Someone set up a script to automatically create daily backups to tape. Unfortunately, it's still the first tape that was put in there 3.5 years ago, every backup since that one filled up failed. It might as well have failed silently because everyone who received the email with the error message filtered them to a folder they generally ignored.

And no one ever tried to restore it.

Happened to me as well, after a year I learned incremental DB backups were wrongly offset by GMT diff, so we were losing hours every time. Fun.

Luckily we never needed them.

And now we have Postgres with WAL archiving and I sleep so much better.