[libvirt-users] Need help using libvirt with qcow2 delta and base images

Hi, I am having trouble configuring a virtual machine domain and its corresponding xml definition to use a qcow2 delta disk. The delta disk is backed by a qcow2 base disk. I am able to successfully start the guest OS with the delta disk at the command line using qemu. However, I am not able to start the guest OS using the libvirt tools including virsh and virt-manager. I am hoping that someone knows how to configure a virtual machine domain that works with a qcow2 delta disk, and have it managed by the virt-family tools. First, I create a delta and base disk from a raw image file with the following commands: qemu-img convert ubuntu910server64.img -O qcow2 ubuntu910server64_base.qcow2 qemu-img create -b ubuntu910server64_base.qcow2 -f qcow2 ubuntu910server64_delta.qcow2 Then, I can successfully start the guest OS on the command line with qemu-system-x86_64 -m 256 -hda ubuntu910server64_delta.qcow2 My attempt to modify the virtual machine domain configuration fails. Here are my steps: -- Edit the configuration # virsh edit ubuntu910server64 -- Replace some lines <disk type='file' device='disk'> - <source file='/var/lib/libvirt/images/ubuntu910server64.img'/> - <target dev='vda' bus='virtio'/> + <source file='/var/lib/libvirt/images/ubuntu910server64_delta.qcow2'/> + <target dev='hda' bus='ide'/> </disk> -- Attempt to start the machine # virsh start ubuntu910server64 Connecting to uri: qemu:///system error: Failed to start domain ubuntu910server64 error: internal error unable to start guest: qemu: could not open disk image /var/lib/libvirt/images/ubuntu910server64_delta.qcow2 If I have posted this to the wrong forum, please direct me to the right location. Thanks! -dave