Erin Stellato walks through capacity planning:
Capacity planning for a new solution is really tricky. You have to come up with estimates about workload based on information you collect from the business. This means you have to ask hard questions about how much data they will expect in the first month, the first six months, and the first year. When a new solution is coming in, this is often the LAST thing the business is thinking about, so very often you’re going to get vague answers. In the case of a new solution, you really have make a best guess effort. Don’t pull your hair out trying to get exact numbers.
If the solution is from a vendor, you must ask the vendor for planning recommendations about both space needed and the resources needed. I admit, they may not have that data, but you don’t get what you don’t ask for. It never hurts to try.
Click through for Erin’s discussion points across hardware and storage requirements over time.