I have the ac version of the airport extreme. I have formatted my 8TB seagate drive to Mac OSX Extended (Journaled) several times and repaired it. The Mac immediately asks me if I want to use it for time machine but the airport cannot see it. It is a powered drive. The drive has its own proprietary USB 3.0 cable. I have successfully used it with an airport extreme (ac) before. Additionally, I have tried putting a powered USB hub between it and the airport. How do I fix this?