After you create a cluster, you can configure admission control to specify whether virtual machines can be started if they violate availability constraints. The cluster reserves resources so that failover can occur for all running virtual machines on the specified number of hosts.

The Admission Control page appears only if you activated vSphere HA.


  1. In the vSphere Client, browse to the vSphere HA cluster.
  2. Click the Configure tab.
  3. Select vSphere Availability and click Edit.
  4. Click Admission Control to display the configuration options.
  5. Select a number for the Host failures cluster tolerates. This is the maximum number of host failures that the cluster can recover from or guarantees failover for.
  6. Select an option for Define host failover capacity by.
    Option Description
    Cluster resource percentage Specify a percentage of the cluster’s CPU and memory resources to reserve as spare capacity to support failovers.
    Slot Policy (powered-on VMs) Select a slot size policy that covers all powered on VMs or is a fixed size. You can also calculate how many VMs require multiple slots.
    Dedicated failover hosts Select hosts to use for failover actions. Failovers can still occur on other hosts in the cluster if a default failover host does not have enough resources.
    Disabled Select this option to deactivate admission control and allow virtual machine power ons that violate availability constraints.
  7. Set the percentage for the Performance degradation VMs tolerate.
    This setting determines what percentage of performance degradation the VMs in the cluster are allowed to tolerate during a failure.
  8. Click OK.


Your admission control settings take effect.