Re: mpt Serious performance issues

[Manuel Bouyer <bouyer%antioche.eu.org@localhost>]

On Fri, Feb 04, 2011 at 09:17:01AM +0100, Stephan wrote:
> Now this is REALLY strange. I was wondering about why the read speed
> is sometimes high (~70MB/s) and sometimes very slow (~2MB/s). So I
> repeated the test utilizing
> 
> find / -exec cat {} \; > /dev/null &
> 
> to read everything from the filesystem while watching the physical
> disks with my eyes and the throughput with sysstat. The findings is
> 
> -that sometimes the upper disks is 100% busy while the lower disk is
> NOT being accessed at all, and the read speed is ~2MB/s
> -then sometimes the adapter switches to the lower disk while the upper
> disk isn´t utilised anymore, and the read speed increases to ~70MB/s
> -until the adapter again switches to the upper disk which leads to the
> massive decrease in speed
> 
> So what do you think about that?

I'd try swapping the 2 drives, and see if the one with the lowest BW is
still the same. If still the same it's an issue with the disk; otherwise
it looks like it's tied to the scsi ID and could be related to the
controller setup.

-- 
Manuel Bouyer <bouyer%antioche.eu.org@localhost>
     NetBSD: 26 ans d'experience feront toujours la difference
--