Virtualization provides the possibility of whole machine migration and thus enables a new form of fault tolerance that is completely transparent to applications and operating systems. The most seamless virtualization-based fault tolerance configuration is an active/active master-slave configuration, in which the memory states of the master and slave virtual machine are periodically synchronized and the slave can immediately take over when the master dies without losing any on-going connections. The frequency of memory state synchronization has a direct impact on the performance overhead, the application response time, and the fail-over delay. This paper describes a speculative memory state synchronization technique that could effectively reduce the synchronization frequency without increasing the performance overhead, and presents a comprehensive performance study of these techniques under three realistic workloads, the TPC-E benchmark, the SPECsfs 2008 CIFS benchmark, and a Microsoft Exchange workload. We show that the proposed technique can effectively cut down the amount of memory state synchronization traffic by more than an order of magnitude. © 2012 IEEE.