Disable Atomic Test and Set for Incompatible Storage Arrays
After performing an upgrade from ESXi 4.1/ESXi 5.0 to ESXi 5.5 u2 I noticed increased latency events on hosts. More troubling, the affected hosts were frequently dropping all presented datastores, though they would reconnect within a few seconds. The events may appear in your event log as below:
While there are many possible causes to explore these sorts of connectivity issues, one that is often overlooked is how ESXi heartbeating to the datastores.