1. A design structure embodied in a machine readable medium for a first memory module, the design structure comprising: a plurality of addressable storage locations for storing data; a first interface for receiving data access command for accessing data stored in said addressable storage locations; control logic which supports at least one mode of operation wherein said first memory module re-transmits a plurality of copies of at least some said data access commands received in said first interface, each copy being transmitted using a respective interface of a plurality of second interfaces, each copy being transmitted to a respective one or more memory modules other than said first memory module.