http://www.openafs.org/pages/doc/AdminGuide/auagd007.htm#HDRWQ52
In that section, it says:
If your cell has more than one server machine, it is best to run
more than one
as a database server machine (but more than three are rarely necessary).
But, the last paragraph in the section says:
Ok, here's the clarification:
A machine can be a database server or a fileserver, or both.
You have to have at least one machine providing database service. It is
preferrable that you have multiple machines -- either 3 or 5 -- 3 is
usually sufficient. It's important that they be an odd
