For anyone else interested in Clustra: Sun used to have decent HADB docs and whitepapers on bigadmin, but I can't find them any more in the new Oracle world. The two Sun projects that used HADB were Glassfish (clustered fault-tolerant app server, used HADB for session persistence data) and Honeycomb (clustered fault-tolerant archival storage, used HADB for metadata). Examples of how these systems used Clustra are on the web; in both cases the database size was small.