Re: mpt Serious performance issues

[Matthew Mondor <mm_lists%pulsar-zone.net@localhost>]

On Fri, 4 Feb 2011 09:17:01 +0100
Stephan <stephanwib%googlemail.com@localhost> 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 isnÂt 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?

Just in case, none of those disks show any reallocated sectors using
atactl smart status?  I'm asking because I've seen very inconsistent
speeds on some drives whenever the remapping logic had to be turned
on.  Also, nothing in dmesg about read error retries?  As I've also
seen brand new disks with very high read error rates but otherwise
normal smart stats.  They two would crawl when reading certain areas.
Unfortunately I'm seeing this later defect more often recently.
-- 
Matt