From: "Fernando Hevia" <fhevia@ip-tel.com.ar>
To: "'cluster'" <skrald@amossen.dk>,
	<pgsql-performance@postgresql.org>
References: <g96ttt$2l3m$1@news.hub.org>
Subject: Re: Best hardware/cost tradoff?
Date: Thu, 28 Aug 2008 17:04:46 -0300
Organization: IP-TEL
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> -----Mensaje original-----
> De: pgsql-performance-owner@postgresql.org 
> [mailto:pgsql-performance-owner@postgresql.org] En nombre de cluster
> 
> I'm about to buy a combined web- and database server. When 
> (if) the site gets sufficiently popular, we will split the 
> database out to a separate server.
> 
> Our budget is limited, so how should we prioritize?
> 
> * We think about buying some HP Proliant server with at least 
> 4GB ram and at least a duo core processor. Possibly quad 
> core. The OS will be debian/Linux.
> 
> * Much of the database will fit in RAM so it is not *that* 
> necessary to prefer the more expensive SAS 10000 RPM drives 
> to the cheaper 7500 RPM SATA drives, is it? There will both 
> be many read- and write queries and a *lot* (!) of random reads.
> 
> * I think we will go for hardware-based RAID 1 with a good 
> battery-backed-up controller. I have read that software RAID 
> perform surprisingly good, but for a production site where 
> hotplug replacement of dead disks is required, is software 
> RAID still worth it?
> 
> Anything else we should be aware of?
> 

I havent had any issues with software raid (mdadm) and hot-swaps. It keeps
working in degraded mode and as soon as you replace the defective disk it
can reconstruct the array on the fly. Performance will suffer while at it
but the service keeps up.
The battery backup makes a very strong point for a hw controller. Still, I
have heard good things on combining a HW controller with JBODS leaving the
RAID affair to mdadm. In your scenario though with "*lots* of random reads",
if I had to choose between a HW controller & 2 disks or software RAID with 4
or 6 disks, I would go for the disks. There are motherboards with 6 SATA
ports. For the money you will save on the controller you can afford 6 disks
in a RAID 10 setup. 

Cheers,
Fernando.