Data center consolidation drives network redesign
Data center consolidation requires extensive network redesign. Replacing individual servers in remote sites with a smaller number of higher-capacity servers in a central data center requires adding high-throughput WAN links from the remote sites to the consolidated data center.
Within the central data center, multiple virtual servers executing on a single physical server generate higher data rates than would typically be generated by a single server. In many cases, this will mean replacing 1-GbE links with 10 GbE. Network cabling and switches must be upgraded and in many cases replaced. Combining network and storage traffic on a single set of interconnects further increases throughput requirements and adds complexity to the design task.
Network simulation and planning software can aid the design process. Channel partners can recommend a planning tool from commercial vendors such as Opnet Technologies or Shunra Software or assist the customer in using an open-source tool such as NS-2 or OMNet++.
Most planning tools create detailed network documentation. If the customer does not have processes in place to maintain up-to-date network documentation, the major redesign period is a good opportunity to begin. Work with the customer to create a network update process that ensures that future changes will be documented.
Selecting a cable technology to support 10 GbE
A variety of interface and cable types, both copper and optical fiber, support 10 GbE. The choice between copper and fiber is dictated mainly by interconnect distance, but consider also interface power usage and packet latency. Customer experience and familiarity with each type of cable can be factors in the decision.
Cable types can be mixed in the same data center. For example SFP+ copper can be used for the short run from a server to a top-of-rack switch, with fiber used for longer interconnects.
Whichever cable technology is chosen, careful attention must be given to cable placement. Twisted pair cable to support 10 GbE is thicker and heavier than twisted pair sufficient for lower data rates. It is not always possible to simply replace the cable in existing trays. Additional trays may be needed and existing trays moved.
Problems with thickness or weight are unlikely when replacing twisted pair with fiber or replacing multi-mode fiber with single-mode, but pay close attention to fiber minimum bend radius. Paths that may have been acceptable for twisted pair may not meet minimum radius requirements for fiber.
It is critical to use compatible cabling components -- including patch panels, patch cords and cables -- from end to end, says Stephan Fowler, infrastructure engineer with Celergy Networks Inc., a California-based network integrator.
Some vendors manufacture all of these components, while others have formed partnerships to produce and test compatible components. Individual components from various manufacturers may be rated at 10 gigabits, but the end-to-end network may not support this rate if components that have not been tested together are used.
Upgrade switches for 10 GbE
All of the major switch vendors have released products supporting 10 GbE, and most have announced support for Converged Enhanced Ethernet. Examine vendor claims carefully. Some vendors have made more progress than others in implementing these protocols; announced support does not always translate to availability on a shipping product.
Suggest that customers examine even lower rate switches as part of the overall network redesign. Many switch ports that previously supported desktop users may be unused as a result of staff reductions or a switch to WLANs. Power usage and rack space can be reduced by eliminating unneeded switches.
Consider next year's requirements
Finally, consider possible future applications in the plan. There may be no current plan for VoIP, but planning for it now may be simpler than retrofitting it on the network later.
Consider also that data rates will continue to increase. The IEEE 802.3ba Committee expects to complete standards for 40- and 100-gigabit Ethernet in 2010, and vendors have announced plans to support these rates. Consider next-generation data rates when choosing cable technology and switches.
David B. Jacobs of The Jacobs Group has more than twenty years of networking industry experience. He has managed leading-edge software development projects and consulted to Fortune 500 companies as well as software start-ups.
This was first published in September 2009