Once experience the classic "single tape" cock-up
"Yes we have backups every night, without fail for the last 18 months."
"Oh great, should save some time. We need to test restores for the auditors. Who changes the tapes and what's the offsite storage like, fire-proof that sort of thing?"
"Change the tape? No need, it's big enough, well it's never run out yet."
"No, you only have 150MB of space on a tape and the server is holding 40MB of data, so that's only 5 days worth!" ( 40MB on a server, that shows you how long ago this was! )
"There is no way that tape could do more than 3 nights of backups before it fills up. You've most likely overwritten the same tape hundreds of times, so you have no historical data available."
( You will be! )
Quick check and yep, they'd run 450 backups on the same tape, over and over and over and over...the software didn't bother to check the tapes had data, it just rewound and overwrote it.
Needless to say the auditors were not in the least bit impressed and lots of shouting ensued at management level and plenty of overtime was paid out to IT to make sure it did not happen again!