It is a Rodime 200 series drive, reputedly of 21M capacity.
My drive is simply labeled "Series RO 200" The manual tells me that the 201 has 1 disk, the 202 has 2, the 203 has 3, and the 204 has 4.With 4 physical disks, the raw capacity is 27M, and when formatted it would be 21M.
Formats can be 32 sectors per track with 256 byte sectors, or 17 sectors per track with 512 byte sectors.
The drive has 320 cylinders.
Tom's Computer Info / tom@mmto.org