> I have had similar problems in the past. I interpret "medium errors"
> to be when the disk has used up all of its 'bad block' allocation area
> and there isn't any more space.

No.  SCSI drives do automatic sector forwarding only if they know what data
should go in the new sector; i.e. on write or on a read where the data is
successfully recovered late enough in the retry algorithm that the drive
concludes the sector is a lost cause.

I have a drive that has grown about 5 bad sectors, and each one had to be
explicitly remapped with Adaptec's utility (gee, gotta write one for NetBSD,
where's my SCSI spec...?).