The old adage that history repeats itself is very true. If we don't learn from history, we are doomed to repeat it. Many data centers today are victims of historical point-to-point cabling practices.
Direct connections - "Point-to-Point" (i.e. from switches to servers, servers to storage, servers to other servers, etc.) are problematic and costly for a variety of reasons. In the best of data center ecosystems, a standards-based structured cabling system will provide functionality and scalability with the maximum available options for current and future equipment. While Top of Rack (ToR) and End of Row (EoR) equipment mounting options are now available, these should supplement, not replace, a structured cabling system. ToR and EoR equipment placement both rely heavily on point to point cables, typically fiber jumpers and either twinax copper assemblies or stranded patch cords to connect the network or storage equipment ports to servers.
Data centers are evolving in a rather cyclical manner. When data centers (the original computer rooms) were first built, computing services were provided via a mainframe (virtualized) environment. End users' dumb terminals were connected via point to point with coax or bus cabling using twinax. Enter the PC and Intel based server platforms, and new connections were needed. We have gone through several generations of possible cabling choices: coax (thicknet, thin net), category 3, 4, 5, 5e, 6. Now, the recommended 10 Gigabit capable copper choices for a data center are category 6A, 7 and 7A channels, OM3 grade fiber for multimode capable electronics and single mode fiber for longer range electronics. In some data centers, samples of each of these systems can still be found under the raised floor or in overhead pathways, many of which originally were point-to-point. Today however, the "from" point and "to" point are a mystery, making cable abatement (removal of abandoned cable) problematic at best. Compounding this problem was a lack of naming conventions. If the cables were labeled at both ends, the labeling may not make sense anymore. For instance, a cable may be labeled "Unix Row, Cabinet 1."
Years later, the Unix row may have been replaced and new personnel may not know where the Unix row was. There are two standards for structured cabling systems in a data center: TIA 942 and draft ISO 24764, the latter of which is slated to publish in September, 2009.
These standards were created out of need. Both data center standards have language stating that cabling should be installed to accommodate growth over the life of the data center. Moves, adds and changes for a single or a few runs are expensive compared to the same channels run as part of an overall multi-channel installation project. For the larger projects, the end user realizes benefits from project pricing, economies of scale, and lower labor rates per channel. Single channels are typically more expensive, as it is more expensive to send personnel to run one channel. The risk of downtime increases with continual moves, adds and changes. Pathways and spaces can be properly planned and sized up front, but can become unruly and overfilled with additional channels being added on a regular basis.
Data centers that have issues with cable plant pathways typically suffer from poor planning. Growth and new channels were added out of need without regard to pathways. In some cases, pathways do not accommodate growth or maximum capacity over the life of the data center. Overfilled pathways cause problems with airflow, and in some cases cabling becomes deformed due to the weight load, which can adversely affect transmission properties of the channel. This is particularly true in point-to-point systems that have grown into spaghetti-like conditions over time. Likewise, data centers that have not practiced cable abatement or removal of old cabling as newer, higher performing systems are installed experience the same disheveled pathways.