Green Data Centers: A Survey, Perspectives, and Future Directions <s> B. Temperature-Reliability Trade-off <s> Local thermal hot-spots in microprocessors lead to worst-case provisioning of global cooling resources, especially in large-scale systems where cooling power can be 50~100% of IT power. Further, the efficiency of cooling solutions degrade non-linearly with supply temperature. Recent advances in active cooling techniques have shown on-chip thermoelectric coolers (TECs) to be very efficient at selectively eliminating small hot-spots. Applying current to a superlattice TEC-film that is deposited between silicon and the heat spreader results in a Peltier effect, which spreads the heat and lowers the temperature of the hot-spot significantly and improves chip reliability. In this paper, we propose that hot-spot mitigation using thermoelectric coolers can be used as a power management mechanism to allow global coolers to be provisioned for a better worst case temperature leading to substantial savings in cooling power. In order to quantify the potential power savings from using TECs in data center servers, we present a detailed power model that integrates on-chip dynamic and leakage power sour-ces, heat diffusion through the entire chip, TEC and global cooler efficiencies, and all their mutual interactions. Our multi-scale analysis shows that, for a typical data center, TECs allow global coolers to operate at higher temperatures without degrading chip lifetime, and thus save ~27% cooling power on average while providing the same processor reliability as a data center running at 288K. <s> BIB001 </s> Green Data Centers: A Survey, Perspectives, and Future Directions <s> B. Temperature-Reliability Trade-off <s> The energy consumed by data centers is starting to make up a significant fraction of the world's energy consumption and carbon emissions. A large fraction of the consumed energy is spent on data center cooling, which has motivated a large body of work on temperature management in data centers. Interestingly, a key aspect of temperature management has not been well understood: controlling the setpoint temperature at which to run a data center's cooling system. Most data centers set their thermostat based on (conservative) suggestions by manufacturers, as there is limited understanding of how higher temperatures will affect the system. At the same time, studies suggest that increasing the temperature setpoint by just one degree could save 2-5% of the energy consumption. This paper provides a multi-faceted study of temperature management in data centers. We use a large collection of field data from different production environments to study the impact of temperature on hardware reliability, including the reliability of the storage subsystem, the memory subsystem and server reliability as a whole. We also use an experimental testbed based on a thermal chamber and a large array of benchmarks to study two other potential issues with higher data center temperatures: the effect on server performance and power. Based on our findings, we make recommendations for temperature management in data centers, that create the potential for saving energy, while limiting negative effects on system reliability and performance. <s> BIB002
Several other efforts have focused on supplying data centers with relatively warm air to reduce cooling costs, i.e., increasing/controlling the temperature setpoint. Studies show that increasing the temperature setpoint by merely one degree can yield an energy savings of 2-5%  . However, raising the temperature of the server's components can reduce the system reliability. Based on the critical observation that hot spots can be selectively cooled, BIB001 proposed a cooling-power management mechanism to allow global data center coolers to operate at a higher temperature while achieving the same level of chip reliability. The authors integrated thermal models of various components, such as the silicon in the chip, embedded thermo-electric coolers, and air conditioners, and quantified the expected savings in cooling power for the entire data center. Upon evaluating over 43 applications from the SPECcup 2000 benchmark, they reported a cooling power savings of 12% on average. However, there is a limited understanding of how higher temperatures will affect data center systems. In BIB002 , the authors presented a multi-faceted study of temperature management in data centers. By analyzing a large collection of field data from different production environments, the authors studied the influence of higher temperatures on 1) hardware reliability, such as storage subsystem reliability, memory subsystem reliability, and server reliability as a whole, as well as 2) server performance and power consumption. They concluded that the operators could run their data centers hotter than they currently were to save energy while still limiting the resultant negative effects on system reliability and performance.