1. In a storage system having a storage controller with cache memory coupled to a plurality of disk drives each having a local disk controller with local cache memory, a method operable in the storage controller comprising: receiving in the storage controller a write request from an attached host system; storing host data associated with the write request in the cache memory of the storage controller; transferring the host data from the storage controller's cache memory to the local cache memory of a disk drive of the plurality of disk drives using a write-back mode of operation wherein the step of transferring is adapted to maintain integrity of the host data stored on the disk drive with respect to the host data in the storage controller's cache memory.