CROSS-REFERENCE TO RELATED APPLICATIONS

This application is based upon and claims the benefit of priority from Japanese Patent Applications No. 2020-042783, filed Mar. 12, 2020; and No. 2021-012149, filed Jan. 28, 2021, the entire contents of all of which are incorporated herein by reference.

FIELD

Embodiments described herein relate generally to a memory system including a nonvolatile memory.

BACKGROUND

In recent years, memory systems including nonvolatile memories are widely used. As a type of the memory systems, a solid state drive (SSD) having a NAND flash memory is known. SSDs are used as a main storage of various computing devices.

The nonvolatile memory includes physical blocks. Nowadays, the size of a physical block has been increasing, and the number of physical blocks in a nonvolatile memory has decreased accordingly.

In addition, a controller of the memory system may have a function for recovering data in a defective physical block. The controller has an error correction function that corrects data in which an error occurs by using, for example, an error correction code (ECC).

In order to increase the amount of user data that can be stored in the nonvolatile memory, it is desirable that a ratio of ECCs in data stored in the nonvolatile memory be lower. In other words, it is desirable to be able to cope with defects of the physical blocks at a lower ratio of ECCs.

