I am trying to enable FT on a VM that has a virtual RDM disk but whenever I do it I got an error message saying "Device "Hard disk" is raw disk which is not supported" but to the best of my knowledge, the vRDM is supported on FT. Check it out here and you can see that it says physical RDM is not supported but the virtual one is.
Information that you may find helpful:
- vCenter and ESXi version are 6.5
- Number of ESXi servers is 2
- CPU = 1
- Cores per socket = 1
- FT works only if vRDM removed