more than one backup

[has55]

You wrote on another thread, " My general suggestion is to have more than one backup. It's faster to create and maintain two backups then it is to verify one, and it has additional benefits, too.

" You also wrote in the user guide-But, it is possible that a user won’t notice a problem in a “bad file” until they’ve already overwritten their backup, thus losing any chance of recovery with a “full copy”. While this is a problem for some, we have a good solution: rotate more than one full backup.
Any need for this kind of “temporal rollback” can be significantly reduced with a single rotation – say, on a weekly basis – and nearly eliminated with two, a weekly and a monthly. It’s incredibly rare that, on a non-archival basis, you’d need to go back more than four weeks.

Does that mean I need more than one external drive. one for each backup?

[dnanian]

That's the most redundant thing to do, yes. But you can also use multiple partitions on the same drive.