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Re: questions about disk configurations

From: Josh Berkus <josh(at)agliodbs(dot)com>
To: depesz(at)depesz(dot)pl, pgsql-performance(at)postgresql(dot)org
Subject: Re: questions about disk configurations
Date: 2002-12-09 19:53:03
Message-ID: 200212091153.03762.josh@agliodbs.com (view raw or flat)
Thread:
Lists: pgsql-performance
Depesz,

> i have a question about best harddisk configuration for postgresql
> performance.
> of course i know that:
> - scsi is better than ide
> - 2 disks are better than 1
> - 3 disks are better than 2
> 
> i know that with 3 disks one should move xlog to one drive, index files
> to second and tables to third.
> that's clear.

Er, no, it's not.  In fact, for a 3-disk config, I reccommend:

Disk 1: OS, swap, system logs
Disk 2: Data + Indexes
Disk 3: Transaction Log

> but:
> will making software raid on this discs provide performance increase or
> decrease?

Hardware RAID can improve *read* performance, particilarly RAIDs 1, 01, and 
10.  For writing, the best you can do is having it not inhibit performance.   
The general testament is that *software* RAID does not improve things at all; 
actually, the best that can be said for Linux Software RAID 1 is that it does 
not harm performance much.

> i'd like to know what are the options to store all this information
> (xlog, indices and tables). what configurations are best, what medium
> and what should be avoided at all cost.

Ask specific questions.  If you want the full performance tutorial, you'd have 
to pay a steep fee for 1-3 days of training.

-- 
-Josh Berkus
 Aglio Database Solutions
 San Francisco


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