVs and snapshots
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.br
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.B Manually manage free data space of thin pool LV
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.br
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.B Manually manage free metadata space of a thin pool LV
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.br
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.B Using fstrim to increase free space in a thin pool LV
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.br
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.B Automatically extend thin pool LV
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.br
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.B Data space exhaustion
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.br
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.B Metadata space exhaustion
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.br
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.B Zeroing
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.br
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.B Discard
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.br
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.B Chunk size
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.br
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.B Size of pool metadata LV
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.br
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.B Create a thin snapshot of an external, read only LV
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.br
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.B Convert a standard LV to a thin LV with an external origin
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.br
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.B Single step thin pool LV creation
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.br
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.B Single step thin pool LV and thin LV creation
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.br
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.B Merge thin snapshots
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.br
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.B XFS on snapshots
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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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.B lvcreate \-n ThinDataLV \-L LargeSize VG LargePV
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.br
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.B lvcreate \-n ThinMetaLV \-L SmallSize VG SmallPV
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.br
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.B lvconvert \-\-thinpool VG/ThinDataLV \-\-poolmetadata VG/ThinMetaLV
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.I Example
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.br
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.nf
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# lvcreate \-n pool0 \-L 10G 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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.BR lvm.conf (5)
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.B thin_pool_metadata_require_separate_pvs
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.br
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controls the default PV usage for thin pool creation.
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\&
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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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.B lvcreate \-\-type raid1 \-m 1 \-n ThinMetaLV \-L SmallSize VG PVA PVB
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.br
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.B lvcreate \-\-type raid1 \-m 1 \-n ThinDataLV \-L LargeSize VG PVC PVD
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.br
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.B lvconvert \-\-thinpool VG/ThinDataLV \-\-poolmetadata VG/ThinMetaLV
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.I Example
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.br
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.nf
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# lvcreate \-\-type raid1 \-m 1 \-n pool0 \-L 10G 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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.I Example
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.br
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.nf
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# lvcreate \-n pool0 \-L 10G vg
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# lvcreate \-n pool0meta \-L 1G 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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.BR lvm.conf (5)
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.B thin_check_executable
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.br
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can be set to an empty string ("") to disable the thin_check step.
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This is not recommended.
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.BR lvm.conf (5)
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.B thin_check_options
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.br
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controls the command options used for the thin_check command.
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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:
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.br
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.B lvconvert \-\-repair VG/ThinPoolLV
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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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.B lvconvert \-\-thinpool VG/ThinPoolLV \-\-poolmetadata VG/NewThinMetaLV
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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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.B lvcreate \-n ThinDataLV \-L LargeSize VG
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.br
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.B lvconvert \-\-thinpool VG/ThinDataLV
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.I Example
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.br
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.nf
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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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.br
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.B lvchange \-ay \-K VG/SnapLV
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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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.br
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.B lvcreate \-kn \-n SnapLV \-s VG/ThinLV
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Command to remove the activation skip flag from a snapshot LV:
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.br
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.B lvchange \-kn VG/SnapLV
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.BR lvm.conf (5)
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.B auto_set_activation_skip
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.br
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controls the default activation skip setting used by lvcreate.
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.SS Removing thin pool LVs, thin LVs and snapshots
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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
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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 LVs, thin LVs and snapshots cannot be
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reversed with vgcfgrestore.
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vgcfgbackup does not back up thin pool metadata.
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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
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with the lvs command. Free space can be added by extending
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the thin pool LV.
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Command to extend thin pool data space:
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.br
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.B lvextend \-L Size VG/ThinPoolLV
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.I Example
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.br
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.nf
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1. A thin pool LV is using 26.96% of its data blocks.
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# lvs
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LV VG Attr LSize Pool Origin Data%
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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.
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# lvs
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LV VG Attr LSize Pool Origin Data%
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pool0 vg twi-a-tz-- 20.00g 13.48
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|
.fi
|
|
|
|
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.
|
|
|
|
Command to extend thin pool metadata space:
|
|
.br
|
|
.B lvextend \-L Size VG/ThinPoolLV_tmeta
|
|
|
|
.I Example
|
|
.br
|
|
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.
|
|
|
|
.I Example
|
|
.br
|
|
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
|
|
|
|
The "Discard" section covers an option for automatically freeing data
|
|
space in a thin pool.
|
|
|
|
|
|
.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:
|
|
|
|
.B lvchange \-\-monitor {y|n} VG/ThinPoolLV
|
|
|
|
.BR lvm.conf (5)
|
|
.B thin_pool_autoextend_threshold thin_pool_autoextend_percent
|
|
.br
|
|
control the default 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%.
|
|
|
|
.I Example
|
|
.br
|
|
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 Data space exhaustion
|
|
|
|
\&
|
|
|
|
If thin pool data space is exhausted, writes to thin LVs will be queued
|
|
until the the data space is extended. Reading is still possible.
|
|
|
|
When data space is exhausted, the lvs command displays 100 under Data% for
|
|
the thin pool LV:
|
|
|
|
.nf
|
|
# lvs vg/pool0
|
|
LV VG Attr LSize Pool Origin Data%
|
|
pool0 vg twi-a-tz-- 512.00m 100.00
|
|
.fi
|
|
|
|
A thin pool can run out of data blocks for any of the following reasons:
|
|
|
|
1. Automatic extension of the thin pool is disabled, and the thin pool is
|
|
not manually extended. (Disabling automatic extension is not
|
|
recommended.)
|
|
|
|
2. The dmeventd daemon is not running and the thin pool is not manually
|
|
extended. (Disabling dmeventd is not recommended.)
|
|
|
|
3. 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.)
