Patent ID: RE43600

Claim:
A first external storage control device which is connected to a first group of external storage devices and controls data transfer between said first group of external storage devices and a host, wherein said first external storage control device is connected to a second external storage control device which is connected to a second group of external storage devices; said first external storage control device being equipped with a storing means that stores write data transferred by a write command from the host and means that transfers the write data stored in said storing means to the second external storage control device according to a write command; the first external storage control device also having means for storing the write data to both an external storage device belonging to said first group of external storage devices and to an external storage device belonging to said second group of external storage devices; means for estimating the command-chaining time between said first and second external storage control devices; means for estimating a time for a write process, including said estimated command-chaining time, to one of said second group of external storage devices; and command means for writing data in the write process in a single operation; wherein in a case where said first external storage control device has received plural write commands for said data from the host, said first external storage control device transfers said write data to said second external storage control device by selecting a transfer method with the shortest processing time; said transfer method with the shortest processing time is selected by considering the command-chaining time between said first external storage control device and said second external-storage control device; and said means for estimating a time for a write process estimates the time before starting the write process to said second external storage control device according to said selected transfer method.