Hi,
This is a new one on me. You might try pulling the drives out completely and removing any volumes and partitions on the drives in your Windows machine, Disk Manager, and then try to reinstall them both and start over from that point. The 2.68 TB is probably all you are going to get if you are successful with the Raid 1. Some folks think it is safer to do 2 Standard drives and then use the local backup function to copy one drive to the other. You could do that even 2 or more times a day to keep the data pretty up to date. Anyway, please post back with your results. Good luck