On 05/28/2010 02:15 AM, íÁÒË ëÏÒÅÎÂÅÒÇ wrote: > The description was got from qemu manual. > > Please review, edit, apply adn update the website :) > Hmm, I don't think we should duplicate the qemu cache value descriptions in our docs, it might be a better idea to link to qemu docs with a note to check the hypervisor docs for meaning of the different values. > 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> I know this 'since' piece is from the existing docs, but it's not really correct: it only applies to the <driver> tag in general. We should have a separate 'since 0.6.0' for the cache attribute. - Cole -- libvir-list mailing list libvir-list@xxxxxxxxxx https://www.redhat.com/mailman/listinfo/libvir-list