When the calculated result starts exceeding what is reasonable or makes any sense. It varies, and is a gut feeling. The more you have, the better. Having 100 o

When the calculated result starts exceeding what is reasonable or makes any sense. It varies, and is a gut feeling. The more you have, the better. Having 100 of this model would predict a failure about every three years (but that doesn’t mean it’d take 300 years to fail all of them). I’d be suspicious of a three year calculation, but it very well might turn out to be accurate. Remember that lifetime and failure rate are independent metrics. They’re warranted for five years, which is probably close to their predicted lifetime, and one drive of 100 failing in that time is certainly plausible. Having 10 basically implies none of them will fail within a five-year lifetime. Again, plausible, but I think less likely.