1. 분산처리 - 2011 년 가을학기 Chapter 1 – Introduction 부산대학교 정보컴퓨터 공학부 이 기준 http://isel.cs.pusan.ac.kr/~lik

2. Some Questions 2

3. 질문 1: 매우 중요한 금융 데이터베이스를 10 개의 분산된 작은 시스템에 나누어 저장하여 관리하는 것과 하나의 커다란 시스 템에 저장하여 관리하는 것과 어느 방법이 더 안전한가 ?

4. 질문 2: 중요한 금융 데이터베이스를 10 개의 분산된 작은 컴퓨 터에 나누어 저장하여 관리하는 시스템을 구축하는 것과 하나 의 커다란 컴퓨터에 저장하여 관리하는 시스템을 구축하는 방 법 중 어느 방법이 더 경제적인가 ?

5. 질문 3: 매우 중요한 금융 데이터베이스를 10 개의 분산된 작은 컴퓨터에 나누어 저장하여 관리하는 것과 하나의 커다란 컴퓨 터에 저장하여 관리하는 것과 어느 방법이 더 좋은 성능을 보여 줄까 ?

6. 다음 주 발표 : ( 질문 1 - 질문 3) 의 결론을 정리하여 분산 시스템과 집 중형 시스템의 장단점을 정리하여 창의적으로 발표하여라.

7. Distributed system : 1) A collection of (scalability) 2) independent computers that (heterogeneity) 3) appears to its users as a single coherent system (transparency) Distributed System versus Parallel System –Separated Operating System vs. Single Operating System –Message Passing vs. Shared Memory 7

8. Why Distributed Systems? Performance Incremental Growth (Scalability) –1 single mainframe of price W –N small machines of price W/N Fault Tolerance –1 single mainframe : critical weak point –Failure of a machine : replacement by other machines Geographical Distribution and Availability –Flexible configuration e.g. 1 Disk server, 3 Computing servers, 1 Graphic server, etc. –Geographical availability 8

9. Scalability and Heterogeneity 9

10. 10 Server A Driver for A Driver for B Server B Server C Driver for C Application Program or Client Server A Server B Server C Application Program or Client Predefined interface Versus

11. Transparency 11 TransparencyDescription AccessHide differences in data representation and how a resource is accessed LocationHide where a resource is located MigrationHide that a resource may move to another location RelocationHide that a resource may be moved to another location while in use ReplicationHide that a resource may be shared by several competitive users ConcurrencyHide that a resource may be shared by several competitive users FailureHide the failure and recovery of a resource PersistenceHide whether a (software) resource is in memory or on disk

12. Issues in System Design 12 Transparency Flexibility Reliability Performance Scalability Interoperability

13. Transparency: Hiding physical details about –Location –Migration –Duplication –Relocation –Concurrency –Parallelism –Location –Access 13

14. Flexibility –Should be easy to modify functionality and architecture –To provide with Configurability, Availability and Autonomy –Micro-Kernel vs. Monolithic Kernel Monolithic Kernel : Provides all functionalities of OS, e.g. UNIX Micro-Kernel: Minimal subset of OS + what users want. –e.g. Kernel Watch 14

15. Reliability –Important Goal of Distributed System Reliability Security Fault-Tolerance –Failure Probability P Should be P = P 1 ·P 2 ·P 3 … ·P n But often P = P 1 + P 2 + P 3 … + P n in reality 15

16. Performance and Scalability –Improve performance by parallelism –Throughput T Ideally should be T = T·n when n is the number of sites In reality T < T·n –Due to some Bottleneck 16 Number of sites Throughput ??

17. Granularity of Parallelism –Unit of Task Fine-Granularity vs. Coarse Granularity –Fine-Granularity Large number of small tasks Need a large amount of inter-task communication Not good for distributed system (good for Parallel system) –Coarse-Granularity Small number of big tasks Only small amount of inter-task communication Good for distributed system 17

18. Interoperability –Easy to collaborate with other systems in run-time Compatibility, Portability –How to achieve Interoperability Well-Defined API set Standardization 18