VMware High Availability (VMware HA) is a feature of vSphere used to reduce unplanned downtime by leveraging multiple VMware ESXi hosts configured as a cluster to provide rapid recovery from outages as well as high availability for applications running in virtual machines.
VMware HA protects application availability in case of hardware failure by restarting the virtual machines on other hosts within the cluster or It protects against operating system failure by continuously monitoring a virtual machine and resetting it when an operating system (OS) failure is detected.
VMware vSphere Fault Tolerance (FT) enables a virtual machine to survive in case of a physical server failure. vSphere FT automatically creates an exact replica of virtual machine files (including VMX and VMDK files) and keeps it in sync. When a physical server fails, one of the replicas will resume execution on another host that can take over at the time of failure. The transition of a vSphere FT virtual machine from one physical server to another is seamless and results in zero downtime, zero data loss, zero connection loss, continuous service availability, and complete transaction integrity.
All Esxi Hosts (Two or more) details
All ESX/ESXi hosts must be same version and same patch level.