Data Center Power Minimization with Placement Optimization of Liquid-Cooled Servers and Free Air Cooling

        Most of today's data centers are equipped with servers that rely on air cooling, which is well known to have low cooling efficiency due to undesired air recirculation. As a result, many data centers have started to adopt liquid cooling and free air cooling for improved cooling efficiency. In this paper, we make two key observations. First, since data centers normally replace only a portion of their servers at a time, an important problem is where in the data center to place those new liquid-cooled servers for the best return on their investment. Given the complex thermal dynamics in a data center, we find, in our process of deploying liquid-cooled servers, different placement strategies lead to significantly different cooling power consumption. Second, different cooling techniques, including traditional air cooling, liquid cooling, and the emerging free air cooling, must be intelligently coordinated with dynamic workload allocation in order to minimize the cooling and server power of a data center. Based on the two observations, we propose SmartPlace, an intelligent placement algorithm that deploys liquid-cooled servers to minimize the power consumption of the data center cooling system. SmartPlace also takes into account the coordination with free air cooling and dynamic workload distribution among servers for jointly minimized cooling and server power in the entire data center. We compare SmartPlace with a state-of-the-art cooling optimization solution for two data centers with 1,280 and 10,240 servers, respectively. The results show that SmartPlace achieves up to 26.7% (with an average of 15%) less total power consumption with dynamically guaranteed application response time. Our hardware testbed results also demonstrate the effectiveness of SmartPlace. Moreover, we analyze how soon a data center can gain a full return on the capital investment of liquid-cooled servers.