<domainsnapshot>
  <name>my snap name</name>
  <description>!@#$%^</description>
  <disks>
    <disk name='hdd' snapshot='external'>
      <source file='/path/to/new'/>
      <driver type='qcow2'>
        <metadata_cache>
          <max_size unit='bytes'>1234</max_size>
          </metadata_cache>
      </driver>
    </disk>
  </disks>
</domainsnapshot>