</listitem>
</itemizedlist></para>
</section>
- <section remap="h3">
+ <section remap="h3" xml:id="dbdoclet.balancing_free_space">
<title><indexterm>
<primary>proc</primary>
<secondary>free space</secondary>
</indexterm>Allocating Free Space on OSTs</title>
- <para>Free space is allocated using either a round-robin or a weighted algorithm. The allocation
- method is determined by the maximum amount of free-space imbalance between the OSTs. When free
- space is relatively balanced across OSTs, the faster round-robin allocator is used, which
- maximizes network balancing. The weighted allocator is used when any two OSTs are out of
- balance by more than a specified threshold.</para>
- <para>Free space distribution can be tuned using these two <literal>/proc</literal>
- tunables:</para>
+ <para>Free space is allocated using either a round-robin or a weighted
+ algorithm. The allocation method is determined by the maximum amount of
+ free-space imbalance between the OSTs. When free space is relatively
+ balanced across OSTs, the faster round-robin allocator is used, which
+ maximizes network balancing. The weighted allocator is used when any two
+ OSTs are out of balance by more than a specified threshold.</para>
+ <para>Free space distribution can be tuned using these two
+ <literal>/proc</literal> tunables:</para>
<itemizedlist>
<listitem>
- <para><literal>qos_threshold_rr</literal> - The threshold at which the allocation method
- switches from round-robin to weighted is set in this file. The default is to switch to the
- weighted algorithm when any two OSTs are out of balance by more than 17 percent.</para>
+ <para><literal>qos_threshold_rr</literal> - The threshold at which
+ the allocation method switches from round-robin to weighted is set
+ in this file. The default is to switch to the weighted algorithm when
+ any two OSTs are out of balance by more than 17 percent.</para>
</listitem>
<listitem>
- <para><literal>qos_prio_free</literal> - The weighting priority used by the weighted
- allocator can be adjusted in this file. Increasing the value of
- <literal>qos_prio_free</literal> puts more weighting on the amount of free space
- available on each OST and less on how stripes are distributed across OSTs. The default
- value is 91 percent. When the free space priority is set to 100, weighting is based
- entirely on free space and location is no longer used by the striping algorithm.</para>
+ <para><literal>qos_prio_free</literal> - The weighting priority used
+ by the weighted allocator can be adjusted in this file. Increasing the
+ value of <literal>qos_prio_free</literal> puts more weighting on the
+ amount of free space available on each OST and less on how stripes are
+ distributed across OSTs. The default value is 91 percent weighting for
+ free space rebalancing and 9 percent for OST balancing. When the
+ free space priority is set to 100, weighting is based entirely on free
+ space and location is no longer used by the striping algorithm.</para>
</listitem>
<listitem>
- <para condition="l29"><literal>reserved_mb_low</literal> - The low watermark used to stop
- object allocation if available space is less than it. The default is 0.1 percent of total
- OST size.</para>
+ <para condition="l29"><literal>reserved_mb_low</literal> - The low
+ watermark used to stop object allocation if available space is less
+ than it. The default is 0.1 percent of total OST size.</para>
</listitem>
<listitem>
<para condition="l29"><literal>reserved_mb_high</literal> - The high watermark used to start
git://git.whamcloud.com / doc / manual.git / blobdiff