brent Well with the old hard drives I would delete all partitions and make a new ntfs and format
it then delete that partition and install new most time that would work.
If that didnt yield results would do a disk wipe that would 99% time take care of it.
If that didnt yield results would test the disk and usually found issues.
But I do the first step with SSD (Of coarse you dont want to wipe a SSD)
To answer I leave it Unallocated That way nothing is on it.
(I Dunno Seems kinda unneeded but always got me out of sticky spots.)
Oh to comment on your calmares comment on their website they recommend you erase disk first.