On Fri, Feb 13, 2009 at 02:00:28PM -0600, Nicolas Williams wrote: > Ordering matters for atomic operations, and filesystems are full of > those.
Also, note that ignoring barriers is effectively as bad as dropping writes if there's any chance that some writes will never hit the disk because of, say, power failures. Imagine 100 txgs, but some writes from the first txg never hitting the disk because the drive keeps them in the cache without flushing them for too long, then you pull out the disk, or power fails -- in that case not even fallback to older txgs will help you, there'd be nothing that ZFS could do to help you. Of course, presumably even with most lousy drives you'd still have to be quite unlucky to lose writes written more than N txgs ago, for some value of N. But the point stands; what you lose will be a matter of chance (and it could well be whole datasets) given the kinds of devices we've been discussing. Nico -- _______________________________________________ zfs-discuss mailing list zfs-discuss@opensolaris.org http://mail.opensolaris.org/mailman/listinfo/zfs-discuss
