Data storage system and data retention method thereof

PURPOSE: A data storage system and a data retention method thereof are provided to guarantee the data reliability of a data storage device connected with a host by performing retention operation to data not executed during an offline state of the data storage device. CONSTITUTION: Non-volatile memory devices(100) write data inputted by a host(20). A controller(200) outputs sampling data by performing sampling for searching for retention information corresponding to the memory devices. The host controls the memory devices to perform retention operation according to a retention cycle of the memory devices by determining the performance of the retention operation for the memory devices based on the determination result of the sampling data.