Fault Tolerance Performance in VMware vSphere 6
VMware has published a technical white paper about vSphere 6 Fault Tolerance architecture and performance. The paper describes which types of applications work best in virtual machines with vSphere FT enabled.
VMware vSphere Fault Tolerance (FT) provides continuous availability to virtual machines that require a high amount of uptime. If the virtual machine fails, another virtual machine is ready to take over the job. vSphere achieves FT by maintaining primary and secondary virtual machines using a new technology named Fast Checkpointing. This technology is similar to Storage vMotion, which copies the virtual machine state (storage, memory, and networking) to the secondary ESXi host. Fast Checkpointing keeps the primary and secondary virtual machines in sync.
vSphere FT works with (and requires) vSphere HA—when an administrator enables FT, vSphere HA selects the secondary VM (admins can vMotion the VM to another server if needed). vSphere HA also creates a new secondary if the primary fails—the original secondary becomes the new primary, and vSphere HA selects an available virtual machine to use as the new secondary.
Read the entire article here, Fault Tolerance Performance in VMware vSphere 6