man/lvmcache.7.in - manifest_repos/lvm2 - Git at Google

 .TH "LVMCACHE" "7" "LVM TOOLS #VERSION#" "Red Hat, Inc" "\""
 .SH NAME
 lvmcache \(em LVM caching

 .SH DESCRIPTION

 The \fBcache\fP logical volume type uses a small and fast LV to improve
 the performance of a large and slow LV.  It does this by storing the
 frequently used blocks on the faster LV.
 LVM refers to the small fast LV as a \fBcache pool LV\fP.  The large
 slow LV is called the \fBorigin LV\fP.  Due to requirements from dm-cache
 (the kernel driver), LVM further splits the cache pool LV into two
 devices - the \fBcache data LV\fP and \fBcache metadata LV\fP.  The cache
 data LV is where copies of data blocks are kept from the
 origin LV to increase speed.  The cache metadata LV holds the
 accounting information that specifies where data blocks are stored (e.g.
 on the origin LV or on the cache data LV).  Users should be familiar with
 these LVs if they wish to create the best and most robust cached
 logical volumes.  All of these associated LVs must be in the same VG.

 .SH Cache Terms
 .nf
 origin LV           OriginLV      large slow LV
 cache data LV       CacheDataLV   small fast LV for cache pool data
 cache metadata LV   CacheMetaLV   small fast LV for cache pool metadata
 cache pool LV       CachePoolLV   CacheDataLV + CacheMetaLV
 cache LV            CacheLV       OriginLV + CachePoolLV
 .fi

 .SH Cache Usage

 The primary method for using a cache type logical volume:


 .SS 0. create OriginLV

 Create an LV or identify an existing LV to be the origin LV.

 .B lvcreate \-n OriginLV \-L LargeSize VG SlowPVs

 .I Example
 .br
 # lvcreate \-n lvol0 \-L 100G vg


 .SS 1. create CacheDataLV

 Create the cache data LV.  This LV will hold data blocks from the
 OriginLV.  The size of this LV is the size of the cache and will be
 reported as the size of the cache pool LV.

 .B lvcreate \-n CacheDataLV \-L CacheSize VG FastPVs

 .I Example
 .br
 # lvcreate \-n cache0 \-L 10G vg /dev/fast


 .SS 2. create CacheMetaLV

 Create the cache metadata LV.  This LV will hold cache pool metadata.  The
 size of this LV should be 1000 times smaller than the cache data LV, with
 a minimum size of 8MiB.

 .B lvcreate \-n CacheMetaLV \-L MetaSize VG FastPVs

 .I Example
 .br
 # lvcreate \-n cache0meta \-L 12M vg /dev/fast

 .nf
 # lvs -a vg
   LV         VG   Attr       LSize   Pool Origin
   cache0     vg   -wi-a-----  10.00g
   cache0meta vg   -wi-a-----  12.00m
   lvol0      vg   -wi-a----- 100.00g
 .fi


 .SS 3. create CachePoolLV

 Combine the data and metadata LVs into a cache pool LV.
 The behavior of the cache pool LV can be set in this step.
 .br
 CachePoolLV takes the name of CacheDataLV.
 .br
 CacheDataLV is renamed CachePoolLV_cdata and becomes hidden.
 .br
 CacheMetaLV is renamed CachePoolLV_cmeta and becomes hidden.

 .B lvconvert \-\-type cache-pool \-\-poolmetadata VG/CacheMetaLV
 .RS
 .B VG/CacheDataLV
 .RE

 .I Example
 .br
 # lvconvert \-\-type cache\-pool \-\-poolmetadata vg/cache0meta vg/cache0

 .nf
 # lvs -a vg
   LV              VG   Attr       LSize   Pool Origin
   cache0          vg   Cwi---C---  10.00g
   [cache0_cdata]  vg   Cwi-------  10.00g
   [cache0_cmeta]  vg   ewi-------  12.00m
   lvol0           vg   -wi-a----- 100.00g
 .fi


 .SS 4. create CacheLV

 Create a cache LV by linking the cache pool LV to the origin LV.
 The user accessible cache LV takes the name of the origin LV,
 while the origin LV becomes a hidden LV with the name
 OriginLV_corig.  This can be done while the origin LV is in use.
 .br
 CacheLV takes the name of OriginLV.
 .br
 OriginLV is renamed OriginLV_corig and becomes hidden.

