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Re: Poatgresql database on more than one disk

From: Oliver Elphick <olly(at)lfix(dot)co(dot)uk>
To: Barry <bgraetz(at)bigpond(dot)net(dot)au>
Cc: pgsql-general(at)postgresql(dot)org
Subject: Re: Poatgresql database on more than one disk
Date: 2004-05-31 21:33:01
Message-ID: 1086039181.27765.175.camel@linda (view raw or flat)
Thread:
Lists: pgsql-general
On Wed, 2004-05-26 at 07:24, Barry wrote:
> Gaetano Mendola <mendola(at)bigfoot(dot)com> wrote in message news:<40B3E30C(dot)3020408(at)bigfoot(dot)com>...
> > Barry wrote:
...
> > > The test system I am using has a 2 channel raid card with a disk pack
> > > connected to each channel. The OS and Postgresql sits on its own internal 
> > > disk.
> > > 
> > > I would like to be able to use one disk pack for development and the
> > > other for end user testing / verification (the tape drive can only backup 
> > > one disk pack completely, not both)
> > > 
> > > I have spent a fair amount of time researching how I can run two
> > > databases, one on each disk pack but have not been able to find a
> > > solution.
> > > 
> > > Is it possible to configure Postgresql to have seperate databases
> > > on seperate disks ?
> > 
> > Not easily as will be with the Table Space feature that most probably
> > will be present on 7.5
> > 
> > With 7.3.6 what you can do is move your db and create a link in the
> > original place:
...
> Works like a treat, thank you for your time.

You need to be aware that certain files in the top level of ${PGDATA}
(pg_clog/* and pg_xlog) are essential for reading your data and apply
globally to all databases.  If pg_clog is destroyed, the database is
effectively destroyed too.  It's not clear that your arrangements will
get that copied to tape.

You may also not be aware that simply dumping the files to tape is not
necessarily going to give you a consistent or recoverable database
unless you stop the postmaster first.  pg_dumpall (or pg_dump for single
databases) can be used to dump transaction-consistent backups that
include every transaction completed at the time it begins to run; it is
also likely to take less space on tape than a dump of the raw database
files.  If you recover a set of files that have been copied to tape by
an external utility while the database is active, you may find that some
transactions at least are unrecoverable and at the worst tables may be
corrupted.  See the chapter on backups in the manual.

-- 
Oliver Elphick                                          olly(at)lfix(dot)co(dot)uk
Isle of Wight                              http://www.lfix.co.uk/oliver
GPG: 1024D/A54310EA  92C8 39E7 280E 3631 3F0E  1EC0 5664 7A2F A543 10EA
                 ========================================
     "How precious also are thy thoughts unto me, O God! how
      great is the sum of them! If I should count them, they
      are more in number than the sand; when I awake, I am 
      still with thee."    Psalms 139: 17,18 


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