There is *usually* a fair amount of tape left behind the EOV marker. (Or at least there was in the good old days -- I have not fiddled with a physical EOV marker since the days of 2400' reels. I'm sure someone will point it out if what I say is not relevant to carts.) The exact amount of tape left is somewhat variable. There is no absolute guarantee that any particular amount of tape remains. However, there is usually "plenty" of room for several more blocks and the EOV labels. A sophisticated program like for example a backup program might want to write blocks in some sort of logical groups and could probably count on generally getting away with writing two or three or more blocks after the EOV marker, with no ill effects. OTOH, again in the good old days, sometimes an EOV marker was applied too close to the end of the reel, and the tape would come off the reel, much to the amusement of the operators. I suspect the manufacturing process is now more automated and consistent.
I think to answer your specific question, the drive detects EOV during the writing of a block. I believe that block is written without error, and then EOV is signaled back to the channel, the IOS, the access method, and the application if indicated. The block being written when EOV is detected would typically become the last data (non-label) block on the volume (but not necessarily -- see above). Does anyone know if EOV breaks a CCW chain? If the software is writing a chain of (say) 5 blocks, and EOV is detected during the writing of the second block, does it break the chain? Does I/O error recovery have to re-issue the EXCP for the last three blocks, presumably on the new volume? Charles -----Original Message----- From: IBM Mainframe Discussion List [mailto:[EMAIL PROTECTED] On Behalf Of Joel C. Ewing Sent: Thursday, April 12, 2007 5:52 PM To: [EMAIL PROTECTED] Subject: Re: EOV detection on tape volume [EMAIL PROTECTED] wrote: > Is EOV detected when the last record is written, or, when an attempt > is done to > write the last record? > EOV is detected as the tape drive is writing a block of records and a physical EOV position is detected by the drive. There is still enough usable tape past that point for the drive to complete writing the block and for the Operating System to then write the required trailing tape marks and labels before unloading the tape and requesting another output tape volume. ---------------------------------------------------------------------- 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
