A fault-tolerant replication system includes a first machine running a first hypervisor. A second machine is failure-independent of the first machine. The second machine runs a second hypervisor. A first plurality of virtual machines runs on the first hypervisor. A second plurality of virtual machines runs on the second hypervisor. Each of the virtual machines of the first and second plurality of virtual machines constitutes either a virtual machine replica server of a fault-tolerant replicated state machine or a backup corresponding to a virtual machine replica server of the fault-tolerant replicated state machine. Every backup is embodied on a different machine, of the first and second machines, from its corresponding virtual machine replica server.
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