Umm, yes, you can defrag a SCSI drive. First, I would just reboot. Second, if that didn't work, see if there are updated drivers for your hard drive controller. If it's an outboard (not built-in) controller, then go to the site of the maker of the unit. If it is built-in, then go to the motherboard manufacturer. Try these first, as they are simple solutions.
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Regards,
clutch