From: Craig James <craig_james@emolecules.com>
To: Matthew <matthew@flymine.org>
Cc: pgsql-performance <pgsql-performance@postgresql.org>
Subject: Re: How to allocate 8 disks
Date: Mon, 03 Mar 2008 06:53:48 -0800
Message-ID: <47CC10FC.4090605@emolecules.com> (raw)
In-Reply-To: <Pine.LNX.4.64.0803031206340.20402@aragorn.flymine.org>
References: <1204285894.11773.33.camel@franck-gusty>
<dcc563d10802290613v482f52dr43ea95b52886de31@mail.gmail.com>
<1204296705.11773.51.camel@franck-gusty>
<Pine.GSO.4.64.0802291019570.28452@westnet.com>
<47C88826.4040209@paradise.net.nz>
<47C99B3E.4010606@emolecules.com>
<20080301130347.0832b323@commandprompt.com>
<47C9D05C.3040908@emolecules.com>
<Pine.LNX.4.64.0803031206340.20402@aragorn.flymine.org>
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
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To: pgsql-performance@postgresql.org
Cc: craig_james@emolecules.com, matthew@flymine.org
Subject: Re: How to allocate 8 disks
In-Reply-To: <47CC10FC.4090605@emolecules.com>
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