 .B lvconvert \-\-type cache \-\-cachepool VG/CachePoolLV VG/OriginLV

 .I Example
 .br
 # lvconvert \-\-type cache \-\-cachepool vg/cache0 vg/lvol0

 .nf
 # lvs -a vg
   LV              VG   Attr       LSize   Pool   Origin
   cache0          vg   Cwi---C---  10.00g
   [cache0_cdata]  vg   Cwi-ao----  10.00g
   [cache0_cmeta]  vg   ewi-ao----  12.00m
   lvol0           vg   Cwi-a-C--- 100.00g cache0 [lvol0_corig]
   [lvol0_corig]   vg   -wi-ao---- 100.00g
 .fi


 .SH Cache Removal

 .SS Split a cache pool LV off of a cache LV

 \&

 A cache pool LV can be disconnected from a cache LV, leaving an
 unused cache pool LV, and an uncached origin LV.  This command
 writes back data from the cache pool to the origin LV when necessary.

 .B lvconvert --splitcache VG/CacheLV

 .SS Removing a cache pool LV without removing its linked origin LV

 \&

 This writes back data from the cache pool to the origin LV when necessary,
 then removes the cache pool LV, leaving the uncached origin LV.

 .B lvremove VG/CachePoolLV

 An alternative command that also disconnects the cache pool from the cache
 LV, and deletes the cache pool:

 .B lvconvert --uncache VG/CacheLV

 .I Example
 .nf
 # lvs vg
   LV     VG   Attr       LSize   Pool   Origin
   cache0 vg   Cwi---C---  10.00g
   lvol0  vg   Cwi-a-C--- 100.00g cache0 [lvol0_corig]

 # lvremove vg/cache0

 # lvs vg
   LV    VG   Attr       LSize   Pool Origin
   lvol0 vg   -wi-a----- 100.00g
 .fi

 .SS Removing a cache LV: both origin LV and the cache pool LV

 \&

 Removing a cache LV removes both the origin LV and the linked cache pool
 LV.

 .B lvremove VG/CacheLV


 .SH Cache Topics

 .SS Tolerate device failures in a cache pool LV

 \&

 Users who are concerned about the possibility of failures in their fast
 devices that could lead to data loss might consider making their cache
 pool sub-LVs redundant.

 .I Example
 .nf
 0. Create an origin LV we wish to cache
 # lvcreate \-L 10G \-n lv1 vg /dev/slow_devs

 1. Create a 2-way RAID1 cache data LV
 # lvcreate \-\-type raid1 \-m 1 \-L 1G -n cache1 vg \\
 	/dev/fast1 /dev/fast2

 2. Create a 2-way RAID1 cache metadata LV
 # lvcreate \-\-type raid1 \-m 1 \-L 8M -n cache1meta vg \\
 	/dev/fast1 /dev/fast2

 3. Create a cache pool LV combining cache data LV and cache metadata LV
 # lvconvert \-\-type cache\-pool \-\-poolmetadata vg/cache1meta vg/cache1

 4. Create a cached LV by combining the cache pool LV and origin LV
 # lvconvert \-\-type cache \-\-cachepool vg/cache1 vg/lv1
 .fi

 .SS Cache mode

 \&

 The default cache mode is "writethrough".  Writethrough ensures that any
 data written will be stored both in the cache pool LV and on the origin
 LV.  The loss of a device associated with the cache pool LV in this case
 would not mean the loss of any data.

 A second cache mode is "writeback".  Writeback delays writing data blocks
 from the cache pool back to the origin LV.  This mode will increase
 performance, but the loss of a device associated with the cache pool LV
 can result in lost data.

