After you create a cluster, Host Monitoring enables the vSphere HA primary host to respond to host or virtual machine failures and management network isolation. Admission control allows you to specify whether virtual machines can be started if they violate availability constraints. The cluster reserves resources to allow failover for all running virtual machines on the specified number of hosts.

The Host Monitoring and Admission Control page appears only if you enabled vSphere HA.


Launch the vSphere Client and log in to a vCenter Server system.


  1. In the vSphere Client, display the cluster in the inventory.
  2. Right-click the cluster and select Edit Settings.
  3. In the left pane of the Cluster Settings dialog box, select vSphere HA.
  4. (Optional) Select Enable Host Monitoring.
  5. Select an Admission Control option.
    • Enable: Disallow VM power on operations that violate availability constraints.

      Enabling admission control enforces availability constraints and preserves failover capacity. Any operation on a virtual machine that decreases the unreserved resources in the cluster and violates availability constraints is not permitted.

    • Disable: Allow VM power on operations that violate availability constraints.

      Disabling admission control allows a virtual machine to be powered on even if it causes insufficient failover capacity. When this happens, no warnings are presented, and the cluster does not turn red. If a cluster has insufficient failover capacity, vSphere HA can still perform failovers and it uses the VM Restart Priority setting to determine which virtual machines to power on first.

      Note: Select this option to power on more virtual machines than the vSphere HA failover level can support. If you select this option, failover is no longer guaranteed.
  6. Select an admission control policy to apply to the cluster.
    Option Description
    Host failures the cluster tolerates Select the maximum number of host failures that you can recover from or to guarantee failover for.
    Percentage of cluster resources reserved as failover spare capacity Specify a percentage of the cluster’s CPU and Memory resources to reserve as spare capacity to support failovers.
    Specify failover hosts Click to select hosts to use for failover actions. Failovers can still occur to other hosts in the cluster if a default failover host does not have enough resources.
  7. (Optional) Select Advanced Options to configure automation mode options.
    Change these settings only when instructed to do so by VMware technical support or when you are following specific instructions in VMware documentation.
  8. Click OK.