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Extending the Lifetime of NAND Flash Memory by Salvaging Bad Blocks

Extending the Lifetime of NAND Flash Memory by Salvaging Bad Blocks. Chundong Wang and Weng -Fai Wong DATE’12. Outline. Introduction Wear Leveling Bad blocks Salvaging Experiments results Conclusions. Introduction.

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Extending the Lifetime of NAND Flash Memory by Salvaging Bad Blocks

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  1. Extending the Lifetime of NAND Flash Memory by Salvaging Bad Blocks ChundongWang and Weng-Fai Wong DATE’12

  2. Outline • Introduction • Wear Leveling • Bad blocks Salvaging • Experiments results • Conclusions

  3. Introduction • Flash memory is widely utilized for secondary storage today.(ex. embedded devices,SSD…) However, its further use is hindered by the lifetime issue.

  4. Introduction

  5. Wear Leveling • Hot date -> young blocks • Cold data -> old blocks Ex. Lazy wear leveling[3]

  6. Bad blocks Salvaging • The unit of write (a page) is different from that of erasure (a block). • It is very likely that some pages may be reprogrammed much more than others in a block. Moreover, the failure of a page does not affect data in other pages in the same block

  7. Bad blocks Salvaging • bad blocks can be classified into three categories : • backing blocks • discarded blocks • salvaged blocks

  8. Bad blocks Salvaging

  9. Wear leveling Procedure with BBS

  10. Experiments results • We implemented the BBS-based FTL in FlashSimsimulator [6] for SLC NAND flash. • We have used three families of disk traces from [13], [14] and [11].

  11. Experiments results

  12. Experiments results

  13. Experiments results

  14. Experiments results

  15. Conclusions • This paper proposed a design that reuses worn-out blocks to prolong the lifespan of flash chips. • Our design can reduce the number of worn-out blocks by 46.5% on average with 1.2% performance penalties at most.

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