CS6601 DISTRIBUTED SYSTEM / 2 MARK

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1 UNIT III PEER TO PEER SERVICE AND FILE SYSTEM 1. Define Peer-Peer System. Part A - Questions Peer-to-peer system is a paradigm for the construction of distributed system and application in which data and computational resources are contributed by many hosts on the internet, all of which participate in the provision of a uniform service. 2. Write the characteristics of Peer to Peer system. Each user in the design contributes some resources to the system. All the nodes have the same functional capabilities and responsibilities. Limited degree of anonymity is offered to the providers and users of resources. The efficiency depends on the algorithm chosen for placement of data across many hosts and subsequent access should balances the workload and availability is ensured without adding any excessive overheads. 3. What are the three generations of Peer to Peer system? The Napster music exchange service [Open Nap 2001]. File-sharing application- Freenet. Middleware layers- pastry. 4. What are the advantages of Napster? Music files are never updated, avoiding any need to make sure all the replicas of the files remain consistent after updates. No arguments are required concerning the availability if individual files- if a music file is temporarily unavailable, it can be downloaded later. This reduces the requirement for dependability of individual computer and their connections to the internet. 5. Why the term overlay is used in routing mechanism? It is termed an overlay since it implements a routing mechanism in the application layer that is quite separate from any other routing mechanisms deployed at the network level such as IP routing. Ms P.ILAKIYA AP/CSE Page 1

2 6. What is the need for Distributed Systems? A distributed file system allows the programmer to store and access remote files through programs and also allows the users to access files from any computer on a network. 7. Give some example of file system used in Distributed Systems. The Sun Network File System, NFS; The Andrew File System, AFS. 8. Define Andrew File System. The Andrew File System (AFS) is a location-independent file system. It is a distributed file system which is easier to access files stored on a remote computer as files stored on the local disk. 9. Which file model is used by modern operating system and why? Unstructured file model is used by modern Operating system because sharing of files by different applications is easier with this model. Since no structure is for files; different application can interpret the contents of a file in different ways. 10. What are the issues arises when AFS operation is implemented? How does AFS gain control when an open or close system call referring to a file in the shared file space is issued by a client? How is the server holding the required file located? What space is allocated for cached files in workstations? How does AFS ensure that the cached copies of files are up-to-date when files may be updated by several clients? 11. What is the goal of Cache consistency? The goal of cache-consistency mechanism is to achieve the best approximation to one-copy file semantics that is practicable without serious performance degradation. 12. List the non functional requirements of peer to peer middleware. Global scalability Load balancing Ms P.ILAKIYA AP/CSE Page 2

3 Optimization for local interaction between neighboring peers Accommodating to highly dynamic host availability Security of data in an environment with heterogeneous trust Anonymity, deniability and resistance to censorship 13. What is the main task of a routing overlay and write some other task performed by it. Routing of request to objects is the main task. Routing overlay must also perform some other tasks such as Insertion, Deletion of objects and Node addition and removal. 14. What are the modules of file system? Directory module File module Access control module File access module Block module Device module 15. What is the role of file system? File system takes the responsibility for the organizing, storage, retrieval, naming, sharing and protection of files. Files are usually stored on disks or other non-volatile storage types. 16. What is purpose of lseek function? Write its syntax also. The syntax is Iseek moves the read-write pointer to offset. Pos=Iseek (filedes, offset, whence) 17. Write the syntax for creating new file and to open existing file? Filedes=creat (name, mode) Ms P.ILAKIYA AP/CSE Page 3

4 Filedes=open (name, mode) 18. What are the two file models? Unstructured and structured files Mutable and immutable files 19. What are the file models of unit of data transfer? File-level transfer model Block-level transfer model Byte-level transfer model Record-level transfer model 20. What are the four sharing semantics? UNIX semantics Session semantics Immutable shared-files semantics Transaction-like semantics 21. Define name resolution. The process of looking up a name is called name resolution. Name resolution can also be used to merge different name spaces. Mounting is an example (one way) of merging different name spaces. 22. Define LDAP. LDAP(Lightweight Directory access Protocol) is a software protocol for enabling anyone to locate organizations, individuals and other resources such as file and devices in a network, whether on the public internet or on a corporate intranet. 23. What is meant by DNS? The domain name system (DNS) is the way that internet domain names are located and translated into Internet Protocol addresses. A domain name is a meaningful and easy-to-remember handle for an Internet address. Ms P.ILAKIYA AP/CSE Page 4

5 24. Define directory services. A directory is a file, often of a special type, that provides a mapping from text names to internal file identifiers. Directory may include the names of other directories, leading to the familiar hierarchic file-naming scheme and the multi-part path names for files used in UNIX and other operating systems. Ms P.ILAKIYA AP/CSE Page 5

Slides for Chapter 10: Peer-to-Peer Systems

Slides for Chapter 10: Peer-to-Peer Systems From Coulouris, Dollimore, Kindberg and Blair Distributed Systems: Concepts and Design Edition 5, Addison-Wesley 2012 Overview of Chapter Introduction Napster