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Deconstructing Storage Arrays

Learn about the Gray-box approach to deconstruct storage arrays, utilizing the Shear Algorithm to identify characteristics such as disk number, chunk size, and layout scheme for optimized file system performance and array management.

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Deconstructing Storage Arrays

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  1. Timothy E. Denehy, John Bent, Florentina I. Popovici, Andrea C. Arpaci-Dusseau, Remzi H. Arpaci-Dusseau University of Wisconsin, Madison Deconstructing Storage Arrays

  2. Gray-box Research • Computer systems becoming more complex • Transistors • Lines of code • Each component is becoming more complex • Interactions between subsystems can affect • Performance • Reliability • Power • Security

  3. Gray-box Research • Interfaces remain the same • Changes can be difficult and impractical • Support multiple platforms or legacy systems • Commercial acceptance for wide-spread adoption • Hardware and software phenomenon • IA-32 instruction set, POSIX OS, SCSI storage • Problem: lack of information

  4. Gray-box Solution • Treat target system as a gray-box • General characteristics are known • Extract information from an existing interface • e.g. determine cache contents • Exploit information to control system behavior • e.g. access cached data first

  5. Gray-box Information Techniques • Make assumptions about target system • Observe system inputs and outputs • Statistical methods • Draw inferences about internal structure • Microbenchmarks and probes • Parameterize system components • Observe system under controlled input

  6. Gray-box Applications • Gray-box techniques have been used to identify • Memory hierarchy parameters [Saavedra and Smith] • Processor cycle time [Staelin and McVoy] • Low-level disk characteristics [Worthington et al.] • Buffer cache replacement algorithms [Burnett et al.] • File system data structures [Sivathanu et al.] • storage array characteristics: Shear

  7. Shear • Software tool that automatically determines the important properties of a storage array • Enables file system performance tuning with knowledge of storage array characteristics • Acts as a management tool to help configure, monitor, and maintain storage arrays

  8. Outline • Introduction • Shear • Background • Algorithm • Case Studies • Performance: Stripe-aligned Writes • Management: Detecting Misconfiguration, Failure • Conclusion

  9. 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 Shear Goals • Determine storage array characteristics SCSI SCSI

  10. 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 Shear Goals • Determine storage array characteristics • Number of disks SCSI SCSI

  11. 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 Shear Goals • Determine storage array characteristics • Number of disks • Chunk size SCSI SCSI

  12. 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 Shear Goals • Determine storage array characteristics • Number of disks • Chunk size • Layout and redundancy scheme SCSI SCSI RAID-0

  13. 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 16 17 18 19 20 21 22 23 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 24 25 26 27 28 29 30 31 Shear Goals • Determine storage array characteristics • Number of disks • Chunk size • Layout and redundancy scheme SCSI SCSI RAID-1

  14. 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 P P P P 0 1 2 3 4 5 6 7 8 9 10 11 P P P P 16 20 21 22 23 17 18 19 12 13 14 15 P P P P 32 33 34 35 24 25 26 27 28 29 30 31 P P P P 36 37 38 39 40 41 42 43 44 45 46 47 Shear Goals • Determine storage array characteristics • Number of disks • Chunk size • Layout and redundancy scheme SCSI SCSI RAID-5

  15. Shear Motivation • Performance • Tune file systems to array characteristics • Management • Verify configuration • Detect failure

  16. Shear Techniques • Microbenchmarks and probes • Controlled, random access read and write patterns • Measure response time of access patterns • Measure steady-state performance • Statistical clustering • Automatically classify fast and slow regimes • Identify patterns that utilize only a single disk

  17. Shear Assumptions • Storage array • Layout follows a repeatable pattern • Composed of homogeneous disks • System • Able to bypass the file system and buffer cache • Little traffic from other processes

  18. Outline • Introduction • Shear • Background • Algorithm • Case Studies • Performance: Stripe-aligned Writes • Management: Detecting Misconfiguration, Failure • Conclusion

  19. Shear Algorithm • Pattern size • Chunk size • Layout of chunks to disks • Level of redundancy

  20. Determining the Pattern Size • Find the size of the layout's repeating pattern • Not always the stripe size • Choose a hypothetical pattern size • Perform random reads at multiples of that distance • Repeat for a range of pattern sizes • Cluster results and identify actual pattern size

  21. RAID-0 4 Disks 8 KB Chunks Pattern Size Example

  22. RAID-0 4 Disks 8 KB Chunks Testing 2 KB Pattern Size Example

  23. RAID-0 4 Disks 8 KB Chunks Testing 4 KB Pattern Size Example

  24. RAID-0 4 Disks 8 KB Chunks Testing 6 KB Pattern Size Example

  25. RAID-0 4 Disks 8 KB Chunks Testing 8 KB Pattern Size Example

  26. RAID-0 4 Disks 8 KB Chunks Testing 10 KB Pattern Size Example

  27. RAID-0 4 Disks 8 KB Chunks Testing 12 KB Pattern Size Example

  28. RAID-0 4 Disks 8 KB Chunks Testing 14 KB Pattern Size Example

  29. RAID-0 4 Disks 8 KB Chunks Testing 16 KB Pattern Size Example

  30. RAID-0 4 Disks 8 KB Chunks Testing 18 KB Pattern Size Example

  31. RAID-0 4 Disks 8 KB Chunks Testing 20 KB Pattern Size Example

  32. RAID-0 4 Disks 8 KB Chunks Testing 22 KB Pattern Size Example

  33. RAID-0 4 Disks 8 KB Chunks Testing 24 KB Pattern Size Example

  34. RAID-0 4 Disks 8 KB Chunks Testing 26 KB Pattern Size Example

  35. RAID-0 4 Disks 8 KB Chunks Testing 28 KB Pattern Size Example

  36. RAID-0 4 Disks 8 KB Chunks Testing 30 KB Pattern Size Example

  37. RAID-0 4 Disks 8 KB Chunks Testing 32 KB Pattern Size Example

  38. RAID-0 4 Disks 8 KB Chunks Pattern Size Example

  39. RAID-0 4 Disks 8 KB Chunks Actual 32 KB cluster cluster cluster Pattern Size Example

  40. Shear Algorithm • Pattern size • Chunk size • Layout of chunks to disks • Level of redundancy

  41. Determining the Chunk Size • Chunk size • amount of data contiguously allocated to one disk • Find the boundaries between disks • Choose a hypothetical boundary offset • Perform random reads on both sides of that offset • Repeat for all offsets in the pattern size • Cluster results and identify actual chunk size

  42. RAID-0 4 Disks 8 KB Chunks Chunk Size Example

  43. RAID-0 4 Disks 8 KB Chunks Testing 0 KB Chunk Size Example

  44. RAID-0 4 Disks 8 KB Chunks Testing 2 KB Chunk Size Example

  45. RAID-0 4 Disks 8 KB Chunks Testing 4 KB Chunk Size Example

  46. RAID-0 4 Disks 8 KB Chunks Testing 6 KB Chunk Size Example

  47. RAID-0 4 Disks 8 KB Chunks Testing 8 KB Chunk Size Example

  48. RAID-0 4 Disks 8 KB Chunks Testing 10 KB Chunk Size Example

  49. RAID-0 4 Disks 8 KB Chunks Testing 12 KB Chunk Size Example

  50. RAID-0 4 Disks 8 KB Chunks Testing 14 KB Chunk Size Example

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