- Just reading through your post, you mention you are running vSphere 6 on an "appliance" but then mention the appliance is a Dell Server. So just to confirm, are you talking about upgrading vCenter or an ESXi server?
It sounds like you asking about vCenter, but if it is a Dell Server, then I assume it is running on Windows Server, in which case it is not an appliance. The vCenter (VCSA) appliance is a Virtual Machine instance running Photon OS. Can you clarify, and hopefully someone can help further.
Just to add, assuming we are talking about vCenter, and given it is so old, is it worth considering skipping straight to vCenter 7 (or even 8 ) which are both supported, and deploying that as a brand new vCenter, than migrating everything across. It would probably be a far more controlled upgrade route, and a lot less hassle.
HTH