1. A 2 TH OS: 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 A 2 TH OS AND/OR dependency Algorithm A 2 TH OS 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 A 2 TH OS A 2 TH OS, 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 A 2 TH OS 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 A 2 TH OS 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 I.Zambon, E., Etalle, S., & Wieringa, R. J. (2012). A2thOS: availability analysis and optimisation in SLAs. International Journal of Network Management, 22(2), 104-130. II.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.