... For robustness you have two systems and switch to the backup if you get problems you witch to the backup. ... MySQL doesn't (yet) have database replication, but here are some info on how do to it. ... You probably want to keep the old version to help with deciding what has been updated. ... DATABASE() . ... If you want to run multiple servers, the easiest way is to compile the servers with different TCP/IP ports and socket files so they are not both listening to the same TCP/IP port or socket file. ...