merging two systems

[Blake Hudson]

I have two systems that both use freeradius out of MySQL. I would like 
to consolidate onto a single system, but maintain the database 
separation to ensure there are no username collisions and ease in 
auditing/reporting, etc. System A already has a database of freeradius_A 
and system B has a database of freeradius_B.

What is the preferred method to configure freeradius to authenticate two 
sets of users out of two databases? Should I look at running multiple 
instances of freeRADIUS or can I utilize both databases with one instance?

--Blake