<disk type='network' device='disk'>
      <driver name='qemu' type='rbd'/>
      <auth username='admin'>
        <secret type='ceph' uuid='3d5a5fe8-af8a-8739-f90f-ac54f21e1711'/>
      </auth>
      <source protocol='rbd' name='rbd/gw4'/>
      <target dev='vda' bus='virtio'/>
      <alias name='virtio-disk0'/>
      <address type='pci' domain='0x0000' bus='0x00' slot='0x04' function='0x0'/>
    </disk>