Re: 3Ware 9550SX and latency/system responsiveness

[Pasi Kärkkäinen <pasik@xxxxxx>]

On Tue, Oct 02, 2007 at 09:39:09AM -0400, Ross S. W. Walker wrote:
> Simon Banton wrote:
> > 
> > At 12:30 +0200 2/10/07, matthias platzer wrote:
> > >
> > >What I did to work around them was basically switching to XFS for 
> > >everything except / (3ware say their cards are fast, but only on 
> > >XFS) AND using very low nr_requests for every blockdev on the 3ware 
> > >card.
> > 
> > Hi Matthias,
> > 
> > Thanks for this. In my CentOS 5 tests the nr_requests turned out by 
> > default to be 128, rather than the 8192 of CentOS 4.5. I'll have a go 
> > at reducing it still further.
> 
> Yes, the nr_requests should be a realistic reflection of what the
> card itself can handle. If too high you will see io_waits stack up
> high.
> 
> 64 or 128 are good numbers, rarely have I seen a card that can handle
> a depth larger then 128 (some older scsi cards did 256 I think).
> 

Hmm.. let's say you have a linux software md-raid array made of sata
drives.. what kind of nr_request values you should use for that for optimal
performance? 

Thanks!

-- Pasi
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