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From: =?iso-8859-1?Q?Ragnar_Kj=F8rstad?= <lvm@ragnark.vestdata.no>
Subject: Re: [linux-lvm] PostgreSQL and file system level backup
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In-Reply-To: <2D92FEBFD3BE1346A6C397223A8DD3FC09208C@THOR.goeci.com>; from murthy.kambhampaty@goeci.com on Fri, Nov 15, 2002 at 04:25:49PM -0500
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Date: Fri Nov 15 20:11:02 2002
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Cc: Postgres Admin List <pgsql-admin@postgresql.org>, "Linux-Xfs (E-mail)" <linux-xfs@oss.sgi.com>

On Fri, Nov 15, 2002 at 04:25:49PM -0500, Murthy Kambhampaty wrote:
> "Unless the postmaster is shut down meanwhile, you'll probably end up w=
ith a
> corrupt database.  The problem is that xfsdump does not give you an
> instantaneous snapshot of the filesystem state, so you will probably co=
llect
> inconsistent contents of the various files that make up the database."
>=20
> Which gives rise to my present question: given that LVM DOES give an
> instantaneous snapshot of the filesystem, would an xfsdump of an LVM
> snapshot of an XFS filesystem give usable backups?

Yes, it should.

Allthough, some of the postgresql-developers use the term "corrupt
database" of a database where the table-files are inconsistant. That's
generally _always_ the case when the server is running, as the latest
updates are only available in the database-log. That's also the case for
the LVM-snapshot.

This "inconsistancy" will be fixed by log-replay when you start the serve=
r
(after restore).

If you want to avoid it, you can:
- shut down databasee
- take snapshot
- start database
- backup from snapshot



There was a long thread on this subject on the postgresql-list a month
or two ago.




--=20
Ragnar Kj=F8rstad
Big Storage