More on simple databases

When I think about it some more, the difference between something like MS SQL Server or DB2 vs Hibernate + MySQL with MyISAM, is that the traditional way is for the RDBMS to be a single system, relational management AND static data storage. The persistence layer/db strategy is separating the RMS (relational management system) from the DB (static storage). By separating out the relational management portion, and moving that into the persistence layer, you have the ability to run one processing cluster which serves your application and handles the persistence layer/rms, as opposed to running two clusters, one to serve your application, and one to handle the traditional RDBMS. I would think that combining your servers into one larger cluster to handle more of the computing would be more efficient than splitting it into two clusters, in which case one cluster may hit max load while the other sits idle.

By the way, I know that there are measurable differences between MyISAM, InnoDB, or other storage engines, like row level locking as opposed to table locking on updates.