From: Greg Smith <greg@2ndquadrant.com>
To: Yeb Havinga <yebhavinga@gmail.com>
Cc: pgsql-performance@postgresql.org
Subject: Re: Testing Sandforce SSD
Date: Sat, 24 Jul 2010 18:01:00 -0400
Message-ID: <4C4B629C.70501@2ndquadrant.com> (raw)
In-Reply-To: <4C4B5984.4010705@gmail.com>
References: <4C4A9452.9070100@gmail.com>
<4C4B1F84.5030306@2ndquadrant.com>
<4C4B43DA.90201@gmail.com>
<4C4B4512.2060007@gmail.com>
<4C4B5984.4010705@gmail.com>
Yeb Havinga wrote:
> Writes/s start low but quickly converge to a number in the range of
> 1200 to 1800. The writes diskchecker does are 16kB writes. Making this
> 4kB writes does not increase writes/s. 32kB seems a little less, 64kB
> is about two third of initial writes/s and 128kB is half.
Let's turn that into MB/s numbers:
4k * 1200 = 4.7 MB/s
8k * 1200 = 9.4 MB/s
16k * 1200 = 18.75 MB/s
64kb * 1200 * 2/3 [800] = 37.5 MB/s
128kb * 1200 / 2 [600] = 75 MB/s
For comparison sake, a 7200 RPM drive running PostgreSQL will do <120
commits/second without a BBWC, so at an 8K block size that's <1 MB/s.
If you put a cache in the middle, I'm used to seeing about 5000 8K
commits/second, which is around 40 MB/s. So this is sitting right in
the middle of those two. Sequential writes with a commit after each one
like this are basically the worst case for the SSD, so if it can provide
reasonable performance on that I'd be happy.
--
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, yebhavinga@gmail.com
Subject: Re: Testing Sandforce SSD
In-Reply-To: <4C4B629C.70501@2ndquadrant.com>
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