As I found out now, replication flag can be enabled on File-I/O volumes after creation. The GUI is misleading a bit: when I choose 'modify lv...' , the replication-checkbox is grayed, but can be activated by deselecting the default initializing checkbox. I'll try to create the volume without replication, and add the replication thereafter.
No effect. When trying to enable the replication flag:

2009/07/30 11:25:49 Unable to initialize volume replication for the following logical volume: lvdaten15k00. Please increase the Vmalloc size in console tools: CTRL-ALT-W --> Tuning options --> Vmalloc size



Robert