After configuring a Virtual SAN cluster, an administrator using the vSphere Web Client notices that the Virtual
SAN datastore is smaller than expected. The cluster contains:
Three ESXi hosts
Each host has one 10GB SDD
Each host has one 100GB HDD
Why would the Virtual SAN datastore show as 100GB instead of 300GB?

A.
There is a network problem with the Virtual SAN vmkernel ports.

B.
The Virtual SAN VASA provider is disabled.

C.
vSphere High Availability is enabled on the Virtual SAN cluster.

D.
The Virtual SAN cluster must be managed using the vSphere Web Client.

Explanation:

Reference: http://kb.vmware.com/selfservice/microsites/search.do?
language=en_US&cmd=displayKC&externalId=2058368