On Mon, May 11, 2009 at 07:49:37PM +0300, Avi Kivity wrote: > Maybe we should add a fourth cache= mode then. But > cache=writeback+fsync doesn't correspond to any real world drive; in the > real world you're limited to power failures and a few megabytes of cache > (typically less), cache=writeback+fsync can lose hundreds of megabytes > due to power loss or software failure.
cache=writeback+fsync is exactly the same model as a normal writeback cache disk drive. (Well, almost as we currently don't use tag ordering but drain flushes as a Linux implementation detail, but the disks also support TCQ-based ordering). The cache size on disks is constantly growing, and if you lose cache it doesn't really matter how much you lose but what you lose. > Oh, and cache=writeback+fsync doesn't work on qcow2, unless we add fsync > after metadata updates. If you care about data integrity in case of crashes qcow2 doesn't work at all. -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
