My experience with MIH in general has been that it is a throwback to the
days when an I/O got lost and everything just hung. For those old enough to
remember the 3330, you could pop the plug on the disk to force an interrupt
to wake it up. IBM added the MIH to say basically, that if I haven't heard
anything about that I/O in that interval, cancel the first I/O and redrive
it. I doubt seriously that too many I/o's are lost anymore so I would say
just take it up to about 15 minutes. Use the setios command.
This is a very misunderstood parameter. For many years working for a major
disk vendor, systems programmers would set the value low if they wanted good
response time from a volume. All it did is actually elongate the I/O because
it redrove it several times. If the MIH is large enough, the I/O will finish
the first time.
You will see this on programs like syncsort that may read an entire disk in
1 i/o. 5-10 secs will never be enough. Even if only to take MIH out of the
picture, set it high. Most disk vendors now are probably recommending at
least 5 minutes or larger.
Bill Wilkie
Dino Software
From: "Alan C. Field" <[EMAIL PROTECTED]>
Reply-To: IBM Mainframe Discussion List <IBM-MAIN@BAMA.UA.EDU>
To: IBM-MAIN@BAMA.UA.EDU
Subject: FICON CTC MIH
Date: Mon, 29 Jan 2007 10:04:37 -0600
The archive search and I aren't getting along this morning.
Are there any recommendations for a MIH value for FICON CTCs?
We haven't got anything specified in IECIOSxx but are having some
difficulty getting VARY commands to them to complete.
We're wondering if there is a recommendation or what other sites are
using.
Thanks,
Alan
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