Message-ID: <4C58216B.7050401@2ndquadrant.com>
Date: Tue, 03 Aug 2010 10:02:19 -0400
From: Greg Smith <greg@2ndquadrant.com>
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To: Yeb Havinga <yebhavinga@gmail.com>
CC: Scott Marlowe <scott.marlowe@gmail.com>, Josh Berkus <josh@agliodbs.com>,
	pgsql-performance@postgresql.org
Subject: Re: Testing Sandforce SSD
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Yeb Havinga wrote:
> Small IO size: 4 KB
> Maximum Small IOPS=86883 @ Small=8 and Large=0
>
> Small IO size: 8 KB
> Maximum Small IOPS=48798 @ Small=11 and Large=0

Conclusion:  you can write 4KB blocks almost twice as fast as 8KB ones.  
This is a useful observation about the effectiveness of the write cache 
on the unit, but not really a surprise.  On ideal hardware performance 
should double if you halve the write size.  I already wagered the 
difference in pgbench results is caused by the same math.

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