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A 2 TH OS: availability analysis and optimisation in SLAs

A 2 TH OS: availability analysis and optimisation in SLAs. Group 7: Deyang Rao Chenhao Cui Yichi Zhang Luyang Li. Outline. Enterprise IT Services SLAs Availability (FCAPS) Introducing A 2 TH OS AND/OR dependency Algorithm A 2 TH OS prototype Device set-up Performance Examples:

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A 2 TH OS: availability analysis and optimisation in SLAs

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  1. A2THOS: availability analysis and optimisation in SLAs Group 7: Deyang Rao Chenhao Cui Yichi Zhang Luyang Li

  2. Outline • Enterprise IT Services • SLAs • Availability (FCAPS) • Introducing A2THOS • AND/OR dependency • Algorithm • A2THOS prototype • Device set-up • Performance • Examples: • Eg.1: Oxygen • Eg.2: Hydrogen • Reference

  3. Enterprise IT Service • Complicated, separated into different segments. • Commonly partly or fully outsourced to other company, or even different companies. • Based on the basic approach: Service Level Agreement (SLA). • Included with the Availability of certain service(s).

  4. Availability (FCAPS) • Availability based on Node’s dependency. • Dependency always analysed with Fault Trees (FT) and Reliability Block diagrams (RBD). • Previous algorithm based on the Mean Time To Failure (MTTF) and Mean Time To Restore (MTTR). • Availability = MTTF/(MTTF+MTTR) • However the outsource service provider would not provide these data to the customer. (Who would?) So no way to calculate or estimate the availability of a higher service that depended on many basic services.

  5. Introducing A2THOS • A2THOS, an new approach to calculate/optimise the availability of a certain service provided. • Based on the dependency of the infrastructure to evaluate the system’s performance. • Improved dependency relations: AND/OR relations.

  6. AND/OR Graph AND Node: service would be available ONLY IF ALL sub nodes are available. OR Node: service would be unavailable ONLY IF ALL sub nodes become unavailable. Internal Node: a virtual node represents internal failure of the equipment.

  7. Definition of Availability • Target Availability (What we want) [1] • Modeling the Availability level the service has to achieve. • Variable Availability (What they provide) [2] • Models different options with different associated price. • Given Availability (Trust your hardware) [3] • Components’ minimal availability (Provided by hardware manufacturer) Using components with given property [3] to build candidate systems [2] to provide the service with a certain desired level[1] .

  8. Prototype of A2THOS Provide separate sub-systems for future expansion.

  9. Benchmarks: availability analysis and optimisation algorithm • Exponential relationship between nodes number and calculation time. • Average 25 nodes for a mid-sized IT service.

  10. Practical use of A2THOS • Company size: multinational company 100,000-200,000 employees • IT facilities for European branch 100,000 employee workstations many hundreds of business partners

  11. Example 1: Oxygen • AND/OR:65 nodes, 112 edges

  12. Example 2: Hydrogen • Service building on-going. • AND/OR：26 nodes, 33 edges • Outsourcer offer 3 levels: 0.995/0.998/0.999 • Cost: optimal combination —— cost is 2% greater 0.990 —— 30% lower Company have to renegotiate!

  13. Reference • Zambon, E., Etalle, S., & Wieringa, R. J. (2012). A2thOS: availability analysis and optimisation in SLAs. International Journal of Network Management, 22(2), 104-130. • Boudali, H., Crouzen, P., & Stoelinga, M. (2007). A compositional semantics for Dynamic Fault Trees in terms of Interactive Markov Chains. In Automated Technology for Verification and Analysis (pp. 441-456). Springer Berlin Heidelberg.

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