This paper reports on the study of the superresolution volume of the focal spot by focusing a radially polarized beam. This feature is achieved by increasing the inner radius of a high NA annular objective to break the diffraction-limited volume of a focal spot. The application of this finding into two-photon induced three-dimensional optical data storage leads to an enhanced photoreduction threshold effect in recording. As such, multilayer subdiffraction optical recording is experimentally demonstrated with an equivalent capacity of 3.0 Tbytes/disk.