Re: IBM disk arm reduction "rule of thumb"

[Larry Bolhuis <lbolhuis@xxxxxxxxxx>]

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.
>
>
>