Cloud computing enables a vast deployment of online services in virtualized infrastructures, making it crucial to provide fast fault-tolerance for virtual machines (VM). Unfortunately, despite much effort, achieving fast and multi-core scalable VM fault-tolerance is still an open problem. A main reason is that the dominant primary-backup approach (e.g., REMUS) transfers an excessive amount of memory pages, all of them, updated by a service replicated on the primary VM and the backup VM. This approach makes the two VMs identical but greatly degrades the performance of services.
State machine replication (SMR) enforces the same total order of inputs for a service replicated across physical hosts. This makes most updated memory pages across hosts the same and they do not need to be transferred. We present Virtualized SMR (VSMR), a new approach to tackle this open problem. VSMR enforces the same order of inputs for a VM replicated across hosts. It uses commodity hardware to efficiently compute updated page hashes and to compare them across replicas. Therefore, VSMR can efficiently enforce identical VMs by transferring only divergent pages. An extensive evaluation on PLOVER, the first VSMR system, shows that PLOVER’s throughput on multi-core is 2.2X to 3.8X higher than three popular primary-backup systems. Meanwhile, PLOVER consumed 9.2X less network bandwidth than both of them. PLOVER’s source code and raw results are released on github.com/hku-systems/plover.