Hi ...
do the following steps carfully :
1- shutdown your machine using the command # init 5 as root
2- Connect your SCSI device , and make sure of the good terminaton and SCSI type (single ended or differential)
3- Power on your device
4- Power on your machine
5- When you got the startup screen , press stop+a
6- type ok probe-scsi-all , you should see your new hardware
7- type ok boot -r , for reconfiguration and driver building
8- enjoy your device