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Grids currently in production can be broadly classified as either service Grids, composed of dedicated resources, or opportunistic Grids that harvest the computing power of non-dedicated resources when they are idle. While a service Grid provides high and well defined levels of quality of service, an opportunistic Grid provides only a best-effort service. Nevertheless, since opportunistic Grids do not require resources to be fully dedicated to the Grid, they have the potential to assemble a much larger number of resources. Moreover, these Grids cater very well to the execution of the so-called embarrassingly parallel applications, a type of application that is frequently found in practice, and that comprises the largest portion of the typical workload processed in production Grid systems. The EELA-2 e-infrastructure is comprised of a service Grid and an opportunistic Grid that federates computing resources from scientific institutions in both Europe and Latin America. Due to the complementary characteristics of these two types of Grids, a lot of attention has recently been placed in how to interoperate them. In this paper we focus on the less studied problem of assessing the feasibility of such interoperation. We analyse different prioritisation policies that define when the resources of one Grid can be used to run jobs originating from the other. Our results show that in the absence of a suitable prioritisation policy, the benefits that the users of one Grid may have, frequently come with an important negative impact on the users of the other Grid. We also show that a simple reciprocation mechanism is capable of arbitrating the interoperation in such a way that, whenever possible, users profit from the interoperation and, in no case, this benefit leads to a noticeable reduction on the quality of service that the users would experience were the Grids not to interoperate. We conclude discussing how we have implemented, in the context of the EELA-2 project, this prioritisation mechanism, allowing the effective interoperation of a service Grid based on the gLite middleware with an opportunistic Grid that uses the OurGrid middleware.

Desktop Grids, such as XtremWeb and BOINC, and Service Grids, such as EGEE, are two different approaches for science communities to gather computing power from a large number of computing resources. Nevertheless, little work has been done to combine these two Grid technologies in order to establish a seamless and vast Grid resource pool. In this paper we present the EGEE Service Grid, the BOINC and XtremWeb Desktop Grids. Then, we present the EDGeS solution to bridge the EGEE Service Grid with the BOINC and XtremWeb Desktop Grids.

Production Grids are becoming widely utilized by the e-Science community to run computation and data intensive experiments more efficiently. Unfortunately, different production Grid infrastructures are based on different middleware technologies, both for computation and for data access. Although there is significant effort from the Grid community to standardize the underlying middleware, solutions that allow existing non-standard tools to interoperate are one of the major concerns of Grid users today. This paper describes the generic requirements towards the interoperation of Grid data resources within computational workflows, and suggests integration techniques that allow workflow engines to access various heterogeneous data resources during workflow execution. Reference implementations of these techniques are presented and recommendations on their applicability and suitability are made.

Over recent years a number of Grid projects have emerged which have built Grid infrastructures that are now the computing backbones for various user communities. A significant number of these communities are limited to one Grid Infrastructure due to the different middleware and operations procedures used. Grid Interoperation is trying to bridge these differences and enable Virtual Organizations to access resources independent of the Grid project affiliation. Building upon the experiences the authors have gained while working on interoperation between EGEE and various other Grid infrastructures as well as through co-chairing the Grid Interoperation Now (GIN) efforts of the Open Grid Forum (OGF), this paper gives an overview of Grid Interoperation and describes various methods that can be used to connect Grid Infrastructures. The case is made for standardization in key areas and why the Grid community should move more aggressively towards standards.

In global Grids, interoperation is important. It enables communities to work together, helps prevent vendor lock-in, and in principle enables “cloud-like” resource provision by permitting different resources to meet needs from other communities. In this paper, we discuss a practical example of achieving interoperation between storage resources, and the lessons learned. The aim is to meet current use cases for interoperation with no additional software development. Apart from the practical results, experiences from this work will be relevant to other interoperation activities.