RE: IBM disk arm reduction "rule of thumb"

["Chris Bipes" <chris.bipes@xxxxxxxxxxxxxxx>]

It depends?  We went from 42 disk drives attached to our 820 down to 27.
We replaced 30 drives, 20 8.58GB/10K and 10 17.5GB/10K with 15 35GB/15K.
Two 2741 DASD controllers with one 2780 DASD controller.  We replaced
the HSL1 migration tower with a 5094 HLS2 expansion tower.  We doubled
our memory from 8GB to 16GB.  We kept the 12 17.5GB/10K drive that were
in the 820 unit and put them in an existing 5095 HSL2 expansion tower
also moving the 2778 DASD controller.

Our disk arms seem to be working fine and not over stressed. 

So what are the 18 you are replacing with the 8?  What DASD controllers
are you looking at? 


Chris Bipes
Information Services Director
CrossCheck, Inc.

-----Original Message-----

Hello All,

Does anyone know if IBM has a "rule of thumb" on the acceptable level of

disk arm reductions?  We are in the process of developing a
configuration 
for a new 520.  Our current 820 has 18 disk arms.  One vendor suggests 
reducing to 8 in the main box (no tower).  Another vendor recommends 12 
utilizing a tower.  The reasoning is that at our current peak disk 
accesses, we would need that many to keep the disk ops/second at 60 or 
below.   Both quotes are for 4326 35G/15K disk units.