Automated Back-up solution

I am looking for a backup solution which can run on a clients server (windows and linux) and automatically backup data (chosen directories and files) to an external server (my own data center). The client will pay a fee per month for the back-up solution. Remotely (from my end) I need to be able to: 1. Set the amount of data allowed to be backed up (eg. 500gb) 2. Interval of backing up data (eg. daily, weekly etc.) 3. Activate / Deactivate Back-up service The client will pay a monthly fee depending on how much data and how often he/she wants to back up, so eg. 500gb daily would cost $49.95 a month (just a? sample price). I need a version for windows server and a version for linux. I am looking forward to see comments and bids and I also welcome ideas on how to improve the service. In short terms I will be selling back-up space and because the client has software running on his server the back-up to my server (externally from the client) will happen automatically. In case of data loss, I need to be able to recove the data for the client or give the client access to an area where he/she can retrieve the backed up data from. Thank you so much.