Memory system and method for controlling nonvolatile memory

A memory system connectable to a host, the host including a first buffer, the memory system comprising:

• a nonvolatile memory, a data write operation to the nonvolatile memory being to be performed in a unit of a first size;
• and
• a controller electrically connected to the nonvolatile memory and configured to:
• after receiving, from the host, a first write command instructing to write first data of a second size from a first location of the first buffer of the host to the nonvolatile memory, the second size being smaller than the first size, wait for receiving a second write command without obtaining the first data from the first location of the first buffer of the host;
• and
• in response to receiving, from the host, the second write command instructing to write second data of a third size from a second location of the first buffer of the host to the nonvolatile memory, a sum of the second size and the third size being larger than or equal to the first size,
• transfer third data of the first size from the first buffer of the host to the nonvolatile memory, the third data including at least part of the first data and at least part of the second data;
• and
• instruct the nonvolatile memory to write the third data.