(laughs) I've actually been prepping a pair of USB drives for offsite backup since Friday. It takes 2-4 days to run "badblocks" with three clean passes, then another day to run "shred" on the drive. If it passes that burn-in test, then the drive is generally good to go for a few years of service.
You just reminded me that my shred pass was finished and that I should finish setting up LUKS encryption and add them to the backup pool.
My backups are all written to a central file server, which has a 4-bay USB enclosure attached. So once per day, the server copies the backup files off to one of the four USB enclosure drives. Then I also have a pool of external USB drives that get carted offsite semi-frequently to a safe-deposit box. Then there's the annual backup to a trio of SD cards, kept in the safe.
At the last company, we had six generations of external USB drives that went offsite each week. That may not sound like a long retention period, but using rdiff-backup or attic-backup, each drive had incrementals going back 27 or 54 weeks. I'm pushing them to ramp up to eight generations.