Date: Fri, 2 Feb 2007 10:49:30 -0800 (PST)
From: Ben <bench@silentmedia.com>
To: Jeff Frost <jeff@frostconsultingllc.com>
cc: pgsql-performance@postgresql.org
Subject: Re: drive configuration for a new server
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	<Pine.LNX.4.64.0702021011540.4629@discord.home.frostconsultingllc.com>
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Thanks Jeff, this was exactly the kind of answer I was looking for.

On Fri, 2 Feb 2007, Jeff Frost wrote:

> On Thu, 1 Feb 2007, Ben wrote:
>
>> I'm looking to replace some old crusty hardware with some sparkling new 
>> hardware. In the process, I'm looking to move away from the previous 
>> mentality of having the Big Server for Everything to having a cluster of 
>> servers, each of which handles some discrete subset of data. But rackspace 
>> isn't inifinte, so I'm leaning towards cases that give me 8 drive bays. 
>> This leaves me with an interesting problem of how to configure these 
>> limited number of drives.
>> 
>> I know that ideally I would have seperate spindles for WAL, indexes, and 
>> data. But I also know that I must be able to survive a drive failure, and I 
>> want at least 1TB of space for my data. I suspect with so few drive bays, I 
>> won't be living in an ideal world.
>> 
>> With an even mix of reads and writes (or possibly more writes than reads), 
>> is it better to use RAID10 and have everything on the same partition, or to 
>> have data and indexes on a 6-drive RAID5 with WAL on its own RAID1?
>
> I'm surprised I haven't seen any responses to this, but maybe everyone's 
> tired of the what to do with X drives question...perhaps we need a 
> pgsql-perform FAQ?
>
> At any rate, I just recently built a new PG server for a client which had 8 
> Raptors with an Areca 1160 controller that has the 1GB battery backed cache 
> installed.  We tested a few different configurations and decided on an 8 disk 
> RAID10 with a separate WAL partition.  The separate WAL partition was 
> marginally faster by a few percent.
>
> The 8 disk RAID5 was actually a bit faster than the 8 disk RAID10 in overall 
> throughput with the Areca, but we opted for the RAID10 because of reliability 
> reasons.
>
> The moral of the story is to test each config with your workload and see what 
> performs the best.  In our case, the battery backed write cache seemed to 
> remove the need for a separate WAL disk, but someone elses workload might 
> still benefit from it.
>
> -- 
> Jeff Frost, Owner 	<jeff@frostconsultingllc.com>
> Frost Consulting, LLC 	http://www.frostconsultingllc.com/
> Phone: 650-780-7908	FAX: 650-649-1954
>