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Reliability Enhancement of SSD-based Storage Systems Using Erasure Codes

Mozaffari, Fereshte | 2015

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 47753 (19)
  4. University: Sharif University of Technology
  5. Department: Computer Engineering
  6. Advisor(s): Miremadi, Ghasem
  7. Abstract:
  8. The use of flash-based Solid State Disks (SSDs) has been increased in the past decades because of their high performance and low power consumption. As SSDs have no moving mechanical parts, they are more reliable than HDDs. SSDs have specific errors, such as read, program, and erase disturbs, data retention, and endurance. It is so common in storage systems to apply an array of disks called Redundant Array of Independent Disks (RAID) together for the aim of reliability and performance. Erasure codes are one of the main methods applied in storage systems for the aim of reliability. Erasure codes increase the reliability of storage systems by protecting them against disk failures and sector failures. The recovery from disk failure affects the Program/Erase (P/E) cycles which may accelerate the Solid State Drive (SSD)’s wear-out. The wear-out problem, i.e., endurance limit, is one of the main reliability threats in the SSDs. Another failure, which is most common is sector failure. This failure not only affects on SSD disks, but also causes wear-out on SSDs. As a property of SSDs, the pages of SSD cannot be updated in-place. When one page is written, the previous page becomes invalid and new value is written in the new free page. Moreover, writing a page in SSD needs to update not only the data block, but also the corresponding parity blocks, both of which are written in the places different from their original device locations. Thus, for the sake of endurance, it is important to update the minimum number of parities in SSDs. An erasure code provides better endurance if the minimum number of parities are updated for each updated data. This paper presents an erasure code, called LRSD code. LRSD code protects both disk and sector failures with respect to the endurance limitation of SSDs. The basic idea of this code is to decrease the number of parity writes by changing the pattern of grouping data and sector-parities. The results of simulation show that LRSD code improves the endurance of storage systems in terms of average number of cleans and the variance of cleans by 26.2% and 65.2, respectively. In addition, LRSD code improves the performance by 15.7%
  9. Keywords:
  10. Erasure Code ; Storage Systems ; Error ; Reliability ; Storage Systems ; Solid State Disk Drive ; Endurance Assessment

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