uh, no. 20MB drives dont exist anymore that arnt vintage. You can partition it at 20MB, but it would be a waste.
and the 20MB drives left in the wild, probably are dying or dead. actually the majority of old SCSI drives are dying off. unfortunately they are all senior citizens and they dont live forever.
Without retrofitting what your asking for is impossible. Unfortunately. You may get lucky and find a working or NOS old school drive but your only delaying the inevitable = Failure.