US Patent 7715411 Storage apparatus and data transfer method

A controller controls exchange of data between a plurality of storage units based on transfer rates of the storage units and a fixed rate. If at least one of the transfer rates of a transfer-source storage unit and a transfer-destination storage unit are different than the fixed rate, the controller accumulates a certain amount of data, and outputs accumulated data to the transfer-destination storage unit at the transfer rate of the transfer-destination storage unit so that data is transferred from the transfer-source storage unit to the transfer-destination storage unit at apparently at the fixed rate.