 With the \-\-cachemode option, the cache mode can be set when creating a
 cache LV, or changed on an existing cache LV.  The current cache mode of a
 cache LV can be displayed with the cache_mode reporting option:

 .B lvs \-o+cache_mode VG/CacheLV

 .BR lvm.conf (5)
 .B allocation/cache_mode
 .br
 defines the default cache mode.

 .I Example
 .nf
 0. Create an origin LV we wish to cache (yours may already exist)
 # lvcreate \-L 10G \-n lv1 vg /dev/slow

 1. Create a cache data LV
 # lvcreate \-L 1G \-n cache1 vg /dev/fast

 2. Create a cache metadata LV
 # lvcreate \-L 8M \-n cache1meta vg /dev/fast

 3. Create a cache pool LV
 # lvconvert \-\-type cache\-pool \-\-poolmetadata vg/cache1meta vg/cache1

 4. Create a cache LV by combining the cache pool LV and origin LV,
    and use the writethrough cache mode.
 # lvconvert \-\-type cache \-\-cachepool vg/cache1 \\
 	\-\-cachemode writethrough vg/lv1
 .fi


 .SS Cache policy

 \&

 The cache subsystem has additional per-LV parameters: the cache policy to
 use, and possibly tunable parameters for the cache policy.  Three policies
 are currently available: "smq" is the default policy, "mq" is an older
 implementation, and "cleaner" is used to force the cache to write back
 (flush) all cached writes to the origin LV.

 The "mq" policy has a number of tunable parameters. The defaults are
 chosen to be suitable for the majority of systems, but in special
 circumstances, changing the settings can improve performance.

 With the \-\-cachepolicy and \-\-cachesettings options, the cache policy
 and settings can be set when creating a cache LV, or changed on an
 existing cache LV (both options can be used together).  The current cache
 policy and settings of a cache LV can be displayed with the cache_policy
 and cache_settings reporting options:

 .B lvs \-o+cache_policy,cache_settings VG/CacheLV

 .I Example
 .nf
 Change the cache policy and settings of an existing cache LV.
 # lvchange \-\-cachepolicy mq \-\-cachesettings \\
 	\(aqmigration_threshold=2048 random_threshold=4\(aq vg/lv1
 .fi

 .BR lvm.conf (5)
 .B allocation/cache_policy
 .br
 defines the default cache policy.

 .BR lvm.conf (5)
 .B allocation/cache_settings
 .br
 defines the default cache settings.


 .SS Chunk size

 \&

 The size of data blocks managed by a cache pool can be specified with the
 \-\-chunksize option when the cache LV is created.  The default unit
 is KiB. The value must be a multiple of 32KiB between 32KiB and 1GiB.

 Using a chunk size that is too large can result in wasteful use of the
 cache, where small reads and writes can cause large sections of an LV to
 be mapped into the cache.  However, choosing a chunk size that is too
 small can result in more overhead trying to manage the numerous chunks
 that become mapped into the cache.  Overhead can include both excessive
 CPU time searching for chunks, and excessive memory tracking chunks.

 Command to display the cache pool LV chunk size:
 .br
 .B lvs \-o+chunksize VG/CacheLV

 .BR lvm.conf (5)
 .B cache_pool_chunk_size
 .br
 controls the default chunk size used when creating a cache LV.

 The default value is shown by:
 .br
 .B lvmconfig \-\-type default allocation/cache_pool_chunk_size


 .SS Spare metadata LV

 \&

 See
 .BR lvmthin (7)
 for a description of the "pool metadata spare" LV.
 The same concept is used for cache pools.

 .SS Automatic pool metadata LV

 \&

 A cache data LV can be converted to cache pool LV without specifying a
 cache pool metadata LV.  LVM will automatically create a metadata LV from
 the same VG.

