Storage is the most essential part of the hardware for Data protection Manager. In most cases you will use disk for your short term protection.
But how many disk space to you need?
To answer this question Microsoft has developed three Excel calculation sheets (still in draft) for: Exchange, SharePoint and Hyper-V
As you can see in the examples above, the sheets calculate more then only the required disk space. It also calculate the number of DPM servers required, hardware for DPM server needed. Configuration of the DPM server; like page file and Database size. You will also find an estimated backup and recovery time for your protected servers.
The sheets are available at the Microsoft download site: http://www.microsoft.com/downloads/details.aspx?displaylang=en&FamilyID=c136c66c-bd4a-4fb1-8088-f610cd02dc51