FTL BAST Policy and Strategy

1 Aug

As users demand access to data, the traditional structure of the system and the external storage disk I / O delay limits the storage system performance. In order to meet the needs of high-performance mass data storage, new storage devices came into being. NAND flash-based solid state disk with its non-volatile, fast access, high reliability and low power consumption and many other advantages, can better alleviate the I / O performance bottlenecks, and gradually become a research hotspot. But before writing erasure characteristics and limited erase cycles a serious impact on the performance and reliability of SSDs.

  • In this paper, flash-based SSDs technical characteristics and the internal composition of the flash-based SSDs some of the key technology improvements. The research work mainly includes the following aspects:
  • Studied the flash-based SSDs basic principles of the structure and key technologies;
  • Disksim simulator designed and implemented based on the SCSI interface and flash memory interface;
  • Studied the flash-based SSD Cache works, focused on the Cache replacement policy. By analyzing CFLRU defect replacement policy proposed CFLRU / AF-E strategy, frequency of visits and page by wear leveling into account, effectively improve the Cache hit rate and reduce the number of write-back, good wear leveling obtained better degrees. Then design experiments from Cache hit rate, the total number of write-back, with a total running time and wear-leveling degree four angles CFLRU / AF-E strategy and tactics CFLRU comparative analysis;
  • Brought before the erase flash memory rewriting for wear problems, the first analysis of the Dual-Pool advantages and disadvantages of wear leveling algorithm proposed Advanced Dual-Pool algorithm, improved its position in the lack of garbage collection, wear leveling does not affect the treatment effect the premise of improving the efficiency of garbage collection. Through simulation experiments proved Advanced Dual-Pool algorithm is better than in the Dual-Pool algorithm processing performance in wear leveling similar, but garbage collection efficiency has been greatly improved;
  • Designed a flash translation layer strategy. FAST from the analysis of strategies and tactics BAST defects, combining their strengths, proposed a hybrid FTL strategy, a combination of hot and cold properties of the data block consideration solves FAST log block is exhausted in the idle poor performance, and effectively improves write performance. Through simulation experiments proved that hybrid FTL policy strategies with respect BAST and FAST strategy has greatly improved overall performance, and can effectively reduce FTL strategy caused by the number of erase operations.

In summary, the article from the SSD Cache technology, wear leveling and flash translation layer strategy three aspects of research, improved CFLRU / AF-E strategy to improve the Cache hit rate and reduce the number of write-back, improving write performance; proposed algorithm Advanced Dual-Pool obtain a higher recovery efficiency; the hybrid strategy combines FTL BAST policy and FAST strategy has the advantage, to effectively improve the write performance.

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