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November 20, 2008

Incoming: 10 Gigabit Ethernet for HPC

by Dan Tuchler

Sure, it’s proven, and a lot of people use it. But like many proprietary technologies, it also has some unappealing characteristics. It demands specialized expertise. It’s not always as fast as advertised. It’s not completely reliable. It certainly doesn’t work and play well with others. Yes, we are talking about InfiniBand.

InfiniBand has been a comfort zone for those tightly-coupled HPC applications that can’t live without their addiction to low latency and high speed. If your application is a science experiment with good funding and no firm schedule, that’s OK. If your application involves business, deadlines, and ROI, it’s time to break out of that comfort zone and acquaint yourself with 10 Gigabit Ethernet (10GE).

Fifty seven percent of the TOP500 Supercomputer Sites are already using Gigabit Ethernet interconnects. For many of those sites, that one Gigabit will give them all the speed they’ll ever need. For those applications that really do need a higher performance interconnect, 10GE can provide it — and a host of other advantages as well.

Technology You Know

InfiniBand might be the obvious choice in the HPC world, but compared to the well-known and widely-used Ethernet standard, the comfort level of InfiniBand might be equated to sleeping on a bed of nails. IT executives, network administrators, server vendors, and managed service providers around the world understand Ethernet. They can integrate and update an Ethernet installation within an existing infrastructure, without specialized gateways. They know how to manage it and how to benchmark it. They know what to do if something goes wrong. When it comes to Ethernet, familiarity breeds peace of mind.

More Cost-Effective and Already There

With costs going up, power at a premium, and manageability critical, it’s no surprise that converging and consolidating have become central themes in networking. Converged voice and data networks are becoming pervasive. Fibre Channel over Ethernet (FCoE) will merge storage and standard network applications on a common infrastructure. Virtualization is fast becoming a critical technology to support server and storage consolidation in the datacenter.

When it comes to reducing capital and operating expenses, one infrastructure is simply better than two — or more — and the HPC environment is no exception. High-performance computing clusters that use an InfiniBand interconnect also use Ethernet. Ethernet is necessary for user and storage connectivity, and for the management network that orchestrates the cluster. Replacing the InfiniBand interconnect with 10GE to create a single, all-inclusive infrastructure will cut hardware and power costs, and simplify manageability. And, that infrastructure combines high performance with low power needs and a sufficiently low latency for many HPC applications, making it an excellent fit for technical and budget requirements.

Prices are Plummeting

As with many technologies, 10GE was not initially cost-effective for widespread use. In fact, at one point a 10GE connection cost more than the server. But that ship has sailed. Now 10GE is so cost-effective that server vendors are starting to include the technology as a built-in standard feature. And switch prices are falling too. A number of switch vendors are offering 10 GE switches with a list price less than $500 per port.

Stable Network Interface

Some early adopters of 10GE were discouraged by problems with network interface cards (NICs). These problems were related to immature hardware and software drivers and have since been corrected. NIC vendors that could not adapt have dropped out of the market, and 10GE now has a stable network interface environment.

Physical Layer Selected

Many users expected that 10GBase-T would provide a simple, cost-effective solution, but were disappointed with the high cost, high power requirements and 2.6 µsec latency per cable hop. Multiple optics standards also led to some customer confusion, with XenPak, X2, XFP, and now SFP+.

It took a while for 10GE to converge on a single type of attachment, but many users today believe that SFP+ Direct Attach Cable (also known as twinax) is the right solution. SFP+ Direct Attach Cable is a low-cost, low-latency, interoperable solution that uses existing SFP+ sockets and addresses most 10GE challenges for distances up to around ten meters.

Broad Vendor Support

Every networking vendor supports Ethernet, and that support will extend to 40GE and 100GE in the future. Support for InfiniBand is limited to a handful of vendors. With less competition, there will be less innovation, and less incentive to offer competitive pricing and to increase reliability.

It’s Time

New products and advancing technologies have overcome the last hurdles that prevented 10GE from addressing HPC needs:

  • NIC prices will continue to drop as LAN-on-Motherboard (LOM) technology lets NIC vendors reach the high volumes they need to keep costs down.

  • Switch prices are also dropping–prices under $500 per port make 10GE switches cost-effective for business applications.
  • The emerging SFP+ Direct Attach cabling standard avoids the problem of expensive optics and presents a clear solution.
  • Many HPC applications such as Reuter’s RMDS and others achieve equivalent performance numbers on 10GbE and InfiniBand
  • Using some of the latest server blades and comparing DDR InfiniBand with RDMA to 10GE iWarp using a BLADE Network Technologies switch, we have observed similar performance on common HPC applications such as FLUENT, PAM CRASH, VASP and others.

It’s time to bring the benefits of ubiquitous 10GE to the HPC community. For most clusters and most applications, Ethernet brings the advantages of better pricing, higher reliability, plenty of performance, and lower operating costs than InfiniBand. A holistic approach with a single infrastructure will also contribute to reduced costs, while widespread Ethernet expertise will reduce management headaches and support a more efficient environment.

When InfiniBand is Necessary

Some applications will still require the extremely high performance and low latency that is achievable only with InfiniBand. However, IT teams should evaluate project needs carefully before selecting an interconnect technology. Situations that invite InfiniBand include:

The Need For Speed — Performance is a key driver for InfiniBand, but designers need to be aware of the bottom line for performance statistics. Double Data Rate (DDR) technology claims to provide 20 Gbps performance, but the reality is closer to 16 Gbps. Hardware limits in the PCIe gen1 bus in many machines reduce this number even further. With a measurable performance of about 13 Gbps, InfiniBand isn’t a whole lot faster than 10GE. Similarly, Quad Data Rate (QDR) claims 40 Gbps performance, but actually delivers closer to 26 Gbps due to the PCIe gen2 bus–not that much faster than a two-port 10GE switch.

Really Low Latency — Some compute-intensive, tightly-coupled applications, such as those found in the largest national science labs, do demand the extremely low latency that only InfiniBand can provide. However, other applications that are either loosely coupled or simply don’t have an excessive demand for low latency can run perfectly well over 10GE. Many TCP/IP-based applications fall into this category, and many more can be supported by adapters that offload TCP/IP processing. In fact, some TCP/IP applications actually run faster and with lower latency over 10GE than over InfiniBand.

About the Author

Dan Tuchler is Vice President of Strategy and Product Management at BLADE Network Technologies (www.bladenetwork.net). His technology experience spans emerging Ethernet standards, InfiniBand, security, load balancing, content-aware networking, and high-availability.