Patent ID: 7788453
Filing Date: 2010-08-31
Classification: G06F

Abstract:
1. A system comprising a controller coupled to a primary storage control unit and a secondary storage control unit, the system comprising: memory; and processor coupled to the memory, wherein the processor is capable of performing operations, the operations comprising: (A) receiving a request at the controller from one of a plurality of hosts, wherein the controller is a storage area network volume controller that controls storage volumes in a primary storage control unit and a secondary storage control unit, wherein the controller includes a cache, and wherein data is replicated synchronously from the primary storage control unit to the secondary storage control unit; (B) determining whether write caching is enabled in the controller; (C) in response to determining that write caching is not enabled in the controller, sending the request to the primary storage control unit if the primary storage control unit is operational and sending the request to the secondary storage control unit if the primary storage control unit is not operational; and (D) in response to determining that write caching is enabled in the controller, wherein if the request is a write request then performing: