Message-ID: <47CC10FC.4090605@emolecules.com>
Date: Mon, 03 Mar 2008 06:53:48 -0800
From: Craig James <craig_james@emolecules.com>
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To: Matthew <matthew@flymine.org>
CC: pgsql-performance <pgsql-performance@postgresql.org>
Subject: Re: How to allocate 8 disks
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Matthew wrote:
> On Sat, 1 Mar 2008, Craig James wrote:
>> Right, I do understand that, but reliability is not a top priority in 
>> this system.  The database will be replicated, and can be reproduced 
>> from the raw data.
> 
> So what you're saying is:
> 
> 1. Reliability is not important.
> 2. There's zero write traffic once the database is set up.

Well, I actually didn't say either of those things, but I appreciate the feedback.  RAID 0 is an interesting suggestion, but given our constraints, it's not an option.  Reliability is important, but not as important as, say, a banking system.

And as far as zero write traffic, I don't know where that came from.  It's a "hitlist" based system, where complex search results are saved for the user in tables, and the write traffic can be quite high.

> If this is true, then RAID-0 is the way to go. I think Greg's options 
> are good. Either:
> 
> 2 discs RAID 1: OS
> 6 discs RAID 0: database + WAL
> 
> which is what we're using here (except with more discs), or:
> 
> 8 discs RAID 10: everything

Right now, an 8-disk RAID 10 is looking like the best choice.  The Dell Perc 6i has configurations that include a battery-backed cache, so performance should be quite good.

> However, if reliability *really* isn't an issue, and you can accept 
> reinstalling the system if you lose a disc, then there's a third option:
> 
> 8 discs RAID 0: Everything

I imagine the MTBF on a system like this would be < 1 year, which is out of the question, even with a backup system that can take over.  A failure completely wipes the system, OS and everything, so you're guaranteed that once or twice a year, you have to rebuild your system from the ground up.  I'd rather spend that time at the beach!

Craig