> > It'd be handy to have a mechanism where > applications could register for > > snapshot notifications. When one is about to > happen, they could be told > > about it and do what they need to do. Once all the > applications have > > acknowledged the snapshot alert--and/or after a > pre-set timeout--the file > > system would create the snapshot, and then notify > the applications that > > it's done. > > > Why would an application need to be notified? I think > you're under the > misconception that something happens when a ZFS > snapshot is taken. > NOTHING happens when a snapshot is taken (OK, well, > there is the > snapshot reference name created). Blocks aren't moved > around, we don't > copy anything, etc. Applications have no need to "do > anything" before a > snapshot it taken.
It would be nice to have applications request to be notified before a snapshot is taken, and when that have requested notification have acknowledged that they're ready, the snapshot would be taken; and then another notification sent that it was taken. Prior to indicating they were ready, the apps could have achieved a logically consistent on disk state. That would eliminate the need for (for example) separate database backups, if you could have a snapshot with the database on it in a consistent state. If I undertand correctly, _that's_ what the notification mechanism on Windows achieves. Of course, another approach would be for a zfs aware app to be keeping its storage on a dedicated filesystem or zvol, and itself control when snapshots were taken of that. As lightweight as zvols and filesystems are under zfs, having each app that needed such functionality have its own would be no big deal, and would even be handy insofar as each app could create snapshots on its own independent schedule. Either way, the apps would have to be aware of how to participate in coordinating their logical consistency on disk with the snapshot (or vice versa). > > Given that snapshots will probably be more popular > in the future (WAFL > > NFS/LUNs, ZFS, Btrfs, VMware disk image snapshots, > etc.), an agreed upon > > consensus would be handy (D-Bus? POSIX?). Hypothetically, one could hide some of the details with suitable libraries and infrastructure. -- This message posted from opensolaris.org _______________________________________________ zfs-discuss mailing list zfs-discuss@opensolaris.org http://mail.opensolaris.org/mailman/listinfo/zfs-discuss
