{HEAD ~ Diagnosis} of {TAIL ~ the spare magnetic disk unit} 191 is conducted when a fixed time has elapsed 
of
{ HEAD ~ Diagnosis } of { TAIL ~ the spare magnetic disk unit } 191 is conducted when a fixed time has elapsed
HEAD HEAD HEAD HEAD HEAD REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH