What you should see is a single DEB that shows ALL the extents, on ALL
the volumes. you should be able to loop through all the extent
descriptors in the DEB, calculating the extent numbers and CCHHR values
in a fairly simple fashion. This will also help you detrmine the correct
extent number. The MBBCCHHR values that you supply to IOS via your EXCP
blocks need to be correct in both respects or the I/O will fail.
You don't get that when you open for EXCP or BSAM. OPEN only allows you
to access one volume at a time in those circumstances. Hence the need to
manage a seperate DCB for each volume.
When you declare DISP=NEW, there is no second volume. It won't be added
until you actually try to write something in the 17th extent.
I appreciate that. There is a second volume, and inded in my example
third and forth, by the time that I've extended the dataset sufficiently
using EOV.
Why not just open it for QSAM access and avoid the entire problem?
Unless you're trying to do something "funky", there are very few good
reasons to use EXCP.
But the whole point is that I am trying to do something "funky". Well,
to a PC programmer it's hardly funky. All I want is a large random
access scratch file with optimal performance. Doesn't sound too hard. By
large I mean > 4GB which restricts you. Got to be multi volume. VSAM LDS
fits the bill and works fine, so long as you don't use DIV which can't
cope with >4GB, but performance requirements and the acceptance of
customers requires a physical sequential based solution. Meaning that
you have to use EXCP and manage the seperate volumes yourself.
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