Jan 11, 2016

Infrastructure Matters – LAN/Campus vs. Data Center Structured Cabling

Many people think increasing bandwidth in a storage network is  always a good thing. But there are some drawbacks. For example, as bandwidth increases, the margin for error regarding link loss budget decreases. The complication  is many data center storage infrastructures stem from LAN/Campus network products and philosophies instead of a data center based infrastructure strategy.   What is Link Loss Budget?   Link loss budget is the total allowable loss of signal between a director class switch to a server or a storage system. When a data center upgrades from 8Gbps Fibre Channel to 16Gbps Fibre Channel, the allowable link loss and distance between active devices changes dramatically. With 1.5 dB mated pair signal loss on OM4 fiber cable, the distance limitation with 8Gbps FC was 190 meters, with 16Gbps FC the distance limitation reduces to 125 meters with 1.5 dB of mated pair signal loss. A mated pair is a term that  describes the connection between two fiber segments, either cable to cable or cable to the port, not including the connection into the transceivers.   LAN/Campus Networking Wastes Link Loss Budget   The primary issue with LAN/Campus Networking is the design’s use of MTP Cassettes. MTP stands for Multifiber Termination Push-on connector. The advantage of MTP is that pulling a single cable results in eight fiber connections. The problem is the MTP Cassettes insert additional link loss as each mated low loss MTP connection introduces an additional 0.35 dB of signal loss. The typical LAN/Campus infrastructure design will route each active connection through as many as three MTP cassettes. As a result, the MTP Cassettes by themselves may consume the entire Link Loss Budget. MTP cassettes make the job of the cabling installer easier but may make storage communications less reliable.   A structured cabling approach eliminates the use of MTP Cassettes and uses LC to LC connections. It uses LC to LC adapter panels on the central access point direct from the director class switch to the patch panel and direct to the attaching server or storage system. Another benefit of eliminating the MTP cassettes is the ability to troubleshoot individual channels without taking down up to 5 other active channels on the cassette.   LAN/Campus Networking is Designed for Static Systems   LAN/Campus networking is intended to connect users to the data center. Specific locations like offices and cubicles within the building are wired once, even though the computer in the office may change the cabling connection rarely does.   In the data center, the opposite is true. Storage systems and servers are added, moved, or their connections are changed very frequently. Knowing exactly where each cable connects is critical as is identifying corresponding ports. Structured Cabling the way we design it at DCS, makes dealing with frequent moves, adds and changes easy. We use a mimic panel when we design your system, custom designed to match your director class switch so that each port on the patch panel matches the ports on your director.   Carl's Conclusion   LAN/Campus networking has its place, connecting users to the data center. But in the data centers, IT professionals need an infrastructure that will keep pace with the demands that the organization places on IT. Structured cabling with direct LC to LC connections and a central access point that mimics the director class switch enable IT to be  more flexible and agile as equipment speeds increase