In the KVM case define your backing store as non-cached:
<disk type='block' device='disk'> <driver name='qemu' type='raw' cache='none'/> <source dev='/dev/XXX'/> <target dev='vda' bus='virtio'/> </disk>
In the KVM case define your backing store as non-cached:
<disk type='block' device='disk'>
<driver name='qemu' type='raw' cache='none'/>
<source dev='/dev/XXX'/>
<target dev='vda' bus='virtio'/>
</disk>