-<?xml version='1.0' encoding='UTF-8'?><chapter xmlns="http://docbook.org/ns/docbook" xmlns:xl="http://www.w3.org/1999/xlink" version="5.0" xml:lang="en-US" xml:id="dataonmdt"
- condition="l2B">
+<?xml version='1.0' encoding='UTF-8'?>
+<chapter xmlns="http://docbook.org/ns/docbook"
+ xmlns:xl="http://www.w3.org/1999/xlink" version="5.0" xml:lang="en-US"
+ xml:id="dataonmdt" condition="l2B">
<title xml:id="dataonmdt.title">Data on MDT (DoM)</title>
<para>This chapter describes Data on MDT (DoM).</para>
<section xml:id="dbdoclet.domintro">
<para>The <literal>lfs setstripe</literal> command is used to create
DoM files.</para>
<section><title>Command</title>
- <para><screen>lfs setstripe --component-end|-E end1 --layout|-L \
-mdt [--component-end|-E end2 [STRIPE_OPTIONS] ...] <filename>
+ <para><screen>
+lfs setstripe --component-end|-E end1 --layout|-L mdt \
+ [--component-end|-E end2 [STRIPE_OPTIONS] ...] <filename>
</screen>
The command above creates a file with the special composite
layout, which defines the first component as an MDT component. The
<replaceable>end1</replaceable> is also the stripe size of this
component, and is limited by the
<literal>lod.*.dom_stripesize</literal> of the MDT the file is
- created on. No other options are required. The rest of the
- components use the normal syntax for composite files creation.
+ created on. No other options are required for this component.
+ The rest of the components use the normal syntax for composite
+ files creation.
</para>
<note><para>If the next component doesn't specify striping, such
as:
</para>
<section><title>LFS limits for DoM component size</title>
<para><literal>lfs setstripe</literal> allows for setting the
- component size for MDT layouts up to 1GB, however, the size must
+ component size for MDT layouts up to 1GB (this is a compile-time
+ limit to avoid improper configuration), however, the size must
also be aligned by 64KB due to the minimum stripe size in Lustre
- (see <xref linkend="settinguplustresystem.tab2"/>). This value
- represents the maximum possible size of the component on the MDT.
- Meanwhile, there is another limit which is checked by
- <literal>lfs setstripe</literal> and is provided by the MDT
- server itself.</para>
+ (see <xref linkend="settinguplustresystem.tab2"/>
+ <literal>Minimum stripe size</literal>). There is also a limit
+ imposed on each file by <literal>lfs setstripe -E end</literal>
+ that may be smaller than the MDT-imposed limit if this is better
+ for a particular usage.</para>
</section>
<section><title>MDT Server Limits</title>
- <para>The LOD parameter <literal>dom_stripesize</literal> is used
- to control the per-server maximum size for a DoM component. It is
- 1MB by default and can be changed with the
+ <para>The <literal>lod.$fsname-MDTxxxx.dom_stripesize</literal>
+ is used to control the per-MDT maximum size for a DoM component.
+ Larger DoM components specified by the user will be truncated to
+ the MDT-specified limit, and as such may be different on each
+ MDT to balance DoM space usage on each MDT separately, if needed.
+ It is 1MB by default and can be changed with the
<literal>lctl</literal> tool. For more information on setting
<literal>dom_stripesize</literal> please see
<xref linkend="dbdoclet.dom_stripesize" />.</para>
the parameter <literal>dom_stripesize</literal> in the LOD device.
The <literal>dom_stripesize</literal> can be set differently for each
MDT, if necessary. The default value of the parameter is 1MB and can
- be changed with <literal>lclt</literal> tool.</para>
+ be changed with <literal>lctl</literal> tool.</para>
<section><title>Get Command</title>
<para><screen>lctl get_param lod.*MDT<index>*.dom_stripesize
</screen></para>
<primary>dom</primary>
<secondary>disabledom</secondary>
</indexterm>Disable DoM</title>
- <para>When <literal>lclt set_param</literal> or
- <literal>lctl conf_param</literal> sets
- <literal>dom_stripesize</literal> to <literal>0</literal>, DoM
- file creation will be prohibited on the selected server.</para>
+ <para>When <literal>lctl set_param</literal> or
+ <literal>lctl conf_param</literal> sets
+ <literal>dom_stripesize</literal> to <literal>0</literal>, DoM
+ component creation will be disabled on the selected server, and
+ any <emphasis>new</emphasis> layouts with a specified DoM component
+ will have that component removed from the file layout. Existing
+ files and layouts with DoM components on that MDT are not changed.
+ </para>
<note><para>DoM files can still be created in existing directories
- with the default DoM layout</para></note>
+ with a default DoM layout.</para></note>
</section>
</section>
</chapter>
+<!--
+ vim:expandtab:shiftwidth=2:tabstop=8:
+ -->
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