------------------------<snip>-----------------------
I'm trying to read a dataset that will potentially have many volumes
each of which has up to 16 extents. I'm trying to open the dataset in
a way that I get one volume at a time, with the DEB reflecting the
extents of that volume.
What you're talking about sounds like BDAM where you get a single
logical view of a multivolume dataset?
I'm wanting to do EXCP access and my understanding is that when you do
this you get a "simple" DCB which is "connected" to one volume at a
time and for which the DEB just reflects however many extents are on
that volume. Certainly this is what I see, and this is how I'm
performing my I/O.
-----------------------<unsnip>---------------------
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.
----------------------<snip>----------------------
The question is why, when I declare my dataset DISP=OLD, do I get this
behaviour, where when I open volume sequence number 2 I look at the
DEB and the associated UCBs and they are indeed on the volume that I
know to be the second one, whereas when I do the same with DISP=NEW
the extents in the DEB are all on the first volume.
-----------------------<unsnip>---------------------
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.
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.
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