synchronize accounting

Hi, I'm testing freeradius 2.1 from debian stable. I'd like to set two independent serwer with the same configuration but the problem is with synchronize active sessions radutmp. I use simultaneous-use = 1. So if first server is broken client won't be able to authorise :/ How can I achieve synchronized two servers with active sessions? I don't want to using sql database to avoind problems with other servers, daemons. -- Pozdrawiam Marcin / nicraM