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An source at IBM to remain unnamed told me once that 2 to 1 is reasonable if going from 10K or slower drives to 15K drives with Jumbo cache cards. This means that the CEC slots in 520/550/570 machines don't count because they only have medium size caches.

Of course YMMV!

 - Larry

Al Barsa wrote:

Unfortunately, I don't know of a rule of thumb.

However, this is why IBM is adding faster drives, and more cache on the
IOAs.

Al

Al Barsa, Jr.
Barsa Consulting Group, LLC




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.

All comments/suggestions would be most appreciated.




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