Abstract
The energy consumption of server farms is steadily increasing. This is mainly due to an increasing number of servers which are often underutilized most of the time. In this paper we discuss various strategies to improve the energy e ciency of a datacenter measured by the average number of operations executed per Joule. We assume a collection of heterogeneous server nodes that are characterized by their SPECpower-benchmarks. If a time-variable divisible (work)load should to be executed on such a datacenter the energy e ciency can be improved by a smart decomposition of this load into appropriate chunks. In the paper we discuss a sophisticated load distribution strategy and extend it by an adaptive power management for dynamically switching underutilized servers to performance states with lower energy consumption. Of course,also transitions to higher performance/energy states are possible if required by the current load. We introduce a new time slice model that allows a reduction of the switching overhead by means of a few merge and adjust cycles. The resulting ALD+ strategy was evaluated in a webserver environment with real Wikipedia traces. It achieved signi cant reductions of the energy consumption by the combination of load distribution and server switching by means of the time slice model. Moreover, ALD+ can be easily integrated into any parallel webserver setup.