 .B lvcreate -n CacheDataLV -L CacheSize VG
 .br
 .B lvconvert --type cache\-pool VG/CacheDataLV


 .SS Create a new cache LV without an existing origin LV

 \&

 A cache LV can be created using an existing cache pool without an existing
 origin LV.  A new origin LV is created and linked to the cache pool in a
 single step.

 .B lvcreate \-\-type cache \-L LargeSize \-n CacheLV
 .RS
 .B \-\-cachepool VG/CachePoolLV VG SlowPVs
 .RE


 .SS Single step cache pool LV creation

 \&

 A cache pool LV can be created with a single lvcreate command, rather than
 using lvconvert on existing LVs.  This one command creates a cache data
 LV, a cache metadata LV, and combines the two into a cache pool LV.

 .B lvcreate \-\-type cache\-pool \-L CacheSize \-n CachePoolLV VG FastPVs


 .SS Convert existing LVs to cache types

 \&

 When an existing origin LV is converted to a cache LV, the specified cache
 pool may be a normal LV, rather than a cache pool LV.  In this case, lvm
 will first convert the normal LV to a cache pool LV.  A pool metadata LV
 may optionally be specified.

 .B lvcreate -n OriginLV -L LargeSize VG
 .br
 .B lvcreate -n CacheDataLV -L CacheSize VG
 .br
 .B lvconvert --type cache --cachepool VG/CataDataLV VG/OriginLV

 This is equivalent to:

 .B lvcreate -n OriginLV -L LargeSize VG
 .br
 .B lvcreate -n CacheDataLV -L CacheSize VG
 .br
 .B lvconvert --type cache-pool VG/CacheDataLV
 .br
 .B lvconvert --type cache --cachepool VG/CachePoolLV VG/OriginLV


 .SH SEE ALSO
 .BR lvm.conf (5),
 .BR lvchange (8),
 .BR lvcreate (8),
 .BR lvdisplay (8),
 .BR lvextend (8),
 .BR lvremove (8),
 .BR lvrename (8),
 .BR lvresize (8),
 .BR lvs (8),
 .BR vgchange (8),
 .BR vgmerge (8),
 .BR vgreduce (8),
 .BR vgsplit (8)
	.TH "LVMCACHE" "7" "LVM TOOLS #VERSION#" "Red Hat, Inc" "\""
	.SH NAME
	lvmcache \(em LVM caching

	.SH DESCRIPTION

	The \fBcache\fP logical volume type uses a small and fast LV to improve
	the performance of a large and slow LV. It does this by storing the
	frequently used blocks on the faster LV.
	LVM refers to the small fast LV as a \fBcache pool LV\fP. The large
	slow LV is called the \fBorigin LV\fP. Due to requirements from dm-cache
	(the kernel driver), LVM further splits the cache pool LV into two
	devices - the \fBcache data LV\fP and \fBcache metadata LV\fP. The cache
	data LV is where copies of data blocks are kept from the
	origin LV to increase speed. The cache metadata LV holds the
	accounting information that specifies where data blocks are stored (e.g.
	on the origin LV or on the cache data LV). Users should be familiar with
	these LVs if they wish to create the best and most robust cached
	logical volumes. All of these associated LVs must be in the same VG.

	.SH Cache Terms
	.nf
	origin LV OriginLV large slow LV
	cache data LV CacheDataLV small fast LV for cache pool data
	cache metadata LV CacheMetaLV small fast LV for cache pool metadata
	cache pool LV CachePoolLV CacheDataLV + CacheMetaLV
	cache LV CacheLV OriginLV + CachePoolLV
	.fi

	.SH Cache Usage

	The primary method for using a cache type logical volume:


	.SS 0. create OriginLV

	Create an LV or identify an existing LV to be the origin LV.

	.B lvcreate \-n OriginLV \-L LargeSize VG SlowPVs

	.I Example
	.br
	# lvcreate \-n lvol0 \-L 100G vg


	.SS 1. create CacheDataLV

	Create the cache data LV. This LV will hold data blocks from the
	OriginLV. The size of this LV is the size of the cache and will be
	reported as the size of the cache pool LV.

