We already have small 2TB drives -- 4TB shouldn't be too far away
You should look at pictures of old circa 1974 IBM mainframe 2314 Disc drives -- these were HUGE and only had I think it was around 29 MB (yes MB) capacity.
Moore's Law still has a LONG way to go yet before we run out of storage capacity.
Incidentally I never did see the point of CLOUD backup -- running APPLICATIONS however is a different issue.
For those interested here's a snippet from old IBM archives on the 2314. Note that for it's time it was a really brand new technology and some of the ideas such as incorporating independent disk controllers so I/O could take placer CONCURRENTLY with SYSTEM PROCESSING instead of having to wait for I/O to complete before continuing execution was the foundation for I/O handling in modern OS'es such as Windows and Linux. IBM Archives: IBM 2314 direct access storage facility