On Fri, Mar 21, 2008 at 09:55:38AM -0700, Tim Wood wrote: > Hi, > I'm interested in the overhead of making, cloning, and destroying snapshots. > It sounds like the cost for all of these is low, but how low?? > > For example, could I make snapshots of a system every 5 seconds? > every second? More often than that?
I'm pretty sure that you'll have to write a checkpoint for any snapshot. That's normally delayed to every 5 seconds or so for performance. So snapshotting faster seems likely to slow something down. > I'm primarily interested in the time/computation cost of doing these > operations, but also about the storage cost. > > Would it be plausible to do something like take snapshots twice a > second on a disk with a low/moderate load? If I only cared about the > last 60 seconds worth of snapshots, would that make things much slower > since I'd constantly be eliminating old checkpoints? The deletions would probably slow things down a bit, but I don't have a good idea how much. The load of the system is almost certain to be the limit on how many snaps you can do. I did a little test. On an otherwise idle VMware host, with ZFS to a non-allocated VMware disk, I was able to create 1000 snapshots in 80 seconds. So twice a second should be doable with some load, especially with reasonable hardware. (The corresponding destruction of the snapshots took a hair over 60 seconds). I added in a very low level of I/O with some writes every second and it didn't affect the speed appreciably. I'm assuming you'll need to test with your load to see how it works. -- Darren Dunham [EMAIL PROTECTED] Senior Technical Consultant TAOS http://www.taos.com/ Got some Dr Pepper? San Francisco, CA bay area < This line left intentionally blank to confuse you. > _______________________________________________ zfs-discuss mailing list zfs-discuss@opensolaris.org http://mail.opensolaris.org/mailman/listinfo/zfs-discuss