	.B lvcreate \-n CacheDataLV \-L CacheSize VG FastPVs

	.I Example
	.br
	# lvcreate \-n cache0 \-L 10G vg /dev/fast


	.SS 2. create CacheMetaLV

	Create the cache metadata LV. This LV will hold cache pool metadata. The
	size of this LV should be 1000 times smaller than the cache data LV, with
	a minimum size of 8MiB.

	.B lvcreate \-n CacheMetaLV \-L MetaSize VG FastPVs

	.I Example
	.br
	# lvcreate \-n cache0meta \-L 12M vg /dev/fast

	.nf
	# lvs -a vg
	LV VG Attr LSize Pool Origin
	cache0 vg -wi-a----- 10.00g
	cache0meta vg -wi-a----- 12.00m
	lvol0 vg -wi-a----- 100.00g
	.fi


	.SS 3. create CachePoolLV

	Combine the data and metadata LVs into a cache pool LV.
	The behavior of the cache pool LV can be set in this step.
	.br
	CachePoolLV takes the name of CacheDataLV.
	.br
	CacheDataLV is renamed CachePoolLV_cdata and becomes hidden.
	.br
	CacheMetaLV is renamed CachePoolLV_cmeta and becomes hidden.

	.B lvconvert \-\-type cache-pool \-\-poolmetadata VG/CacheMetaLV
	.RS
	.B VG/CacheDataLV
	.RE

	.I Example
	.br
	# lvconvert \-\-type cache\-pool \-\-poolmetadata vg/cache0meta vg/cache0

	.nf
	# lvs -a vg
	LV VG Attr LSize Pool Origin
	cache0 vg Cwi---C--- 10.00g
	[cache0_cdata] vg Cwi------- 10.00g
	[cache0_cmeta] vg ewi------- 12.00m
	lvol0 vg -wi-a----- 100.00g
	.fi


	.SS 4. create CacheLV

	Create a cache LV by linking the cache pool LV to the origin LV.
	The user accessible cache LV takes the name of the origin LV,
	while the origin LV becomes a hidden LV with the name
	OriginLV_corig. This can be done while the origin LV is in use.
	.br
	CacheLV takes the name of OriginLV.
	.br
	OriginLV is renamed OriginLV_corig and becomes hidden.

	.B lvconvert \-\-type cache \-\-cachepool VG/CachePoolLV VG/OriginLV

	.I Example
	.br
	# lvconvert \-\-type cache \-\-cachepool vg/cache0 vg/lvol0

	.nf
	# lvs -a vg
	LV VG Attr LSize Pool Origin
	cache0 vg Cwi---C--- 10.00g
	[cache0_cdata] vg Cwi-ao---- 10.00g
	[cache0_cmeta] vg ewi-ao---- 12.00m
	lvol0 vg Cwi-a-C--- 100.00g cache0 [lvol0_corig]
	[lvol0_corig] vg -wi-ao---- 100.00g
	.fi


	.SH Cache Removal

	.SS Split a cache pool LV off of a cache LV

	\&

	A cache pool LV can be disconnected from a cache LV, leaving an
	unused cache pool LV, and an uncached origin LV. This command
	writes back data from the cache pool to the origin LV when necessary.

	.B lvconvert --splitcache VG/CacheLV

	.SS Removing a cache pool LV without removing its linked origin LV

	\&

	This writes back data from the cache pool to the origin LV when necessary,
	then removes the cache pool LV, leaving the uncached origin LV.

	.B lvremove VG/CachePoolLV

	An alternative command that also disconnects the cache pool from the cache
	LV, and deletes the cache pool:

	.B lvconvert --uncache VG/CacheLV

	.I Example
	.nf
	# lvs vg
	LV VG Attr LSize Pool Origin
	cache0 vg Cwi---C--- 10.00g
	lvol0 vg Cwi-a-C--- 100.00g cache0 [lvol0_corig]

	# lvremove vg/cache0

	# lvs vg
	LV VG Attr LSize Pool Origin
	lvol0 vg -wi-a----- 100.00g
	.fi

	.SS Removing a cache LV: both origin LV and the cache pool LV

	\&

	Removing a cache LV removes both the origin LV and the linked cache pool
	LV.

