here is a a word of advice. if you already know you are going to get 10TB, then why start off with 4TB? it's going to be very disruptive to your enterprise, particularly if your DSS server takes an essential role, to add the key, then the additional capacity, etc.

if you don't want my advice , then somone else will have to speak up here. I'm not sure how DSS handles seeing the additional storage.