Reclaiming a Formerly Spanned Drive

I have a drive that was once part of a spanned pair (yeah, I know, big mistake, lesson learned) and I want to go back to using it as a single drive. When I load Disk Management (Windows 10) it shows the size of the drive to be the original spanned volume size, not the drive's physical size. When I try to do anything in Disk Management, it just tells me "There were not enough physical disks to complete the requested operation." I tried using diskpart (clean, create, convert, whatever) with no joy. How do I correct this? Is there a way to reset this drive to factory defaults?

volumen

The problem is that Disk Management will only let me create a 2TB volume. But the original span consisted of two 5TB drives, one of which died. Disk Management shows the capacity of the remaining drive to be the size of the two spanned drives, not the size of the physical drive. Everything above 2TB shows as Unallocated, and all options for that unallocated space are greyed out, as is the Extend Volume option for the 2TB volume.

The only other option that is not greyed out is the Convert to GPT Disk, which is enabled after I delete the 2TB volume. But when I try that I get the "not enough physical disks" error. Apparently, DM thinks that the drive is still part of a span. How do I unspan it?

Thanks, Dave. The screen shot is attached. Disk 8 is the one in question.

As mentioned, I did try to convert to GPT, but get the "not enough physical disks" error.

I have in fact tried AOMEI. It allows me to create a 4TB volume (still short of the 5TB capacity of the physical drive), but the format fails, and it still shows the wrong capacity. I can't try AOMEI's GPT conversion, because that feature is not part of the free version that I have.

In AOMEI, the Resize option for the unallocated part is greyed out. The only option is Create Partition, which just creates an additional 2TB partition, the rest remaining unallocated. If I try to create a partition out of the remainder, it fails because of what it sees as a ton of bad sectors (duh, there's no physical disk there).

When I use diskpart to convert to GPT, I get this:

DISKPART> convert gpt

Virtual Disk Service error:
The specified disk is not convertible. CDROMs and DVDs
are examples of disks that are not convertable.

Here it is: