The Data Shadowing System comprises a memory module that is connected to the monitored computer system via an existing input/output port to store the shadowed data. The memory module includes a memory device for data storage as well as software, including a control software component that is automatically installed on the monitored computer system when the memory module is first connected to the monitored computer system, as well as associated module software for maintaining a record of the data stored on the memory device. The Data Shadowing System automatically stores the data on the memory module in a single format, while representing it in a data management database in two formats: disk sectors and files. The Data Shadowing System thereby efficiently tracks and stores the state of multiple file systems over time, while allowing for correct disk-level and file-level restoration to a point-in-time without storing redundant data.