Re: Help with low raid5 performance

[Chuck Swiger <cswiger%mac.com@localhost>]

Hi, Peter--

On Nov 9, 2010, at 7:38 AM, Peter Kerwien wrote:
> But cannot understand what I'm doing wrong. I'm experimenting with 3 x WD 
> 500GB RE2 drives, which give approx. 55-60MB/s when using them as separate 
> disks (measured with iostat during a file copy to the drive). But when 
> setting up a RAID-5 configuration with all three drives, I'm seeing something 
> between 10-20 MB/s. Never above 20MB/s.
[ ... ]
> What important thing have I missed or done wrong??

You're expecting RAID-5 to perform better than a bare drive.  See:

  http://lists.freebsd.org/pipermail/freebsd-questions/2006-March/116122.html

...for the tradeoffs between performance, reliability, and cost.

Regards,
-- 
-Chuck