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
>