linking the original value of the data unit to the update data before transferring the update data to the storage layer if transferring the update data to {HEAD ~ the storage layer results} in updating {TAIL ~ a value} of the data unit 
linking the original value of the data unit to the update data before transferring the update data to the storage layer if transferring the update data to { HEAD ~ the storage layer results } in updating { TAIL ~ a value } of the data unit
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD REL REL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH