[lvm-devel] main - man: describe profile support lvmcache.7
Zdenek Kabelac
zkabelac at sourceware.org
Tue Mar 30 11:10:13 UTC 2021
Gitweb: https://sourceware.org/git/?p=lvm2.git;a=commitdiff;h=ff5776024f056aeff0f1dac9f028e55761e7c24b
Commit: ff5776024f056aeff0f1dac9f028e55761e7c24b
Parent: 2aaea13aaa2935905a6d1cb32db4e2cd477c22f4
Author: Zdenek Kabelac <zkabelac at redhat.com>
AuthorDate: Mon Mar 29 18:55:47 2021 +0200
Committer: Zdenek Kabelac <zkabelac at redhat.com>
CommitterDate: Tue Mar 30 13:08:14 2021 +0200
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.
---
man/lvmcache.7_main | 160 ++++++++++++++++++++++++++++++++++++----------------
1 file changed, 112 insertions(+), 48 deletions(-)
diff --git a/man/lvmcache.7_main b/man/lvmcache.7_main
index 85d4d9e34..182dc0a79 100644
--- a/man/lvmcache.7_main
+++ b/man/lvmcache.7_main
@@ -63,17 +63,21 @@ To start caching the main LV, convert the main LV to the desired caching
type, and specify the fast LV to use as the cache:
.nf
-using dm-cache:
+using dm-cache (with cachepool):
+
+ $ lvconvert --type cache --cachepool fast vg/main
+
+using dm-cache (with cachevol):
$ lvconvert --type cache --cachevol fast vg/main
-using dm-writecache:
+using dm-writecache (with cachevol):
$ lvconvert --type writecache --cachevol fast vg/main
-using dm-cache (with cachepool):
-
- $ lvconvert --type cache --cachepool fast vg/main
+For more alteratives see:
+dm-cache command shortcut
+dm-cache with separate data and metadata LVs
.fi
.B 4. Display LVs
@@ -85,31 +89,31 @@ suffix. It is displayed by lvs -a. The _corig or _wcorig LV represents
the original LV without the cache.
.nf
-using dm-cache:
+using dm-cache (with cachepool):
- $ lvs -a
- LV Pool Type Devices
- main [fast_cvol] cache main_corig(0)
+ $ lvs -ao+devices
+ LV Pool Type Devices
+ main [fast_cpool] cache main_corig(0)
+ [fast_cpool] cache-pool fast_pool_cdata(0)
+ [fast_cpool_cdata] linear /dev/fast_ssd
+ [fast_cpool_cmeta] linear /dev/fast_ssd
+ [main_corig] linear /dev/slow_hhd
+
+using dm-cache (with cachevol):
+
+ $ lvs -ao+devices
+ LV Pool Type Devices
+ main [fast_cvol] cache main_corig(0)
[fast_cvol] linear /dev/fast_ssd
[main_corig] linear /dev/slow_hhd
-using dm-writecache:
+using dm-writecache (with cachevol):
- $ lvs -a
- LV Pool Type Devices
+ $ lvs -ao+devices
+ LV Pool Type Devices
main [fast_cvol] writecache main_wcorig(0)
[fast_cvol] linear /dev/fast_ssd
[main_wcorig] linear /dev/slow_hhd
-
-using dm-cache (with cachepool):
-
- $ lvs -a
- LV Pool Type Devices
- main [fast_cpool] cache main_corig(0)
- [fast_cpool] cache-pool fast_pool_cdata(0)
- [fast_cpool_cdata] linear /dev/fast_ssd
- [fast_cpool_cmeta] linear /dev/fast_ssd
- [main_corig] linear /dev/slow_hhd
.fi
.B 5. Use the main LV
@@ -118,26 +122,26 @@ Use the LV until the cache is no longer wanted, or needs to be changed.
.B 6. Stop caching
-To stop caching the main LV, separate the fast LV from the main LV. This
-changes the type of the main LV back to what it was before the cache was
-attached.
+To stop caching the main LV and also remove unneeded cache pool,
+use the --uncache:
.nf
- $ lvconvert --splitcache vg/main
+ $ lvconvert --uncache vg/main
$ lvs -a
- LV VG Attr Type Devices
- fast vg -wi------- linear /dev/fast_ssd
+ LV VG Attr Type Devices
main vg -wi------- linear /dev/slow_hhd
-To stop caching the main LV and also remove unneeded cache pool,
-use the --uncache:
+To stop caching the main LV, separate the fast LV from the main LV. This
+changes the type of the main LV back to what it was before the cache was
+attached.
.nf
- $ lvconvert --uncache vg/main
+ $ lvconvert --splitcache vg/main
$ lvs -a
LV VG Attr Type Devices
+ fast vg -wi------- linear /dev/fast_ssd
main vg -wi------- linear /dev/slow_hhd
.fi
@@ -167,14 +171,6 @@ for the fast LV.
\&
-.B --cachevol
-.I LV
-.br
-
-Pass this option a fast LV that should be used to hold the cache. With a
-cachevol, cache data and metadata are stored in different parts of the
-same fast LV. This option can be used with dm-writecache or dm-cache.
-
.B --cachepool
.IR CachePoolLV | LV
.br
@@ -189,6 +185,14 @@ that cannot be used directly. If a standard LV is passed with this
option, lvm will first convert it to a cache pool by combining it with
another LV to use for metadata. This option can be used with dm-cache.
+.B --cachevol
+.I LV
+.br
+
+Pass this option a fast LV that should be used to hold the cache. With a
+cachevol, cache data and metadata are stored in different parts of the
+same fast LV. This option can be used with dm-writecache or dm-cache.
+
.B --cachedevice
.I PV
.br
@@ -318,10 +322,25 @@ cleaner mode, and any required flushing is performed in device suspend.
\&
-When using dm-cache, the cache metadata and cache data can be stored on
-separate LVs. To do this, a "cache pool" is created, which is a special
+Preferred way of using dm-cache is to place the cache metadata and cache data
+on separate LVs. To do this, a "cache pool" is created, which is a special
LV that references two sub LVs, one for data and one for metadata.
+To create a cache pool of given data size and let lvm2 calculate appropriate
+metadata size:
+
+.nf
+$ lvcreate --type cache-pool -L DataSize -n fast vg /dev/fast_ssd1
+.fi
+
+To create a cache pool from separate LV and let lvm2 calculate
+appropriate cache metadata size:
+
+.nf
+$ lvcreate -n fast -L DataSize vg /dev/fast_ssd1
+$ lvconvert --type cache-pool vg/fast /dev/fast_ssd1
+.fi
+
To create a cache pool from two separate LVs:
.nf
@@ -374,8 +393,12 @@ mode can be displayed with the cache_mode reporting option:
defines the default cache mode.
.nf
-$ lvconvert --type cache --cachevol fast \\
- --cachemode writethrough vg/main
+$ lvconvert --type cache --cachemode writethrough \\
+ --cachepool fast vg/main
+
+
+$ lvconvert --type cache --cachemode writethrough \\
+ --cachevol fast vg/main
.nf
.SS dm-cache chunk size
@@ -480,6 +503,39 @@ defines the default cache policy.
.br
defines the default cache settings.
+.SS dm-cache using metadata profiles
+
+\&
+
+Cache pools allows to set a variety of options. Lots of these settings
+can be specified in lvm.conf or profile settings. You can prepare
+a number of different profiles in the #DEFAULT_SYS_DIR#/profile directory
+and just specify the metadata profile file name when caching LV or creating cache-pool.
+Check the output of \fBlvmconfig --type default --withcomments\fP
+for a detailed description of all individual cache settings.
+
+.I Example
+.nf
+# cat <<EOF > #DEFAULT_SYS_DIR#/profile/cache_big_chunk.profile
+allocation {
+ cache_pool_metadata_require_separate_pvs=0
+ cache_pool_chunk_size=512
+ cache_metadata_format=2
+ cache_mode="writethrough"
+ cache_policy="smq"
+ cache_settings {
+ smq {
+ migration_threshold=8192
+ random_threshold=4096
+ }
+ }
+}
+EOF
+
+# lvcreate --cache -L10G --metadataprofile cache_big_chunk vg/main /dev/fast_ssd
+# lvcreate --cache -L10G --config 'allocation/cache_pool_chunk_size=512' vg/main /dev/fast_ssd
+.fi
+
.SS dm-cache spare metadata LV
\&
@@ -518,16 +574,24 @@ $ lvconvert --type cache --cachevol fast vg/main
\&
-A single command can be used to create a cache pool and attach that new
-cache pool to a main LV:
+A single command can be used to cache main LV with automatic
+creation of a cache-pool:
+
+.nf
+$ lvcreate --cache --size CacheDataSize VG/LV [FastPVs]
+.fi
+
+or the longer variant
.nf
-$ lvcreate --type cache --name Name --size Size VG/LV [PV]
+$ lvcreate --type cache --size CacheDataSize \\
+ --name NameCachePool VG/LV [FastPVs]
.fi
In this command, the specified LV already exists, and is the main LV to be
-cached. The command creates a new cache pool with the given name and
-size, using the optionally specified PV (typically an ssd). Then it
+cached. The command creates a new cache pool with size and given name
+or the name is automatically selected from a sequence lvolX_cpool,
+using the optionally specified fast PV(s) (typically an ssd). Then it
attaches the new cache pool to the existing main LV to begin caching.
(Note: ensure that the specified main LV is a standard LV. If a cache
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