1. A storage unit management method, comprising: providing a storage unit comprising a plurality of physical blocks, wherein each has one of a plurality of block type definitions; obtaining a sub-write command requesting to write data to at least one logical page of a logical block; determining whether a candidate block having a sequential block definition exists in the storage unit, wherein the logical page of the logical block cannot map to the candidate block based on the sequential block definition; if the candidate block exists, transforming the block type definition of the candidate block from the sequential block definition to a dedicated block definition; writing data to a specific page of the candidate block having the dedicated block definition, and recording a mapping relationship between the logical page of the logical block and the specific page of the candidate block, wherein the sub-write command comprises mapping directory number, block offset and page offset; locating a specific block mapping table from a plurality of block mapping tables according to the mapping directory number; locating a first specific entry from the specific block mapping table according to the block offset, wherein the first specific entry comprises a mapping mode setting and a block information; and when the mapping mode setting indicates a page mapping mode, locating a second specific entry from a page mapped block table according to the block information of the first specific entry, wherein the second entry of the page mapped block table records a beginning address of a specific page mapping table.