USing an IBM XT 640K with an IBM 1816101 hard drive controller and a Rodime RO204 hard drive.
I "low level" formatted the drive using the IBM XT reference disk and fdisk'd with DOS 3.3. I then ran the format command /s. There were no errors, the correct number of cylinders were counted off (320cyl, 8heads) appeared.
For some reason it formatted to ~10MB not ~20MB. Do you know why that happens?