(Not considering as a counterpoint, just want to point this out for whomever.) When (not if) it does go down, however long it takes to replace is downtime that

(Not considering as a counterpoint, just want to point this out for whomever.) When (not if) it does go down, however long it takes to replace is downtime that has to be amortized over the entire X years, to get an accurate picture. If it takes > 260 minutes to detect, replace, and fully recover, then you've already blown the four nines budget you "saved up" for the past five years, when amortizing. Side-note from a recent twitter thread: If you're not rigorously monitoring availability (preferably with canaries/probes), it's probably much lower than you think. (Using the royal 'you' here, not pointing any fingers.)