It is recommended that the VSAN datastore contain 20 percent free space to enable ideal placement decisions and effective rebalancing of storage objects.
Your VSAN should be deployed and functional as per Chapter 2, Initial Configuration and Validation of Your VSAN Cluster.
From the vSphere Web Client, navigate to Home | Storage | VSAN Datastore.
Click on the Summary tab.
Examine the capacity and number of connected hosts. You should find that the capacity is consistent with the aggregated size of your disk groups, and that the correct number of hosts is connected to the datastore.