	.B lvremove VG/CacheLV


	.SH Cache Topics

	.SS Tolerate device failures in a cache pool LV

	\&

	Users who are concerned about the possibility of failures in their fast
	devices that could lead to data loss might consider making their cache
	pool sub-LVs redundant.

	.I Example
	.nf
	0. Create an origin LV we wish to cache
	# lvcreate \-L 10G \-n lv1 vg /dev/slow_devs

	1. Create a 2-way RAID1 cache data LV
	# lvcreate \-\-type raid1 \-m 1 \-L 1G -n cache1 vg \\
	/dev/fast1 /dev/fast2

	2. Create a 2-way RAID1 cache metadata LV
	# lvcreate \-\-type raid1 \-m 1 \-L 8M -n cache1meta vg \\
	/dev/fast1 /dev/fast2

	3. Create a cache pool LV combining cache data LV and cache metadata LV
	# lvconvert \-\-type cache\-pool \-\-poolmetadata vg/cache1meta vg/cache1

	4. Create a cached LV by combining the cache pool LV and origin LV
	# lvconvert \-\-type cache \-\-cachepool vg/cache1 vg/lv1
	.fi

	.SS Cache mode

	\&

	The default cache mode is "writethrough". Writethrough ensures that any
	data written will be stored both in the cache pool LV and on the origin
	LV. The loss of a device associated with the cache pool LV in this case
	would not mean the loss of any data.

	A second cache mode is "writeback". Writeback delays writing data blocks
	from the cache pool back to the origin LV. This mode will increase
	performance, but the loss of a device associated with the cache pool LV
	can result in lost data.

	With the \-\-cachemode option, the cache mode can be set when creating a
	cache LV, or changed on an existing cache LV. The current cache mode of a
	cache LV can be displayed with the cache_mode reporting option:

	.B lvs \-o+cache_mode VG/CacheLV

	.BR lvm.conf (5)
	.B allocation/cache_mode
	.br
	defines the default cache mode.

	.I Example
	.nf
	0. Create an origin LV we wish to cache (yours may already exist)
	# lvcreate \-L 10G \-n lv1 vg /dev/slow

	1. Create a cache data LV
	# lvcreate \-L 1G \-n cache1 vg /dev/fast

	2. Create a cache metadata LV
	# lvcreate \-L 8M \-n cache1meta vg /dev/fast

	3. Create a cache pool LV
	# lvconvert \-\-type cache\-pool \-\-poolmetadata vg/cache1meta vg/cache1

	4. Create a cache LV by combining the cache pool LV and origin LV,
	and use the writethrough cache mode.
	# lvconvert \-\-type cache \-\-cachepool vg/cache1 \\
	\-\-cachemode writethrough vg/lv1
	.fi


	.SS Cache policy

	\&

	The cache subsystem has additional per-LV parameters: the cache policy to
	use, and possibly tunable parameters for the cache policy. Three policies
	are currently available: "smq" is the default policy, "mq" is an older
	implementation, and "cleaner" is used to force the cache to write back
	(flush) all cached writes to the origin LV.

	The "mq" policy has a number of tunable parameters. The defaults are
	chosen to be suitable for the majority of systems, but in special
	circumstances, changing the settings can improve performance.

	With the \-\-cachepolicy and \-\-cachesettings options, the cache policy
	and settings can be set when creating a cache LV, or changed on an
	existing cache LV (both options can be used together). The current cache
	policy and settings of a cache LV can be displayed with the cache_policy
	and cache_settings reporting options:

	.B lvs \-o+cache_policy,cache_settings VG/CacheLV

	.I Example
	.nf
	Change the cache policy and settings of an existing cache LV.
	# lvchange \-\-cachepolicy mq \-\-cachesettings \\
	\(aqmigration_threshold=2048 random_threshold=4\(aq vg/lv1
	.fi

	.BR lvm.conf (5)
	.B allocation/cache_policy
	.br
	defines the default cache policy.

