Used DiskPart to 'Clear' the drives (hoping that it would also clear whatever header information is making the two-disk distinction'. Deleted the drivers entirely and re-attached the enclosure.

I supposed I could implement a work-around by creating a spanned volume, but since I just lost an impressive amount of data (see 'Further Background'), I'm a little gun-shy of sketchy solutions. I'm vaguely aware of LUNs, but have only encountered them when working with VMs or clustered storage, never on a desktop and certainly not without Windows Server, which means I'm lacking the tools that I would usually use to manage clustered storage. This is the drive that I assume to be 'fake'. The second disk is identified by Windows as Disk 8 and Device Manager as ST300DM 001-9YN166 LUN1 USB Device. The first disk is identified by Windows as Disk 8 and Device Manager as ST3000DM 001-9YN166 USB Device (as expected) I can use each of these disks normally, they'll format, accept new partitions, etc., but can find no way to tell Windows that they're both actually the same disk. However, when the drive is powered up, Disk Management shows two physical disks - one at 2048GB and one at 746.5GB. I have a 3TB Seagate drive in a USB 2.0 enclosure.

Usb shows up as 2 drives