Why does a VM with Direct-LUN disk fail to start?

Issue

• After assigining direct LUN disk to a virtual machine, it fails to start with permission denied error.
• The virtual machines with direct LUN is not getting started.
• Logs from Red Hat Enterprise Virtualization Manager:

2012-12-27 13:49:27,586 ERROR [org.ovirt.engine.core.vdsbroker.VdsUpdateRunTimeInfo] (QuartzScheduler_Worker-9) Rerun vm d483e80f-a085-4d13-9ff8-0ca258f6244e. Called from vds rhev-h20

• Logs from Red Hat Enterprise Virtualization Hypervisor:

Thread-418094::DEBUG::2012-12-27 18:50:00,210::vm::607::vm.Vm::(_startUnderlyingVm) vmId=`d483e80f-a085-4d13-9ff8-0ca258f6244e`::_ongoingCreations released
Thread-418094::ERROR::2012-12-27 18:50:00,214::vm::631::vm.Vm::(_startUnderlyingVm) vmId=`d483e80f-a085-4d13-9ff8-0ca258f6244e`::The vm start process failed
Traceback (most recent call last):
  File "/usr/share/vdsm/vm.py", line 597, in _startUnderlyingVm
  File "/usr/share/vdsm/libvirtvm.py", line 1448, in _run
  File "/usr/lib64/python2.6/site-packages/vdsm/libvirtconnection.py", line 83, in wrapper
  File "/usr/lib64/python2.6/site-packages/libvirt.py", line 2489, in createXML
libvirtError: internal error process exited while connecting to monitor: qemu-kvm: -drive file=/dev/mapper/350002ac000540cd9,if=none,id=drive-virtio-disk0,format=raw,serial=,cache=none,werror=stop,rerror=stop,aio=native: could not open d
isk image /dev/mapper/350002ac000540cd9: Permission denied

Thread-418094::DEBUG::2012-12-27 18:50:00,216::vm::965::vm.Vm::(setDownStatus) vmId=`d483e80f-a085-4d13-9ff8-0ca258f6244e`::Changed state to Down: internal error process exited while connecting to monitor: qemu-kvm: -drive file=/dev/mapp
er/350002ac000540cd9,if=none,id=drive-virtio-disk0,format=raw,serial=,cache=none,werror=stop,rerror=stop,aio=native: could not open disk image /dev/mapper/350002ac000540cd9: Permission denied

Thread-418098::DEBUG::2012-12-27 18:50:02,093::BindingXMLRPC::894::vds::(wrapper) client [172.20.12.131]::call vmGetStats with ('d483e80f-a085-4d13-9ff8-0ca258f6244e',) {} flowID [59674ba0]
Thread-418098::DEBUG::2012-12-27 18:50:02,094::BindingXMLRPC::900::vds::(wrapper) return vmGetStats with {'status': {'message': 'Done', 'code': 0}, 'statsList': [{'status': 'Down', 'hash': '0', 'exitMessage': 'internal error process exit
ed while connecting to monitor: qemu-kvm: -drive file=/dev/mapper/350002ac000540cd9,if=none,id=drive-virtio-disk0,format=raw,serial=,cache=none,werror=stop,rerror=stop,aio=native: could not open disk image /dev/mapper/350002ac000540cd9: 
Permission denied\n', 'vmId': 'd483e80f-a085-4d13-9ff8-0ca258f6244e', 'timeOffset': '-18000', 'exitCode': 1}]}