Re: DASD Performance

[bclark@xxxxxxxxxxxx (Bob Clark)]

Yes.  It was my understanding that it was one arm per bus, except for Ultra 
SCSI,
which I thought suppported two channels.

Larry Bolhuis wrote:

> 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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