From: Greg Smith <greg@2ndQuadrant.com>
To: pgsql-performance@postgresql.org
Subject: Re: Intel 320 SSD info
Date: Wed, 24 Aug 2011 13:41:29 -0400
Message-ID: <4E5537C9.9080308@2ndQuadrant.com> (raw)
In-Reply-To: <1314206629.63488.YahooMailNeo@web111301.mail.gq1.yahoo.com>
References: <4E552DCF.80802@boreham.org>
<1314206629.63488.YahooMailNeo@web111301.mail.gq1.yahoo.com>
On 08/24/2011 01:23 PM, Andy wrote:
> According to the specs for database storage:
>
> "Random 4KB arites: Up to 600 IOPS"
>
> Is that for real? 600 IOPS is *atrociously terrible* for an SSD. Not
> much faster than mechanical disks.
>
> Has anyone done any performance benchmark of 320 used as a DB storage?
> Is it really that slow?
>
Many SSDs that claim better are cheating though, or only quoting under
conditions that don't take into account drive cleanup operations.
That's fine in a non-database context, but if the data isn't any good to
you unless it's guaranteed to be safe either on disk or on a
non-volatile cache, Intel's numbers are the more relevant ones. I
wouldn't assume other drives really are better unless it's in a true
apples to apples fair comparison.
I published some numbers at
http://archives.postgresql.org/message-id/4D9D1FC3.4020207@2ndQuadrant.com
that suggested 400 TPS was the worst-case for this drive on database
random writes running the pgbench workload, which does a couple of
writes per commit. That's only 2X as fast as a typical mechanical hard
drive running the same workload. On random reads, the performance gap
is much bigger, in favor of the SSD.
I've measured the performance of this drive from a couple of directions
now, and it always comes out the same. For PostgreSQL, reading or
writing 8K blocks, I'm seeing completely random workloads hit a
worst-case of 20MB/s; that's just over 2500 IOPS. It's quite possible
that number can go lower under pressure of things like internal drive
garbage collection however, which I believe is going into the 600 IOPS
figure. I haven't tried to force that yet--drive is too useful to me to
try and burn it out doing tests like that at the moment.
--
Greg Smith 2ndQuadrant US greg@2ndQuadrant.com Baltimore, MD
PostgreSQL Training, Services, and 24x7 Support www.2ndQuadrant.us
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To: pgsql-performance@postgresql.org
Cc: greg@2ndQuadrant.com
Subject: Re: Intel 320 SSD info
In-Reply-To: <4E5537C9.9080308@2ndQuadrant.com>
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