2 vdev with 6 2tb drives

[admiral2145]

I want to make sure that I set this up correctly... I want to be able to run 2+1 x2 with 6 2tb drives, so that I could only upgrade 3 of the 6 drives to get a larger drive. Is there a guide on how to do this with freenas 9.2.1? I think I did it correctly from the setup but, I'm not sure :(
also wanted to be able to say add another 3 drives to the 6... at a later date