degraded RAID performance after OS upgrade, and drives added.

On Nov 30, 2006, at 11:40 AM, Derrick MacPherson wrote:
> That seems like a pretty crazy drop in performance,
more than one  
> would expect. The machine is busy but not busy enough
to warrant  
> this.. Imo.. Is there a way to test to confirm?

Using dd is a trivial benchmark, and not especially precise
but good  
enough to give rough answers; otherwise, there are lots of
I/O  
benchmarks in ports like iozone or even "diskinfo
-t".  Try using  
different block sizes while reading and writing with dd, and
you'll  
probably find some useful info.

While it is likely that you can adjust the RAID-5 stripe
size, change  
the write-caching from write-thru to write-back (if your
RAID has a  
battery, anyway, otherwise this is dangerous), etc, using a
3-disk  
RAID-5 volume is just not a great idea-- RAID-5 is happier
with more  
drives than the minimum of 3 to get better parallelism and
reduce the  
overhead for parity info.

-- 
-Chuck

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