I see the allure of dedicated servers. All is great when everything works. What I miss in this picture is failure scenarios. How many dedicated servers do you

I see the allure of dedicated servers. All is great when everything works. What I miss in this picture is failure scenarios. How many dedicated servers do you need to run to afford losing one of them to a hardware failure? What is the cost and lead time for a replacement? How much overprovisioning do you need to do, and how well ahead, in anticipation of seasonal spikes, or a wave of signups from a marketing campaign?