Multi-level data storage device and operation method thereof

An operation method of a multi-level data storage device including a first storage device storing data by performing a first write operation and a second storage device storing data by moving the data stored in the first storage device to the second storage device by performing a second write operation, the operation method comprising:

• generating a first write set when a sum of a number of first write operations and a number of second write operations becomes a predetermined number;
• calculating an imbalance index corresponding to the first write set by using a latency of a first write operation and a latency of a second write operation corresponding to the first write set;
• determining an imbalance state based on the imbalance index;
• and
• controlling imbalance of write operations performed in the multi-level data storage device by controlling the first write operation or the second write operation so that an imbalance index corresponding to a second write set is reduced when the imbalance state is determined, the second write set being generated to follow the first write set.