> > 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 > omething 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 > ype of even faster nonvolatile storage.
Both frames are FC connected with Flash devices in the frame. Latencies are additive, so there is benefit to a logging device. The cluster is a standard HA cluster about 10km apart with identical storage in both locations, mirrored using ZFS. Think about the potential problems if I don't mirror the log devices across the WAN. > > _______________________________________________ > zfs-discuss mailing list > zfs-discuss@opensolaris.org > http://mail.opensolaris.org/mailman/listinfo/zfs-discu > ss > -- This message posted from opensolaris.org _______________________________________________ zfs-discuss mailing list zfs-discuss@opensolaris.org http://mail.opensolaris.org/mailman/listinfo/zfs-discuss