|
|
|
|
4. The VG does not have enough free blocks to extend the thin pool.
|
|
|
|
The response to data space exhaustion is to extend the thin pool. This is
|
|
described in the section "Manually manage free data space of thin pool
|
|
LV".
|
|
|
|
|
|
.SS 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:
|
|
|
|
.nf
|
|
# lvs \-o lv_name,size,data_percent,metadata_percent vg/pool0
|
|
LV LSize Data% Meta%
|
|
pool0 100.00
|
|
.fi
|
|
|
|
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.
|
|
.br
|
|
See "Metadata check and repair".
|
|
|
|
3. Extend pool metadata space with lvextend VG/ThinPoolLV_tmeta.
|
|
.br
|
|
See "Manually manage free metadata space of a thin pool LV".
|
|
|
|
4. Check and repair file system with fsck.
|
|
|
|
|
|
.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:
|
|
.br
|
|
.B lvconvert \-Z{y|n} \-\-thinpool VG/ThinDataLV \-\-poolmetadata VG/ThinMetaLV
|
|
|
|
Command to change the zeroing mode of an existing thin pool LV:
|
|
.br
|
|
.B 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.
|
|
|
|
.BR lvm.conf (5)
|
|
.B thin_pool_zero
|
|
.br
|
|
controls the default zeroing mode used when creating a thin pool.
|
|
|
|
|
|
.SS 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 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:
|
|
.br
|
|
.B lvs \-o+discards VG/ThinPoolLV
|
|
|
|
Command to set the discard mode when creating a thin pool LV:
|
|
.br
|
|
.B lvconvert \-\-discards {ignore|nopassdown|passdown}
|
|
.br
|
|
.B " " \-\-thinpool VG/ThinDataLV \-\-poolmetadata VG/ThinMetaLV
|
|
|
|
Command to change the discard mode of an existing thin pool LV:
|
|
.br
|
|
.B lvchange \-\-discards {ignore|nopassdown|passdown} VG/ThinPoolLV
|
|
|
|
.I Example
|
|
.br
|
|
.nf
|
|
# lvs \-o name,discards vg/pool0
|
|
pool0 passdown
|
|
|
|
# lvchange \-\-discards ignore vg/pool0
|
|
.fi
|
|
|
|
.BR lvm.conf (5)
|
|
.B thin_pool_discards
|
|
.br
|
|
controls the default discards mode used when creating a thin pool.
|
|
|
|
|
|
.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:
|
|
.br
|
|
.B lvs \-o+chunksize VG/ThinPoolLV
|
|
|
|
.I Example
|
|
.br
|
|
.nf
|
|
# lvs \-o name,chunksize
|
|
pool0 64.00k
|
|
.fi
|
|
|
|
.BR lvm.conf (5)
|
|
.B thin_pool_chunk_size
|
|
.br
|
|
controls the default chunk size used when creating a thin pool.
|
|
|
|
|
|
.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.
|
|
|
|
.B lvcreate \-n SnapLV \-s VG/ExternalOriginLV \-\-thinpool VG/ThinPoolLV
|
|
|
|
.I Example
|
|
.br
|
|
.nf
|
|
# 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
|
|
.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.
|
|
|
|
.B lvconvert \-\-type thin \-\-thinpool VG/ThinPoolLV
|
|
.br
|
|
.B " " \-\-originname NewExternalOriginLV \-\-thin VG/ExampleLV
|
|
|
|
.I Example
|
|
.br
|
|
.nf
|
|
# 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.
|
|
|
|
.B lvcreate \-L LargeSize \-\-thinpool VG/ThinPoolLV
|
|
|
|
.I Example
|
|
.br
|
|
.nf
|
|
# lvcreate \-L8M \-\-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.
|
|
|
|
.B lvcreate \-L LargeSize \-V VirtualSize \-n ThinLV \-\-thinpool VG/ThinPoolLV
|
|
|
|
Equivalent to:
|
|
.br
|
|
.B lvcreate \-L LargeSize \-\-thinpool VG/ThinPoolLV
|
|
.br
|
|
.B lvcreate \-n ThinLV \-V VirtualSize \-\-thinpool VG/ThinPoolLV
|
|
|
|
.I Example
|
|
.br
|
|
.nf
|
|
# 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
|
|
|
|
|
|
.SS 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.
|
|
|
|
.B lvconvert \-\-merge VG/SnapLV
|
|
|
|
.I Example
|
|
.br
|
|
.nf
|
|
# 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
|
|
.fi
|
|
|
|
.I Example
|
|
.br
|
|
.nf
|
|
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
|
|
|
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# lvs \-a vg
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LV VG Attr LSize Pool Origin
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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
|
|
thin1 vg Owi-a-tz-- 100.00g pool0
|
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[thin1s1] vg Swi-a-tz-k 100.00g pool0 thin1
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|
|
|
# lvchange \-an vg/thin1
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|
# lvchange \-ay vg/thin1
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|
|
|
# mount /dev/vg/thin1 /mnt/X
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|
|
|
# ls /mnt/X
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|
file3 file4 file5
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|
.fi
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|
|
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|
.SS XFS on snapshots
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|
|
|
\&
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|
|
|
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
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|
|
|
Or, the uuid can be changed on disk before mounting:
|
|
|
|
xfs_admin \-U generate /dev/VG/SnapLV
|
|
.br
|
|
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
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|
|
|
|
|
.SH SEE ALSO
|
|
.BR lvm (8),
|
|
.BR lvm.conf (5),
|
|
.BR lvcreate (8),
|
|
.BR lvconvert (8),
|
|
.BR lvchange (8),
|
|
.BR lvextend (8),
|
|
.BR lvremove (8),
|
|
.BR lvs (8),
|
|
.BR thin_dump (8),
|
|
.BR thin_repair (8)
|
|
.BR thin_restore (8)
|
|
|