> -----Original Message----- > From: IBM Mainframe Discussion List > [mailto:[EMAIL PROTECTED] On Behalf Of Charles Mills > Sent: Thursday, July 06, 2006 2:25 PM > To: [email protected] > Subject: Re: avgrec/avgblk history ? > > > That is true for any dataset. If you "create" (allocate space > to and write > an entry in the VTOC) a dataset but never open it for output, > a subsequent > step, or even a subsequent job days later, can open that > dataset and read > it, getting whatever data happens to be on those tracks, with no error > indication, unless the reading program happens to get an > S013(?) because the > blocks are the wrong size, not valid RECFM=V format, etc. Results are > unpredictable: one day you will get an ABEND, the next day > you will read in > unexpected data, and on the third try you will be lucky > enough to hit an EOF > marker (or empty tracks followed by an EOF marker) right away. > > An interesting mainframe "hack" would be to write a program > that allocated > vast quantities of DASD DISP=NEW and then read whatever > happened to be there > (RECFM=U, of course), looking for "interesting" data. > > Charles
Charles, Remember that for some dataset DSORGs, allocation may do some I/O. In particular, when you define a PDS, the directory is created and formatted. And when you create a file with DSORG=PS (or if it is defaulted via an assigned DATACLAS), then allocation will write an EOF marker (this is new in SMS). If you want avoid this, then I think you'd need to use RECFM=U,DSORG=DA,BLKSIZE=32756 on your allocation request. I'm fairly sure that would result in your program being able to read any residual data. Which, of course, means that in a truly secure environment, RACF should be use to do an "erase" function when the dataset is scratched. This is not NSA-proof, of course, but a simple rewriting of the tracks with, I think, binary zeros on all allocated tracks. That would stop the above. But it is costly in terms of I/O and CPU. -- John McKown Senior Systems Programmer HealthMarkets Keeping the Promise of Affordable Coverage Administrative Services Group Information Technology This message (including any attachments) contains confidential information intended for a specific individual and purpose, and its content is protected by law. If you are not the intended recipient, you should delete this message and are hereby notified that any disclosure, copying, or distribution of this transmission, or taking any action based on it, is strictly prohibited. ---------------------------------------------------------------------- For IBM-MAIN subscribe / signoff / archive access instructions, send email to [EMAIL PROTECTED] with the message: GET IBM-MAIN INFO Search the archives at http://bama.ua.edu/archives/ibm-main.html
