I’m sure many of you know VSAN’s Failures To Tolerate, or FTT, is something that adds overhead to both your cluster & your data. It’s no secret FTT of 1 doubles your data, think of it as N+1 copies of your data. You could essentially have two, three, or four copies of your data, redundancy is a good thing!
When you look at the cluster side of it, there is another ‘gotcha’. The host needs becomes 2N+1. Let’s look at FTT of one, that’s saying you need 2(1)+1 hosts, so 2+1 = 3. And of course, FTT2 requires 5 hosts, and FTT3 requires 7.