A Japanese research team has developed a technology to significantly improve the writing speed, power efficiency and product life of SSDs.
The team is led by Ken Takeuchi, professor at the Department of Electrical, Electronic and Communication Engineering, Faculty of Science and Engineering of Chuo University.
With NAND flash memory, it is not possible to overwrite data on the same memory area, making it necessary to write data on a different area and, then, invalidate the old area. As a result, data is fragmented, increasing invalid area and decreasing storage capacity. To cope with the issue, NAND flash memories carry out "garbage collection," which rearranges fragmented data in a continuous way and erases blocks of invalid area. This process takes 100ms or longer, drastically decreasing the writing speed of SSD.
To address this issue, last year a research team at the Department of Electrical, Electronic and Communication Engineering, Faculty of Science and Engineering of Chuo University, developed a method to prevent data fragmentation by making improvements to middleware that controls a storage for database applications. It makes the "SE (storage engine)" middleware, which assigns logical addresses when an application software accesses a storage device, and the FTL (flash translation layer) middleware, which converts logical addresses into physical addresses on the side of the SSD controller, work in conjunction.
Now the same team has developed a more versatile method that can be used for a wider variety of applications.
The new method forms a middleware layer called "LBA (logical block address) scrambler" between the file system (OS) and FTL. The LBA scrambler works in conjunction with the FTL and converts the logical addresses of data being written to reduce the effect of fragmentation.
Specifically, instead of writing data on a new blank page, data is written on a fragmented page located in the block to be erased next. As a result, the ratio of invalid pages in the block to be erased increases, reducing the number of valid pages that need to be copied to another area at the time of garbage collection.
In a simulation, the research team confirmed that the new technology improves the writing speed of SSD by up to 300% and reduces power consumption by up to 60% and the number of write/erase cycles by up to 55%, increasing product life. Because, with the new method, it is not necessary to make any changes to NAND flash memory, and the method is completed within the middleware, it can be applied to existing SSDs.