Memory system and read method

A memory system includes non-volatile memory cells for storing multiple bit data and a controller configured to control to apply read voltages to the non-volatile memory cells at different threshold levels to read data written to the non-volatile memory cells. The non-volatile memory cells comprise different sub-groups. The controller stores first information indicating a first initial value for each of the different threshold level of the read voltages, second information that indicates whether data can be successfully read from each sub-group when the respective different threshold levels of the read voltages are set to the first initial values, and third information that indicates a second initial value for each different threshold level of the read voltages for at least one sub-group for which data reading was unsuccessful when a read voltage was set to the first initial value.