Server Parking in Virtualized Cloud Data Centers

Luiz Barroso in his classic 2007 paper posited that given that servers in data centers were loaded between 10 and 50 percent of peak, it would be beneficial from an energy perspective to have servers with a large power dynamic ratio, the ratio of power consumed at full workload to power at idle.  The figure below actually represents the state of the art today with a dynamic ratio of about 2:1 and efficiency that can drop below 20 percent.  The operating band depicted is more conservative than what Barroso indicated, with a CPU utilization that rarely surpasses 40 percent.


The next figure illustrates what happens if we improve the dynamic ratio to 5:1.  This is not possible today for single servers, but it is attainable for cloud data centers and as a matter of fact, for any environment where servers can be managed as pools of fungible resources and where server parking is in effect.


The improved dynamic ratio also dramatically improves the operating efficiency in the operating band of the data centers, but it gets even better:  the servers in the active pool are kept in the sweet spot of utilization in the range of 60 to 80 percent.  If the CPU utilization in the active pool gets below 60 percent, the management application starts removing servers from the active pool to the parked pool until the utilization starts inching up.  If the CPU utilization gets close to the upper range, the management applications starts bringing back servers from the parked pool into the active pool to provide relief and bring the utilization numbers down.