VMware Fault Tolerance provides continuous availability for virtual machines by creating and maintaining a secondary virtual machine that is identical to, and continuously available to replace the primary virtual machine in the event of a failover situation.

You can enable Fault Tolerance for the most critical virtual machines. A secondary virtual machine is created and runs in virtual lockstep with the primary virtual machine. VMware vLockstep captures inputs and events that occur on the primary virtual machine and sends them to the secondary virtual machine, which is running on another host. Using this information, the secondary virtual machine runs similar to that of the primary virtual machine. Because the secondary virtual machine is in virtual lockstep with the primary virtual machine, it can take over execution at any point without interruption, by providing fault tolerant protection.