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