Thread: Snapshot as Backup

Snapshot as Backup

From

"Ed Murphy"

Date:

13 January 2004, 16:16:18

Hello,

I'm using Red Hat Enterprise v2.1 and PostgreSQL v7.3.4. Our hardware setup includes a large Storage Area Network (SAN). The systems folks are going to utilize a snapshot type backup to backup the file system. This snapshot will include PGDATA and all the PostgreSQL files. My question is if I restore this snapshot will PostgreSQL work? I know if doing a typical file system backup of PostgreSQL I must first stop the postmaster or the backup will not produce a useable PostgreSQL system. Is it necessary to stop the postmaster for this snapshot backup also?

Thanks,

Ed Murphy

The University of Arizona

Re: Snapshot as Backup

From

"Matt Clark"

Date:

13 January 2004, 16:59:52

The consensus from previous discussions (search for 'LVM' in the archives) is essentially that it definitely *should* work, some people *do* use it successfully, but that you *must* test it thoroughly in your own setup under heavy write load before relying on it.

PG will believe it has 'crashed' when you start it from a restored snapshot, and PG is designed to recover perfectly well from crashes. If you stop the postmaster before the snapshot is taken then it will definitely work fine.

Matt

-----Original Message-----
From: pgsql-admin-owner@postgresql.org [mailto:pgsql-admin-owner@postgresql.org]On Behalf Of Ed Murphy
Sent: 13 January 2004 17:16
To: pgsql-admin@postgresql.org
Subject: [ADMIN] Snapshot as Backup

Hello,

I'm using Red Hat Enterprise v2.1 and PostgreSQL v7.3.4. Our hardware setup includes a large Storage Area Network (SAN). The systems folks are going to utilize a snapshot type backup to backup the file system. This snapshot will include PGDATA and all the PostgreSQL files. My question is if I restore this snapshot will PostgreSQL work? I know if doing a typical file system backup of PostgreSQL I must first stop the postmaster or the backup will not produce a useable PostgreSQL system. Is it necessary to stop the postmaster for this snapshot backup also?

Thanks,

Ed Murphy
The University of Arizona

Re: Snapshot as Backup

From

Sai Hertz And Control Systems

Date:

13 January 2004, 19:25:11

Dear Ed Murphy  ,

> and all the PostgreSQL files.  My question is if I restore this
> snapshot will PostgreSQL work?  I know if doing a typical file system
> backup of PostgreSQL I must first stop the postmaster or the backup
> will not produce a useable PostgreSQL system.  Is it necessary to stop
> the postmaster for this snapshot backup also?
>
Yes if the snapshot (filesystem) backup and restore is performed when
postmaster is NOT running  you can reproduce it.
I have done this with command
dump  <-- for file system backup
Filesystem ext3

Regards
Vishal Kashyap

Re: Snapshot as Backup

From

Jeff

Date:

16 January 2004, 13:52:30

On Wed, 14 Jan 2004 02:00:45 +0530
Sai Hertz And Control Systems <sank89@sancharnet.in> wrote:

>
> > and all the PostgreSQL files.  My question is if I restore this
> > snapshot will PostgreSQL work?  I know if doing a typical file
> > system backup of PostgreSQL I must first stop the postmaster or the
> > backup will not produce a useable PostgreSQL system.  Is it
> > necessary to stop the postmaster for this snapshot backup also?
> >

I've done testing on this. It works fine.
Just make sure you're doing a filesystem snapshot and not a "cp".
To PG it just looks like the power went out or some other failure.
It'll replay parts of its log and be on its merry way.  This is *much*
faster than using pg_dump / pg_restore, especially on huge db's.

If you are using xfs you may want to wrap the snapshot call with
xfs_freeze/unfreeze.

It may also be nice every once in a while to do a normal pg_dump..

--
Jeff Trout <jeff@jefftrout.com>
http://www.jefftrout.com/
http://www.stuarthamm.net/