Sunday, October 22, 2006

A cautionary tale about tape labels

I recall that in the 1980s, at a Texas credit reporting company (then, Chilton), we had gotten used to coding a label parameter to save tape datasets as LABEL=EXPDT-99000 to assume catalog control. That is, the tape could not be written over unless uncatalogued. We had used a third party vendor tape management system.

In 1988 I took a new job in a small shop in Washington DC that had a 4341 and 4381, which at the time were the small mainframe computers that could run MVS (or VM, which actually emulated a PC on the mainframe). I had created and saved a lot of data tapes and coded them the same way. Lo and behold, one summer evening in 1989 (after a small data center move) I find out that all of the tapes are unprotected. Fortunately, none of them had yet been written over. But if they had been, a whole business could have been lost. My career could have ended right then and there.

The new shop used IBM's own standard only, which at the time were EXPDT=yyddd, where 99365 or 99366 kept the tape indefinitely.

It appears that all of this changed with Y2K. The correct way to code is yyyy/ddd (1999/365 or 1999/366 still gives permanent retention).

The lesson is, if you are a consultant and work in a shop where you have some responsibility for manually managing data resources, be very sure that you know the exact rules for your shop. And know the official IBM standards, which may appear on certification quizzes.

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