Installing vCenter Server in an Enhanced Linked Mode Group

What is an enhanced linked mode (ELM) group, and why might you want to install multiple instances of vCenter Server into such a group? If you need more ESXi hosts or more VMs than a single vCenter Server instance can handle, or if you need more than one instance of vCenter Server, you can install multiple instances of vCenter Server to scale outward or sideways and have those instances share licensing and permission information. The multiple instances of vCenter Server that share information among them are referred to as an enhanced linked mode group, or simply enhanced linked mode. In an enhanced linked mode environment, there are multiple vCenter Server instances, and each of the instances has its own set of hosts, clusters, and VMs. They are all registered back to the same PSC and SSO instance.

Prior to vSphere 6, vCenter Server linked mode, as it was previously called, used Microsoft Active Directory Application Mode (ADAM...