Cheapest solution I found was to buy a 80-pin SCA SCSI drive and an external case and sit it in the top. Suns '611' Ultra SCSI boxes are fairly easy to find and a re totally plug-and-play on a Quadra (they auto-terminate which is REALLY handy 
). You'll need to find a 68-pin to 25-pin SCSI cable for one of those, unless you have a Wide SCSI card in the Mac then you can use the 68-pin external port (if it has one - both the SEIV and Jackhammer do) and a 68-68 cable. If you are feeling really enthusiastic you could buy a Sun 711 'Multipack' desktop array. They hold 6 or 12 drives (depending on the model) and are sound deadened to minimise noise.
SCA disks are pretty cheap as a lot of people don't like them because they require some kind of back-plane board. If you have ample internal space then you can always buy a SCA to 50-pin (or 68-pin if you have a Wide SCSI card) adapter. A word of warning though - I've found if you use one of those you need an insulator between the back of the board and the body oft he disk - I used a folded up piece of copier paper.
). You'll need to find a 68-pin to 25-pin SCSI cable for one of those, unless you have a Wide SCSI card in the Mac then you can use the 68-pin external port (if it has one - both the SEIV and Jackhammer do) and a 68-68 cable. If you are feeling really enthusiastic you could buy a Sun 711 'Multipack' desktop array. They hold 6 or 12 drives (depending on the model) and are sound deadened to minimise noise.SCA disks are pretty cheap as a lot of people don't like them because they require some kind of back-plane board. If you have ample internal space then you can always buy a SCA to 50-pin (or 68-pin if you have a Wide SCSI card) adapter. A word of warning though - I've found if you use one of those you need an insulator between the back of the board and the body oft he disk - I used a folded up piece of copier paper.