Message-ID: <4B8DA42A.7020806@2ndquadrant.com>
Date: Tue, 02 Mar 2010 18:50:02 -0500
From: Greg Smith <greg@2ndquadrant.com>
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To: Francisco Reyes <lists@stringsutils.com>
CC: Pgsql performance <pgsql-performance@postgresql.org>
Subject: Re: 10K vs 15k rpm for analytics
References: <cone.1267562557.293175.32557.1000@shelca>
In-Reply-To: <cone.1267562557.293175.32557.1000@shelca>
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Francisco Reyes wrote:
> Anyone has any experience doing analytics with postgres. In particular 
> if 10K rpm drives are good enough vs using 15K rpm, over 24 drives. 
> Price difference is $3,000.
> Rarely ever have more than 2 or 3 connections to the machine.
> So far from what I have seen throughput is more important than TPS for 
> the queries we do. Usually we end up doing sequential scans to do 
> summaries/aggregates.

For arrays this size, the first priority is to sort out what controller 
you're going to get, whether it can keep up with the array size, and how 
you're going to support/monitor it.  Once you've got all that nailed 
down, if you still have the option of 10K vs. 15K the trade-offs are 
pretty simple:

-10K drives are cheaper
-15K drives will commit and seek faster.  If you have a battery-backed 
controller, commit speed doesn't matter very much.

If you only have 2 or 3 connections, I can't imagine that the improved 
seek times of the 15K drives will be a major driving factor.  As already 
suggested, 10K drives tend to be larger and can be extremely fast on 
sequential workloads, particularly if you short-stroke them and stick to 
putting the important stuff on the fast part of the disk.

-- 
Greg Smith  2ndQuadrant US  Baltimore, MD
PostgreSQL Training, Services and Support
greg@2ndQuadrant.com   www.2ndQuadrant.us