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Reliability Improvement in SSD-based Storage Systems with Endurance Enhancement

Alinezhad Chamazcoti, Saeideh | 2016

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  1. Type of Document: Ph.D. Dissertation
  2. Language: Farsi
  3. Document No: 48400 (19)
  4. University: Sharif University of Technology
  5. Department: Computer Engineering
  6. Advisor(s): Miremadi, Ghassem
  7. Abstract:
  8. As a new technology, the use of Solid State Disk (SSD) in storage systems is increasing due to its higher performance and lower power consumption as compared to the traditional Hard Disk Drive (HDD). On the contrary, the SSD technology has two serious shortcomings, i.e., 1) it has a higher Bit Error Rate (BER) as the number of Program/Erase (P/E) cycles increases, and 2) it can endure a specific number of P/E cycles, called the write endurance limitation. To overcome the endurance limitation of SSDs, several solutions have been proposed in previous literature. These solutions can be categorized in two levels: 1) SSD-controller, and 2) RAID–Controller. Moreover, it is necessary to consider the variant BER of disks in reliability evaluation of SSD-based systems. Due to the importance of endurance in SSD-based storage systems, the main contributions of this dissertation are as follow: 1) exploring the main effective factors on endurance; 2) proposing an endurance aware architecture in RAID-level including: a) endurance aware erasure code (called EA-EO); b) hybrid approach for parity distribution among disks of array (called Hy-RAID); 3) introducing the reliability metrics for evaluating the reliability of SSD-based systems; and 4) modeling for reliability and endurance. In this dissertation, at the first step, it has been investigated and explored which factors affect the endurance of storage systems. The results of investigation show that erasure codes and parity distribution have effect on the endurance. Therefore, at the second step, EA-EO and Hy-RAID are proposed as a solution for enhancing the endurance of storage systems. EA-EO as an endurance aware erasure code enhances the endurance of storage systems by 4-44% as compared to EVENODD. Furthermore, by applying smart parity distribution among disks in Hy-RAID, the probability of simultaneous failures is decreased by 2X-8X, and the first failure is postponed in the system by 1.9X. In the third step, the metrics for evaluating the endurance of erasure codes (named DPD factor and GDP pattern), and the reliability of SSD-based systems (named interval metric) have been introduced. Finally, a model for the relation between reliability and endurance has been stated
  9. Keywords:
  10. Storage Systems ; Reliability ; Solid State Disk Drive ; Erasure Code ; Endurance Time Method

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