Once in a while, the question of what is a grid is raised. One attitude is that if you can sell it as grid - then it is a grid. This is done by some of the software companies. In fact, it does not matter at all what is a grid.
But since mathematicians (and computer scientists) need definitions, I prefer to use Ian Fosters definition taken from What is the Grid ? :
(1) Coordinates resources that are not subject to centralized control
(2) Using standard, open, general-purpose protocols and interfaces
(3) Delivers nontrivial qualities of service
This definition actually requests a group of clusters that each belong to an other sys-admin (that are not under the same management to achieve non centralized control) that share resources based on open-standard protocols (as Open Grid Forum).
One of the implementation based on Globus is the EU project named EGEE-II. The project added or designed some of the components different of the original GGf (ancestor of OGF) like Resource Broker (RB) which is the node that gets the job and looks for the most appropriate site to send the job to. After it finds a site, the job is translated for the site queuing system (which is called LRMS).
In order to submit a job, one has to have X.509 certificate approved by a known CA. The user ID is translated in each site according to the local gridmap file (where each certificate DN appears). There is a pool of users that each user is mapped into according to users virtual organization belonging. A dynamic system named Virtual Organization Management System (VOMS) was developed that brings (2) main benefits:
(1) Users can have roles in the VO (opposed to flat mapping in the gridmap file).
(2) same certificate DN can belong to more than one VO. Especially in the academic environment, a user mighr work in more than one project that share different resources.
Sunday, February 25, 2007
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