On Mon, 12 Mar 2012 12:18:23 -0500, Mark Zelden wrote: > >>But why not write the EOF unconditionally, ... > >I don't know under what thread subject and when, but this has been >discussed on IBM-MAIN before. I'm not going to try and find it, >but you can. I'm sure there's a good reason. :-) > As has the OP's question been discussed in these fora, perhaps even more often. Perhaps the answer to him should have been "Search the archives."
Now, perhaps wandering into new territory, IBM's z/VM CMS and IBM's z/OS UNIX System Services, both employing a simulated FBA DASD architecture, allocate a block only when it is written. An attempt to read a block that hasn't been allocated and written returns binary zeroes. (An attempt to read a block beyond the highest relative block written returns some sort of EOF indication.) This gives some faint hope that when the mythical FBA for z/OS comes to pass it could be implemented in a likewise orderly manner. I suppose the same could be achieved for CKD data sets by maintaining a bitmap of used tracks, which would add only .00025% overhead to the size of a data set. -- gil ---------------------------------------------------------------------- For IBM-MAIN subscribe / signoff / archive access instructions, send email to [email protected] with the message: INFO IBM-MAIN
