I was just wondering whether anyone had experiences with synchronizing two basex databases (same server or not) at a lower level for example using (r)sync or nfs or even Hdfs. Would it be feasible?

The most important thing is that no updates should take place while copying the database. You could trigger the rsync call via the Process Module to ensure (at least on one side) that other operations will be blocked [1].

Christian

[1] http://docs.basex.org/wiki/Process_Module