WattValet: Heterogenous Energy Storage Management in Data Centers for Improved Power Capping

This paper presents WattValet, an efficient solution to reduce data center peak power consumption by using heterogeneous energy storage. We henceforth call an energy storage device, a battery, with the understanding that the discussion applies to other devices as well such as pumped hydraulic and thermal systems. Previous work on energy storage management in data centers often ignores or underestimates their degree of heterogeneity. Even if batteries used in a data center are of the same model and purchased at the same time, differences in storing temperature and humidity, as well as discharging cycles and depth, gradually drive their characteristics apart. We show that differences in battery characteristics, such as discharge rates, if not fully accounted for, can lead to significantly suboptimal power caps. A new algorithm, called WattValet, is described that reduces peak power consumption by efficiently exploiting heterogeneity. Evaluation using Wikipedia traces shows that the power cap generated by WattValet is within 2% of the optimal solution, whereas WattValet finishes the computation orders of magnitude faster than the optimal solution even in small-scale experiments.