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[libvirt] [patch] libvirt documentation - disk cache description



The description was got from qemu manual.

Please review, edit, apply adn update the website :)

-- 
Segmentation fault
diff -u docs/formatdomain.html.in docs.new/formatdomain.html.in
--- docs/formatdomain.html.in	2010-05-27 11:35:33.995122526 +0600
+++ docs.new/formatdomain.html.in	2010-05-27 13:36:27.362623268 +0600
@@ -517,10 +520,30 @@
       <dt><code>driver</code></dt>
       <dd>If the hypervisor supports multiple backend drivers, then the optional
         <code>driver</code> element allows them to be selected. The <code>name</code>
-        attribute is the primary backend driver name, while the optional <code>type</code>
-        attribute provides the sub-type. The optional <code>cache</code> attribute
+        attribute is the primary backend driver name (for example, "qemu"),
+        while the optional <code>type</code> attribute provides the sub-type.
+        For qemu, possible values are: "raw", "qcow", "qcow2", "vmdk" and some other.
+
+	<p>The optional <code>cache</code> attribute
         controls the cache mechanism, possible values are "default", "none",
-        "writethrough" and "writeback". <span class="since">Since 0.1.8</span>
+        "writethrough" and "writeback".</p>
+
+        <p>Writethrough caching means that the host
+        page cache will be used to read and write data but write notification will
+        be sent to the guest only when the data	has been reported as written by the
+        storage subsystem.</p>
+
+        <p>Writeback caching will report data writes as completed as soon as
+        the data is present in the host page cache.  This is safe as long as you trust your host.
+	If your host crashes or loses power, then the guest may experience data corruption.</p>
+
+	<p>The host page cache can be avoided entirely with <code>cache='none'</code>.
+	This will attempt to do disk IO directly to the guests memory.</p>
+
+	<p>As said in qemu-kvm-0.12.3 manual: Some block drivers perform badly with <code>cache='writethrough'</code>, most notably,
+	qcow2. If performance is more important than correctness, <code>cache='writeback'</code>
+	should be used with qcow2.</p>
+        <span class="since">Since 0.1.8</span>
       </dd>
       <dt><code>encryption</code></dt>
       <dd>If present, specifies how the volume is encrypted.  See

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