A log-structured block system is provided in which writing log-structured data is done. A space is defined between the cylinder and an inner periphery of the barrel. A small aperture laser is operated during read and write operations at a bias current which is higher than the threshold currents associated with feedback from high and low reflectivity regions of an optical medium. Alkylene oxide reacts with carbon dioxide in the absorber, forming alkylene carbonate, and fat absorbent comprising alkylene carbonate is withdrawn from the absorber.