In a message dated 2/4/2008 9:32:48 A.M. Central Standard Time, [EMAIL PROTECTED] writes: >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. I don't know how to open the data set in such a way, nor do I see why you need to do so. Suppose there are 16 volumes in the data set and each volume has 16 extents. Your DCB has a DDNAME=WHATEVER. Your DD statement for WHATEVER points to the data set name. You OPEN the DCB. Your DEB that will be constructed has 256 extent entries in it, with the first 16 pointing to the UCB for the first of the 16 volumes, the second set of 16 extent entries in the DEB all point to the UCB for the second of the 16 volumes, etc. You use EXCP to read this file. You construct your own MBBCCHHR in the IOB before doing the EXCP. You can put any value you want into the M byte. If you put a value between X'00' and X'0F' you will use one of the first 16 extent entries in the DEB and thus access volume 1. Etc. Whenever you want to go from volume(n) to volume(N+1) you will need a new M value, as also you will if you move from extent(x) to extent(x+1) within the same volume. >What you're talking about sounds like BDAM where you get a single logical view of a multivolume dataset? The access method is irrelevant. You will get the same kind of multi-extent DEB whether you use EXCP, XDAP, BDAM, BSAM , QSAM, BISAM, QISAM, or BPAM. >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. I don't know where you "see" this, because this is not what you get. You get a "simple" DCB, whatever that means, that is connected to (points to) a single "complex" DEB (I just made up the descriptor "complex") that points to ALL the extents in the file regardless of the volume involved. Create a multi-volume file, OPEN a "simple" DCB to it, ABEND, and study the construction of the DEB, not the DCB. Bill Fairchild Rocket Software
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