I am using 3 servers. 1 main server that holds the database and website. 1 search/images server and 1 fileserver/mirrorserver.
Databases are replicated from the main, and files are synced.
Anyway. IPB as it is now does not have much "features" that would enable the users from distributing load.
Maybe it's time to think about the bigger users of IPB and enable some stanard features which could help out at balancing/distributing the load. (besides the "external images"-urlsetting. But the smilies-table and several of other images are still loaded form the main site anyway
)What I have done and should be easy to enable.:
-The search-feature changed to make use of a seperate server only for searches (the biggest load of IPB). While my main server uses InnoDB, my searchserver uses myisam for fulltextsearch.
-A new setting had been made to enable "files" to be shared off another server. I'm talking about jscripts, css files, etc.
-Changed the default skin/hardcoded image-urls into using the external image-url.
-Added another setting to enable select-queries to be made directly from another database (in this case, the local, replicated database). Updates and such will still go to the masterDB.
This is merely a suggestion for you to consider. It doesn't bother me much if you don't make it standard, since I'm able to do such changes myself fairly easily.