mirror of
git://sourceware.org/git/lvm2.git
synced 2024-12-22 17:35:59 +03:00
278 lines
7.6 KiB
Groff
278 lines
7.6 KiB
Groff
.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.
|
|
|
|
.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 \-\-cachepool VG/CacheDataLV \-\-poolmetadata VG/CacheMetaLV
|
|
|
|
.I Example
|
|
.br
|
|
# lvconvert \-\-cachepool vg/cache0 \-\-poolmetadata vg/cache0meta
|
|
|
|
.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 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 un-cached origin LV.
|
|
|
|
.B lvremove VG/CachePoolLV
|
|
|
|
.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 an origin LV without removing its linked cache pool LV
|
|
|
|
\&
|
|
|
|
This removes the origin LV, leaving the cache pool LV which can be linked
|
|
to another origin LV.
|
|
|
|
.B lvremove 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/lvol0
|
|
|
|
# lvs vg
|
|
LV VG Attr LSize Pool Origin
|
|
cache0 vg Cwi---C--- 10.00g
|
|
.fi
|
|
|
|
|
|
.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.
|
|
|
|
.nf
|
|
0. Create an origin LV we wish to cache
|
|
# lvcreate \-L 10G \-n lvx vg /dev/slow_devs
|
|
|
|
1. Create a 2-way RAID1 cache data LV
|
|
# lvcreate \-\-type raid1 \-m 1 \-L 1G -n lvx_cache vg \\
|
|
/dev/fast1 /dev/fast2
|
|
|
|
2. Create a 2-way RAID1 cache metadata LV
|
|
# lvcreate \-\-type raid1 \-m 1 \-L 8M -n lvx_cache_meta vg \\
|
|
/dev/fast1 /dev/fast2
|
|
|
|
3. Create a cache pool LV combining cache data LV and cache metadata LV
|
|
# lvconvert \-\-cachepool vg/lvx_cache \-\-poolmetadata vg/lvx_cache_meta
|
|
|
|
4. Create a cached LV by combining the cache pool LV and origin LV
|
|
# lvconvert \-\-type cache \-\-cachepool vg/lvx_cache vg/lvx
|
|
.fi
|
|
|
|
.SS Writethough caching
|
|
|
|
\&
|
|
|
|
Writethrough caching 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.
|
|
When combining the cache data LV and the cache metadata LV to form the
|
|
cache pool LV, properties of the cache can be specified - in this case,
|
|
\fIwritethrough\fP vs. \fIwriteback\fP.
|
|
|
|
.nf
|
|
0. Create an origin LV we wish to cache (yours may already exist)
|
|
# lvcreate \-L 10G \-n lvx vg /dev/slow
|
|
|
|
1. Create a cache data LV
|
|
# lvcreate \-L 1G \-n lvx_cache vg /dev/fast
|
|
|
|
2. Create a cache metadata LV
|
|
# lvcreate \-L 8M \-n lvx_cache_meta vg /dev/fast
|
|
|
|
3. Create a cache pool LV specifying cache mode "writethrough"
|
|
# lvconvert \-\-cachepool vg/lvx_cache \-\-poolmetadata vg/lvx_cache_meta \\
|
|
\-\-cachemode writethrough
|
|
|
|
4. Create a cache LV by combining the cache pool LV and origin LV
|
|
# lvconvert \-\-type cache \-\-cachepool vg/lvx_cache vg/lvx
|
|
.fi
|
|
|
|
.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 --cachepool VG/CacheDataLV
|
|
|
|
|
|
.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)
|