Distributed Systems And Recent Innovations: Challenges And Benefits

Distributed Systems and Recent Innovations: Challenges and Benefits
Krishna Nadiminti, Marcos Dias de Assunção, and Rajkumar Buyya Grid Computing and Distributed Systems Laboratory Department of Computer Science and Software Engineering The University of Melbourne, Australia http://www.gridbus.org

1. Introduction
The World Wide Web is used by millions of people everyday for various purposesincluding email, reading news, downloading music, online shopping or simply accessing information about anything. Using a standard web browser, the user can access information stored on Web servers situated anywhere on the globe. This gives the illusion that all this information is situated locally on the user’s computer. In reality, the Web represents a huge distributed system that appears as asingle resource to the user available at the click of a button. There are several definitions and view points on what distributed systems are. Coulouris defines a distributed system as “a system in which hardware or software components located at networked computers communicate and coordinate their actions only by message passing” [1]; and Tanenbaum defines it as “A collection of independentcomputers that appear to the users of the system as a single computer” [2]. Leslie Lamport – a famous researcher on timing, message ordering, and clock synchronization in distributed systems once said that “A distributed system is one on which I cannot get any work done because some machine I have never heard of has crashed“ reflecting on the huge number of challenges faced by distributed systemdesigners. Despite these challenges, the benefits of distributed systems and applications are many, making it worthwhile to pursue. Various types of distributed systems and applications have been developed and are being used extensively in the real world. In this article, we present the main characteristics of distributed systems and look at some of the challenges that are faced by designers andimplementers of such systems, and also introduce an example distributed system.

2. Main Features and Benefits of a Distributed System
A common misconception among people when discussing distributed systems is that it is just another name for a network of computers. However, this overlooks an important distinction. A distributed system is built on top of a network and tries to hide the existence ofmultiple autonomous computers. It appears as a single entity providing the user with whatever services are required. A network is a medium for interconnecting entities (such as computers and devices) enabling the exchange of messages based on well-known protocols between these entities, which are explicitly addressable (using an IP address, for example). There are various types of distributedsystems, such as Clusters [3], Grids [4], P2P (Peer-to-Peer) networks [5], distributed storage systems and so on. A cluster is a

dedicated group of interconnected computers that appears as a single super-computer, generally used in high performance scientific engineering and business applications. A grid is a type of distributed system that enables coordinated sharing and aggregation of distributed,autonomous, heterogeneous resources based on users’ QoS (Quality of Service) requirements. Grids are commonly used to support applications emerging in the areas of e-Science and e-Business, which commonly involve geographically distributed communities of people who engage in collaborative activities to solve large scale problems and require sharing of various resources such as computers, data,applications and scientific instruments. P2P networks are decentralised distributed systems, which enable applications such as file-sharing, instant messaging, online multiuser gaming and content distribution over public networks. Distributed storage systems such as NFS (Network File System) provide users with a unified view of data stored on different file systems and computers which may be on the...