Updated March 11th, 2016
Virtualization Manager shows extremely high values (millions of years) on the Device I/O Latency graph for datastores that are managed by vSphere 5.5U2 and later versions.
all VMAN versions
This is an issue in vSphere, Virtualization Manager shows data received through a VMware VI API. You can access the same graph in vSphere under the name of Physical device command latency counter.
The issue should be fixed in a future version of vSphere.