1. PERFORMANCE MANAGEMENT IMPROVING PERFORMANCE TECHNIQUES Network management system 1

2. Improving performance techniques 2 Replication Caching Redundancy Clustering

3. 3 Replication of data : the maintenance of copies of data at multiple computers. Advantages of replication: 1. Performance enhancement 2. Increased availability 3. Fault tolerance Examples: 1. Caching 2. DNS Instructor’s Guide for Coulouris, Dollimore and Kindberg Distributed Systems: Concepts and Design Edn. 4 © Pearson Education 2005 Replication

4. 4 Increased availability: The availability could be affected by:  Server failure  Network partitions and disconnected operation. Availability calculation: If each of n servers has an independent probability p of failing or becoming unreachable, then, the availability of object stored at each of these servers : A=1-Probability(all managers failed or unreachable)=1-p n Instructor’s Guide for Coulouris, Dollimore and Kindberg Distributed Systems: Concepts and Design Edn. 4 © Pearson Education 2005

5. 5 Availability example: If there is a 5% probability of any individual server failure over given time period and if there are two servers then: The availability is: 1-0.05 2 =1-0.0025=99.75% Instructor’s Guide for Coulouris, Dollimore and Kindberg Distributed Systems: Concepts and Design Edn. 4 © Pearson Education 2005

6. 6 Model components: Clients Front end Replica managers Instructor’s Guide for Coulouris, Dollimore and Kindberg Distributed Systems: Concepts and Design Edn. 4 © Pearson Education 2005

7. A basic architectural model for the management of replicated data Instructor’s Guide for Coulouris, Dollimore and Kindberg Distributed Systems: Concepts and Design Edn. 4 © Pearson Education 2005 FE Requests and replies C Replica C Service Clients Front ends managers RM FE RM

8. The passive (primary-backup) model for fault tolerance Instructor’s Guide for Coulouris, Dollimore and Kindberg Distributed Systems: Concepts and Design Edn. 4 © Pearson Education 2005 FE C C RM Primary Backup RM

9. Active replication Instructor’s Guide for Coulouris, Dollimore and Kindberg Distributed Systems: Concepts and Design Edn. 4 © Pearson Education 2005 FEC CRM

10. Caching 10 Web cache keeps a local copy of all recently displayed pages. There are two kinds of web caching: Browser cache Proxy cache https://www.cisco.com/web/about/ac123/ac147/archived_issues/ipj_2-3/ipj_2-3.pdf

11. Instructor’s Guide for Coulouris, Dollimore and Kindberg Distributed Systems: Concepts and Design Edn. 4 © Pearson Education 2005 Web proxy server

12. Web caching 12 Advantages of web caching: Improve performance Reduce outbound traffic load Reduce network delay https://www.cisco.com/web/about/ac123/ac147/archived_issues/ipj_2-3/ipj_2-3.pdf

13. Redundancy 13 Multiple physical links between devices provide redundant paths Advantages: Network redundancy is a key maintaining network reliability ; the network can then continue to operate when a single link or port has failed Redundant links can increase the capacity by sharing the traffic load http://ptgmedia.pearsoncmg.com/images/9781587133282/downloads/9781587133282%20_chapter_2.pdf

14. 14 Redundancy http://ptgmedia.pearsoncmg.com/images/9781587133282/downloads/9781587133282%20_chapter_2.pdf

15. 15 Redundancy http://ptgmedia.pearsoncmg.com/images/9781587133282/downloads/9781587133282%20_chapter_2.pdf

16. Clustering 16 A server cluster is a collection of servers, called nodes that communicate with each other to make a set of services highly available to clients. https://technet.microsoft.com/en-us/library/cc738051(v=ws.10).aspx

17. 17 Typical uses for server clusters include: file servers print servers database servers messaging servers. https://technet.microsoft.com/en-us/library/cc738051(v=ws.10).aspx Clustering

18. 18 Clustering http://tws.trijit.uk/datacenter/clustering-servers

19. 19 Advantages: Ensure high availability Provide increased scalability Reduce downtime The response time of applications can be improved http://www.tech-faq.com/server-clustering-technologies-and-concepts.html Clustering