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From: Sergio de Almeida Lenzi <lenzi.sergio@gmail.com>
To: freebsd-questions@freebsd.org
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References: <espd78-2at.ln1@it-betrieb.de>
Date: Sun, 24 Apr 2011 13:21:34 -0300
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Subject: Re: ZFS performance strangeness
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Em Ter, 2011-04-12 às 13:33 +0200, Lars Wilke escreveu:

> Hi,
> 
> There are quite a few threads about ZFS and performance difficulties,
> but i did not find anything that really helped :)
> Therefor any advice would be highly appreciated.
> I started to use ZFS with 8.1R, only tuning i did was setting
> 
> vm.kmem_size_scale="1"
> vfs.zfs.arc_max="40000M"

For me I solved the ZFS performace in FreeBSD and postgres databases
(about 100GB size) 
by tunning vm.kmem_size to atout 3/4 of the ram size...
in your case, vm.kmem_size=(48 *3/4)=36G, it puts almost all the
database 
in memory and it is now lightning fast...
I use to disable prefetch in zfs.. too 

Hope this can help,

Sergio