Abstract: A data storage medium is provided which is suitable for production or replication by moulding, casting, embossing or a similar process against a tool. The data storage medium comprises an optically sensitive layer at or adjacent to one surface of the medium, said one surface of the medium comprising a plurality of topographical features or structures disposed in a regularly repeating pattern, said pattern being free from undercutting so that the medium can be produced and/or replicated by molding, casting, embossing or similar process against a tool. The optically sensitive layer is preferably overcoated with a thin film of a metallic material which conforms to the topography of said surface.