Memory system and method

A memory system comprising:

• a nonvolatile first memory including a plurality of storage area units, each of the plurality of storage area units being a unit of an erase operation, each of the plurality of storage area units including a plurality of sub storage areas;
• and
• a memory controller configured to:
• manage, for each of the plurality of storage area units, each of the plurality of sub storage areas by using a sub storage area number in accordance with an order of data storage in the corresponding storage area unit;
• and
• execute, on each of the plurality of storage area units, a first operation of storing first information a plurality of times, each of the plurality of times of the first operation including:
• for a first storage area unit that is one of the plurality of storage area units and includes no free area capable of storing the first information, executing the erase operation on the first storage area unit and storing the first information in the first storage area unit after the erase operation;
• for a second storage area unit that is one of the plurality of storage area units and includes a free area capable of storing the first information, storing the first information in the second storage area unit without executing the erase operation on the second storage area unit;
• and
• in at least two of the plurality of storage area units, storing the first information in sub storage areas having different sub storage area numbers, and thereby causing at least one of the at least two storage area units to include the free area after the first operation.