Sites across Multiple servers

[eluser]Otaku Coder[/eluser]
The other thing I'd suggest is to setup an ssh tunnel for the DB traffic as it's encrypted on the fly. I do that for geographically seperate DB clusters and web clusters, but if they're in the same server room then just setup a VLAN and use the spare ethernet ports on the servers. Each webserver would have a public IP and a private IP which would be dedicated DB traffic.

Phil is on the nail with replication, Master/Slave is easier to setup, just make sure you have binary logging turned on in the master config, and this would require a restart of the server so do this while it's not live. The other benefit of using replication is that you can have another slave DB setup purely for taking backups. That way you can stop your backup slave, flush the cache to ensure consistency then take a backup and start it again. In MySQL 5 you can also do Master-Master replication but this is a bit buggy in my opinion.