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Main: The Grid

What are Grids?

Grids are collections of interconnected resources harnessed together in order to satisfy various needs of users. The resources may be administered by different organizations and may be distributed, heterogeneous and fault-prone. The manner in which users interact with these resources may vary widely, as may the usage policies for those resources. A grid infrastructure must manage this complexity so that users can interact with resources as easily and smoothly as possible.

Our definition, and indeed a popular definition, is: A grid system is a collection of distributed resources connected by a network. A grid system, also called a grid, gathers resources – desktop and hand-held hosts, devices with embedded processing resources such as digital cameras and phones or tera-scale supercomputers – and makes them accessible to users and applications in order to reduce overhead and accelerate projects. A grid application can be defined as an application that operates in a grid environment or is "on" a grid system. Grid system software (or middleware), is software that facilitates writing grid applications and manages the underlying grid infrastructure.

A grid enables users to collaborate securely by sharing processing, applications and data across systems with the above characteristics in order to facilitate collaboration, faster application execution and easier access to data. More concretely this means being able to:

Grid Resources

The above definitions of a grid and a grid infrastructure are necessarily general. What constitutes a "resource" is a deep question, and the actions performed by a user on a resource can vary widely. For example, a traditional definition of a resource has been "machine", or more specifically "CPU cycles on a machine". The actions users perform on such a resource can be "running a job", "checking availability in terms of load", and so on. These definitions and actions are legitimate, but limiting. Today, resources can be as diverse as "biotechnology application", "stock market database" and "wide-angle telescope", with actions being "run if license is available", "join with user profiles" and "procure data from specified sector" respectively. A grid can encompass all such resources and user actions. Therefore a grid infrastructure must be designed to accommodate these varieties of resources and actions without compromising on some basic principles such as ease of use, security, autonomy, etc.

The resources in a grid typically share at least some of the following characteristics.

Requirements for Grids

Clearly, the minimum capability needed to develop grid applications is the ability to transmit bits from one machine to another – all else can be built from that. However, several challenges frequently confront a developer constructing applications for a grid. These challenges lead us to a number of requirements that any complete grid system must address. The designers of Legion believed and continue to believe that all of these requirements must be addressed by the grid infrastructure in order to reduce the burden on the application developer. If the system does not address these issues, then the programmer must – forcing programmers to spend valuable time on basic grid functions, thus needlessly increasing development time and costs. The requirements are:

Binary management and application provisioning. The underlying system should keep track of executables and libraries, knowing which ones are current, which ones are used with which persistent states, where they have been installed and where upgrades should be installed. These tasks reduce the burden on the programmer.

Scalability. There are over 500 million computers in the world today and over 100 million network-attached devices (including computers). Scalability is clearly a critical necessity. Any architecture relying on centralized resources is doomed to failure. A successful grid architecture must adhere strictly to the distributed systems principle: the service demanded of any given component must be independent of the number of components in the system. In other words, the service load on any given component must not increase as the number of components increases.

Grid Design Principles

We have developed a set of principles for the architecture and design of grid systems. These include:

Overall, the application of these design principles at every level provides a unique, consistent, and extensible framework upon which to create grid applications.

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Page last modified on October 05, 2011, at 09:56 AM