How do I setup to have my MySQL on one server - seperate from the forum files.

And how do I setup that attachments are in the file system and on which server will they be stored? On the mysql server or the php files server? Is it even possible to put them on another seperate server?

Server 1: Forum Files
Server 2: MySQL database
Server 3: Attachments

Does someone know?

You can put nearly anything on a different server. You can start with the operating system on one hard drive, the program files on another. Store any data on a new server or third hard drive. The database server on a different server on its own drive, and the database data on that same server or different server, on its own drive. The backup goes to a totally seperate server, archive on one hard drive and latest on another.