My experience from 20 years of computer use ...
Anyway, I got several identical PCs (6 in fact) with 2 identical OS-HDDs in each of them and cross-cloned OSes (Windows Server 2003 R2 Enterprise Edition x86 & Windows 7 Ultimate Edition x86), and each of my 2TB-HDDs is backed up fully on another 2TB-HDD ... freshly cloned every 9 months or so. Did I mention that I buy all of my stuff used? Except for the 6 x 2TB-HDDs which I bought new.