No Add Volume Button at Reconfigure VM in VRA 7

Hi,

    I am trying to add volume in my VM using reconfigure action. But I can not see add volume button in storage tab.

    I can modify CPU/Memory/Network. I can also edit the first HDD size (but I did not try it).

    Is it by design or I missed something? I am using VRA 7.

Thanks.

Haining