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man: describe profile support lvmcache.7
Add missing description for profile usage with cache pool. List cache-pools as first option for dm-cache as it provides better performance and more functionality over cachevols.
This commit is contained in:
Zdenek Kabelac
parent
2aaea13aaa
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ff5776024f
@ -63,17 +63,21 @@ To start caching the main LV, convert the main LV to the desired caching
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type, and specify the fast LV to use as the cache:
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.nf
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using dm-cache:
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$ lvconvert --type cache --cachevol fast vg/main
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using dm-writecache:
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$ lvconvert --type writecache --cachevol fast vg/main
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using dm-cache (with cachepool):
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$ lvconvert --type cache --cachepool fast vg/main
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using dm-cache (with cachevol):
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$ lvconvert --type cache --cachevol fast vg/main
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using dm-writecache (with cachevol):
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$ lvconvert --type writecache --cachevol fast vg/main
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For more alteratives see:
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dm-cache command shortcut
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dm-cache with separate data and metadata LVs
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.fi
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.B 4. Display LVs
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@ -85,31 +89,31 @@ suffix. It is displayed by lvs -a. The _corig or _wcorig LV represents
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the original LV without the cache.
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.nf
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using dm-cache:
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$ lvs -a
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LV Pool Type Devices
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main [fast_cvol] cache main_corig(0)
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[fast_cvol] linear /dev/fast_ssd
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[main_corig] linear /dev/slow_hhd
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using dm-writecache:
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$ lvs -a
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LV Pool Type Devices
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main [fast_cvol] writecache main_wcorig(0)
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[fast_cvol] linear /dev/fast_ssd
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[main_wcorig] linear /dev/slow_hhd
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using dm-cache (with cachepool):
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$ lvs -a
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$ lvs -ao+devices
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LV Pool Type Devices
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main [fast_cpool] cache main_corig(0)
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[fast_cpool] cache-pool fast_pool_cdata(0)
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[fast_cpool_cdata] linear /dev/fast_ssd
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[fast_cpool_cmeta] linear /dev/fast_ssd
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[main_corig] linear /dev/slow_hhd
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using dm-cache (with cachevol):
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$ lvs -ao+devices
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LV Pool Type Devices
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main [fast_cvol] cache main_corig(0)
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[fast_cvol] linear /dev/fast_ssd
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[main_corig] linear /dev/slow_hhd
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using dm-writecache (with cachevol):
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$ lvs -ao+devices
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LV Pool Type Devices
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main [fast_cvol] writecache main_wcorig(0)
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[fast_cvol] linear /dev/fast_ssd
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[main_wcorig] linear /dev/slow_hhd
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.fi
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.B 5. Use the main LV
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@ -118,6 +122,16 @@ Use the LV until the cache is no longer wanted, or needs to be changed.
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.B 6. Stop caching
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To stop caching the main LV and also remove unneeded cache pool,
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use the --uncache:
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.nf
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$ lvconvert --uncache vg/main
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$ lvs -a
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LV VG Attr Type Devices
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main vg -wi------- linear /dev/slow_hhd
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To stop caching the main LV, separate the fast LV from the main LV. This
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changes the type of the main LV back to what it was before the cache was
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attached.
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@ -130,16 +144,6 @@ attached.
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fast vg -wi------- linear /dev/fast_ssd
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main vg -wi------- linear /dev/slow_hhd
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To stop caching the main LV and also remove unneeded cache pool,
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use the --uncache:
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.nf
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$ lvconvert --uncache vg/main
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$ lvs -a
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LV VG Attr Type Devices
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main vg -wi------- linear /dev/slow_hhd
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.fi
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.SS Create a new LV with caching.
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@ -167,14 +171,6 @@ for the fast LV.
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\&
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.B --cachevol
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.I LV
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.br
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Pass this option a fast LV that should be used to hold the cache. With a
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cachevol, cache data and metadata are stored in different parts of the
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same fast LV. This option can be used with dm-writecache or dm-cache.
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.B --cachepool
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.IR CachePoolLV | LV
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.br
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@ -189,6 +185,14 @@ that cannot be used directly. If a standard LV is passed with this
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option, lvm will first convert it to a cache pool by combining it with
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another LV to use for metadata. This option can be used with dm-cache.
