To use an external loader, create the target definition in the mapping according to the target database type. The session configures a relational target type by default. To select an external loader connection, you must configure the session to write to a file instead of a relational target. To configure the session to write to a file, change the writer type from relational writer to file writer. You change the writer type using the Writers settings on the Mapping tab.
To change the writer type for the target, select the target instance and change the writer type from Relational Writer to File Writer.