1. In a cache-redundant storage system comprising at least two redundant storage controllers, each of the storage controllers comprising a primary cache memory and a secondary cache memory, a method for preserving cache data of the two redundant storage controllers, comprising: receiving a storage request from a host into one of the redundant storage controllers; recording a data block in response to the storage request in the primary cache memory of the receiving storage controller; creating a cache tag for said recorded data block and recording said cache tag in said primary cache memory of the receiving storage controller; copying the recorded data block and the recorded cache tag to the secondary cache memory of another of the redundant storage controllers; and upon a failure of the primary cache memory of a redundant storage controller, detecting the failure and processing subsequent storage requests from the host, previously intended for processing by the failed storage controller, through the secondary cache memory of said another of the redundant storage controllers.