News

Cabling in the data centre: Just a piece of the puzzle

20th December 2006

Cabling is one part of a series of complex information-technology systems that make up a data centre. While the cabling system is just one consideration in such an environment, it does have the opportunity to positively or negatively affect a data centre’s efficiency.

The obvious manner in which cabling affects data centre administration is the systems’ performance. A cabling-induced downtime episode would be disastrous for a data centre manager, and probably also for the manufacturer whose system failed. Those systems must be robust because today’s data centres are upgrading to the highest available speeds.

When it comes to structured cabling systems capable of supporting 10-Gbit/sec transmission, users have optical and copper options from which to choose. Although copper-based network equipment has not yet hit the market, the structured cabling systems engineered to support that data rate have been available for more than two years. In fact, under certain circumstances and to certain short distances sometimes found in data centres, legacy Category 6 systems will support 10-GbE.

Nonetheless, comments made about new data-centre installations being 10-Gig capable refer to high-performing multimode fiber-optic and pre-standard Augmented Category 6 copper cabling systems. Suffice it to say, data centres require and are receiving the highest-performing structured cabling products available.

Workmanship affects performance

In addition to the logical importance of a cabling system’s throughput capacity, workmanship issues in the design, installation, and maintenance of these systems can have long-term effects on overall data centre operation. In many data centres, the cabling is not a planned system. They first installed some cables because they needed a server and needed connectivity to that server. Plenty of data centres have cables clothes-lined across the room. In some cases like these, tracing the cables is very difficult.

These management problems can create performance problems. A lot of Category 5e cabling won’t pass 5e testing, either because it was pre-standard product that never met the final specifications or, in many cases, because improper management during moves/adds/changes have compromised their performance. Customers in this situation who are trying to run 1-Gig on that cable have to decide whether they want to re-terminate the cable that is in there, or install a new system.

Dense bundles

The sheer density of cables in many data centres creates a challenge even with reasonable cable-management measures. Managers are struggling because many data centres were designed for the technologies of years ago with far less density than we see today.

Proper cable management and routing are essential, and have an impact on cooling and thermal management.

Structured cabling could have an impact on airflow, especially in the perimeter of racks. The number of cables per device is the root of this air-flow restriction. If a customer is deploying high density, they must be aware that their system could impede airflow. A key to battling this is to give as much space in racks as possible.

Cable management can be an issue on both “sides” of the data centre-the local area network (LAN) and storage area network (SAN) sides. Cable management is equally important in the LAN and the SAN, but there is a distinct difference in SANs. It is not uncommon for even a moderate SAN to have terabytes of storage space. Because SANs almost universally operate using the Fibre Channel protocol, fiber connections are ubiquitous.

As a result, the idea of true “structure” to the cabling in a data centre frequently resides on the LAN rather than the SAN side. The situation varies from site to site, but in general terms, that statement often holds true: “Predominantly, the structured cabling group or professionals are responsible for the LAN side. On the SAN side, most often, the installation professionals are integrators, who deal with active equipment.”

For them, cabling takes a rather low place on the totem pole-it’s simply a means of connecting the more-important pieces of storage equipment-and quite often, that is reflected in the extent to which its cable management is a consideration.

Standard guidance

With these structured-cabling issues present in data centres, a logical question is whether system designers, installers, and managers can seek guidance or assistance in any formal standards that address cabling specifically in a data centre. The answer comes in the form of the TIA-942 Telecommunications Infrastructure Standard for Data Centres. Published in April 2005, the standard provides information not only on structured cabling but also on the data centre overall.

Among the overall data centre information in the standard is the concept of tiering, under which data centres are categorized as being anywhere between Tier 1 and Tier 4, depending on a number of use factors. That tiering structure was adopted from The Uptime Institute, which originally developed the concept.

While TIA-942 does not specifically spell out differences between privately owned and collocated data centres, in most cases, the main difference between the two is size: “The standard does take into consideration the data centre’s size, including a topology for what is called a ‘reduced’ data centre and what is called a ‘distributed’ data centre.”

The differences will have an impact on access control, redundancy, and heating / ventilation / air-conditioning requirements. All data centres have these needs, so in one sense their needs are the same, the difference is in the quantities or extents of those needs.

The goal of TIA-942’s creators to provide information on cabling and pathways while also providing the larger perspective of the data centre as a whole, reflects the reality that structured cabling is a small but important part of a data centre.

While its importance should not be overstated, neither should it be understated.