From: Greg Smith <greg@2ndquadrant.com>
To: Matthew Wakeling <matthew@flymine.org>
Cc: Yeb Havinga <yebhavinga@gmail.com>
Cc: pgsql-performance@postgresql.org
Subject: Re: Testing Sandforce SSD
Date: Mon, 26 Jul 2010 11:28:02 -0400
Message-ID: <4C4DA982.5090308@2ndquadrant.com> (raw)
In-Reply-To: <alpine.DEB.2.00.1007261045470.20471@aragorn.flymine.org>
References: <4C4A9452.9070100@gmail.com>
<4C4B1F84.5030306@2ndquadrant.com>
<4C4C83DF.3010703@gmail.com>
<4C4C8CCC.7080406@gmail.com>
<alpine.DEB.2.00.1007261045470.20471@aragorn.flymine.org>
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
greg@2ndQuadrant.com www.2ndQuadrant.us
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To: pgsql-performance@postgresql.org
Cc: greg@2ndquadrant.com, matthew@flymine.org, yebhavinga@gmail.com
Subject: Re: Testing Sandforce SSD
In-Reply-To: <4C4DA982.5090308@2ndquadrant.com>
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