A data storage system, comprising: a first non-volatile mass storage device that interfaces with a host system via a direct file storage interface (106,107,115), hereinafter referred to as DFS interface, arranged to use a file based protocol; and a second non-volatile mass storage device; wherein data from the host system can be stored in the first non-volatile mass storage device and/or the second non-volatile mass storage device, wherein the first non-volatile mass storage device is a solid-state non-volatile memory device and the second non-volatile mass storage device is a magnetic hard disk; and wherein the first non-volatile mass storage device includes a disk file system that maps data files received from the host system via the DFS interface to a logical address space within the second non-volatile mass storage device; wherein the second non-volatile mass storage device interfaces with the first non-volatile mass storage device via the disk file system using the logical address space; characterized in that: the first non-volatile mass storage device stores data on a file by file basis and wherein the second non-volatile mass storage device stores data received via a logical interface; and a memory controller in the first non-volatile mass storage device is configured to segment one or more of the data files into at least a first file segment and a second file segment, wherein the first file segment is stored in the first non-volatile mass storage device and the second file segment is stored in the second non-volatile mass storage device in the event the memory controller determines that the one or more of the data files can be segmented. a first non-volatile mass storage device that interfaces with a host system via a direct file storage interface (106,107,115), hereinafter referred to as DFS interface, arranged to use a file based protocol; and a second non-volatile mass storage device; wherein data from the host system can be stored in the first non-volatile mass storage device and/or the second non-volatile mass storage device, wherein the first non-volatile mass storage device is a solid-state non-volatile memory device and the second non-volatile mass storage device is a magnetic hard disk; and wherein the first non-volatile mass storage device includes a disk file system that maps data files received from the host system via the DFS interface to a logical address space within the second non-volatile mass storage device; wherein the second non-volatile mass storage device interfaces with the first non-volatile mass storage device via the disk file system using the logical address space; the first non-volatile mass storage device stores data on a file by file basis and wherein the second non-volatile mass storage device stores data received via a logical interface; and a memory controller in the first non-volatile mass storage device is configured to segment one or more of the data files into at least a first file segment and a second file segment, wherein the first file segment is stored in the first non-volatile mass storage device and the second file segment is stored in the second non-volatile mass storage device in the event the memory controller determines that the one or more of the data files can be segmented.