N/A wrote:
Chris,
The NAS is a Network Appliance 920c. I understand that an individual file
while be "intact" during a snap, (not sure I believe it, but that's what I'm
told).
Depending on the way that data is journalled, this may be a possibility
(istr XFS is able to do this).
The NAS may be able to monitor the state of an individual file and
not "snap" it if it is on an "open" state or has a pending write, or some
such, but as the NAS has no knowledge of groups of files that need to exist
in a known state, (it deals on the file level), it cannot guarantee a
consistent state across a group of files.
That is a serious concern. Every table in PostgreSQL consists of at
least one physical file. Transactions may touch several of these
files. While it is not impossible to solve this problem (as I
mentioned, I think XFS has this capability), it is hardly trivial or
something you would normally expect.
Also I wonder what the impact of several Postmasters trying to access
data over NFS would be.
Best Wishes,
Chris Travers
