A flat hash table includes a plurality of entries, and each entry includes a hash function index and a usage bitmap. A method for block device level compression mapping using the flat hash table includes compressing uncompressed data to compressed data, retrieving an entry of the flat hash table using an uncompressed block address of the uncompressed data, determining a compressed block address of the compressed data by executing at least one hash function and by determining a hash function in the at least one hash function for mapping the uncompressed block address to the compressed block address that corresponds to a space in a block storage device, storing the compressed data to the space that corresponds to the compressed block address, and updating the hash function index of the entry of the flat hash table with an index indicative of the hash function.