1. A computer controlled data migration method for migrating data from a first storage node including a first logical unit and a first target corresponding to a first initiator to a second storage node having a second logical unit, in a storage system, the storage system further including a name server for managing an interrelation between an initiator and a target set, the data migration method comprising: transmitting, by the first storage node, data stored in the first logical unit to the second storage node; storing the data received by the second storage node from the first storage node in the second logical unit; transmitting, by the first storage node, information about the first target to the second storage node; setting, by the second storage node, a target to the second logical unit using the information about the first target received from the first storage node; notifying, by the second storage node, the name server of information about the target set to the second logical unit; and receiving, by the second storage node, an access request for the second logical unit based on an instruction from the name server.