I have been thinking about how large companies backup their data. I imagine that in some critical enterprises they must consider every possibility and can't afford to lose even one bit of data. Of course they use backups.
But what if the backup fails? The whole thing, not just one or two disk (because they're using RAID of course). No problem, just hurry up and copy the original data to a shiny new disk. But what happens if both systems failed. I don't know maybe zombies bit through the power lines and trashed both data centers, could happen. How do you prevent data loss?
Well, you just have a backup of a backup of a backup of a backup...
Does this problem occur in real life (sans zombies) and how do the pros deal with this conundrum?