	.BR lvm.conf (5)
	.B allocation/cache_settings
	.br
	defines the default cache settings.


	.SS Chunk size

	\&

	The size of data blocks managed by a cache pool can be specified with the
	\-\-chunksize option when the cache LV is created. The default unit
	is KiB. The value must be a multiple of 32KiB between 32KiB and 1GiB.

	Using a chunk size that is too large can result in wasteful use of the
	cache, where small reads and writes can cause large sections of an LV to
	be mapped into the cache. However, choosing a chunk size that is too
	small can result in more overhead trying to manage the numerous chunks
	that become mapped into the cache. Overhead can include both excessive
	CPU time searching for chunks, and excessive memory tracking chunks.

	Command to display the cache pool LV chunk size:
	.br
	.B lvs \-o+chunksize VG/CacheLV

	.BR lvm.conf (5)
	.B cache_pool_chunk_size
	.br
	controls the default chunk size used when creating a cache LV.

	The default value is shown by:
	.br
	.B lvmconfig \-\-type default allocation/cache_pool_chunk_size


	.SS Spare metadata LV

	\&

	See
	.BR lvmthin (7)
	for a description of the "pool metadata spare" LV.
	The same concept is used for cache pools.

	.SS Automatic pool metadata LV

	\&

	A cache data LV can be converted to cache pool LV without specifying a
	cache pool metadata LV. LVM will automatically create a metadata LV from
	the same VG.

	.B lvcreate -n CacheDataLV -L CacheSize VG
	.br
	.B lvconvert --type cache\-pool VG/CacheDataLV


	.SS Create a new cache LV without an existing origin LV

	\&

	A cache LV can be created using an existing cache pool without an existing
	origin LV. A new origin LV is created and linked to the cache pool in a
	single step.

	.B lvcreate \-\-type cache \-L LargeSize \-n CacheLV
	.RS
	.B \-\-cachepool VG/CachePoolLV VG SlowPVs
	.RE


	.SS Single step cache pool LV creation

	\&

	A cache pool LV can be created with a single lvcreate command, rather than
	using lvconvert on existing LVs. This one command creates a cache data
	LV, a cache metadata LV, and combines the two into a cache pool LV.

	.B lvcreate \-\-type cache\-pool \-L CacheSize \-n CachePoolLV VG FastPVs


	.SS Convert existing LVs to cache types

	\&

	When an existing origin LV is converted to a cache LV, the specified cache
	pool may be a normal LV, rather than a cache pool LV. In this case, lvm
	will first convert the normal LV to a cache pool LV. A pool metadata LV
	may optionally be specified.

	.B lvcreate -n OriginLV -L LargeSize VG
	.br
	.B lvcreate -n CacheDataLV -L CacheSize VG
	.br
	.B lvconvert --type cache --cachepool VG/CataDataLV VG/OriginLV

	This is equivalent to:

	.B lvcreate -n OriginLV -L LargeSize VG
	.br
	.B lvcreate -n CacheDataLV -L CacheSize VG
	.br
	.B lvconvert --type cache-pool VG/CacheDataLV
	.br
	.B lvconvert --type cache --cachepool VG/CachePoolLV VG/OriginLV


	.SH SEE ALSO
	.BR lvm.conf (5),
	.BR lvchange (8),
	.BR lvcreate (8),
	.BR lvdisplay (8),
	.BR lvextend (8),
	.BR lvremove (8),
	.BR lvrename (8),
	.BR lvresize (8),
	.BR lvs (8),
	.BR vgchange (8),
	.BR vgmerge (8),
	.BR vgreduce (8),
	.BR vgsplit (8)