Hello, We have a MySQL Version 5.0.95 setup that consists of 1 master server and 3 replication slave servers. Now we want to upgrade these servers to MySQL 5.5 via intermediate step MySQL 5.1. Can we upgrade one MySQL server at a time or do we have to take all servers down and upgrade all at once? In other words, is the binlog replication protocol compatible between all MySQL 5.0.95, 5.1 ja 5.5? Many thanks for the information. Regards, vmk -- ************************************************************************ Tietotekniikkakeskus / Helsingin yliopisto IT department / University of Helsinki ************************************************************************