To ensure that a cluster has enough failover capacity, vSphere HA uses the admission control policy to determine how many host failures your cluster can tolerate, that is, the amount of resources the system should reserve to power on virtual machines in case a host fails.
When admission control has been enabled, actions that may violate the applied policy are not permitted. Powering on, migrating, or increasing the CPU or memory reservation of a virtual machine may be prevented if the cluster doesn't have enough resources available, that is, the admission control policy is violated.
Once the maximum host failures the cluster can tolerate has been specified, there are three ways to define the host ...
