A company is implementing the 3-2-1 backup rule.

The 3-2-1 backup rule is specifically about number of copies, diversity of media, and offsite storage. “2” in 3-2-1 means using two different types of media. The All-in-One guide states the rule plainly: “keep at least three copies of your data on at least two different types of media… and store at least one copy offsite.” Mike Meyers’ Lab Manual repeats the same definition word-for-word, emphasizing two different media types and one off-site copy.

Quentin Docter explains the same method and gives an example: original data plus an on-site backup, plus “a third copy… off site,” such as backing up to the cloud.

Given the options, only D directly satisfies the “two different media” requirement. Option C contradicts the offsite requirement, option B invents a testing interval not defined by 3-2-1, and option A is about backup types rather than the core 3-2-1 rule. Therefore D is correct.