Description of problem:
VM is stopped due to disk write error when boot guest from nfs with qcow2 image format  

Version-Release number of selected component (if applicable):


How reproducible:
100%

Steps to Reproduce:
1. mount nfs
2. boot guest from nfs with werror=stop
/usr/libexec/qemu-kvm  -M rhel5.5.0 -m 2048 -smp 2 -name win7x86-Hel5-Del5 -uuid b51e36f4-ea66-42fa-bd9b-f92f4483bc13 -no-kvm-pit-reinjection -monitor stdio -localtime -boot c -drive file=./win08R2-Hel5-Del5.img,if=virtio,index=0,boot=on,werror=stop -net nic,macaddr=54:52:00:32:a5:12,vlan=0,model=virtio -net tap,script=/usr/local/staf/test/RHEV/kvm-new/autotest/client/tests/kvm/scripts/qemu-ifup-switch,vlan=0,ifname=vnet0 -serial pty -parallel none -usb -usbdevice tablet -vnc :1 -k en-us
3. (qemu) info status 
VM status: paused
(qemu) info stop-reason 
VM is stopped due to disk write error: ide0-hd0: Cannot allocate memory

  
Actual results:


Expected results:


Additional info:
1. guest can boot successfully in local machine
2. guest can boot successfully on nfs with raw format.
3.  free -m
            total       used       free     shared    buffers     cached
 Mem:          7854        137       7717          0          3         39
 -/+ buffers/cache:         93       7760
 Swap:         9855          0