I was reminded today of an oldie but a goodie: the “3-2-1 rule” for data backups. For any critical data you should have:
- 3 copies
- on 2 different forms of media
- with at least 1 copy being off-site
Not a hard and fast rule (this rule dates back to when “two forms of media” implied “disks and tapes”), but a really good starting point still.