A disk array unit connected to {HEAD ~ a host unit} to give {TAIL ~ information} thereto and receive information therefrom 
A disk array unit connected to { HEAD ~ a host unit } to give { TAIL ~ information } thereto and receive information therefrom
OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD REL REL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH