Input/output errors, IMO, simply mean that the drive is not working as the O/S thinks it should.
Something is going wrong, for an indeterminate reason.
First thing I find that I should check: power supply connections and motherboard connections for the drive in question. I seem to be really guilty of not ensuring that there are no bent pins and that the connecting cables are properly seated on the connectors
Second thing: I would run chkdsk /r on the drive. If that was unable to run successfully, I would then download/run a manufacturer's diagnostic on the drive, long test.
Event Viewer is pretty good of advising users when a drive has problems. I would check the System tab carefully, looking for any indications of a problem with any drive/disk.
What is the Event Viewer, and Should I Care - Ask Leo! - http://ask-leo.com/what_is_the_event_viewe...uld_i_care.html
I've no experience with SCSI drives but, IMO, they have the same weaknesses all drives do...it could be the controller, it could be the cables, it could be the drive. I would just try to eliminate them, one by one.