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Re: Testing Sandforce SSD

From: Greg Smith <greg(at)2ndquadrant(dot)com>
To: Matthew Wakeling <matthew(at)flymine(dot)org>
Cc: Yeb Havinga <yebhavinga(at)gmail(dot)com>, pgsql-performance(at)postgresql(dot)org
Subject: Re: Testing Sandforce SSD
Date: 2010-07-26 15:28:02
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Lists: pgsql-performance
Matthew Wakeling wrote:
> Does your latency graph really have milliseconds as the y axis? If so, 
> this device is really slow - some requests have a latency of more than 
> a second!

Have you tried that yourself?  If you generate one of those with 
standard hard drives and a BBWC under Linux, I expect you'll discover 
those latencies to be >5 seconds long.  I recently saw >100 *seconds* 
running a large pgbench test due to latency flushing things to disk, on 
a system with 72GB of RAM.  Takes a long time to flush >3GB of random 
I/O out to disk when the kernel will happily cache that many writes 
until checkpoint time.

Greg Smith  2ndQuadrant US  Baltimore, MD
PostgreSQL Training, Services and Support

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