Storage unit management methods and systems are provided. The storage unit comprises a plurality of physical blocks, wherein each has one of a plurality of block type definitions. First, a sub-write command is obtained, wherein the sub-write command requests to write data to at least one logical page of a logical block. It is determined 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, the block type definition of the candidate block is transformed from the first block type definition to a second block type definition. Data is written to a specific page of the candidate block, and a mapping relationship between the logical page of the logical block and the specific page of the candidate block is recorded.