Ogsa

5.1 Grid Architectures According to Foster and colleagues, three characteristics define a grid application: It should provide decentralized resource coordination, addressing issues of security, policy, payment, and membership. It should be based on standards and open source protocols for authentication, authorization, resource discovery, and access. Finally, it should deliver quality of serviceby using resources in a coordinated fashion, by providing low response times, and high throughput to meet user demands. A grid architecture should be extensible and an open structure designed to solve key VO requirements. Foster and colleagues suggest the following grid architecture, defined by a set of layers (from the bottom to the top) [GridAnatomy01]: Fabric: This is the bottom layer andconsists of resource and connectivity protocols, which facilitate the sharing of individual resources. This layer provides the resources (computational, storage systems, catalogs, and network resources) shared access mediated by grid protocols. Richer fabric functionality provides more sophisticated sharing operations. On the other hand, a simpler fabric simplifies the deployment of grid infrastructure.An example of this is advance reservation, which allows scheduling of resources in ways otherwise impossible to achieve. However, advance reservation increases the cost of incorporating new resources into a grid. At a minimum, the fabric layer should implement enquiry mechanisms for discovery of their structure, state, and capabilities, and resource management mechanisms to deliver quality ofservice. The types of resources manipulated by the fabric can be computational, storage, network, code repositories, and databases. Connectivity: This layer defines communication and authentication protocols for network transactions. The goal is to provide easy and secure communications. Communication protocols include Internet (IP), transport (TCP, UDP), and application (DNS, and so on), with spacefor new protocols as the need arises. Authentication protocols should be able to provide the following: single sign on (log in once and access multiple resources defined by the fabric layer); delegation, to allow a program to run on the user’s behalf so it is able to access the resources on which the user is authorized; integration with local security solutions; and user-based trust relationships,so resource providers are not required to interact before a user to access resources on either provider. Resource: This layer defines protocols for secure negotiation, initiation, monitoring, control, accounting, and payment of sharing operations on individual resources. These protocols deal with individual resources and ignore global state and atomic actions across distributed collections thatare handled by the collections layer. Resource layer protocols can be information protocols used to obtain information about configuration, load, or usage policies, and management protocols that negotiate access to shared resources by handling resource requirements and operation(s) to be performed. Management protocols ensure consistency of operations for a given shared resource. Collective: Thislayer defines protocols and services global in nature and captures interactions across collections of resources. Examples of collective protocols are the following: a. Directory services: for resource properties discovery. b. Coallocation, scheduling, and brokering services: for allocation of one or more resources for a specific purpose and the scheduling of tasks. c. Monitoring and diagnostics:for failure, intrusion detection, overload, and so on. d. Data replication services: for storage management to maximize data access performance. e. Grid-enabled programming systems: to provide a programming model for resource discovery, security, allocation, and others. f. Workload management systems: for description and management of multicomponent workflows. g. Software discovery services: for...