On Fri, 15 Oct 2010 15:54:15 -0400, David Kreiss wrote: >Determine what track the dataset was allocated to then run this utility >specifying the first track of the dataset. > <snip!> ... which can give a false positive if the extent allocated begins, by happenstance, with a residual EOF from prior use.
> >-----Original Message----- >From: IBM Mainframe Discussion List [mailto:ibm-m...@bama.ua.edu] On Behalf Of >Starr, Alan >Sent: Friday, October 15, 2010 12:41 PM > >John McKown's response to Ron's S013-64 issue interested me. I had not >realized that SMS automatically wrote an EOF to newly-allocated datasets. > Depending. >John pointed me to >http://publibz.boulder.ibm.com/cgi-bin/bookmgr_OS390/BOOKS/dgt2i650/8.1 > >which states "For sequential data sets, SMS writes a hardware EOF at the >beginning of the data set at initial allocation. This prevents data integrity >problems when applications try to read the data before data is written in the >data set." > Jim Mulder properly stated this assertion ought not mention security. It doesn't. Regardless, "data integrity" has misleading connotations. I'd replace "prevents data integrity problems" with "prevents unexpected program behavior". >Just for fun, I allocated four new datasets using IEFBR14: >> DSORG=PS SMS-managed >> NO DSORG SMS-managed (had to modify my DC ACS routine to get this) >> DSORG=PS non-SMS >> NO DSORG non-SMS > >All utility programs (e.g. IBMGENER, IDCAMS, IEHLIST and IEBPTPCH) referencing >any of these datasets via any input DD (e.g. SYSIN or SYSUT1) recognized that >there was no data. I wonder, therefore, whether newly-allocated datasets are >now getting initialized with an "EOF". Seems unlikely to me that all are >because all JCL references up to and including V1R12 have a note for DISP=NEW >(Note: Initialize a new data set to ensure that it is empty). > the signal is obscured because most utilities will also check DS1LSTAR as well as for physical EOF, and treat either as end of data. >I don't know of a tool that we have at this organization which indicates the >presence of an "EOF" (count with keylen=0 and datalen=0) in a track. > Assembly language BSAM read. >Would any of you have such a utility and be willing to use it to test the >results of IEFBR14-allocating the aforementioned datasets? > IEFBR14 doesn't allocate; it's much too short to do that sort of thing. >I'm curious to know whether newly-allocated datasets are "empty" (no content) >or "null" (hardware EOF at the beginning). I found a definition of "empty" >versus "null" in the final paragraphs of "DFSMSdfp Storage Administration: >Chapter 7. Defining data classes - Planning data classes" > What's "no content"? Except on a new, freshly unwrapped device, an obtained extent will contain residual data from prior use. The most you can expect is unpredictable content, -- gil ---------------------------------------------------------------------- For IBM-MAIN subscribe / signoff / archive access instructions, send email to lists...@bama.ua.edu with the message: GET IBM-MAIN INFO Search the archives at http://bama.ua.edu/archives/ibm-main.html
