Advice about how do distribute components across servers?

[Jeff Steele]

I have my cluster which back ends a web application set up like this:

server1: httpd and web application (does not use Mysql)
server2: redundant version of server1

server3: tomcat (load balance by server 1 and 2)
server4: tomcat (load balance by server 1 and 2)

server5: ndbmtd and Mysql
server6: ndbmtd and Mysql

server7: ndb_mgmd
server8: ndb_mgmd

I feel like Mysql should not be on the same server as ndbmtd and have tried running in on the servers with tomcat. However, I get much slower performance when doing so. Conversely, I haven't noticed many problems with the current setup.

Does anyone have any words of advice about what would be the correct set up in my situation?