Which feature must be enabled to use vSphere Fault Tolerance?

vSphere DRS (Distributed Resource Scheduler) is used for load balancing and resource optimization and is not a prerequisite for the core functionality of vSphere Fault Tolerance.

vSphere Replication is an asynchronous replication solution for disaster recovery and is distinct from the synchronous, continuous availability provided by Fault Tolerance.

vSphere Fault Tolerance (FT) relies on vSphere HA (High Availability) to ensure protection for both the primary and secondary fault-tolerant virtual machines. If a host running either the primary or secondary FT VM fails, HA restarts the affected VM on another host to maintain continuous service.

vSAN (vSphere Storage Area Network) is VMware's software-defined storage solution; while FT VMs require shared storage, vSAN is not a mandatory prerequisite, as other shared storage types can also be used.