Subject: Re: Bad iostat numbers
From: Scott Marlowe <smarlowe@g2switchworks.com>
To: Alex Turner <armtuk@gmail.com>
Cc: Greg Smith <gsmith@gregsmith.com>, pgsql-performance@postgresql.org
In-Reply-To: <1165249513.14565.329.camel@state.g2switchworks.com>
References: <PEEPKDFEHHEMKBBFPOOKKEHCDKAA.carlos.reimer@opendb.com.br>
	<Pine.GSO.4.64.0612032336250.19679@westnet.com>
	<33c6269f0612032317t9f0bc77n3ff791a5cd88fc80@mail.gmail.com>
	<1165249513.14565.329.camel@state.g2switchworks.com>
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Date: Mon, 04 Dec 2006 10:37:34 -0600

On Mon, 2006-12-04 at 10:25, Scott Marlowe wrote:
> 
> OTOH, with the choice at my last place of employment being LSI or
> Adaptec, LSI was a much better choice.  :)
> 
> I'd ask which LSI megaraid you've tested, and what driver was used. 
> Does RHEL4 have the megaraid 2 driver?  

Just wanted to add that what we used our database for at my last company
was for lots of mostly small writes / reads.  I.e. sequential throughput
didn't really matter, but random write speed did.  for that application,
the LSI Megaraid with battery backed cache was great.

Last point, bonnie++ is a good benchmarking tool, but until you test
your app / postgresql on top of the hardware, you can't really say how
well it will perform.

A controller that looks fast under a single bonnie++ thread might
perform poorly when there are 100+ pending writes, and vice versa, a
controller that looks mediocre under bonnie++ might shine when there's
heavy parallel write load to handle.