ZFS performance strangeness

[Sergio de Almeida Lenzi]

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