two freeradius servers - question for advice

Hi everyone, I'm going to start two freeradius servers to authenticate PPPoE users, both independent of the other. First as primary and second as secondary. I'm going to start PostgreSQL server also, but in case of unavailability of sql server freeradius server must have work properly. Both freeradius have to have actual data of arleady logged users to provide simultanieusly use. I'm going to check authenticate in db and if if failed get user from files (created in background). accounitng i'm going to do with linelog and afterwards put in to database. I need advice from you, more advanced users than me. How to achieve that HA and avablitity. Thanks in advance. -- Best Regards Marcin / nicraM