Neither voodoo nor sabotage was behind the mysterious Monday tape overload problem. Nevertheless, it took a year to find a solution.
Years ago, I ran a small VAX network for an engineering company. 8mm tape was just emerging as a backup technology, and I eagerly went for it. The high-density tapes we used would do an entire system backup on one tape, with room to spare, in a relatively short time. We could back up daily, unattended. What a nice change from mounting a dozen 9-track tapes and babysitting the process over several hours every weekend.
Everything worked fine until one Tuesday morning when I came down to take out the Monday backup tape and replace it with Tuesday's. The backup program was asking for a second tape for Monday's backup. Oh, no! Our files had finally exceeded the capacity of one tape!
This was a bad situation, because we had only a single-tape deck and putting a second tape in after the workday was underway would be useless. So I spent that day looking for files I could delete (there were always plenty) to get it back down to one tape's worth. I must have done well; Tuesday's backup needed just one tape.
Things went fine until I went down to change out the next Monday's backup, and discovered it wanted another tape. This time I did a painstaking analysis of that night's backup logs and determined that there was essentially no more data to back up that night than any other. Must be a bad tape, I thought. So I swapped it for a new one.
Next Monday, same thing -- the new tape had also "run out of space." I considered all sorts of voodoo causes, one of them being that we had changed to daylight-saving time the weekend before the Monday when this all started, but I couldn't get that to make any sense, either. I jumped on to a VAX/VMS discussion group on the Web, and described my situation in detail, including all of the possibilities I had ruled out, but no one had any fresh ideas.
This went on for about a year. We changed back to standard time: no difference. Tried other new tapes but always had the same problem: Monday backups would not fit on one tape, while all others did.
One day, while doing something else, I had a Eureka moment. I went down to the computer room to check, and found what I was looking for. Took care of it, and never had the problem again.