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Date: Mon, 27 Apr 2009 12:27:27 -0400
From: Steve Polyack <korvus@comcast.net>
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To: Ghirai <ghirai@ghirai.com>
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Cc: freebsd-questions@freebsd.org
Subject: Re: quick vfs tuning
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Ghirai wrote:
> The author suggested that increasing the default value of 8 to 16
> resulted in increased read speed, and that increasing it further
> resulted in no noticeable performance gain.
>
>   

Personally, I've seen changes in vfs.read_max to provide anywhere from a 
50-100% improvement in disk read performance.  As you have also found, 
the "sweet spot" is sometimes higher than 16.  I've seen significant 
benefits up to vfs.read_max=128 on *some* disk controllers.  It really 
seems dependent on the disks/controllers, but setting 16 has always 
shown a significant improvement over the default 8 for me.