SAN JOSE, Calif. Developers of the Infiniband system-to-system interconnect will meet Monday (Feb. 16) to lay out a plan that revs the technology to 100 Gbit/s.
During a developer's conference in San Francisco the group will discuss whether it should move to 5- or 6.25-Gbit/s signaling and possibly wider links for its next generation.
At the same time, engineers working on the emerging chip-to-chip PCI Express are starting similar discussions about whether 5- or 6.25-Gbits/s should be their next-generation signaling rate. Infiniband is primarily being used to cluster servers and storage systems for high-performance computing apps; PCI Express is aimed at chip-to-chip links in a broad range of PCs and eventually embedded systems.
New Infiniband features for reliability will also be up for discussion at the San Francisco event, but "the real, central issue is what will be our next-generation signaling rate. We will at least double it," said Allison Klein, an Infiniband initiatives manager for Intel Corp.
For both Infiniband and PCI Express the debate is essentially whether to simply double their current 2.5 Gbit/s data rate as a simple, backward-compatible move forward, or to stretch to 6.25 Gbit/s signaling to get a greater performance boost and leverage an emerging class of 6.25 serializer/deserializer chips.
"There are good reasons for both of them," said Klein, adding that the Infiniband Trade Association's work group on the issue is open to feedback from membership as it approaches a final decision. The IBTA expects to complete the spec and have it reviewed and approved by members before the end of the year. The whole process could take as little as 60 days.
"Infiniband will be the first interconnect to hit 100Gbit/s," said Michael Krause, a senior I/O engineering manager for Hewlett-Packard who has tracked the technology closely. "I think [next-generation signaling for] Infiniband will end up being 5Gbits/s. That's the targeted rate they have been working on," he added.
In meetings for both Infiniband and PCI Express, Krause has advocated moving Infiniband to 5Gbits/s, but Express to the faster 6.25 Gbits/s to provide the internal system bandwidth needed to handle the Infiniband upgrade. "If you only have 5-Gbit Express, you will never get to 5Gbit Infiniband rates," Krause said.
"The interoperability [of 6.25- and 2.5-G Express] is fairly straightforward to solve. And if you design the loss budgets right they should be able to handles the distance you need," he added.
The Express working group on electricals, under the PCI-SIG, has kicked off the discussion on next-generation signaling and is taking position statements from companies. However, a decision is not expected immediately. First-generation 2.5 Gbits/s Express chips are just starting to ship, with first system announcements not expected until this summer.
Separately, an old battle between using PCI Express or a faster version of PCI-X in servers seems to be shaking out, with few vendors adopting the version 2.0 of PCI-X. Most chip and card makers seem to be supporting the 133 MHz PCI-X version 1.0 and then moving to Express, with only a handful supporting PCI-X at the 2.0 rates of 266 MHz and beyond.
"For 80-90 percent of the companies that's their strategy. There are really not a lot of applications for 266 MHz PCI-X beyond 10G Ethernet and 10G Fibre Channel," Krause said.
"There are a class of systems from Sun, HP and IBM that will do 266 MHz PCI-X, and another class that stays at 133 MHz PCI-X and moves to Express," he added.
The move toward Express in mainstream servers marks a shift of sorts. At one time many top server makers suggested they would not support PCI Express at all until it reached its second-generation signaling rate. They argued that PCI-X provided an easier upgrade path and server customers were often slow to adopt new technologies.