Hi, I am trying to benchmark disk I/O performance on VM running with "-snapshot" option enabled. In order to do that I specify cache=none in the -drive parameter (yes I am running qemu-kvm at command line0. The problem is that if I use this option kvm seems to ignore the cache=none directive and I get weird output from iozone (I/O values are better than on the real machine, indicating that caching is enabled). The same command line, without "-snapshot" gives a correct output.

Has anyone a clue about that? I succeeded in disabling cache in the past (with -snapshot enabled), but apparently this is not working anymore and I can't explain why.

If this can help, here is the command line I am using:

/usr/libexec/qemu-kvm -m 2048 -smp 1 -name test-1 \ -boot c -drive file=/var/lib/libvirt/images/test-1.img,if=virtio,index=0,boot=on,cache=none \ -net nic,macaddr=54:52:00:37:a9:eb,model=virtio -net tap \ -vnc 127.0.0.1:10 -k en-us -snapshot &

the host is running centos5 and all latest updates are applied.

Cheers,

Andrea