Re: Shared disk storage

On Tue, Sep 06, 2005 at 13:47:42 -0500,
"Jim C. Nasby" <jnasby(at)pervasive(dot)com> wrote:
> On Tue, Sep 06, 2005 at 10:13:33AM -0500, Bruno Wolff III wrote:
> > On Mon, Sep 05, 2005 at 12:20:24 +0300,
> > Peter Nixon <listuser(at)peternixon(dot)net> wrote:
> > > Hi List
> > >
> > > Does anyone have any comments, HOWTOs and experience running multiple
> > > Postgres servers with a shared disk (SAN) in a Hot standby configuration?
> > >
> > > Can someone please point me in the direction of any docs on this subject?
> >
> > Be sure to have some failsafe to prevent two servers from running at the
> > same time on the same data. If that ever happens your database will be hosed.
>
> I thought PostgreSQL already had such a safeguard? Or is it only against
> starting two backends against the same PGDATA on the same machine?

Yes, but it is more likely to have problems when there are two machines
involved. One is that the file may not be on the cross mounted file
system (on FC4 it is in /var/run) and even if it is on the cross mounted
file system, there is a good chance the lock file will appear to be stale
because the process id is for the other machine. I am not sure if there are
other gotchas, but you definitely want to be careful, since a mistake is
going to defeat the purpose of having the hot spares.