The Hour-Glass Model of Grid Computing Architecture

The term “the Grid” was coined in the mid-1990s to denote a (then) pro-posed distributed computing infrastructure for advanced science and engineering. A key issue in a grid computing system is that resources from different organizations are brought together to allow the collaboration of a group of people or institutions. Such a collaboration is realized in the form of a virtual organization (VO).

Definitions

[I] “A computational grid is a hardware and software infrastructure that provides dependable, consistent, pervasive, and inexpensive access to high-end computational capabilities.” – Foster & Kesselman, 1998

[II] “Grid computing is concerned with coordinated resource sharing and problem solving in dynamic, multi-institutional virtual organizations. The key concept is the ability to negotiate resource-sharing arrangements among a set of participating parties (providers and consumers) and then to use the resulting resource pool for some purpose.”                                                           - Foster & Tuecke, 2000

Grid Computing Architecture

The hour-glass model of grid computing architecture as proposed by Dr. Ian Foster (2001) consists of thin center, wide top and wide bottom with layered combinations.

Figure 2: Layered Architecture of Grid Computing System

The architecture consists of four layers. The lowest fabric layer provides interfaces to local resources at a specific site. These interfaces are tailored to allow sharing of resources within a virtual organization.

The connectivity layer consists of communication protocols for supporting grid transactions that span the usage of multiple resources. For example, protocols are needed to transfer data between resources, or to simply access a resource from a remote location. In addition, the connectivity layer will contain security protocols to authenticate users and resources.

The resource layer is responsible for managing a single resource. It uses the functions provided by the connectivity layer and calls directly the interfaces made available by the fabric layer. For example, this layer will offer functions for obtaining configuration information on a specific resource.

The next layer in the hierarchy is the collective layer. It deals with handling access to multiple resources and typically consists of services for resource discovery, allocation and scheduling of tasks onto multiple resources, data replication, and so on. Unlike the connectivity and resource layer, which consist of a relatively small, standard collection of protocols, the collective layer may consist of many different protocols for many different purposes, reflecting the broad spectrum of services it may offer to a virtual organization.

Finally, the application layer consists of the applications that operate within a virtual organization and which make use of the grid computing environment.

Typically the collective, connectivity, and resource layer form the heart of what could be called a grid middleware layer. These layers jointly provide access to and management of resources that are potentially dispersed across multiple sites.

References

[1] Ian Foster. (July 20, 2002). "What is the Grid? A Three Point Checklist ". Argonne National Laboratory & University of Chicago, USA.

[2] Prof. Robert van Engelen. (2008). "Concepts and Architecture of Grid Computing". Leiden University, Netherlands.