Faulty cables, SFP modules, or flapping SAN switch ports can cause intermittent interruptions long enough to trigger the 16-second timeout.
When this event occurs, you may observe the following issues in your environment: esx.problem.vmfs.heartbeat.timedout
When this happens, the datastore is marked offline, and all I/O from virtual machines on that host is suspended until the heartbeat is restored. Common Causes Faulty cables, SFP modules, or flapping SAN switch
"Great," Elias muttered, reaching for his coffee. "The SAN is lying to us." the datastore is marked offline
He closed his laptop. The heartbeat was back, but the system was telling him it was running on borrowed time. He'd deal with it in the morning.