Found the problem - should have read the documentation! I was running the enclosure from an eSata port and it was a basic eSata port - i.e. can only handle one drive. I thought it would see all the drives but it turns out you need a port multiplier enabled eSata port for that. When connected via USB all is fine and I see all the drives. I’ve ordered a PCIe eSata card that is a port multiplier too and that should solve my problem.
Martin.
