Dynamic server consolidation algorithms: a profit model for evaluation and an improvement.

Dynamic Server Consolidation (DSC) uses the live migration facility of virtualization technology to consolidate virtual machines (VMs) on fewer physical machines (PMs) when demand is low, to use minimal PMs without violating the Service Level Agreements (SLAs). The implicit goal of DSC is to maximize the data center profit, or minimize the cost, which is generally approximated in terms of PM operational cost and some direct cost given to migrations. In this paper we propose a profit model in which costs of actions, such as VM migrations, manifest as SLA penalties and increased operating costs, rather than some direct artificial costs given to them. The model can be used as an important tool to evaluate different consolidation algorithms, in terms of single cost metric. We also propose an algorithm for DSC, based on the stability of VM placements, which is an improved form of an existing algorithm, and use our metric to compare the two algorithms for different values of cost parameters. In most cases our algorithm reduces costs by upto 28%.