Storage system using a flash memory partitioned with write-once and rewritable blocks

A storage system, comprising:

• a nonvolatile memory which erases data for respective blocks;
• and
• a controller for inputting and outputting the data to and from the nonvolatile memory,
• wherein the controller assigns at least one of the blocks in the nonvolatile memory as a rewritable area where stored data can be erased, and assigns at least a portion of the rest of the blocks in the non-volatile memory as a write once area where the stored data cannot be erased;
• wherein the controller determines a block belonging to the rewritable area based on an attribute of the block, and performs a wear leveling process and a reclamation process only on the block determined as belonging to the rewritable area,
• wherein the block stores retention period information of the stored data,
• wherein the storage system has a storage area including:
• the rewritable area where the stored data can be erased;
• the write-once area where the stored data cannot be erased;
• and an unused area for which the attribute is not determined;
• and
• wherein the controller erases data whose retention period expires from the block that stores the data, and changes the write-once area to the unused area by changing the attribute of the block.