Message-ID: <4E5537C9.9080308@2ndQuadrant.com>
Date: Wed, 24 Aug 2011 13:41:29 -0400
From: Greg Smith <greg@2ndQuadrant.com>
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To: pgsql-performance@postgresql.org
Subject: Re: Intel 320 SSD info
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	<1314206629.63488.YahooMailNeo@web111301.mail.gq1.yahoo.com>
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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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On 08/24/2011 01:23 PM, Andy wrote:
<blockquote
 cite="mid:1314206629.63488.YahooMailNeo@web111301.mail.gq1.yahoo.com"
 type="cite">
  <div
 style="color: rgb(0, 0, 0); background-color: rgb(255, 255, 255); font-family: times new roman,new york,times,serif; font-size: 12pt;">
  <div><span>According to the specs for database storage:</span></div>
  <div><span><br>
  </span></div>
  <div><span>"Random 4KB arites: Up to 600 IOPS"</span></div>
  <div><span><br>
  </span></div>
  <div><span>Is that for real? 600 IOPS is *atrociously terrible* for
an SSD. Not much faster than mechanical disks.</span></div>
  <div><span><br>
  </span></div>
  <div><span>Has anyone done any performance benchmark of 320 used as a
DB storage? Is it really that slow?</span></div>
  <br>
  </div>
</blockquote>
<br>
Many SSDs that claim better are cheating though, or only quoting under
conditions that don't take into account drive cleanup operations.&nbsp;
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.&nbsp; I
wouldn't assume other drives really are better unless it's in a true
apples to apples fair comparison.<br>
<br>
I published some numbers at
<a class="moz-txt-link-freetext" href="http://archives.postgresql.org/message-id/4D9D1FC3.4020207@2ndQuadrant.com">http://archives.postgresql.org/message-id/4D9D1FC3.4020207@2ndQuadrant.com</a>
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.&nbsp; That's only 2X as fast as a typical mechanical hard
drive running the same workload.&nbsp; On random reads, the performance gap
is much bigger, in favor of the SSD.<br>
<br>
I've measured the performance of this drive from a couple of directions
now, and it always comes out the same.&nbsp; 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.&nbsp; 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.&nbsp; 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.<br>
<br>
<pre class="moz-signature" cols="72">-- 
Greg Smith   2ndQuadrant US    <a class="moz-txt-link-abbreviated" href="mailto:greg@2ndQuadrant.com">greg@2ndQuadrant.com</a>   Baltimore, MD
PostgreSQL Training, Services, and 24x7 Support  <a class="moz-txt-link-abbreviated" href="http://www.2ndQuadrant.us">www.2ndQuadrant.us</a>
</pre>
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