On 6/18/20 11:49 AM, Paul Förster wrote:
Hi Magnus,
On 18. Jun, 2020, at 16:19, Magnus Hagander <magnus@xxxxxxxxxxxx> wrote:
I don't know specifically about SnapCenter, but for snapshots in general, it does require backup mode *unless* all your data is on the same disk and you have an atomic snapshot across that disk (in theory it can be on different disk as well, as long as the snapshots in that case are atomic across *all* those disks, not just individually, but that is unusual).
according to what I know from our storage guys, Netapp does atomic snapshots for each volume. We have the database and its corresponding WAL files (pg_wal directory) on the same volume and the archived WALs (archive_command) on another. And the snapshots on those two volumes are not taken at the same time. Currently, the database is set to backup mode (using cron) and the storage guys have a window during which they can take the snapshots.
So the upthread suggestion of putting data and wal on different disk and snapshoting them at different times is *NOT* safe. Unless the reference to the directory for the logs means a directory where log files are copied out with archive_command, and it's actually the log archive (in which case it will work, but the recommendation is that the log archive should not be on the same machine).
as I said above, pg_wal is a directory in PGDATA at the default location and WALs are archived using the archive_command to a different volume. So I guess, we should be safe then.
But it's trivial to make pg_xlog a separate mount point.
--
Angular momentum makes the world go 'round.
