Point-to-Point Data Center Cable Will Cost You in the Long Run
Direct cable connections between data center resources such as switches and servers and servers and storage was once common, and unfortunately the practice is surfacing again with the use of top of rack (ToR) and end of row (EoR) equipment mounting options. ToR and EoR equipment placement relies heavily on P2P cables, which can be problematic and costly if viewed as a replacement for standards-based structured cabling systems.
Wed, February 29, 2012
Network World — This vendor-written tech primer has been edited by Network World to eliminate product promotion, but readers should note it will likely favor the submitter's approach.
Direct cable connections between data center resources such as switches and servers and servers and storage was once common, and unfortunately the practice is surfacing again with the use of top of rack (ToR) and end of row (EoR) equipment mounting options. ToR and EoR equipment placement relies heavily on P2P cables, which can be problematic and costly if viewed as a replacement for standards-based structured cabling systems.
OUTLOOK: Trends reshaping networks
Consider the point to point (P2P) connections shown in Figure 1. Rack 1 depicts a ToR patching scenario between switch ports and servers without a structured cabling system, while Rack 2 uses similar server connections to a Rack 3 switch. While proponents of this approach tout a decrease in cabling as a cost offset, further examination may prove otherwise.
As the electronics in the various cabinets are reconfigured and reorganized, it may become hard to maintain neat P2P links and necessitate a move back to a structured system, negating any savings. What's more, trying to retrofit a cable system in a live environment raises many questions about the chance for disturbing other systems and potential downtime.
Efficient port utilization can also be challenging. In a P2P design, switch ports are dedicated to servers within a particular cabinet. This can lead to an oversubscription of ports. Suppose Rack 1 needs only 26 server connections for the entire rack. If a 48-port switch (ToR switching) or 48-port blade (P2P server to switch) is dedicated to the cabinet, 22 unused ports are purchased and powered. A greater problem occurs when the full 48 ports are used. Adding even one new server will require the purchase of another 48 port switch. In this case, assuming two network connections for the new server, an oversubscription of 46 ports will be added to the cabinet.
Further, many of these P2P technologies offer limited channel lengths, ranging from 2-15m, limiting equipment location. With a structured cabling system, 10GBase-T is supported over 100 meters of category 6A, 7 and 7A cabling, allowing plenty of options for equipment placement.
The "any-to-all" alternative
The alternative is an any-to-all structured cabling system. The concept behind any-to-all is simple. Copper patch and fiber panels are installed in each cabinet that correspond to panels in a central patching area. This allows equipment to be installed and connected to any other piece of equipment via copper patch cords or fiber jumpers. The fixed portion of the channel remains unchanged, regardless of how electronics are shuffled between racks. Pathways and spaces are planned upfront to properly accommodate the cabling.
