On Tue, 9 Oct 2012 16:53:49 -0400, Robert A. Rosenberg wrote: >At 21:09 -0500 on 10/06/2012, Paul Gilmartin wrote about Re: Zero >length records outlawed! (Again.): > >> >Note that when you are writing to DASD, the block size is restricted >>>to however much room is left on the track so the last block on a >>>track is shorter than the defined Blocksize. >>> >>I've been told elsewhere that only Binder (Linkage Editor?) performs >>such track balancing. Otherwise access methods will start a new >>track whenever there is insufficent space in the current track for >>BLKSIZE bytes. This could apply as well for RECFM=VB as for >>RECFM=VBS. This provides the rationale for SDB's choice of 32760 >>when RECFM=U and half track for any other RECFM (3380/3390). > >So you are saying that to avoid the need to keep track of the >remaining space on the track the code just wastes space when writing >VBS (and VB) records. > That's what I've been told here; I'm not the expert. Except it doesn't "just [waste] space when writing VBS (and VB) records." It also similarly wastes space when writing FB records.
And "it" (QSAM?) needn't keep track. I've been told there is a Track Balance system call that tells (used to) how much space remained on a track. Of course, I believe that nowadays it instead tells what is the largest block that can be written in the remainder of the track. But QSAM doesn't use it (I've been told). If you use BSAM you're on your own. You can be as clever as you choose. -- gil ---------------------------------------------------------------------- For IBM-MAIN subscribe / signoff / archive access instructions, send email to [email protected] with the message: INFO IBM-MAIN
