After configuring HA for a vSphere 5 cluster, you may encounter the following warning on each ESX host:

Configuration Issues

The number of vSphere HA heartbeat datastores for this host is 1, which is less than required: 2

vSphere 5 introduces datastore heartbeats in addition to network hearts, which allows to distinguish between a network-isolated host and a crashed host. In order for datastore heartbeats to work properly, vSphere requires at least 2 shared datastores available on every host in the cluster. If there's less than 2 shared datastores, datastore heartbeats will not function properly, resulting in the configuration issue message.

If you only have one shared datastore and wish to suppress the message, or you do not want to use datastore heartbeats, you can turn off the message by editing the advanced HA options on the cluster.

1. Log on to the vSphere vCenter using the vSphere client. You need to use an account with permissions to change cluster HA settings.
2. Right-click the vSphere cluster, click Edit Settings, select vSphere HA, and finally click on Advanced Options.
3. Add the advanced option:

   Option	Value
   das.ignoreInsufficientHbDatastore	true

   (The default value for this option is false, by the way.)
4. Reconfigure HA by disabling it for the cluster, then re-enabling it: right-click the cluster, select Edit Settings, select Cluster Features, deselect Turn on vSphere HA, then click OK. Next, re-enable HA by going back to the dialog and selecting Turn on vSphere HA. Leave some time between disabling and enabling HA, allowing the ESX hosts to finish up the reconfiguration of HA. Note that this can be done on a live production system with minimal risk involved.