Although it is integrated with vSphere and exists as a native extension to the ESXi hypervisor, VSAN is a separately licensed product. Like all vSphere products, VSAN will enable without a license for the default 60-day evaluation period. Despite this, it is best to license the VSAN cluster prior to full deployment, so as to avoid potential complications resulting from license expiration.
You should be logged in to the vSphere Web Client as an administrator or user, authorized to alter cluster-level settings and licensing/entitlement.
To add your VSAN license, you must browse the vSphere Web Client:
Navigate to Home | Licensing | License Keys.
Click on the green + icon to add a license key.
Enter or paste your license key into the textbox.
Click on Next.