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From: Ivan Voras <ivoras@freebsd.org>
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Subject: Re: Inconsistent IO performance
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On 13.8.2010 18:01, Kevin Oberman wrote:
> For some time I have seen very odd issues with IO performance on
> 8-Stable. Going back to November of last year when 8.0 was released, I
> see variations of up to 22% in identical operations. This is not a
> degradation as the performance moves up and down.

In 8.0-8.1 span of time there was some work on the ata driver to make it
use MAXPHYS (128 KiB) transfer sizes instead of 64 KiB. Modifying this
will involve changing and recompiling the kernel but if you want to try
something and the hardware is SATA you might try the new AHCI driver
("ada").

http://ivoras.net/blog/tree/2009-11-17.trying-ahci-in-8.0.html