Cooling-aware workload placement with performance constraints

Power optimization in data centers requires either to raise the temperature of the cold air supplied by the air conditioner or to reduce the power consumption of the servers by careful workload allocation. Both the approaches must satisfy a number of constraints, mainly temperature at the server intakes, which should not exceed a critical threshold, and capacity and response time requirements. To tackle these issues, we formulate an optimization problem in which the total data center power has to be minimized subject to the constraints imposed by performance requirements and thermal specifications of the servers. At the heart of the optimization problem is an analytical model which takes into account the complex relationship between the performance of servers, the allocation of workloads, the temperature of the air supplied by the conditioning unit and the heat distribution in the server room. For the easy evaluation of this relationship, we adopt a simplified yet accurate heat flow model, which we extensively validate using the data collected in several months of Computational Fluid Dynamics simulations. Extensive tests on 90 randomly generated scenarios suggest that the proposed coupled thermal-performance model can lead to a power saving of 21%. Finally, a case study is presented which is based on 1164 workload traces collected from the data center of a large telco operator. The cooling-aware workload placement suggests a saving of 8% with respect to a performance-only based strategy.