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Re: Peformance Tuning Opterons/ Hard Disk Layout

From: John Arbash Meinel <john(at)arbash-meinel(dot)com>
To: John Allgood <john(at)turbocorp(dot)com>
Cc: pgsql-performance(at)postgresql(dot)org
Subject: Re: Peformance Tuning Opterons/ Hard Disk Layout
Date: 2005-02-23 20:24:57
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Lists: pgsql-performance
John Allgood wrote:

> This some good info. The type of attached storage is a Kingston 14 bay
> Fibre Channel Infostation. I have 14 36GB 15,000 RPM drives. I think
> the way it is being explained that I should build a mirror with two
> disk for the pg_xlog and the striping and mirroring the rest and put
> all my databases into one cluster. Also I might mention that I am
> running clustering using Redhat Clustering Suite.

So are these 14-disks supposed to be shared across all of your 9 databases?
It seems to me that you have a few architectural issues here.

First, you can't really have 2 masters writing to the same disk array.
I'm not sure if Redhat Clustering gets around this. But second is that
you can't run 2 postgres engines on the same database. Postgres doesn't
support a clustered setup. There are too many issues with concurancy and
keeping everyone in sync.

Since you seem to be okay with having a bunch of smaller localized
databases, which update a master database 1/day, I would think you would
want hardware to go something like this.

1 master server, at least dual opteron with access to lots of disks
(likely the whole 14 if you can get away with it). Put 2 as a RAID1 for
the OS, 4 as a RAID10 for pg_xlog, and then the other 8 as RAID10 for
the rest of the database.

8-9 other servers, these don't need to be as powerful, since they are
local domains. Probably a 4-disk RAID10 for the OS and pg_xlog is plenty
good, and whatever extra disks you can get for the local database.

The master database holds all information for all domains, but the other
databases only hold whatever is the local information. Every night your
script sequences through the domain databases one-by-one, updating the
master database, and synchronizing whatever data is necesary back to the
local domain. I would guess that this script could actually just
continually run, going to each local db in turn, but you may want
nighttime only updating depending on what kind of load they have.


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