Conventional optical data storage such as digital versatile disc (DVD) and Blu-ray disc (BD), provide us inexpensive and compact media for satisfying information storage requirement for decades. As the knowledge and information increase rapidly, the requirement cannot be already satisfied by current data storage systems. As far as we know, the size of recording mark, the critical storage density indicator, depends on recording energy, writing strategies, opto-thermal threshold plane and thermal conductivity. Readout is limited by optical resolution limit, the wavelength of readout laser and numerical aperture (N.A.) of objective lens. In this talk, I will introduce several means to increase the optical storage density. A powerful tool, conductive-tip atomic force microscopy (C-AFM), with the advantages of high spatial resolution, high contrast of conductivity and non-destructive method to help us better understand the formation of recording marks is also presented. Finally, I will show our recent efforts on realizing the extreme of recording mark.