Patent ID: 7366846

Claim:
A method, comprising: receiving, at a controller, a request from one of a plurality of hosts, wherein the controller is coupled to a primary storage control unit and a secondary storage control unit, 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; determining whether write caching is enabled in the controller; 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 in response to determining that write caching is enabled in the controller, wherein if the request is a write request then performing: (a) writing the data to the cache in response to receiving the write request; and (b) responding to the one of the plurality of hosts from which the write request was received that the write request has been executed, wherein the data written to the cache is destaged periodically to: (i) the primary storage control unit, in response to determining that that primary storage control unit is operational; and (ii) the secondary storage control unit, in response to determining that the primary storage control unit is not operational.