A memory system includes a non-volatile memory, a buffer memory, and a controller configured to write data to the non-volatile memory in write units of a predefined size, each write unit including a plurality of data items and log data and to temporarily store the data items and the log data of each write unit in the buffer memory prior to writing the write unit to the non-volatile memory. In response to a write command, the controller calculates a total data size of the data items of the write unit and write data specified in the write command, and a total log size of the log data and log information associated with the write data, and in response to determining that the total data size or the total log size is greater than their respective thresholds, write the write unit stored in the buffer memory to the non-volatile memory.