1. A storage system comprising: a first disk array apparatus configured with first storage areas for storing data sent from a host system; a second disk array apparatus configured with second storage areas for storing back-up data of the first storage areas; and a console terminal which operates the first disk array apparatus, wherein the console terminal includes a setting unit for setting a priority for each first storage area in accordance with an external command with decreasing the priority when the number of times accessed to the each first storage area is within a first predetermined range, not changing the priority when the number is within a second predetermined range, and increasing the priority when the number is within a third predetermined range, wherein the first disk array apparatus includes: a storage unit for storing the priorities set by the priority setting unit; and a transfer unit for reading the priorities from the storage unit upon receiving the data, and transferring the data stored in the first storage areas to the second storage areas of the second disk array apparatus in a descending order according to the priorities of the first storage areas that store the data, and wherein the first disk array apparatus includes a counting unit for counting the number of times data is received for each first storage area.