+ <devices>
+ <emulator>/usr/libexec/qemu-kvm</emulator>
+ <disk type='file' device='disk'>
-+ <driver name='qemu' type='qcow2'/>
++ <driver name='qemu' type='qcow2' cache='writeback'/>
+ <target dev='vda' bus='virtio'/>
+ </disk>
+ <disk type='block' device='cdrom'>