Re: best config

On Feb 6, 2013, at 9:55 AM, Roberto Scattini <roberto(dot)scattini(at)gmail(dot)com> wrote:

>
> hi steven,
>
> > we have two new dell poweredge r720. based on recommendations from this list we have configued the five disks in raid10 + 1 hot spare.
>
> You might mention a bit more about how your drives are configured. 5 drives in a RAID1+0 sounds odd to me.
>
>
> i mean, 4 disks in raid10, plus one disk as hot spare.
>
> also, wasn't this list where recommended this setup, was in debian-user.
>

That makes a lot more sense. Nothing wrong with that setup :-)

> >
> > now we are looking for advice in the postgres installation for our setup.
> >
> > we have two databases. one for a lot of small apps and one for one big app with a lot of data and a lot of usage.
> > we want to use streaming replication to have a functional copy of databases in a failure.
> >
> > one of the ideas is to have one database running on each server, and then have another instance of the other database running in streaming replication (i mean, crossed replications).
> >
> > the other idea is to have both databases running in one server and backup everything in the other with streaming replication.
> >
> > which alternative would you use?
>
> I would not introduce the complexity of having each server be master for half of the data unless you can show that this improves some metric you care a lot about. Any failure or maintenance event will revert you back to the common configuration -- back to having both masters on one system -- until you do another promotion back to the "cross wired" setup. Extra work without a proposed gain.
>
> Plus then you can get away with half as many Postgres installs to maintain.
>
> ok. we thought in this crossed-replication config because one heavy query in one of the databases wouldnt affect the performance of the other.

Both of your servers need to be powerful enough to handle the whole load, otherwise your replication setup will not continue to function acceptably when one of the servers is offline due to a crash or maintenance.

I don't think there is anything necessarily wrong with your proposal, I am just pointing out that simplicity is better than complexity unless you can prove (say, in a test environment) that your application actually performs "better enough to justify the administrative cost" with this cross-wired setup.