http://doc.powerdns.com/modules.html
To launch two backends of the same type, you can assign a name to each launch like this;
launch=gmysql:connection1,gmysql:connection2
gmysql-connection1-host=10.10.10.1
gmysql-connection1-user=pdns
gmysql-connection1-dbname=pdns
gmysql-connection2-host=10.10.10.2
gmysql-connection2-user=pdns
gmysql-connection2-dbname=pdns