HotRestore: A Fast Restore System for Virtual Machine Cluster

A common way for virtual machine cluster (VMC) to tolerate failures is to create distributed snapshot and then restore from the snapshot upon failure. However, restoring the whole VMC suffers from long restore latency due to large snapshot files. Besides, different latencies would lead to discrepancies in start time among the virtual machines. The prior started virtual machine (VM) thus cannot communicate with the VM that is still restoring, consequently leading to the TCP backoff problem.

In this paper, we present a novel restore approach called HotRestore, which restores the VMC rapidly without compromising performance. Firstly, HotRestore restores a single VM through an elastic working set which prefetches the working set in a scalable window size, thereby reducing the restore latency. Second, HotRestore constructs the communication-induced restore dependency graph, and then schedules the restore line to mitigate the TCP backoff problem. Lastly, a restore protocol is proposed to minimize the backoff duration. In addition, a prototype has been implemented on QEMU/ KVM. The experimental results demonstrate that HotRestore can restore the VMC within a few seconds whilst reducing the TCP backoff duration to merely dozens of milliseconds.