On the performance and use of dense servers

Dense servers trade performance at the node level for higher deployment density and lower power consumption as well as the possibility of reduced cost of ownership. System performance and the details of energy consumption for this class of servers, however, are not well understood. In this paper, we describe a research prototype designated as the Super Dense Server (SDS), which was optimized for high-density deployment. We describe its hardware features, show how they challenge the operating system and middleware, and describe how we have enhanced its software to handle these challenges. Our performance evaluation has shown that dense servers are a viable deployment alternative for the edge and application servers commonly found at conventional Web sites and large data centers. Using industry benchmarks, we have shown that SDS outperforms a comparable traditional server by almost a factor of 2 for CPU-bound electronic commerce workloads for the same space and roughly equivalent power budget. We have observed the same advantage in performance when SDS is compared to the alternative solution of virtualizing a high-end server to handle "scaled-down" workloads. We have also shown that SDS offers finer power management control than traditional servers, allowing higher energy efficiency per unit of computation. However, for high-intensity Web-serving workloads, SDS does not perform as well as a traditional server when many nodes must be configured into a cluster to provide a single system image. In that case, the limited memory of each SDS node reduces its performance scalability, and a traditional server is a better alternative. We have concluded that until technology advances allow denser packaging of memory or more efficient use of memory across nodes, the best performance and energy efficiency can be obtained by heterogeneous deployment of both traditional high-end and dense servers.