A:Answer Two, 4 TB drives, 8 TB total, second 4 TB backs up auto the first 4 TB drive. Different ways to configure - User manuals available on line at WD and Best Buy. What's nice is that you get free 30 day toll free customer support at WD, that really works, and they really help if you get hung up for some reason. (Not to short change Best Buy Geeks, but the WD 'horse's mouth' has certain advantages, since they are specialists in WD MyCloud).