A live storage migration mechanism over wan and its performance evaluation

Live migration of virtual machines is a key technology for the next generation of IaaS cloud services, contributing to dynamic portability and mobility of VM-based services among datacenters. The practical use of live migration, however, is still limited inside a single datacenter. In WAN environments, network latencies cause inevitable I/O performance degradation of remotely-shared storage between source and destination sites; which is required to continue disk access of VMs before/after live migration. In our previous work, we proposed a transparent, relocatable I/O mechanism for VM migration, which enables VM disk images to be completely migrated to remote nodes without any modification of virtual machine monitors. In this paper, we present detailed performance evaluation of the proposed system, emulating a realistic WAN environment between remote datacenters. Experiments showed the proposed system achieved feasible I/O performance for various workloads including I/O intensive applications. Its background copy mechanism efficiently prefetches not-yet-cached blocks by exploiting the available bandwidth of WAN, thereby minimizing temporary performance degradation of the migrating VM system.