The items in the Info pane for my external drive are just as you have illustrated above. FWIW, it's a 2TB drive with about 270GB of space available.
I discovered today that I can't run Disk Utility on the drive, nor can I do something as simple as create a new folder.
When I hit First Aid I get an error message that says "First Aid has failed ......" and it shows this when I expand the Details: Updating boot support partitions for the volume as required. Unable to unmount volume for repair. Operation failed ....."
When I try to create a new folder or drag a folder from the desktop to the drive, the error message says: The operation can't be completed. An unexpected error occurred (error code -50).
I can, however, drag a folder from the external drive to the desktop, and it's contents appear to be intact.
I'm leaning toward buying a new drive, formatting it, and copying all of the "problem" drive's content to the new one. I thought this was an issue with iMovie 10.1 and El Capitan, but now I'm not so sure that's correct.
Tom