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man: lvmthin chunk and metadata sizes

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Clear some stale information, and give a suggestion to use
a metadata size of 1GiB.
This commit is contained in:
David Teigland 2015-05-27 15:53:01 -05:00
parent 778b66a719
commit 3225f8d175
1 changed files with 30 additions and 24 deletions
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54
man/lvmthin.7.in
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@ -907,12 +907,12 @@ autoextend the LV by this much additional space.
To see the default values of these settings, run: To see the default values of these settings, run:
.B lvmconfig --type default --withcomment .B lvmconfig \-\-type default \-\-withcomment
.RS .RS
.B activation/thin_pool_autoextend_threshold .B activation/thin_pool_autoextend_threshold
.RE .RE
.B lvmconfig --type default --withcomment .B lvmconfig \-\-type default \-\-withcomment
.RS .RS
.B activation/thin_pool_autoextend_percent .B activation/thin_pool_autoextend_percent
.RE .RE
@ -973,7 +973,7 @@ file with the profile also needs to be moved.
.IP \[bu] 2 .IP \[bu] 2
Only certain settings can be used in a VG or LV profile, see: Only certain settings can be used in a VG or LV profile, see:
.br .br
.B lvmconfig --type profilable-metadata. .B lvmconfig \-\-type profilable-metadata.
.IP \[bu] 2 .IP \[bu] 2
An LV without a profile of its own will inherit the VG profile. An LV without a profile of its own will inherit the VG profile.
@ -986,9 +986,9 @@ Remove a profile from an LV using the command:
.IP \[bu] 2 .IP \[bu] 2
Commands can also have profiles applied to them. The settings that can be Commands can also have profiles applied to them. The settings that can be
applied to a command are different than the settings that can be applied applied to a command are different than the settings that can be applied
to a VG or LV. See lvmconfig --type profilable-command. To apply a to a VG or LV. See lvmconfig \-\-type profilable\-command. To apply a
profile to a command, write a profile, save it in the profile directory, profile to a command, write a profile, save it in the profile directory,
and run the command using the option: --commandprofile ProfileName. and run the command using the option: \-\-commandprofile ProfileName.
.SS Zeroing .SS Zeroing
@ -1076,14 +1076,13 @@ controls the default discards mode used when creating a thin pool.
\& \&
The size of data blocks managed by a thin pool can be specified with The size of data blocks managed by a thin pool can be specified with the
the \-\-chunksize option when the thin pool LV is created. The default \-\-chunksize option when the thin pool LV is created. The default unit
unit is kilobytes and the default value is 64KiB. The value must be a is KiB. The value must be a multiple of 64KiB between 64KiB and 1GiB.
power of two between 4KiB and 1GiB.
When a thin pool is used primarily for the thin provisioning feature, When a thin pool is used primarily for the thin provisioning feature, a
a larger value is optimal. To optimize for a lot of snapshotting, larger value is optimal. To optimize for many snapshots, a smaller value
a smaller value reduces copying time and consumes less space. reduces copying time and consumes less space.
Command to display the thin pool LV chunk size: Command to display the thin pool LV chunk size:
.br .br
@ -1101,25 +1100,32 @@ Command to display the thin pool LV chunk size:
.br .br
controls the default chunk size used when creating a thin pool. controls the default chunk size used when creating a thin pool.
The default value is shown by:
.br
.B lvmconfig \-\-type default allocation/thin_pool_chunk_size
.SS Size of pool metadata LV .SS Size of pool metadata LV
\& \&
The amount of thin metadata depends on how many blocks are shared The amount of thin metadata depends on how many blocks are shared between
between thin LVs (i.e. through snapshots). A thin pool with many thin LVs (i.e. through snapshots). A thin pool with many snapshots may
snapshots may need a larger metadata LV. need a larger metadata LV. Thin pool metadata LV sizes can be from 2MiB
to 16GiB.
The range of supported metadata LV sizes is 2MiB to 16GiB. When using lvcreate to create what will become a thin metadata LV, the
.br size is specified with the \-L|\-\-size option.
The default size is estimated with the formula:
.br
ThinPoolLVSize / ThinPoolLVChunkSize * 64b.
When creating a thin metadata LV explicitly, the size is specified When an LVM command automatically creates a thin metadata LV, the size is
in the lvcreate command. When a command automatically creates a specified with the \-\-poolmetadatasize option. When this option is not
thin metadata LV, the \-\-poolmetadatasize option can be used specify given, LVM automatically chooses a size based on the data size and chunk
a non-default size. The default unit is megabytes. size.
It can be hard to predict the amount of metadata space that will be
needed, so it is recommended to start with a size of 1GiB which should be
enough for all practical purposes. A thin pool metadata LV can later be
manually or automatically extended if needed.
.SS Create a thin snapshot of an external, read only LV .SS Create a thin snapshot of an external, read only LV