User blog comment:DaNASCAT/Technical Update: February 29, 2016/@comment-25739558-20160301161353/@comment--20160301162335

A little bit of both! We have a number of database clusters and usually wikias are assigned to a DB server based upon when they are created. Most of our older communities lived on Cluster A, and then the next oldest batch lived on B. But sometimes we also get extra servers and try to balance out our busiest servers in order to prevent one cluster from being used more than another server. So for instance we moved quite a few wikias last year from Cluster A to the mostly unused Cluster F to give Cluster A some breathing room so to speak.