Many years ago I worked for an insurance company which had a DR plan in place. Since I worked the Wednesday through Sunday swing shift, I got to participate more than once.
The drills were random and could happen anytime on a weekend. They were used to test the complete recovery and uptime of the systems we were using at the time. The mainframe system was offsite since the beginning so all that was needed for that was a network connection.
We sent our tapes to an off-site storage firm. Initially it was a small company which failed the test only once and lost the contract. After that it was a much bigger company who came in daily, including weekends, to pick up the nightly backup tapes from the previous night's backups.
During the tests, we would get a call, that the systems were down. Being in computer operations in the computer room, we would find ourselves in a locked-down type of situation where there was no local network access as someone had pulled the plugs to the concentrators.
The system at the remote location was brought up on line once the tapes arrived and the tapes were restored to the servers. The systems were then brought up online and we were then told to connect to the system and run the batch jobs we were scheduled to do so, except they were running off of the remote location. Everything went as planned.
The only glitch we had was that offsite company who messed up and didn't respond to the phone call.
Granted this was 25 years ago now and stuff was a lot simpler. The servers were '486 Novell servers and the tape backup was perhaps two tapes maximum at 1.2Gigs each.
What's interesting is how this went together like clockwork and how well everything was rehearsed to ensure it did every time. We were usually up and running within a couple of hours.
I have always maintained good backups of everything, even at home as well. The important thing to remember is hardware can always be replaced, software can always be reinstalled from media or these days downloaded off the web. The data is the most important thing to backup, and without a good backup of the most important thing, you have nothing.