What is the 3-2-1 backup rule?

Keep three copies of data, on two types of media, with one copy isolated or off-site.

Answer

The 3-2-1 rule is a useful baseline: keep the working data plus at least two backups, use more than one storage method, and maintain one copy off-site or otherwise isolated. Modern ransomware planning often adds immutability, offline protection, and verified recovery testing.