On Tuesday 09 September 2008 04:37:09 Magnus Hagander wrote: > Greg Smith wrote: > > On Tue, 9 Sep 2008, Magnus Hagander wrote: > >> As long as your SAN guarantees an atomic snapshot of all your data > >> (which every SAN I've ever heard of guarantees if you're on a single > >> volume - entry level SANs often don't have the functionality to do > >> multi-volume atomic snapshots, though), you don't need to set up PITR > >> for simple backups > > > > It's all those ifs in there that leave me still recommending it. It's > > certainly possible to get a consistant snapshot with the right hardware > > and setup. What concerns me about recommending that without a long list > > of caveats is the kinds of corruption you'd get if all those conditions > > aren't perfect will of course not ever happen during testing. Murphy > > says that it will happen only when you find yourself really needing that > > snapshot to work one day. > > Well, I agree one should be careful, but I don't see the risk if you > just change all those ifs into a single one, which is "if all your data > *and* WAL is on the same SAN LUN". > > (heck, you don't need hardware to do it, you can do software snapshot > just fine - as long as you keep all your stuff on the same mountpoint > there as well) > That's pretty key, but there can be advantages to doing it using the pitr tools, and I think in most cases it would be hard to argue it isn't safer. As a counter example to theo's zfs based post, I posted a linux/lvm script that can work as the basis of a simple snapshot backup tool, available at http://people.planetpostgresql.org/xzilla/index.php?/archives/344-ossdb-snapshot,-lvm-database-snapshot-tool.html And yes, I prefer working on the zfs based one :-) -- Robert Treat http://www.omniti.com Database: Scalability: Consulting:
