Message-ID: <432F8F1B.7030901@arbash-meinel.com>
Date: Tue, 20 Sep 2005 00:24:59 -0400
From: John A Meinel <john@arbash-meinel.com>
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To: "bm\\mbn" <miki@canaan.co.il>
Cc: pgsql-performance@postgresql.org
Subject: Re: RAID Stripe size
References: <1126871503.157442.314670@g49g2000cwa.googlegroups.com>
In-Reply-To: <1126871503.157442.314670@g49g2000cwa.googlegroups.com>
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bm\mbn wrote:
> Hi Everyone
>
> The machine is IBM x345 with ServeRAID 6i 128mb cache and 6 SCSI 15k
> disks.
>
> 2 disks are in RAID1 and hold the OS, SWAP & pg_xlog
> 4 disks are in RAID10 and hold the Cluster itself.
>
> the DB will have two major tables 1 with 10 million rows and one with
> 100 million rows.
> All the activities against this tables will be SELECT.

What type of SELECTs will you be doing? Mostly sequential reads of a
bunch of data, or indexed lookups of random pieces?

>
> Currently the strip size is 8k. I read in many place this is a poor
> setting.

From what I've heard of RAID, if you are doing large sequential
transfers, larger stripe sizes (128k, 256k) generally perform better.
For postgres, though, when you are writing, having the stripe size be
around the same size as your page size (8k) could be advantageous, as
when postgres reads a page, it only reads a single stripe. So if it were
reading a series of pages, each one would come from a different disk.

I may be wrong about that, though.

John
=:->

>
> Am i right ?


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