US Patent 7984260 Storage system provided with a plurality of controller modules

A plurality of global LDEV managed by a plurality of controller modules are provided above local LDEV under the control of each controller module. Each global LDEV is correlated to any of the plurality of local LDEV. The controller modules judge whether or not a local LDEV correlated to a global LDEV specified by an I/O request received from a host device or a first other controller module is a management target itself, and if the result of that judgment is affirmative, the controller modules access the local LDEV correlated to the specified global LDEV, while if the result of the judgment is negative, the controller modules transfer the received I/O request to a second other controller module.