On Fri, Feb 02, 2007 at 03:17:17PM -0500, Torrey McMahon wrote: > Nicolas Williams wrote: > >But a continuous zfs send/recv would be cool too. In fact, I think ZFS > >tightly integrated with SNDR wouldn't be that much different from a > >continuous zfs send/recv. > > Even better with snapshots, and scoreboarding, and synch vs asynch and > and and and .....
Right. I hadn't thought of that. A replication system that is well integrated with ZFS should have very similar properties whether designed as a journalling scheme or as a scoreboarding scheme. A continuous zfs send/recv as I imagine it would be like journalling while ZFS+SNDR would be more like scoreboarding. Unlike traditional journalling replication, a continuous ZFS send/recv scheme could deal with resource constraints by taking a snapshot and throttling replication until resources become available again. Replication throttling would mean losing some transaction history, but since we don't expose that right now, nothing would be lost. Scoreboarding (what SNDR does) should perform better in general, but in the case of COW filesystems and databases ISTM that it should be a wash unless it's properly integrated with the COW system, and that's what makes me think scoreboarding and journalling approach each other at the limit when integrated with ZFS. In general I would expect journalling to have better reliability semantics (since you always know exactly the last transaction that was successfully replicated). Nico -- _______________________________________________ zfs-discuss mailing list zfs-discuss@opensolaris.org http://mail.opensolaris.org/mailman/listinfo/zfs-discuss
