Network management system 1 PERFORMANCE MANAGEMENT IMPROVING PERFORMANCE

Replication 3 Replication of data : the maintenance of copies of data at multiple

4 �Increased availability: The availability could be affected by: Server failure Network partitions and

5 Availability example: If there is a 5% probability of any individual server failure

6 Model components: �Clients �Front end �Replica managers Instructor’s Guide for Coulouris, Dollimore and

A basic architectural model for the management of replicated data Requests and replies C

The passive (primary-backup) model for fault tolerance Primary C FE RM RM Backup C

Active replication RM C FE RM Instructor’s Guide for Coulouris, Dollimore and Kindberg Distributed

Caching 10 Web cache keeps a local copy of all recently displayed pages. There

Web proxy server Instructor’s Guide for Coulouris, Dollimore and Kindberg Distributed Systems: Concepts and

Web caching 12 Advantages of web caching: �Improve performance �Reduce outbound traffic load �Reduce

Redundancy 13 Multiple physical links between devices provide redundant paths Advantages: �Network redundancy is

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

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

Clustering 16 A server cluster is a collection of servers, called nodes that communicate

Clustering 17 Typical uses for server clusters include: � file servers � print servers

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

Clustering 19 Advantages: �Ensure high availability �Provide increased scalability �Reduce downtime �The response time

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Network management system 1 PERFORMANCE MANAGEMENT IMPROVING PERFORMANCE TECHNIQUES

Replication 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

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 -pn Instructor’s Guide for Coulouris, Dollimore and Kindberg Distributed Systems: Concepts and Design Edn. 4 © Pearson Education 2005

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. 052=1 -0. 0025=99. 75% Instructor’s Guide for Coulouris, Dollimore and Kindberg Distributed Systems: Concepts and Design Edn. 4 © Pearson Education 2005

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

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

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

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

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/ac 123/ac 147/archived_issues/ipj_2 -3. pdf

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

Web caching 12 Advantages of web caching: �Improve performance �Reduce outbound traffic load �Reduce network delay https: //www. cisco. com/web/about/ac 123/ac 147/archived_issues/ipj_2 -3. pdf

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

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

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

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/cc 738051(v=ws. 10). aspx

Clustering 17 Typical uses for server clusters include: � file servers � print servers �database servers � messaging servers. https: //technet. microsoft. com/en-us/library/cc 738051(v=ws. 10). aspx

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

Clustering 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