The real answer is: both. Fault Tolerance has a direct dependency on the version of vSphere in use and has implications and dependencies on physical hardware as well. For example, if you decide to configure a VM with a single vCPU for fault tolerance you can probably get away with a single 1 GbE uplink. If you're doing vSMP FT (which has a version requirement), you'll need 10 GbE for the vmkernel port tagged for FT traffic. So, therefore, it's both things you mentioned.
No, it's not. Fault Tolerance requires an identical copy of that VM be produced on another host, and it uses a vmkernel network to transfer the changes to the destination host where they are also written down to disk and "replayed" in compute. So it certainly does require network resources--and potentially lots of them--based on what configuration you choose.
But my FT virtual machines are kept on shared storage, so I dont thin it will require 10Gig of ethernet connectivity.
Is your answer specific to VM's residing in local storage
if you are using SMP-FT (meaning enabling FT on a VM with multiple CPUs or cores) then you will require 10GbE. We have extensive documentation by the way for FT and HA, it can be found here:
