All the settings for vSphere HA can be found under the properties of the cluster >> Manage and the Edit button.

Host Monitoring

The host monitoring portion of the Edit Cluster Settings options control whether vSphere HA is turn on or off. As indicated earlier it is possible to turn off Host Monitoring. This controls whether the vSphere host share the network heartbeat that is used to calculate if the host is alive or dead. This can check can be temporarily turned off if you know that some network maintenance (such as physical switch or router upgrade) is likely to cause the network to be down for a period of time. The virtual machine options control what happens by default if there is a failure or isolation event. Two settings are available here, VM Restart Priority and Host Isolation Response. Restart Priority allows for four options – disabled, low, medium, high. By default is medium is selected, and all VMs would have the same restart priority of medium. It’s then possible under the VM Overrides options to add individual VMs, and indicate that some VMs have a low priority, or high priority – are started after or before any VMs with a medium priority. Alternatively, VMs can be excluded from the restart process altogether by using the VM Over-rides to disabled. This can be useful if you have non-critical VMs are that are not needed be available – and frees up resources for the more critical VMs. The Isolation Response controls what happens if a host becomes disconnected from the cluster due to some network outage or configuration error. In this case the isolated host may well be able to communicate to the router, but not the other hosts. Alternatively using what are called “datastore heartbeats” vSphere can work out that the host maybe disconnected from the network, but still connected to shared cluster resources. In such a case the host could still be running, and the VMs are unaffected. In this case the default policy would be to “Leave Powered On”. The alternatively, is assume a failure has occurred and either power of and restart, or shutdown the guest operating system, and restart on to the remaining hosts.

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