1. A storage controller, comprising: four PCIe memory controllers, each having a PCIe front-end path, a PCIe back-end path and a set of memory modules; a PCIe crossover switch having: a front-end PCIe switch having a first plurality of PCIe lanes connected to one or more front-end PCIe host bus adaptors, said front-end host bus adaptors being connectable to one or more host paths, and a second plurality of PCIe lanes connected each of said PCIe front-end paths of said four PCIe memory controllers; and a back-end PCIe switch having a first plurality of PCIE lanes connected to one or more back-end PCIe host bus adaptors, said back-end host bus adaptors being connectable to one or more drive paths, and a second plurality PCIe lanes connected to each of said PCIe back-end paths of said four PCIe memory controllers.