Memory system changing write size and write mode and method of controlling nonvolatile memory by changing write size and write mode

A method of controlling a nonvolatile memory, the nonvolatile memory including a plurality of blocks, each of the plurality of blocks being a unit for a data erase operation, the method comprising:

• managing a plurality of block groups, each of the plurality of block groups including one or more first blocks among the plurality of blocks, data being to be written to each of the one or more first blocks in units of a first minimum write size;
• managing at least one second block among the plurality of blocks, data being to be written to the second block in units of a second minimum write size smaller than the first minimum write size;
• determining that a total size of first data associated with one or more first write commands reaches the second minimum write size, each of the one or more first write commands being received from a host and specifying an identifier corresponding to a first block group among the plurality of block groups;
• in response to determining that the total size of first data reaches the second minimum write size, writing, to the second block, second data which is at least part of the first data and has a size of the second minimum write size;
• determining that a total size of one or more pieces of the second data written to the second block reaches the first minimum write size;
• in response to determining that the total size of the one or more pieces of the second data reaches the first minimum write size, reading, from the second block, third data which includes the one or more pieces of the second data and has a size of the first minimum write size;
• and
• writing the third data to one of the one or more first blocks included in the first block group.