Patent ID: 7155587

Claim:
A method for managing a performance of a storage system, the storage system including a first storage subsystem and a second storage subsystem, the first storage subsystem being coupled to a computer and including a plurality of first logical devices, the second storage subsystem being coupled to the first storage subsystem and including a plurality of second logical devices, the method comprising the steps of: storing, at the first storage subsystem, relationship information indicating a relation between a first logical device of the plurality of first logical devices and a second logical device of the plurality of second logical devices; receiving, at the first storage subsystem, a first access request to said first logical device from the computer; sending, from the first storage subsystem, a second access request for said second logical device to the second storage subsystem via an interface in the first storage subsystem coupled to the second storage subsystem, said second logical device being specified based on the relationship information when the first storage subsystem receives the first access request; calculating, at the first storage subsystem, performance related to the second access request from the interface to said second logical device by using the relationship information, in order to determine operating information associated with said second logical device by the first storage subsystem; reading out, by the first storage subsystem in a manner transparent to the computer, data stored in said second logical device from the second storage subsystem if the operating information associated with said second logical device indicates a predetermined amount of deterioration in performance of the second logical device; storing, at the first storage subsystem in a manner transparent to the computer, the data read out from said second logical device in the second storage subsystem into a storage device in the first storage subsystem; changing the relationship information to indicate a new relation between said first logical device and the storage device; and executing, at the first storage subsystem, a third access request for accessing the storage device in the first storage subsystem in response to receiving a fourth access request for said first logical device at the first storage subsystem after the storing step based on the new relation.