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Reliability in Cloud

Reliability in Cloud. Ranjit Kumar. Talk Outline. Erasure Code Background Applications Terms, basics, the math Info on various Erasure Codes How to classify this space of Algorithms Analysis on What is possible: ATG, Univ. Research What more is possible. Applications.

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Reliability in Cloud

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  1. Reliability in Cloud Ranjit Kumar NetApp Confidential - Internal Use Only

  2. Talk Outline • Erasure Code Background • Applications • Terms, basics, the math • Info on various Erasure Codes • How to classify this space of Algorithms • Analysis on • What is possible: ATG, Univ. Research • What more is possible NetApp Confidential - Internal Use Only

  3. Applications • Some intuitive examples & pictures • Rover • Bar Code Scanning etc • Laptops exchanging data (Butterfly Network) NetApp Confidential - Internal Use Only

  4. Talk Outline • Erasure Code Background • Applications • Terms, basics, the math • Info on various Erasure Codes • How to classify this space of Algorithms • Analysis on • What is possible: ATG, Univ. Research • What more is possible NetApp Confidential - Internal Use Only

  5. Basics, Terms • K data disks • N total disks e.g. 4 data disks, 2 parity disks, 6 total disks in RAID-DP • Rate = K / N • Failure is “erasure” e.g. 1 disk down • MDS – Maximum Distance Separable • Optimize Redundancy (aka Space) vs. Reliability tradeoff NetApp Confidential - Internal Use Only

  6. Data and Coding (Parity) disks ……………… C00 C10 D00 D10 Dn0 C01 C11 D01 D11 Dn1 C.. C.. D.. D.. D.. NetApp Confidential - Internal Use Only

  7. Encoding D00 D10 C00 X = C10 Dn0 NetApp Confidential - Internal Use Only

  8. Encoding n columns D00 D00 1 0 0 0 1 D10 1 0 n 1 0 X = 1 0 Dn0 1 C00 B11 B1n m = 2 Dn0 C10 B21 B2n NetApp Confidential - Internal Use Only

  9. Failure 1 of 2 X = NetApp Confidential - Internal Use Only

  10. Failure 2 of 2 X = B D C NetApp Confidential - Internal Use Only

  11. Recovery (Decoding) • B’ x D = C’ • (B’ x B’-1) x D = C’ x B’-1 • D = C’ x B’-1 • B x D = C NetApp Confidential - Internal Use Only

  12. Talk Outline • Erasure Code Background • The math • Applications • Info on various Erasure Codes • How to classify this space of Algorithms • Analysis on • What is possible: ATG, Univ. Research • What more is possible NetApp Confidential - Internal Use Only

  13. What do we optimize? What is the cost? • Storage Efficiency • Repair Bandwidth • Repair Time • Computation (or energy cost) • Other choices • Update efficiency • Read efficiency • Fault tolerance • Number of nodes contacted for repair NetApp Confidential - Internal Use Only

  14. Erasure Code Algorithms 1. Symbols can have any size from bit to multi-sectors 2. Also for 2 data device failures become serialized NetApp Confidential - Internal Use Only

  15. Talk Outline • Erasure Code Background • The math • Applications • Info on various Erasure Codes • How to classify this space of Algorithms • Analysis on • What is possible: ATG, Univ. Research • What more is possible NetApp Confidential - Internal Use Only

  16. Conclusion: What is possible? • Hierarchical coding with disks and HBAs • NetWorked Coding in RAIN • Functional repair (instead of exact repari) for Archive • Erasure coding instead of TCP/IP to cloud NetApp confidential - Internal Use Only

  17. Conclusion: What is possible? • Archive • Can long term tape archives use functional repair? • Will networked coding, give freedom, from cloud vendor lock-in? • Large Distributed Storage • How can we achieve greater reliability with reduced replication? • How can we enable continually growing storage? • What is the impact of coordinating block placement with storage organization? • Find ways to reduce number of nodes contacted, repair BW used. • What is needed to build efficient edge caching? • Single Node Storage • Many small RAID groups vs. single large RAID group w/ locality of repair. • Reduce repair time - disks are becoming larger, throughput to disk size ratio worsening. • Can we be leveraging locality wrt disk, hba, host? • New directions • Multi-node in-memory computing • Flash, SSD, SCM • Multi-cores, new instructions (SSE on intel), GPU NetApp confidential - Internal Use Only

  18. NetApp Confidential - Internal Use Only

  19. Erasure Code Algorithms NetApp Confidential - Internal Use Only

  20. Backup NetApp Confidential - Internal Use Only

  21. Summary • What Customers Want? • ? • What new is available from Erasure Codes? • ? • What Should We Do? • Need to aggressively start creating RAIN based storage solutions • ? NetApp Confidential - Internal Use Only

  22. Erasure Code Algorithms 1. Symbols can have any size from bit to multi-sectors NetApp Confidential - Internal Use Only

  23. Codes work with words • Each word is w bits long • Where w is such that 2w >= n + m ….. ….. NetApp Confidential - Internal Use Only

  24. Classes of Erasure Coding Cyclic Codes Only MDS code for arbitrary n & m. RS Codes (quadratic over n) LinearBlock Code …… Coding Perfect Codes Convolutional Codes NetApp Confidential - Internal Use Only

  25. Classes of Erasure Code RS Code (1960) Fixed rate Tornado Code Codes First practical realization of rateless code (1998) LT Code Rate-less (1998-2002) Raptor Code NetApp Confidential - Internal Use Only

  26. Codes for Distributed Storage Pyramid Hierarchical Codes for Distributed Storage Regenerating Self-repairing NetApp Confidential - Internal Use Only

  27. Organizing the space of Algorithms • Classification based on functions, tradeoffs etc. of Algorithms NetApp Confidential - Internal Use Only

  28. Math • What has changed? Why renewed interest? • History • Rate-less(?) codes • Simple Math • More detailed Math w/ Matrix example NetApp Confidential - Internal Use Only

  29. Erasure Code Names Space • Why so many names for the same thing? • Erasure Codes • Network Codes • Regenerative Codes • etc. NetApp Confidential - Internal Use Only

  30. NetApp Confidential - Internal Use Only

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