Christopher Weimann <cweimann@k12hq.com> writes:
> You can do snapshots in FreeBSD 5.x with UFS2 as well but that (
> nor XFS snapshots ) will let you backup with the database server
> running. Just because you will get the file exactly as it was at
> a particular instant does not mean that the postmaster did not
> still have some some data that was not flushed to disk yet.
It *will* work, if you have an instantaneous filesystem snapshot
covering the entire $PGDATA directory tree (both data files and WAL).
Restarting the postmaster on the backup will result in a WAL replay
sequence, and at the end the data files will be consistent. If this
were not so, we'd not be crash-proof. The instantaneous snapshot
is exactly equivalent to the on-disk state at the moment of a kernel
crash or power failure, no?
regards, tom lane