On Mon, 13 Nov 2023 at 13:54, Jon Perryman <[email protected]> wrote:
> On Mon, 13 Nov 2023 09:11:19 -0600, Paul Gilmartin <[email protected]> > wrote: > > >>On Mon, 13 Nov 2023 01:10:14 -0600, Jon Perryman <[email protected]> > wrote: > >>z/OS Unix filesystems are linear datasets. > Some are. >No. BLKSIZE is not ignored. > > Incorrect, BLKSIZE has no meaning for VSAM linear datasets. By definition, > "All linear data set bytes are data bytes" which is how a Unix filesystem > functions. > Not all z/OS UNIX filesystems are VSAM linear datasets, nor do such datasets directly match the UNIX file semantics. A Unix file is always 1 logical record. BLKSIZE has no meaning in this > context. While BLKSIZE is stored in the DCB the subsystem ignores it. Any > part of that logical record can be processed or in its entirety (e.g. read > or write at offset 1000 for 100 bytes). > > > for BSAM it affects how many times the WRITE/CHECK is issued, > > This is conjecture because logic for BSAM communications to the Unix file > subsystem is not made publicly. I suspect that CHECK is a simple BR14 but > maybe IBM bypassed this logic. BSAM CHECK has no meaning because the > subsystem will determine to do VSAM CHECK because it must remain compatible > with UNIX. As for the WRITE, we don't know if every program write causes a > transfer to the file subsystem or if BSAM buffers according to the BLKSIZE > before sending to the subsystem. I'm not willing to venture a guess because > there are pro's and con's to both methods. > I think you're muddling interface levels. I'd suggest a high-level read through of the z/OS UNIX System Services File System Interface Reference. There's a good introductory picture at https://www.ibm.com/docs/en/zos/2.5.0?topic=overview-system-structure. Very clearly the xSAM interfaces do not talk directly to an underlying VSAM filestore, if there is one. Tony H. ---------------------------------------------------------------------- For IBM-MAIN subscribe / signoff / archive access instructions, send email to [email protected] with the message: INFO IBM-MAIN
