[JJ_SO]

Harddrives will fail - not a question, if, just when. One backup only? To me not enough. So each new TB I buy is actually 3 new HDs. True, they are cheap. But have you ever copied 3 TB to another drive? And afterwards noticed that a couple of files appear to be defect? That can happen pretty easily during long copy sessions, because I reckon you don't run a UPS (uninterruptible power supply)? If there's power loss during a copy session, the original files can get damaged, too.

 

My principle is trying to reduce the risk, whenever possible.