The DVD-ROM I purchased has a jumper for 512/2k block size selection with regard to CD-ROMs. What is the appropriate selection for a Mac running SSW 7.1.x and has a pre-SCSI Manager 4.3 bus?

Also, when I selected for parity using a jumper, it failed to show in on my system, but when I removed the parity jumper, it showed up. Should one normally leave parity off on external devices?