Attached disk using:

<disk type='file' device='disk'>
                <driver name='qemu' type='raw'/>
                <source file='/opt/recontext/diskimages/5ZlbCJ.iso'/>
                <target dev='sda' bus='usb'/>
              </disk>

---

dumpxml shows:

<domain type='kvm' id='107'>
  <name>debian_test</name>
  <uuid>4736855f-2eba-9c58-e766-df27bc38bd5b</uuid>
  <memory>524288</memory>
  <currentMemory>524288</currentMemory>
  <vcpu>1</vcpu>
  <os>
    <type arch='x86_64' machine='pc-1.0'>hvm</type>
    <boot dev='hd'/>
  </os>
  <features>
    <acpi/>
    <apic/>
    <pae/>
  </features>
  <clock offset='utc'/>
  <on_poweroff>destroy</on_poweroff>
  <on_reboot>restart</on_reboot>
  <on_crash>restart</on_crash>
  <devices>
    <emulator>/usr/bin/kvm</emulator>
    <disk type='file' device='disk'>
      <driver name='qemu' type='raw'/>
      <source file='/opt/recontext/diskimages/debian_squeeze.img'/>
      <target dev='vda' bus='virtio'/>
      <alias name='virtio-disk0'/>
      <address type='pci' domain='0x0000' bus='0x00' slot='0x04' function='0x0'/>
    </disk>
    <disk type='file' device='disk'>
      <driver name='qemu' type='raw'/>
      <source file='/opt/recontext/diskimages/5ZlbCJ.iso'/>
      <target dev='sda' bus='usb'/>
      <alias name='usb-disk0'/>
    </disk>
    <interface type='bridge'>
      <mac address='00:03:0a:00:0a:01'/>
      <source bridge='eth0'/>
      <target dev='vnet0'/>
      <model type='virtio'/>
      <alias name='net0'/>
      <address type='pci' domain='0x0000' bus='0x00' slot='0x03' function='0x0'/>
    </interface>
    <serial type='pty'>
      <source path='/dev/pts/9'/>
      <target port='0'/>
      <alias name='serial0'/>
    </serial>
    <console type='pty' tty='/dev/pts/9'>
      <source path='/dev/pts/9'/>
      <target type='serial' port='0'/>
      <alias name='serial0'/>
    </console>
    <input type='tablet' bus='usb'>
      <alias name='input0'/>
    </input>
    <input type='mouse' bus='ps2'/>
    <graphics type='vnc' port='5900' autoport='yes'/>
    <video>
      <model type='cirrus' vram='9216' heads='1'/>
      <alias name='video0'/>
      <address type='pci' domain='0x0000' bus='0x00' slot='0x02' function='0x0'/>
    </video>
    <memballoon model='virtio'>
      <alias name='balloon0'/>
      <address type='pci' domain='0x0000' bus='0x00' slot='0x05' function='0x0'/>
    </memballoon>
  </devices>
</domain>

----


virsh migrate debian_test qemu://testgrid8/system                                                                                                        
error: operation failed: migration job: is not active


----

virsh dominfo debian_test                                                                                                                              1 
Id:             107
Name:           debian_test
UUID:           4736855f-2eba-9c58-e766-df27bc38bd5b
OS Type:        hvm
State:          running
CPU(s):         1
CPU time:       19.7s
Max memory:     524288 kB
Used memory:    524288 kB
Persistent:     yes
Autostart:      disable
Managed save:   no


-----

virsh version                                                                                                                                            
Compiled against library: libvir 0.9.4
Using library: libvir 0.9.4
Using API: QEMU 0.9.4
Running hypervisor: QEMU 1.0.50

------

libvirt.log at source:

15:15:09.161: 6457: info : brProbeVnetHdr:442 : Enabling IFF_VNET_HDR
15:15:09.164: 6457: warning : qemuDomainObjTaint:1091 : Domain id=107 name='debian_test' uuid=4736855f-2eba-9c58-e766-df27bc38bd5b is tainted: high-privileges
15:15:09.165: 6457: info : virSecurityDACSetOwnership:99 : Setting DAC user and group on '/opt/recontext/diskimages/debian_squeeze.img' to '0:0'
15:15:09.374: 6455: info : virSecurityDACSetOwnership:99 : Setting DAC user and group on '/opt/recontext/diskimages/5ZlbCJ.iso' to '0:0'
15:16:05.325: 6457: error : qemuMigrationUpdateJobStatus:781 : operation failed: migration job: is not active
15:16:05.380: 6456: info : virSecurityDACRestoreSecurityFileLabel:139 : Restoring DAC user and group on '/opt/recontext/diskimages/5ZlbCJ.iso'
15:16:05.380: 6456: info : virSecurityDACSetOwnership:99 : Setting DAC user and group on '/opt/recontext/diskimages/5ZlbCJ.iso' to '0:0'
15:16:05.584: 6458: error : qemuMigrationJobIsActive:2875 : Requested operation is not valid: domain 'debian_test' is not being migrated