Can I start by confirming that a component with a higher MTBF will be up for a longer time between failures and is thus more reliable than a component with a low MTBF. However Reese seems to be using MTBF in the opposite sense (unless I am confused!).

Paragraph starts by stating that a virtual server has a lower MTBF (i.e. less reliable) because it depends on its underlying physical servers and there are less physical servers than virtual ones.

Paragraph finishes by re-stating the idea that the number of physical nodes deterimines MTBF but states that fewer servers means a higher (more reliable) MTBF. I think he meant to say a lower (less reliable) MTBF.

Quote:
"A key challenge for any system requiring long-lived nodes in a cloud infrastructure is the basic fact that the mean time between failures (MTBF) of a virtual server is necessarily less than that for the underlying hardware. An admittedly gross oversimplification of the problem shows that if you have two physical servers with a three-year MTBF, you will be less likely to experience an outage across the entire system than you would be with a single physical server running two virtual nodes. The number of physical nodes basically governs the MTBF, and since there are fewer physical nodes, there is a higher MTBF for any given node in your cloud-based transactional system."