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.B --cachevol
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.I LV
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.br
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Pass this option a fast LV that should be used to hold the cache. With a
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cachevol, cache data and metadata are stored in different parts of the
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same fast LV. This option can be used with dm-writecache or dm-cache.
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.B --cachedevice
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.I PV
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.br
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@ -318,10 +322,25 @@ cleaner mode, and any required flushing is performed in device suspend.
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\&
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When using dm-cache, the cache metadata and cache data can be stored on
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separate LVs. To do this, a "cache pool" is created, which is a special
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Preferred way of using dm-cache is to place the cache metadata and cache data
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on separate LVs. To do this, a "cache pool" is created, which is a special
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LV that references two sub LVs, one for data and one for metadata.
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To create a cache pool of given data size and let lvm2 calculate appropriate
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metadata size:
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.nf
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$ lvcreate --type cache-pool -L DataSize -n fast vg /dev/fast_ssd1
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.fi
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To create a cache pool from separate LV and let lvm2 calculate
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appropriate cache metadata size:
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.nf
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$ lvcreate -n fast -L DataSize vg /dev/fast_ssd1
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$ lvconvert --type cache-pool vg/fast /dev/fast_ssd1
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.fi
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To create a cache pool from two separate LVs:
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.nf
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@ -374,8 +393,12 @@ mode can be displayed with the cache_mode reporting option:
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defines the default cache mode.
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.nf
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$ lvconvert --type cache --cachevol fast \\
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--cachemode writethrough vg/main
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$ lvconvert --type cache --cachemode writethrough \\
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--cachepool fast vg/main
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$ lvconvert --type cache --cachemode writethrough \\
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--cachevol fast vg/main
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.nf
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.SS dm-cache chunk size
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@ -480,6 +503,39 @@ defines the default cache policy.
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.br
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defines the default cache settings.
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.SS dm-cache using metadata profiles
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\&
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Cache pools allows to set a variety of options. Lots of these settings
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can be specified in lvm.conf or profile settings. You can prepare
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a number of different profiles in the #DEFAULT_SYS_DIR#/profile directory
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and just specify the metadata profile file name when caching LV or creating cache-pool.
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Check the output of \fBlvmconfig --type default --withcomments\fP
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for a detailed description of all individual cache settings.
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.I Example
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.nf
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# cat <<EOF > #DEFAULT_SYS_DIR#/profile/cache_big_chunk.profile
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allocation {
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cache_pool_metadata_require_separate_pvs=0
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cache_pool_chunk_size=512
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cache_metadata_format=2
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cache_mode="writethrough"
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cache_policy="smq"
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cache_settings {
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smq {
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migration_threshold=8192
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random_threshold=4096
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}
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}
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}
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EOF
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# lvcreate --cache -L10G --metadataprofile cache_big_chunk vg/main /dev/fast_ssd
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# lvcreate --cache -L10G --config 'allocation/cache_pool_chunk_size=512' vg/main /dev/fast_ssd
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.fi
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.SS dm-cache spare metadata LV
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\&
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@ -518,16 +574,24 @@ $ lvconvert --type cache --cachevol fast vg/main
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\&
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A single command can be used to create a cache pool and attach that new
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cache pool to a main LV:
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A single command can be used to cache main LV with automatic
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creation of a cache-pool:
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.nf
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$ lvcreate --type cache --name Name --size Size VG/LV [PV]
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$ lvcreate --cache --size CacheDataSize VG/LV [FastPVs]
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.fi
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or the longer variant
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.nf
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$ lvcreate --type cache --size CacheDataSize \\
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--name NameCachePool VG/LV [FastPVs]
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.fi
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In this command, the specified LV already exists, and is the main LV to be
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cached. The command creates a new cache pool with the given name and
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size, using the optionally specified PV (typically an ssd). Then it
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cached. The command creates a new cache pool with size and given name
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or the name is automatically selected from a sequence lvolX_cpool,
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using the optionally specified fast PV(s) (typically an ssd). Then it
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attaches the new cache pool to the existing main LV to begin caching.
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(Note: ensure that the specified main LV is a standard LV. If a cache
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