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Data centers attempt to maximize return on investment by achieving high levels of utilization. This means deploying the maximum number of servers possible within existing power supply capabilities. Therefore, a key problem is determining how many servers can be safely accommodated. Recently, a variety of power capping solutions have been proposed to safely allow oversubscription of available power, but they conservatively assume that peak power should never exceed the rated power distribution equipment capacity. Hence, the open question is: how much power oversubscription is indeed safe? In this paper, we focus on data center branch circuits and systematically study the tripping characteristics of their circuit breakers (CBs). Our results on a physical testbed show that instantaneous violations of the rated CB power limit are not necessarily fatal because CBs are designed to sustain a certain amount of power overload. Whether a CB trips or not depends primarily on the transient behaviors of a power overload, such as the magnitude and duration time, as well as ambient temperature. We propose two adaptive power control strategies that utilize the CB tripping characteristics to aggressively optimize the system performance without causing the CB to trip. Our extensive hardware results with SPEC CPU2006, SPECJBB, and LINPACK benchmarks show that the proposed CB-aware power control solutions achieve 38%, 75%, and 68% better average performance, respectively, than a state-of-the-art baseline. A key contribution of our work is to provide a practical upper bound of the server power oversubscription allowed on branch circuits. As a result, our solutions allow a data center to host three times more servers than traditional static power provisioning schemes and 54% more servers than the current power capping practice.
Fu et al. (Tue,) studied this question.