Yonks ago the Jaz (1Gb) disks were about £70 each and in consumer terms they fell between the smaller, cheaper Zip drive's capacity and the very rapidly improving HD.
If you have Jaz disks as well as the drive then treat them just like any other removable drive.
SCSI is a law unto itself, but provided you plug the right things into the correct places the computer will recognise everything during boot-up.
A critical point is to fit a terminator to the end of the SCSI connecting cable. I didn't realise how important that is.
The SCSI cable should plug into the host card, then the Jaz Drive, and there should be another plug at the end of the cable for termination.
Win 98 or the Jaz drive fell over with horrific regularity every time I plugged a SCSI scanner in, until I learned to fit the magic terminator.