Multiple JBOD

I recently got an EX4100 with one 8TB disk installed. I consolidated all my data and now have a bunch of clean 1TB disks, with no partitions. When I insert any of these disks into the EX4100, the light below the drive bay eventually settles as RED.
What can the problem be?

Did you initialize the disk in the EX4 volume / RAID manager?

How would I do that? The disk does not show up in the ‘Storage’ page of the web-interface.