Re: DASD Performance

[Larry Bolhuis <lbolhui@xxxxxxx>]

I hope this is not true.  It was my understanding that in the 'top hats'
there were actually 8 SCSI busses to support the 16 drives.  So even
though only one can be accessed it was per buss.

In the e series boxes it appears that there are up to 5 drives per SCSI
buss (looking at the cabling) but they are Ultra & Wide & Fast so actual
throughput should be similair.

And besides we still get guidlines from IBM that based on model and
feature you need something like x arms for low I/O, x*3 for medium and
x*5 for intense I/O (formula is mine just as an example!).  For an S20
4way I believe the numbers are something like 15, 45, and 70.  Arms DO
matter!

 Larry Bolhuis
 Arbor Solutions, Inc
 lbolhui@ibm.net

DAsmussen@aol.com wrote:
> 
> Hey Folks!
> 
> I heard a _NASTY_ rumor last week, and wanted to confirm it here.  While we've
> had our tuning differences here in the past (I prefer manual tuning, others
> prefer QPFRADJ set on), one thing we've always agreed upon is that the number
> of disc arms is important.  Now I hear that arms are irrelevant on the new
> SCSI-based boxes, because the SCSI architecture will only access one drive at
> a time.  Is this true?  If so, how does one tune hardware under this new
> paradigm?  All the books still talk about arms!!!
> 
> TIA,
> 
> Dean Asmussen
> Enterprise Systems Consulting, Inc.
> Fuquay-Varina, NC  USA
> E-Mail:  DAsmussen@aol.com
> 
> "The two hardest things to deal with in life are failure and success." --
> Unknown
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