Non-volatile memory driver to drastically reduce input-output response time and maintain Linux device-mapper framework

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 reduces the average response time for input-output (IO) accesses by migrating concentrated IO-access areas from an SSD to an NVM. However, the current ATSMF implementation cannot sufficiently reduce the average response time 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 longer than memory-access speed. To sufficiently reduce the average response time, we developed a block-level driver for an NVM called a "two-mode (2M) memory driver." This driver has a .map-access mode and direct-access mode to reduce the response time while maintaining compatibility with the Linux device-mapper framework. The direct-access mode has a drastically lower response time than the Linux brd driver because the ATSMF driver can directly execute the IO-access function of the 2M memory driver. Experimental results indicate that ATSMF using the 2M memory driver reduced the IO access response time to less than that of ATSMF using the Linux brd driver in most cases.