Small versus Large: Switch Sizing in Topology Design of Energy-Efficient Data Centers

Saving power in data-center networks has become a pressing issue as the networks tend to consume steady power even when many servers are idle during nighttime. ElasticTree and CARPO are designed to save the power consumed by a fat-tree data-center network by using Sleep Mode where some components such as ports and switches are turned off when traffic demand in the network is relatively moderate. In this paper, we take a different view by exploring the design stage of a data-center network and focus on how to choose the right switch size that can potentially save the most power during the expected operation of the network. We also consider Speed Scaling where the power of a switch can be varied by adjusting its processing rate according to its traffic demand. We perform both analysis and simulation to investigate the power-saving performance of different switch sizes, power-saving modes and traffic demand patterns. Based on fat-tree networks supporting the same number of servers, our findings reveal that deploying a large number of small switches than a small number of large switches is generally more power-efficient when the traffic demand is relatively moderate or when servers exchanging traffic are in close proximity. Our approach is also extendable to other types of data center networks.