VMCSnap: Taking Snapshots of Virtual Machine Cluster with Memory Deduplication

Virtualization is one of the main technologies currently used to deploy computing systems due to the high reliability and rapid crash recovery it offers in comparison to physical nodes. These features are mainly achieved by continuously producing snapshots of the status of running virtual machines. In earlier works, the snapshot of each individual VM is performed independently, ignoring the memory similarities between VMs within the cluster. When the size of the virtual cluster becomes larger or snapshots are frequently taken, the size of snapshots can be extremely large, consuming large amount of storage space. In this paper, we introduce an innovative snapshot approach for virtual cluster that exploits shared memory pages among all the component VMs to reduce the size of produced snapshot and mitigate the I/O bottleneck. The duplicate memory pages are effectively discovered and stored only once when the snapshot is taken. In addition, our approach can be not only applied to the stop-copy snapshot but also to the pre-copy mechanism as well. Experiments on both snapshot methods are conducted and the result shows our method can reduce the total memory snapshot files by an average of 30% and reach 63% reduction of the snapshot time compared with the default KVM approach with little overhead of rollback time.