Re: RAID0 and pg_xlog

On Fri, 2005-09-09 at 18:16, Jim C. Nasby wrote:
> On Fri, Sep 09, 2005 at 09:43:56AM -0500, Scott Marlowe wrote:
> > On Wed, 2005-09-07 at 16:15, Jim C. Nasby wrote:
> > > On Wed, Sep 07, 2005 at 01:02:18PM -0500, Scott Marlowe wrote:
> > > > On Wed, 2005-09-07 at 12:40, Jim C. Nasby wrote:
> > > > > On Wed, Sep 07, 2005 at 12:47:43PM -0700, Qingqing Zhuo wrote:
> > > > > > Xlog will be the only believable data if your system crashed. So it is a dangerous practice to put xlog stuff in RAID0.
> > > > >
> > > > > No more or less so than putting your main database on RAID0. If any
> > > > > drive fails, you lose everything.
> > > >
> > > > Sounds like a good place to have replication.
> > >
> > > If you used syncronous replication, maybe. Otherwise failure of any
> > > drive means you just lost data. And remember that the more drives you
> > > have in your array the more likely you'll have a failure in a given
> > > time period.
> > >
> > > Basically, if you can afford to setup replication on 2 machines with
> > > RAID0 you can afford to setup RAID10 on one machine, which will usually
> > > be a better bet.
> >
> > Yeah, I was thinking pgpool here.
>
> pgpool is a connection pool; it has (almost) nothing to do with
> replication. It certainly doesn't work to provide any kind of data
> security on a RAID0 setup.
>
> I'm not arguing against anything people have suggested, only pointing
> out that if you're using RAID0 your data is not safe against a drive
> failure, except possible using pgcluster (some would argue that
> statement-based replication isn't as reliable as log-based).

Um. No. It has a synchronous replication mode, which I've used, and it
works quite well.

Look it up, it's pretty cool. Writes to both pg machines synchronously,
reads from them load balanced. Of course, there are some limits imposed
by this methodology, re: things like random() and such.

Now, if you're arguing against statement based replication, that I can
understand. but pgpool can definitely do two box sync replication.