What does he mean by "I do usually try to monitor them with a dead man’s switch.", when talking about backups?
I assume this is opposed to alerting when the backup job fails, which is an issue if the job never runs, or hangs forever, or crashes in a way that doesn't trigger your monitoring.
However I don't see how any of this solves the issue of not testing your backup. Because you can definitely have a backup task succeed regularly but the thing it is backing up is still unusable.
Turns out the backups took 30 hours. The daily backups. That then overwrote each other on the assumption that the backups would not take that long.
Of course we found out the hard way.
In this context it means upon a successful backup, update a timestamp somewhere. Some other system monitors the timestamp and if it ever becomes more than for example 1 day ago, it fires an alert.