Okay, I rebooted and while the Hopper was restating, I took out the 4TB drive and replaced it with the 6TB drive.
Under DVR it sees one External Drive, the 2TB drive
Spinning down the 2TB drive, the 6TB drive is not recognized. Spinning down the 6TB, the Hopper message is «You have disconnected a multimedia device from the USB port: ``”»
Spinning up the 6TB drive brings it back. So I’m willing to bet it is a Total Capacity of 7TB for all EHDs. If I had a 1TB drive or better yet a 1.5 TB drive I’d try that.