1. A method, in a data processing system, for extending cache for a storage system in a storage area network, the method comprising: storing a copy of data in an extended cache card attached to a server, wherein the extended cache card comprises a non-volatile memory for storing copies of data read from or written to an external storage system by the server; responsive to receiving from the server a request to read a first portion of data from the external storage system, determining whether the extended cache card stores an up-to-date copy of the first portion of data; and responsive to a determination that the extended cache card stores an up-to-date copy of the first portion of data, sending the copy of the first portion of data from the extended cache card to the server.