On Tue, May 27, 2014 at 7:25 AM, Mick <michaelkintz...@gmail.com> wrote: > > Also how big is each snapshot of / and why are these necessary on an hourly > basiszfs ?
Btrfs is COW, so snapshots only consume space as files change. If you have a read-only filesystem and snapshot it hourly the only space consumed by a snapshot will be a few metadata records. Snapshotting hourly would mostly be a convenience - in theory it should get you time-machine-like functionality just like hourly backups would, but with far less overhead and space use. In practice I stopped doing this, as btrfs can misbehave when you start getting a lot of snapshots accumulated (we're talking thousands). It probably doesn't help that I have VM images snapshotted (though these images have fairly low write volumes - the most active one does most of its writing to an nfs volume so only OS updates, logs, etc change the VM). When snapper would go to cleanup snapshots I'd get panics. I ended up having to write a script that deleted one snapshot every 30min over the course of days to clean up from that. Now I only manually snapshot periodically and I haven't had a problem with it. I suspect that as with many things btrfs-related that it will be worked out in time, though snapshots will always cause fragmentation as long as the filesystem does partial diffs. Rich
