A method for increasing storage space in a system containing a block data storage device, a memory, and a processor is provided. Generally, the processor is configured by the memory to tag metadata of a data block of the block storage device indicating the block as free, used, or semifree. The free tag indicates the data block is available to the system for storing data when needed, the used tag indicates the data block contains application data, and the semifree tag indicates the data block contains cache data and is available to the system for storing application data type if no blocks marked with the free tag are available to the system.