OPT(4) is nice because it does reduce EXCP's but at least here on 2105
and newer DASD it doesn't have an impact on elapsed time.
I did a fair amount of testing with different DFDSS options when we were
trying to resolve some I/O performance problems for on-lines operating
on F20 Shark DASD concurrently with DFDSS volume backups of point in
time FlashCopy volumes.
I would agree that it would be a good thing if IBM changed the default
for DFDSS from OPT(1) to OPT(4) or provided a way to do this and other
customization via PARMLIB. I don't feel strongly enough about it to
chase a requirement but maybe someone else will:-)
Best Regards,
Sam Knutson, GEICO
Performance and Availability Management
mailto:[EMAIL PROTECTED]
(office) 301.986.3574
The most incomprehensible thing about the world is that it is at all
comprehensible.
Albert Einstein
-----Original Message-----
From: IBM Mainframe Discussion List [mailto:[EMAIL PROTECTED] On
Behalf Of O'Brien, David W. (NIH/CIT) [C]
Sent: Tuesday, June 13, 2006 10:32 AM
To: [email protected]
Subject: Re: DFSMSdss Performance Question
As it was explained to me years ago, IBM is a very conservative company
and the defaults tend to ensure that the smallest configuration will be
able to run. As an example VSE was shipped to allow a single userid to
run at a time.
As far as OPT 1 vs 4 is concerned. I've always run with 4 and never
noticed a performance hit. With older DASD and 4.5mb bus and tag
cabling, a hit might have been noticeable and people who I respect have
told me not to use OPT(4). With the newer technology, I think OPT(4)
ought to be SOP. Just my opinion.
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