Automated tiered storage with fast memory and slow flash storage (ATSMF) is a hybrid storage system located between non-volatile memories (NVMs) and solid state drives (SSDs). ATSMF aims to reduce average response time for inputoutput (IO) accesses by migrating concentrated IO access areas from SSD to NVM. However, the current ATSMF implementation cannot reduce average response time sufficiently because of the bottleneck caused by the Linux brd driver, which is used for the NVM access driver. The response time of the brd driver is more than ten times larger than memory access speed. To reduce the average response time sufficiently, we developed a block-level driver for NVM called a 'two-mode (2M) memory driver.' The 2M memory driver has both the. map IO access mode and direct IO access mode to reduce the response time while maintaining compatibility with the Linux device-mapper framework. The direct IO access mode has a drastically lower response time than the Linux brd driver because the ATSMF driver can execute the IO access function of 2M memory driver directly. Experimental results also indicate that ATSMF using the 2M memory driver reduces the IO access response time to less than that of ATSMF using the Linux brd driver in most cases.