>it gives the same result at the end No, it doesn't. You picked 3% of all drives failing out of the blue. Your next estimate was an order of magnitude too high

>it gives the same result at the end No, it doesn't. You picked 3% of all drives failing out of the blue. Your next estimate was an order of magnitude too high. Your last assumption of p^# drives is not reasonable. The proof is in reality. Backblaze has run over a decade, with all sorts of hardware failures, server configs, running many drive models through their lifetime, across manufacturers, across technologies, across multiple datacenters, and had not seen the level of failures you claim they will. So I suspect their method of estimating is more accurate than yours. So far it matches reality much better.