RE: disk arms (was RE: Tips for user ASP)

["Kirk Goins" <kirkg@xxxxxxxxxxxxxx>]

In general what I am hearing from IBM is on the newer machines, with newer 
"faster" disk controllers and the newer "faster" disks that the numbers of arms 
can be reduced without a performance hit.

Also I've been told the Disk Arm Calculator is "EXTREMELY" conservative.

As Always YOUR mileage may vary...
__________________________________________________
Kirk Goins
IBM Certified iSeries Technical Solutions Expert
Pacific Information Systems - An IBM Premier Business Partner
503-674-2985           kirkg@pacinfosys.com


-----Original Message-----
From: Dan Bale [mailto:dbale@samsa.com]
Sent: Friday, June 28, 2002 8:18 AM
To: midrange-l@midrange.com
Subject: disk arms (was RE: Tips for user ASP)


>I agree Al.  In fact I think the next performance bottleneck _has been_
>DASD arm contention for several years now.  Larry Bolhuis and I have
>beat our drums, and beat our drums, and beat our drums, but everyone
>has said: no, no, no, probably not a problem, because of faster disks,
>faster disk controllers, and write cache, and more write cache, and you
>should believe in the new technology...

I am no performance guru.  I ask this purely for education, since I am a
little bit puzzled by the angst I'm reading here.

With the recent announcements and discussion about the 4gb drives going away
and, now, the smallest drives you can buy are 8gb, and both the 4gb & 8gb
drives have the same number of arms and, so, therefore, the arms must cover
twice the amount of DASD.

However, the other part of the announcement & discussion was that the price
of the 8gb drives dropped to the level of the discontinued 4gb drives.  If
so, what has been lost?  The managers concerned about disk arm performance
now have to, generally speaking (and perhaps easier said than done), ensure
that DASD utilization on the 8gb drives never exceeds half of what they
would allow the 4gb drives to exceed.  Their costs have not been increased,
as far as I can tell.  They are paying the same amount for the number of
arms, which is the critical factor, more so than the drive capacity.

Educate me, please.

- Dan Bale
(I am *NOT* "Dale"
http://archive.midrange.com/midrange-l/200105/msg00281.html )

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