Ross Walker writes: > On Aug 4, 2010, at 9:20 AM, Roch <roch.bourbonn...@sun.com> wrote: > > > > > > > Ross Asks: > > So on that note, ZFS should disable the disks' write cache, > > not enable them despite ZFS's COW properties because it > > should be resilient. > > > > No, because ZFS builds resiliency on top of unreliable parts. it's able to > > deal > > with contained failures (lost state) of the disk write cache. > > > > It can then export LUNS that have WC enabled or > > disabled. But if we enable the WC on the exported LUNS, then > > the consumer of these LUNS must be able to say the same. > > The discussion at that level then needs to focus on failure groups. > > > > > > Ross also Said : > > I asked this question earlier, but got no answer: while an > > iSCSI target is presented WCE does it respect the flush > > command? > > > > Yes. I would like to say "obviously" but it's been anything > > but. > > Sorry to probe further, but can you expand on but... > > Just if we had a bunch of zvols exported via iSCSI to another Solaris > box which used them to form another zpool and had WCE turned on would > it be reliable? >
Nope. That's because all the iSCSI are in the same fault domain as they share a unified back-end cache. What works, in principle, is mirroring SCSI channels hosted on different storage controllers (or N SCSI channels on N controller in a raid group). Which is why keeping the WC set to the default, is really better in general. -r > -Ross > _______________________________________________ zfs-discuss mailing list zfs-discuss@opensolaris.org http://mail.opensolaris.org/mailman/listinfo/zfs-discuss
