Server farms such as Google and Yahoo! provide enough compute capacity for the highest request rate of the day. Imagine that most of the time these servers operate at only 60% capacity. Assume further that the power does not scale linearly with the load; that is, when the servers are operating at 60% capacity, they consume 90% of maximum power. The servers could be turned off, but they would take too long to restart in response to more load. A new system has been proposed that allows for a quick restart but requires 20% of the maximum power while in this “barely alive” state.

a. How much power savings would be achieved by turning off 60% of the servers?

b. How much power savings would be achieved by placing 60% of the servers in the “barely alive” state?

c. How much power savings would be achieved by reducing the voltage by 20% and frequency by 40%?

d. How much power savings would be achieved by placing 30% of the servers in the “barely alive” state and 30% off?