File system snapshots for multiple file systems

Right now it isn't possible to use file system snapshots a reliable
backup if you are using multiple file systems for tablespaces because
most systems don't allow the simultaneous snapshoting of multiple file
system. Our documentation mentions this:

If your database is spread across multiple file systems, there might not
be any way to obtain exactly-simultaneous frozen snapshots of all the
volumes. For example, if your data files and WAL log are on different
disks, or if tablespaces are on different file systems, it might not be
possible to use snapshot backup because the snapshots must be
simultaneous. Read your file system documentation very carefully before
trusting to the consistent-snapshot technique in such situations. The
safest approach is to shut down the database server for long enough to
establish all the frozen snapshots.

However, it occurred to me that if someone turned on continuous arciving
during the file system snapshots, then you could use PITR to recover
from file system snapshots that were not simultaneous.

Should this be documented?

--
Bruce Momjian <bruce(at)momjian(dot)us> http://momjian.us
EnterpriseDB http://enterprisedb.com

+ If your life is a hard drive, Christ can be your backup. +