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