On Hosts dashboards, hovering the mouse over Disk utilization, see graphs which showing like "File System /50.9% used" or "File System C: 46.8% used". Please refer to Disk1.jpg and Disk2.jpg.
These graphs may be causing some confusions, because we can only see Disk utilization are 0% or 1% on Hosts dashboard directly, but when hovering mouse on them, they are showing different values on a graph.
Clicking on Disk utilization, entering "Disk details" page, please refer to Disk3.jpg. There are some graphs: Aggregate Disk I/O Utilization and Top I/O Process Trend, File System / and File System / workspace.
We think maybe Aggregate Disk I/O Utilization is the right graph while hovering mouse on Disk utilization, not File System.