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Sector Level Mapping for Flash Memory: FTL Techniques and Experimental Results on Open-SSD

This tutorial provides a comprehensive overview of sector-level mapping in Flash Translation Layers (FTL) within the Open-SSD framework. It discusses key considerations for managing merge buffers, implementing read and write modules, and presents experimental results showcasing IOPS and throughput performance under various conditions, including both random and sequential workloads. The tutorial aims to enhance understanding of sector mapping techniques, such as static, dynamic, and multi-copy mappings, and highlights the importance of caching in optimizing performance.

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Sector Level Mapping for Flash Memory: FTL Techniques and Experimental Results on Open-SSD

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  1. Sector Level Mappinng FTL Oh Gihwan, Han Gyuhwa, Hong Gyeonghwan Jasmine Open-SSD Project Tutorial 2 - Sector Level Mapping FTL Computer engineering , Sungkyunkwan Univ.

  2. Index • Sector Level Mapping • Consideration : How to Fill Merge Buffer? • Write module for sector level mapping • Read module for sector level mapping • Experiments • Conclusion • Reference

  3. Sector Level Mapping <W, 100, 10> <W, 2, 20> <R, 3, 10> <W, 100, 20> . . <W, 20, 60> Merge Buffer Sector Mapping Table Flash Memory Page

  4. Write module (1/4) <W, 100, 10> <W, 2, 20> <W, 100, 20> . . <W, 20, 60> Merge Buffer Sector Mapping Table Flash Memory Page

  5. Considerations : How to Fill Merge Buffer? • Fill one merge buffer in order of incoming • 1-Buffer : Just put sectors to merge buffer • Multi-copy : Just put sectors, but put sectors with succeeding LBAs at once • Distribute sectors to several merge buffers by banks • Dynamic : Distribute sectors to merge buffers in order of incoming • Static : Distribute sectors to merge buffers, but bank number is fixed by LBA

  6. Write module (2/4) <W, 100, 10> <W, 2, 20> <W, 100, 20> . . <W, 20, 60> Merge Buffer Sector Mapping Table Flash Memory Page

  7. Write module (3/4) <W, 100, 10> <W, 2, 20> <R, 3, 10> <W, 100, 20> . . <W, 20, 60> Merge Buffer Sector Mapping Table Flash Memory Page

  8. Write module (4/4) <W, 100, 10> <W, 2, 20> <R, 3, 10> <W, 100, 20> . . <W, 20, 60> Merge Buffer Sector Mapping Table Flash Memory Page

  9. Read module Sector Mapping Table Merge Buffer <R, 100, 10> <R, 2, 20> <R, 3, 10> <R, 100, 20> . . <R, 20, 60> Flash Memory Page

  10. Experiments • Environment • Application : Iometer • Transfer size • Random test : 512 Bytes, 1 KB , 2KB , 4KB • Sequential test : 128 KB • Target FTL • Tutorial • Greedy • Static Sector mapping • Dynamic Sector mapping • 1 buffer Sector mapping • Multi copy Sector mapping

  11. Experiments results IOPS

  12. Experiments results MB/s

  13. Experiments results x10 • Random Write Test ( Average of four tests ) • Sequential Read/Write Test ( Average of four tests ) x8

  14. Experiments results • Test Without Map Table Caching ( Average of four tests ) • Test with Map Table Caching ( Average of four tests ) x 1/50 ~ 1/20

  15. Conclusion • Small random write performance of sector mapping is GREAT! • Sequential read/write performance of sector mapping is LOW… • Shrinking mapping table OVERHEAD is important.

  16. References • DFTL: a flash translation layer employing demand-based selective caching of page-level address mappings / 저자: AayushGuptaKim, BhuvanUrgaonkarYoungjae • OpenSSD Project - www.openssd-project.org. • The Jasmine OpenSSD Platform: FTL Developer's Guide –http://www.openssd-project.org/ • The Jasmine OpenSSD Platform: Technical Reference Manual- http://www.openssd-project.org/

  17. Q & A

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