I believe in RAID 1 that the data is mirrored on the second drive. Basically you are making 2 copies. A RAID 0 drive that is 2T will only be 1T if setup as RAID 1. In RAID 0 data is on both drives if one goes bad your data is gone. In RAID 1 if one drive goes bad the other has a copy of it. That’s about all I know about it.