> -----Original Message----- > From: IBM Mainframe Discussion List [mailto:ibm-m...@bama.ua.edu] On > Behalf Of Farley, Peter x23353 > Sent: Wednesday, April 01, 2009 7:49 AM > To: IBM-MAIN@bama.ua.edu > Subject: Re: "A foolish consistancy" or "3390 cyl/track architecture" > > > The biggest problem is that estimating file size for many production > batch applications is mostly or totally dependent on input (perhaps > client-supplied) file sizes. And there is no way in JCL to say "this > new output file will be about x(percent) or x(times) the size of the > input file(s) named A (B, C, ...). Today I may have 1M records and > tomorrow I may have 10M records, depending on how active the day's > business has been. The only alternative we have today is to allocate > for the maximum possible size, which is often a very poor estimate of > the actual size. It doesn't really matter that much if one uses > records > or megabytes or cylinders (though I agree that records/megabytes are > probably more application-friendly methods). When the business grows, > the original estimates hard-coded into the JCL become too small.
I don't see the problem with coding over generous space estimates. For most of allocations I don't require a space parameter at all. The default DATACLAS allows a big extended striped dataset. And with SMS compression. We only see x37 abends when the JCL explicitly calls for too small an allocation, and extended/striping/compression isn't selected by DFSMSdfp. Usually due to fragmentation. Yes, I have sizable pools with and generous free space threshold, but DASD is cheap. I've probably spent more writing this note than being stingy on disk space would buy me. >From a user prospective, and even from a z/OS Sysprog perspective, I don't care about the underlying FBA or CKD or QED of the architecture. We still have many outdated parsimonious attitudes from the days when bytes were expensive. DASD is cheap, so is memory. z/OS CPU is also cheap, too bad the software (mostly ISV) is still priced by old time thinking. Dave Gibney Information Technology Services Washington State University > ---------------------------------------------------------------------- For IBM-MAIN subscribe / signoff / archive access instructions, send email to lists...@bama.ua.edu with the message: GET IBM-MAIN INFO Search the archives at http://bama.ua.edu/archives/ibm-main.html
