Cray CTO: Linux clusters don't play in HPC

Supercomputer vendor Cray Inc. shoots down the notion that Linux clusters offer the same price-performance as a supercomputer.

SAN JOSE, Calif. -- Linux clustering was touted as the next big thing by many vendors last week at ClusterWorld Conference & Expo 2004.

But supercomputer vendor Cray Inc. scoffed at the notion of putting Linux clusters in the high-performance computing (HPC) category. In fact, Cray showcased a system -- Cray XD1 with Active Manager -- that will compete in performance and price with some Linux clusters upon its release..

At best, clusters are a loose collection of unmanaged, individual, microprocessor-based computers.
Dr. Paul  Terry
CTOCray Canada

Despite assertions made by Linux vendors, a Linux cluster is not a high performance computer, said Dr. Paul Terry, CTO of Cray Canada. "At best, clusters are a loose collection of unmanaged, individual, microprocessor-based computers."

Businesses shouldn't expect supercomputer performance from Linux clusters, Terry warned.

"Cluster vendors would have you believe that their performance is the linear sum of each of their respective GFLOPS [Giga Floating Point Operations Per Second]," he said. "Most cluster [experts] know now that users are fortunate to get more than 8% of the peak performance in sustained performance."

Linux clusters do have a place. "For applications that require low performance, they are a cheaper solution," said Terry.

With XD1, Cray intends to make HPC a cheaper solution, too. "With the Cray XD1, Cray will introduce new price points that should make HPC solutions more available to industries that before couldn't afford such devices," Terry said.

Cray XD1 was developed by OctigaBay Systems Corp., a Vancouver, B.C., Canada-based company acquired by Cray on April 2. Formerly OctigaBay 12K, Cray XD1 will be released to some companies for testing in May. Full release is expected later this year.

The acquisition of OctigaBay's technology will allow Cray to move into new markets by "doing supercomputing on a smaller scale with some commercial, off-the-shelf components," said analyst Richard Partridge, vice president of Enterprise Server Solutions for DH Brown in Port Chester, N.Y. "Cray just can't shrink its custom-built supercomputer designs," he said. Having the ability to put a value-added HPC solution on AMD processors is a good way to move downmarket.

Cray XD1 marries the performance of large SMPs with the economics of cluster solutions, according to Terry. It will also pair new interconnect and management technologies with AMD Opteron 64-bit processors in a direct-connected processor architecture. Its parallel-processing capabilities will directly link together processors to relieve memory contention and interconnect bottlenecks found in cluster systems.

"The Cray XD1 is not a traditional cluster; it does not use I/O interfaces for memory and message passing semantics," said Terry. "For HPC, the most important thing is application performance, and the Cray XD1 is specifically designed to maximize application performance."

In some situations, XD1 would be a good replacement for very high-end Linux clusters, Partridge said. He sees the XD1 providing more "compute performance for the dollar" for organizations that do heavy number and data crunching and analysis. He noted, however, that Cray has shown analysts a limited amount of information about the new products.

Terry believes that individual copies of Linux used for HPC today are intrinsically "heavy" and run independently on multiple processors, significantly adding to the difficulty of managing clusters.

XD1's integrated management software -- Active Manager -- will eliminate the "FCAPS" management ills common to clusters. "Fault, configuration, accounting, provisioning and security" are not handled well by current cluster management solutions, he said. "Often times, [management] appears to be done as an afterthought instead of being designed into the system from the ground up," he said.

Active Manager, which was demonstrated at ClusterWorld, offers a single-point of system administration and control. By removing the need for the administrator to manually deal with individual copies of Linux running on multiple processors, Active Manager can avoid most of the variability and subsequent loss of quality with system administration, according to Terry.

When Cray XD1 and Active Manage are released next month, it probably won't pose a threat to commercial Linux cluster solutions, such as Oracle Real Application Clusters. "The commercial environment is still best served by Linux clusters," he said.

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