vSphere hot plug

vSphere hot plug is a function lets administrators add additional virtual hardware to running virtual machines (VMs).

VSphere hot plug is not enabled by default. To enable the hot plug function, the VM must be powered off -- which is why administrators should consider enabling hot plug when the VM is created if there's any chance at all that is a VM will need more hardware resources. The guest must be rebooted before it will recognize the new vCPU. 

VSphere requires the administrator to have installed VMware Tools and be running VMware version 7 or greater.