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changing in HPC Connections

At first we connected our computers with Ethernet. Then InfiniBand started to dominate in HPC. Now, with RDMA over Ethernet readily available, we are starting to see a shift back to Ethernet for many systems.

Paul Schreier looks at the prospects ‘I

don’t know the network of the future, but it’s something Ethernet.’ With this play on a quote by Seymour Cray about programming languages, John

Taylor, VP of technical marketing at Gnodal, puts his finger on one of the major trends in HPC interconnect – the re-emergence of the perennial favourite, Ethernet. When computers started getting larger and

more powerful, and able to handle enormously large problems, it soon became apparent that the Ethernet designed for office and enterprise applications was becoming a bottleneck in


terms of latency. In response to this, a number of technologies were developed and they eventually converged on what we today know as InfiniBand. Te major benefit of InfiniBand, in a

nutshell, is RDMA (remote direct memory access). Instead of the need to pass data packets through the operating system as is done with Ethernet, data transfers are made directly from memory to memory. Such transfers require no work on the part of CPUs, caches or context switches, and transfers continue in parallel with other system

operations. Te result is latency far lower than possible with standard Ethernet, a feature very important for today’s sophisticated HPC architectures.

RDMA on Ethernet Meanwhile, engineers have also found a way to use RDMA techniques in conjunction with Ethernet. Te two ‘flavours’ available today are RoCE (RDMA over Converged Ethernet) from Mellanox Technologies and iWARP (Internet Wide Area RDMA Protocol) from Intel. Te latter firm got its InfiniBand technology early this year when it made big news with the purchase of the InfiniBand technology from QLogic, the only competitor to Mellanox in this market. Te resulting True Scale fabric is based on this InfiniBand technology. Interestingly, a few months later Intel also purchased interconnect technology from Cray, including the Gemini interconnect as well as the upcoming Aries, an interconnect chipset follow-on to Gemini with a new system


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