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From: Greg Smith <gsmith@gregsmith.com>
To: Christiaan Willemsen <cwillemsen@technocon.com>
Cc: pgsql-performance@postgresql.org
Subject: Re: How to setup disk spindles for best performance
Date: Thu, 28 Aug 2008 22:43:54 -0400 (EDT)
Message-ID: <Pine.GSO.4.64.0808282231330.11207@westnet.com> (raw)
In-Reply-To: <48AD8465.7090604@technocon.com>
References: <972BDF1A-B4ED-46EC-B416-0CDF15A0439A@technocon.com>
	<b42b73150808201849t3577d65eq76e7484d8519af51@mail.gmail.com>
	<331B8FD1-7460-4B97-BD2C-03D8381E1C4D@technocon.com>
	<48AD022E.7090400@commandprompt.com>
	<48AD288B.8030902@technocon.com>
	<a1ec7d000808210753w3a954e5g1d4f4325775d8eca@mail.gmail.com>
	<48AD8465.7090604@technocon.com>

On Thu, 21 Aug 2008, Christiaan Willemsen wrote:

> Anyway, I'm going to return the controller, because it 
> does not scale very well with more that 4 disks in raid 10. Bandwidth is 
> limited to 350MB/sec, and IOPS scale badly with extra disks...

How did you determine that upper limit?  Usually it takes multiple 
benchmark processes running at once in order to get more than 350MB/s out 
of a controller.  For example, if you look carefully at the end of 
http://www.commandprompt.com/blogs/joshua_drake/2008/04/is_that_performance_i_smell_ext2_vs_ext3_on_... 
you can see that Joshua had to throw 8 threads at the disks in order to 
reach maximum bandwidth.

> The idea for xlog + os on 4 disk raid 10 and the rest for the data sound 
> good

I would just use a RAID1 pair for the OS, another pair for the xlog, and 
throw all the other disks into a big 0+1 set.  There is some value to 
separating the WAL from the OS disks, from both the performance and the 
management perspectives.  It's nice to be able to monitor the xlog write 
bandwidth rate under load easily for example.

--
* Greg Smith gsmith@gregsmith.com http://www.gregsmith.com Baltimore, MD



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