On 2014-12-23, at 15:59, Blaicher, Christopher Y. wrote: > > QSAM and V/VB/VBS format requires a well formed block. The BDW must equal > the total of the RDW's +4. The +4 is for the BDW. You mess that up and QSAM > will throw an error. As long as the BDW is equal to or less than the > BLKSIZE, QSAM will be happy. > Reading Data Sets > BSAM needs to follow the same rules as QSAM, especially on writing, so that > someone using QSAM can read what the person using BSAM wrote. Needless to > say, you have far more opportunities to mess things up with BSAM because you > point at a block and tell BSAM to write it. If you format the block badly, > BSAM isn't going to tell you about it, it will just write the block. That is > especially true for RECFM=V/VB/VBS, although if you try to write longer than > the BLKSIZE, it will give you an error. I can't remember, but BSAM may, and > I stress may, check the block length is a multiple of the LRECL. I tend to > include that sanity check in my own code, so I haven't seen it in BSAM in > years. > I had asked a related question on IBMVM, citing: http://www-01.ibm.com/support/knowledgecenter/api/content/nl/en-us/SSLTBW_2.1.0/com.ibm.zos.v2r1.idad400/d4361.htm Null Segments z/OS DFSMS Using Data Sets SC23-6855-00
I could find no affirmative statement in op. cit. either affirming or forbidding that the physical block may be longer than the count in the BDW, and Alan Altmark followed up: On 2014-12-22, at 10:13, Alan Altmark wrote: > ... > MVS has no problem with short records in a block for VB[S] files. Padding > the last record doesn't hurt because MVS writes ECKD records that are > BLKSIZE in length, but you must not modify the RDW to include the pad > bytes. > ... which raises lotsa questions. Is this BLKSIZE in the DCB, BLKSIZE in the JFCB, or other? What goes in the CKD COUNT field? For EKCD RECFM=FB, how does the access method recognize a short block that may occur at the end of the data set (or even in the interior). Does ECKD prohibit DISP=MOD for RECFM=FB? Etc. -- gil ---------------------------------------------------------------------- For IBM-MAIN subscribe / signoff / archive access instructions, send email to lists...@listserv.ua.edu with the message: INFO IBM-MAIN
