Note: this is a "vintage" tip for older computers/systems.
if you are using an old Mac, SCSI Probe is a very useful control panel which can be used to examine and control SCSI devices attached to your computer running Mac OS 9 and older. If you do install it note that the default key combination for mounting hard disks is command-space which is also used by many programs such as Photoshop. If you find Photoshop and others temporarily freezing when you use these keys, change the keys used in SCSI Probe.