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 notbe any way to obtain exactly-simultaneous
frozensnapshots of all thevolumes. For example, if your data files and WAL log are on differentdisks, or if tablespaces
areon different file systems, it might not bepossible to use snapshot backup because the snapshots must besimultaneous.
Readyour file system documentation very carefully beforetrusting to the consistent-snapshot technique in such
situations.Thesafest approach is to shut down the database server for long enough toestablish 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@momjian.us>        http://momjian.us EnterpriseDB
http://enterprisedb.com
 + If your life is a hard drive, Christ can be your backup. +