Re: Basic question on recovery and disk snapshotting

On Apr 27, 2013, at 10:40 AM, Yang Zhang wrote:

> My question really boils down to: if we're interested in using COW
> snapshotting (a common feature of modern filesystems and hosting
> environments), would we necessarily need to ensure the data and
> pg_xlog are on the same snapshotted volume? If not, how should we be
> taking the snapshots - should we be using pg_start_backup() and then
> taking the snapshot of one before the other? (What order?) What if
> we have tablespaces, do we take snapshots of those, followed by the
> cluster directory, followed by pg_xlog?

We do this, using xfs to take advantage of being able to freeze the filesystem. (Because we're also using software raid.) The process looks like:

1. pg_start_backup()
2. xfs_freeze both the data and xlog filesystems.
3. snapshot all volumes.
4. unfreeze
5. stop backup