> From: zfs-discuss-boun...@opensolaris.org [mailto:zfs-discuss- > boun...@opensolaris.org] On Behalf Of John Hoogerdijk > > I'm building a campus cluster with identical storage in two locations > with ZFS mirrors spanning both storage frames. Data will be mirrored > using zfs. I'm looking for the best way to add log devices to this > campus cluster.
Either I'm crazy, or I completely miss what you're asking. You want to have one side of a mirror attached locally, and the other side of the mirror attached ... via iscsi or something ... across the WAN? Even if you have a really fast WAN (1Gb or so) your performance is going to be terrible, and I would be very concerned about reliability. What happens if a switch reboots or crashes? Then suddenly half of the mirror isn't available anymore (redundancy is degraded on all pairs) and ... Will it be a degraded mirror? Or will the system just hang, waiting for iscsi IO to timeout? When it comes back online, will it intelligently resilver only the parts which have changed since? Since the mirror is now broken, and local operations can happen faster than the WAN can carry them across, will the resilver ever complete, ever? I don't know. anyway, it just doesn't sound like a good idea to me. It sounds like something that was meant for a clustering filesystem of some kind, not particularly for ZFS. If you are adding log devices to this, I have a couple of things to say: The whole point of a log device is to accelerate sync writes, by providing nonvolatile storage which is faster than the primary storage. You're not going to get this if any part of the log device is at the other side of a WAN. So either add a mirror of log devices locally and not across the WAN, or don't do it at all. > I am considering building a separate mirrored zpool of Flash disk that > span the frames, then creating zvols to use as log devices for the > data zpool. Will this work? Any other suggestions? This also sounds nonsensical to me. If your primary pool devices are Flash, then there's no point to add separate log devices. Unless you have another type of even faster nonvolatile storage. _______________________________________________ zfs-discuss mailing list zfs-discuss@opensolaris.org http://mail.opensolaris.org/mailman/listinfo/zfs-discuss
