Add a FAQ entry for ZFS TRIM support.

svn path=/head/; revision=40660

en_US.ISO8859-1/books/faq/book.xml

@@ -4500,6 +4500,31 @@ C:\="DOS"</programlisting>
 	    </note>
 	  </answer>
 	</qandaentry>
+
+	<qandaentry>
+	  <question id="zfs-ssd-trim">
+	    <para>Does ZFS support TRIM for Solid State Drives?</para>
+	  </question>
+
+	  <answer>
+	    <para>ZFS TRIM support was added to &os;&nbsp;10-CURRENT
+	      with revision r<svnref>240868</svnref>.  ZFS TRIM
+	      support is not yet available on the -STABLE
+	      branches.</para>
+
+	    <para>ZFS TRIM is enabled by default, and can be turned
+	      off by adding this line to
+	      <filename>/etc/sysctl.conf</filename>:</para>
+
+	    <programlisting>vfs.zfs.trim_disable=1</programlisting>
+
+	    <note>
+	      <para>ZFS TRIM may not work with all configurations,
+		such as a ZFS filesystem on a GELI-backed
+		device.</para>
+	    </note>
+	  </answer>
+	</qandaentry>
       </qandaset>
     </sect1>
   </chapter>