Figure 1 shows a typical Grid infrastructure deployment for medical research. A Grid storage system in one trusted administrative domain is used for storing medical research data. Although data is often replicated across different domains to enhance availability and reliability, we assume here that all storage facilities reside in only one administrative domain trusted by the data owner. Different incarnations of storage infrastructure exist, e.g., SDSC SRB and dCache (dCache, n.d.). In this paper, we refer to the storage infrastructure as a Storage Resource Broker (SRB) in a general way, without referring to a particular implementation.
A use-case for medical imaging research showing grid resources in different administrative domains, with an emphasis on data and job flow
First, Researcher A (data owner) uploads the data to an SRB he or she trusts, e.g., using gridFTP. Researcher B can now submit a job on the Grid through a Compute Resource Broker (CRB) which can reside in any administrative domain. The CRB transparently selects a cluster, typically based on load, where the job is scheduled for execution. The user controls job submission via some job description, e.g., using a Job Submission Description Language (JSDL), which describes the binary to execute on the compute element and input files. In addition, the job description can specify a specific cluster, or resource requirements, to be matched with available Grid resources prior to scheduling. Running jobs can access files that the job's owner is authorized to access. In some cases, the Grid middleware pre-fetches required input files using the job's credentials prior to job execution.
Figure 1 also shows a File Catalog that provides a mapping between Grid 'logical file names' and the underlying physical files, which may be replicated on different storage systems on the Grid. Additionally, an SRB may also maintain a metadata service (not shown). Since metadata and file names may contain privacy sensitive information, both services should be managed by a trusted domain.