redundancy questionj

Hello all, I'm new to FreeRADIUS and I'm planning to use Ver 2.2.0 on Ubuntu 12.04 server. Have 1 central office and 6 remote locations. 1. Is it standard to put one server in each of the remote locations which each remote back to the central office server? Fail-over is a term used in the wiki, is that the same as redundancy? 2. How stable is FreeRadius...should I consider a primary and secondary server in each remote location? Or is that over kill? Thanks, Jeremy