linux-kernel - Linux IO service time - a perfect source of randomness ?

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Date:	Fri, 9 Oct 2009 18:44:12 +0200 (CEST)
From:	Tobias Oetiker <tobi@...iker.ch>
To:	linux-kernel@...r.kernel.org
Subject: Linux IO service time - a perfect source of randomness ?

I have just completed extensive benchmarking of ext3 on 2.6.31.2
both on HW RAID6 as well as single Hard Drive. I have written a new
file system benchmark that creates load by reading and writing large
file trees in paralle to simulate a busy fileserver.

The results are as follows:

 * as soon as the system comes under strain the service time
   for single io operations becomes almost random with huge
   outliers of several seconds.

 * on HW RAID the best performance is to be gained with
   data=ordered and cfq scheduler

 * on single HDD setups, only (!) data=writeback with cfq provides
   good performance.

 * the deadline scheduler did not perform well in any of the
   read/write scenarios.

 * btrfs has fantastic read performance but does not (yet?) do well
   when readers and writers are competing.

my report is on

  http://insights.oetiker.ch/linux/fsopbench/

cheers
tobi

-- 
Tobi Oetiker, OETIKER+PARTNER AG, Aarweg 15 CH-4600 Olten, Switzerland
http://it.oetiker.ch tobi@...iker.ch ++41 62 775 9902 / sb: -9900
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