Monitoring VSAN resync activity in vSphere 5.5 involves the use of the Ruby vSphere Console (RVC); in vSphere 6.0, the process can be monitored directly in the vSphere Web Client. This addition to the vSphere Web Client is available only with version 6.0.
You should be logged in to the vSphere Web Client as an administrator or user entitled to view VSAN configurations.
From the vSphere Web Client, navigate to Home | Hosts and Clusters | Datacenter | Cluster | Monitor | Virtual SAN | Resyncing Components. Any resyncing components will be reflected in the window:
While there are no resyncing components in this example, you can see how much data is left to sync and how long the operations will take to complete. Any VMs associated with syncing components will be listed in the lower pane.