In this work we investigate the implications on the energy consumption of different popular file systems and propose a novel, log-structured file system aiming at minimized energy consumption by avoiding expensive disk seeks and introduced latencies due to rotational delays. We show that the energy efficiency of file systems is heavily influenced by the underlying data layout and file organization. Guidelines for a low power file system design are developed and evaluated with measurements of the energy consumption of a prototype implementation. As on-going work we investigate different approaches to free space management. We discuss design choices for the implementation of a family of free space managers and their implications on energy consumption.