1. SSDs: advantages exhibit higher speed than disks drive down power consumption offer standard interfaces like HDDs do

2. SSDs: critical technical constraints the absence of in-place update the absence of random writing on pages erasure limit : wear out after a certain number of program cycles

3. Erasure limit: SLC vs MLC SLC: 100,000 cycles MLC: 10,000 cycles

4. Erasure limit: RBER vs UBER

5. Solution: SSD-RAID RAID offers device-level redundancy RAID is an effective method of constructing large-scale, high- performance, and high-reliability storage systems SSD-RAID combines the advantages of the classic RAID and state-of- the-art SSDs

6. Two parity-based SSD-RAID systems Differential RAID CSWL-RAID: Cross-SSD Wear-Leveling They have a same assumption: parity blocks are updated more often than data blocks, and devices holding more parity receive more writes and consequently age faster

7. Differential RAID The Problem with RAID for SSDs: they cause multiple SSDs to wear out at approximately the same rate

8. Differential RAID: RAID5 case

9. Differential RAID: features Uneven Parity Distribution Parity-Shifting Drive Replacement

10. Uneven Parity Distribution: example RAID-4: ( 100, 0, 0, 0, 0) RAID-5: ( 20, 20, 20, 20, 20) Diff-RAID: ( 40, 15, 15, 15, 15)

11. Uneven Parity Distribution: aging rate

12. Parity-Shifting Drive Replacement: example

14. Analysis of Age Distribution Convergence Distribution of device ages at replacement time for (80,5,5,5,5) parity assignment

15. Analysis of Age Distribution Convergence Convergent distribution of ages at replacement time for different parity assignments

16. Trade-off between reliability and throughput the more skewed the parity distribution towards a single device the higher the age differential the higher the reliability the lower throughput

17. Diff-RAID Reliability Evaluation Reliability of Diff-RAID Reliability of Diff-RAID Configurations Reliability with Different Flash Types Reliability with Different ECC Levels Reliability Beyond Erasure Limit Reliability on Real Workloads

18. Reliability of Diff-RAID Diff-RAID reliability changes over time and converges to a steady state

19. Reliability of Diff-RAID Configurations

20. Reliability with Different Flash Types

21. Reliability with Different ECC Levels

22. Reliability Beyond Erasure Limit

23. Reliability on Real Workloads

24. Diff-RAID Performance Evaluation Diff-RAID Throughput Performance Under Real Workloads Recovery Time

25. Diff-RAID Throughput

26. Performance Under Real Workloads

27. Recovery Time

28. Differential RAID: disadvantages Assuming a perfectly random workload: without considering the actual age of devices Parity-Shifting Drive Replacement: the procedure of reconstructing data and redistributing parity is complex and very time consuming Trade-off between reliability and throughput: hard to determine a trade-off point

29. CSWL-RAID: Why is CSWL needed RAID5 and RAID6 cannot ensure wear leveling among devices under a imperfectly random workload

30. CSWL-RAID: features Age-driven parity distribution Less replacement and reconstruction in the life cycle of entire RAID systems Optimized data layout and addressing method with age-driven parity distribution

31. CSWL-RAID: Basic Principle change the wearing rate of some SSDs by dynamically adjusting the fraction of parity on them

32. CSWL-RAID: Practical Architecture

33. CSWL-RAID: Basic data layout Age distribution (1,1,1,1) Age distribution (3,3,3,1) Age distribution (2,2,1,1)

34. CSWL-RAID: Improved data layout Age distribution (1,1,1,1) Age distribution (3,3,3,1) Age distribution (2,2,1,1)

35. CSWL-RAID: Addressing Method RAID4 case RAID5 case Basic CSWL-RAID5 case

36. CSWL-RAID: Addressing Method Improved CSWL-RAID5 case

37. CSWL-RAID: Addressing Method Improved CSWL-RAID5 case

38. CSWL-RAID: Average latency

39. CSWL-RAID: Redistribution time CSWL-RAID5 caseCSWL-RAID6 case

40. CSWL-RAID: Age difference

41. CSWL-RAID: Reliability

42. CSWL-RAID: disadvantages All SSDs wear out at approximately the same rate: lower reliability and shorter lifetime Addressing method is too complex: the complexity of the addressing algorithm is O(t), where t denotes redistribution times