To enable vSphere Fault Tolerance for your cluster, you must meet the feature's prerequisites and you must perform certain configuration steps on your hosts. After those steps are accomplished and your cluster has been created, you can also check that your configuration complies with the requirements for enabling Fault Tolerance.
The tasks you should complete before attempting to enable Fault Tolerance for your cluster include the following:
Ensure that your cluster, hosts, and virtual machines meet the requirements outlined in the Fault Tolerance checklist.
Configure networking for each host.
Create the vSphere HA cluster, add hosts, and check compliance.
After your cluster and hosts are prepared for Fault Tolerance, you are ready to turn on Fault Tolerance for your virtual machines. See Turn On Fault Tolerance for Virtual Machines in the vSphere Client.