Adaptive Live VM Migration over a WAN: Modeling and Implementation

Recent advances in virtualization technology enable high mobility of virtual machines (VMs) and resource provisioning at a data-center level. Various strategies have been proposed for fast VM live migration over a local-area network (LAN). The most common solution uses memory pre-copying and assumes storage is shared on the LAN. When applied to a wide-area network (WAN), a new design philosophy in VM live migration algorithms is necessary to address like challenges of long latency, limited or unstable bandwidth and storage relocation. This paper proposes a three-phase, fractional, hybrid pre-copy and post-copy solution for both memory and storage to achieve highly adaptive and responsive WAN-wide migration. Our strategy is to selectively migrate an important fraction of memory and storage in the pre-copy and freeze-and-copy phases, while the rest (non-critical data set) is post-copied or demand-paged. We propose a new metric called performance restoration agility, which considers both the downtime and VM speed degradation during the post-copy phase, to evaluate the migration process. We also develop a profiling framework and a novel probabilistic prediction model to adaptively find a predictably optimal combination of the memory and storage fractions to migrate. Our solution is implemented on Xen and evaluated in an emulated WAN environment. Experimental results show that the solution achieves better adaptiveness than others for various applications over a WAN while retaining the responsiveness of post-copy algorithms.