SRM and SRB are both ways of accessing the storage available on a grid—either using tapes, disks or disk arrays. Usually, storage elements running SRB can’t be seen by a grid running SRM, and vice versa. Most grids run one or the other technology, but if different grids are to interoperate, the two standards will need to work together.

“SRM and SRB are traditionally the two separate ‘storage islands’ in grids,” says Jens Jensen, of Rutherford Appleton Laboratory, “each providing interoperability within its own island, but not between the islands. We used the GridFTP protocol and advanced data management tools from the EGEE project to transfer data between SRM and SRBs, and bridge these islands.”

GridPP and NGS: our powers combined

The team built on a GridFTP server developed for SRB by the San Diego Supercomputer Center and Argonne National Laboratory, to make an SRB look like a Classic Storage Element. This allowed the gLite tools to transfer files between SRMs and SRBs.

One of Jensen’s activities is working on interoperability between the UK’s two main science grids: GridPP, the UK particle physics grid, which runs various implementations of SRM, and the UK National Grid Service, which mainly runs SRB.

This work also opens up opportunities for other grids to share data—for example between Worldwide LHC Computing Grid and the U.S. TeraGrid.

Grid Interoperation Now

Erwin Laure, technical director of the EGEE project, is also coordinator of the Grid Interoperation Now activities in the Open Grid Forum. He says interoperability of different grid infrastructures is a necessity for many applications. “The OGF GIN community is aiming at pragmatic solutions for achieving interoperation,” he says. “This interoperation between the two most commonly deployed data solutions, SRM and SRB, achieved by Jens’ team, is a great step forward towards achieving this goal.”

Alex Sim of Lawrence Berkeley National Laboratory in the U.S. demonstrated the data transfer for the UK team at SC07.

“The demo showed interoperability of eleven different SRM implementations around the world based on the same specification, including data transfers between an SRB at Rutherford Appleton Laboratory and BeStMan SRM at Lawrence Berkeley National Laboratory,” Sim explains. “This caused great interest among delegates, and it is of interest for scientists—especially in the Worldwide LHC Computing Grid Project, as they can now access data directly in SRB.”

Jensen is particularly enthusiastic about how well the current work fits the GIN group. “The important aspect of this work is that it builds on existing tools and requires no development effort. It really is Grid Interoperability Now!”