WD20EARX don't like each other

This is an odd one and I need some help. I have 2 WD20EARX drives that individually work fine (I put either drive into my drive enclosure and they work fine). But when I put both drives into the enclosure I can only see one drive. The drive I see is in the first occupied slot - I can swap the drives around and then I see the other drive because it is in the first slot. I can put them in slots 2and 4 (or any other combination you like) but I only see the drive in the lowest numbered slot.

Is there a problem with these drives that I need to know about??

If I had to guess, both disks have partitions that have the same UUID (Universally Unique IDentifier) for some reason.

That’s not a problem with the disks, per se.

Is this a NAS enclosure, or a USB or Firewire or other type of direct-attach enclosure?

If it’s a NAS, it’d be a problem with your enclosure in properly dealing with that circumstance.

If it’s a USB enclosure (or similar) then your host OS will need to correct for it.

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.