See discussion in bug #525890 We should backport: http://git.kernel.org/?p=linux/kernel/git/torvalds/linux-2.6.git;a=commitdiff;h=f1b0ef0626 virtio_blk: add support for cache flush Recent qemu has added a VIRTIO_BLK_F_FLUSH flag to advertise that the virtual disk has a volatile write cache that needs to be flushed. In case we see this feature implement tell the Linux block layer about the fact and use the new VIRTIO_BLK_T_FLUSH to flush the cache when required. This allows for an correct and simple implementation of write barriers. This mail from Christoph is a good writeup on the background: http://www.mail-archive.com/kvm@vger.kernel.org/msg21559.html We should get this into F-12 GA even if qemu doesn't yet support it in F-12 so that F-12 guest installer kernels have this feature.
This has been added to the F-12 kernel and should be available in the next kernel tagged.