Hard Drive Question

I have a WD My World Book Edition II Blue Ring model. 

Which type of WD Caviar Green drive would I use with the Blue Ring model? 

Can I ONLY use 1 Caviar Green drive at a time or do I have to install 2 drives?


They should be the same that were inside of that unit… same capacity and same model. I believe that those unit are manufacture depending on what units are available on the warehouse.