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With the growing prevalence of cloud computing and the increasing number of CPU cores in modern processors, symmetric multiprocessing (SMP) Virtual Machines (VM), i.e. virtual machines with multiple virtual CPUs, are gaining significance. However, accommodating SMP virtual machines with high availability at low overhead is still an open problem. Checkpoint-recovery based VM replication is an emerging approach, but it comes with the price of significant performance degradation of the application executed in the VM due to the large amount of state that needs to be synchronized between the primary and the backup machines. Advanced features of high performance interconnects, such as Remote Direct Memory Access (RDMA), on the other hand, offer extreme network throughput. As such feature may provide an opportunity for acceptable performance degradation even for multi-core replicated virtual machines, the impact of such technologies in the domain of VM replication is important to assess. In this paper, we take a first look at the performance advantages of RDMA for SMP virtual machine replication. Moreover, in order to alleviate VM downtime during replication, we propose fine-grained copy-on-write (COW), which protects only memory pages that need to be transferred to the backup host allowing simultaneous execution of the VM with the replication. We find that the performance of replicated virtual machines over high performance interconnects scales well with the number of vCPUs in multiprocessor virtual machines, and that RDMA based replication in conjunction with fine-grained COW imposes acceptable overhead compared to the native VM execution when applied to virtual machines with up to 16 vCPUs.
Date of Conference: 26-30 Sept. 2011