Best answer by Jon
RF 2 = 2 copies
RF 3 = 3 copies.
i.e: RF2 for random-file-name-here.exe, which is 10G would take up 20G of storage
RF3 for that same file would be 30G of storage
This assumes no data reduction, or use of erasure coding.
Erasure coding, Compression, Dedupe, and Zero suppression could make that 20G (or 30G) of storage much, much, much less