performing data migration by the data migration node from {TAIL ~ the first storage} to {HEAD ~ the second storage} 
performing data migration by the data migration node from { TAIL ~ the first storage } to { HEAD ~ the second storage }
OTH OTH OTH OTH OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD