Staged request routing for reduced carbon footprints of large scale server systems

The power consumption of server systems used as part of online services is an important problem as these have become major energy users. Generally, such systems are dimensioned for peak loads and typically have average utilisations of 20-30%. This paper introduces a simple routing mechanism that uses overflow techniques to assign requests to these servers. As these mechanisms employ a staged process, idle systems can be suspended. For a rising number of servers, this yields a load proportional power profile. Request distribution is implemented by a router device; servers report their utilisation to the router. Idle systems suspend their operation; suspended systems are returned to the active state by the Wake-on-LAN function. The system design, performance models and initial results are presented.