Hoyer, Marko and Schlitt, Daniel, Schröder, Kiril, Nebel, Wolfgang
Dynamically reassigning virtual machines (VMs) to servers is a widely addressed idea to save energy in data centers. VMs are consolidated in times of low overall resource demand. Unused servers are switched off to save energy. Mainly two major chal¬lenges must be addressed to realize this approach. First, the re¬source demand of VMs expected in the future must be estimated to take care of delays caused by VM migrations and server start¬ups. An upcoming resource shortage must have been resolved right before it actually occurs. Second, a scheduling algorithm is needed that, based on a current distri¬bu¬tion of VMs to servers, can guarantee to find a sequence of operations that resolves any upcoming resource shortage right in time. Within this paper, we present a novel approach that addresses both of these challenges. In contrast to previous work, this approach can guarantee not to cause any resource shortages, if the actual resource demand of the VMs meets the expected one. We performed a simulation based evaluation with a set of VMs. The underlying resource demand time series were measured in a data center operated by a medium-sized IT service provider. A data center model was used to esti¬mate the energy consumption. Overall energy savings of about 23% could be achieved compared to a static approach. Resource shortages occurred in less than 0.1% of time. They could be resolved by the approach in less then 20 minutes.