Patent ID: 7337350

Claim:
A data storage system comprising: a first platform storage system including a first network interface to communicate with a host computer, a first storage unit to provide storage volumes, a first storage controller to control the first storage unit, and a first memory to store a first control program to process an input/output (I/O) request received by the first platform storage system; a second platform storage system including a second network to communicate with the host computer, a second storage unit to provide storage volumes, a second storage controller to control the second storage unit, and a second memory to store a second control program to process an I/O request received by the second platform storage system; an external storage system coupled to the first and second platform storage systems, the external storage system including a third storage unit to provide storage volumes and a third storage controller to control the third storage unit, wherein the first and second platform storage systems are configured to present the storage volumes of the external storage system to the host computer, so that the host computer can access the storage volumes of the external storage system via one of the first and second platform storage systems if the host computer is unable to access the storage volumes of the external storage system via the other platform storage system.