All the documentation I read suggested that a latest incomplete track, when present, is not written to with DISP=MOD. My experiments bore this out.
It is possible that I misread everything and borked all the experiments. I can perhaps re-check at some point if this (MOD backfills empty space on a partially used track) is the predominant feeling. Here is the JCL Reference: "S (1) For fixed-length records, indicates that the records are written as standard blocks, that is, no truncated blocks or unfilled tracks within the data set, with the exception of the last block or track." If tracks were backfilled, that "or unfilled tracks" would be redundant. No, I've nothing to back that up. Whilst it may seem profligate with space, probably more determinant on why would be "how fast does it take to slap this data onto DASD, given that in 99.9999% (or more) of slaps, the particular slap is not the first slap to a DISP=MOD with prior data. On Fri, 6 Jan 2017 14:12:16 +0000, J R <[email protected]> wrote: >MOD, I believe, does start by filling the last track; but it would be sheer >luck if the erstwhile last block were a standard block. Consequently, the >odds are stacked against the dataset remaining properly standard. > >In any event, DISP=MOD with RECFM=FBS leaves the dataset labelled as RECFM=FB >to obviate behavior unexpected by subsequent users. > >Sent from my iPhone > >> On Jan 6, 2017, at 08:13, Tom Marchant >> <[email protected]> wrote: >> >> Are you sure? I'm not sure, but I thought that MOD would start by >> filling up the last track. > >---------------------------------------------------------------------- >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
