<listitem>
<para><xref linkend="lustremaint.setMDTReadonly"/></para>
</listitem>
+ <listitem>
+ <para><xref linkend="lustremaint.tunefallocate"/></para>
+ </listitem>
</itemizedlist>
<section xml:id="lustremaint.inactiveOST">
<title>
mds# lctl set_param mdt.fs-MDT0000.readonly=0
mdt.fs-MDT0000.readonly=0</screen>
</section>
+ <section xml:id="lustremaint.tunefallocate" condition="l2E">
+ <title><indexterm><primary>maintenance</primary>
+ <secondary>Tune fallocate</secondary></indexterm>
+ Tune Fallocate for ldiskfs</title>
+ <para>This section shows how to tune/enable/disable fallocate for
+ ldiskfs OSTs.</para>
+ <para>The default <literal>mode=0</literal> is the standard
+ "allocate unwritten extents" behavior used by ext4. This is by far the
+ fastest for space allocation, but requires the unwritten extents to be
+ split and/or zeroed when they are overwritten.</para>
+ <para> The OST fallocate <literal>mode=1</literal> can also be set to use
+ "zeroed extents", which may be handled by "WRITE SAME", "TRIM zeroes data",
+ or other low-level functionality in the underlying block device.</para>
+ <para><literal>mode=-1</literal> completely disables fallocate.</para>
+ <para>Example: To completely disable fallocate</para>
+ <screen>lctl set_param osd-ldiskfs.*.fallocate_zero_blocks=-1</screen>
+ <para>Example: To enable fallocate to use 'zeroed extents'</para>
+ <screen>lctl set_param osd-ldiskfs.*.fallocate_zero_blocks=1</screen>
+ </section>
</chapter>
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