On Fri, 2006-05-26 at 17:40, Bart Smaalders wrote: > Gregory Shaw wrote: > > I had a question to the group: > > In the different ZFS discussions in zfs-discuss, I've seen a > > recurring theme of disabling write cache on disks. I would think that > > the performance increase of using write cache would be an advantage, and > > that write cache should be enabled. > > Realistically, I can see only one situation where write cache would > > be an issue. If there is no way to flush the write cache, it would be > > possible for corruption to occur due to a power loss. > > There are two failure modes associated with disk write caches: > > 1) the disk write cache for performance reasons doesn't write back > data (to diff. blocks) to the platter in the order they were > received, so transactional ordering isn't maintained and > corruption can occur. >
That's a pretty nasty situation. I would think that behaviour would violate some SCSI out-of-order standard. > 2) writes to different can disks have different caching policies, so > transactions to files on different filesystems may not complete > correctly during a power failure. > I've always felt that drives should have a small battery for this purpose. However, what seems to make sense doesn't usually make it into products. > ZFS enables the write cache and flushes it when committing transaction > groups; this insures that all of a transaction group appears or does > not appear on disk. > Really? It enables cache on disabled devices? That's pretty cool, if so. > - Bart > > > > > -- > Bart Smaalders Solaris Kernel Performance > [EMAIL PROTECTED] http://blogs.sun.com/barts _______________________________________________ zfs-discuss mailing list zfs-discuss@opensolaris.org http://mail.opensolaris.org/mailman/listinfo/zfs-discuss
