Adding SCSI drive to W2K server

We are running Exchange 2000 with W2K on an IBM e-Server X200 series, which boots from an 18Gb drive on the Adaptec 29160 SCSI card at SCSI ID 0. We added an external SCSI drive at SCSI ID 3 and carried out a low level format on the drive. On restarting the server, the Exchange drive M had disappeared, and Exchange did not start. Removing the drive restored the system to a working state. How do we prepare this new drive so that W2K sees it correctly and we don’t lose our Exchange drive?