On Tue, 19 Jul 2016 16:14:20 -0500, Bill Woodger wrote: >DISP=MOD does lead to a way to accidentally (or deliberately, as an exercise) >create a "zero" BDW. With RECFM=F/FB/U and some LRECL, specified on the DD, >write a lump of data with two bytes of binary zeros. Then with DISP=MOD again, >and the "normal" RECFM/LRECL, write a good record. Then try to read the data. > I don't believe DISP=MOD will ever extend an existing block if that's what you were expecting; it will always start a new block.
Tricky to do accidentally, but sometimes you find someone who errs, and then tries to "correct" without realising the full consequences. > That sort of thing should always be done with a copy of the data. But I believe the OP has explained that a dump of the disk file showed that BDW was valid but corrupted on input by ?SAM. -- gil ---------------------------------------------------------------------- For IBM-MAIN subscribe / signoff / archive access instructions, send email to [email protected] with the message: INFO IBM-MAIN
