Once you have created a vDS, the next step is to add ESXi hosts to it. This process essentially associates the desired ESXi hosts with the vDS. However, mapping just the ESXi hosts to the vDS doesn't make them usable. You will need to map physical uplinks from the ESXi hosts to the dvSwitch. The number of physical adapters that can be mapped to a dvSwitch depends on the number of dvUplinks that were configured on the vDS. The default is 4 (the maximum is 32).