Collinear holography proposed by OPTWARE Corporation is the most promising method for ultra-high density volumetric optical data storage system. A servo technology is introduced to control the objective lens to be stopped relatively to the disc during the recording and the reconstructing process. Experimental and theoretical studies suggest that the proposed system and media structure are indeed very effective for materializing a small optical storage system with huge density. Further investigations have been underway to balance the data density and the transfer rate by incorporating newly designed optical and electronic components. Collinear holography can also be applied into other optical information storage systems in the future.