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 first block type definition exists in the storage unit, wherein the logical page of the logic block cannot map to the candidate block based on the first block type definition; if the candidate block exists, transforming the block type definition of the candidate block from the first block type definition to a second block type definition; and writing data to a specific page of the candidate block, and recording a mapping relationship between the logical page of the logical block and the specific page of the candidate block.