It's not a waste of time once you know the figures. All my 'canned' JCL has had the corresponding directory blocks for years. I may have mis-stated the exact number of corresponding blocks to fill the first block, incorrectly. But, my points were: 1. I'm anal enough to care. 2. 15 blocks are not too many.
But, teto! - Ted MacNEIL [email protected] Twitter: @TedMacNEIL -----Original Message----- From: Paul Gilmartin <[email protected]> Sender: IBM Mainframe Discussion List <[email protected]> Date: Sun, 25 Aug 2013 13:39:42 To: <[email protected]> Reply-To: IBM Mainframe Discussion List <[email protected]> Subject: Re: SCRT question On Sun, 25 Aug 2013 13:17:21 -0400, Gerhard Postpischil wrote: >On 8/24/2013 10:06 AM, John Gilmore wrote: >> A preoccupation with having a first PDS member begin on a notional >> track boundary of an emulated device strikes me as misplaced, even >> bizarre; but it would be my guess that it is also benign. > Benign except for being a waste of developer time, But, hey, that's what happens here. >> (This calculation is trivial, but I have suppressed its >> result here to avoid encouraging its misuse.) > (There's a table in the Reference Manual.) >This is far from trivial. I just ran some tests, and an allocation of >the number of directory blocks you posit, on a 3390, will place the >directory EOF block on the next track. There were some device types >where there was enough space on a track to place the EOF, but on the >3390 there isn't, and if you change the allocation to one block less, >there is not only room for the EOF, but possibly also a (small) block of >the first member. > Your experiment discovers the geometry. Have you evaluated the difference in performance? You might consider creating a dummy member so the first real member begins on a track boundary. In fact you might consider doing so for each interval between members. But if the first member begins (or is fully contained) in the track containing the directory, doesn't it save the expense of repositioning the heads between the BLDL and the READ? PDSE, with its undisclosed data format renders all this exercise pointless. Small wonder old-timers resent the advent of PDSE. (is it still Friday?) -- gil ---------------------------------------------------------------------- For IBM-MAIN subscribe / signoff / archive access instructions, send email to [email protected] with the message: INFO IBM-MAIN ---------------------------------------------------------------------- For IBM-MAIN subscribe / signoff / archive access instructions, send email to [email protected] with the message: INFO IBM-MAIN
