Sorting out data center tiers and cabling specs

Jan. 1, 2011
The tier concept was included in TIA-942, but the tier system's creator warns against confusing the two.

The tier concept was included in TIA-942, but the tier system's creator warns against confusing the two.

by Patrick McLaughlin

How many times have you heard someone talk about the tier rating of a data center, whether their own or one in which they've worked? A Tier IV data center is viewed as the ultimate in redundancy and availability according to the Tier Classification System established by The Uptime Institute (TUI; Established more than a decade ago by TUI, the Tier classification system has been widely referenced.

One reference to TUI's Tier classification system can be found in the TIA-942 Telecommunications Infrastructure Standard for Data Centers. Prior to that standard's publication in 2005, its primary creators Chris DiMinico and Jonathan Jew wrote the following in an article published by Cabling Installation & Maintenance: "The standard provides specifications corresponding to industry-standard data center reliability tiers, where Tier I has no redundancy and Tier IV provides the highest degree of fault tolerance. The architecture, security, structural, electrical, grounding, mechanical and fire protection guidelines are organized into four tiers."

Because TUI's Tier classification system has been so widely accepted across the data center industry and so frequently referenced, it has at times been subject to loose interpretation. Professionals in data center circles have probably heard at one time or another someone describe a facility as "Tier 3.5" because it fulfills all the requirements of a Tier III data center and some but not all of the requirements of a Tier IV data center. Such interpretations–or misinterpretations–have bedeviled TUI. For more than a year the organization has waged a campaign against what it describes as "Tier myths and misconceptions." Of particular note to professionals in the cabling industry, the TIA-942 standard was the subject of one such myth-busting effort by TUI.

Busting myths

In March 2010 TUI published a round of rebuttals to myths it encountered during site visits in Latin America, Europe, Russia, Africa and Asia. "These myths have taken attention away from the fundamental concepts of the Tier classification system," TUI said. "The result has been shortfalls in design topology despite adequate budgeting. These shortfalls put the data center's ongoing uptime at risk." Among the myths debunked at that time was that TIA-942 is a guideline for Uptime Institute Tiers. TUI's response to that notion was the following. "The similarities between Uptime Institute Tiers and TIA-942 stop at the surface. Uptime Institute Tiers is functionally disconnected from TIA-942. The core objective of Uptime Institute Tiers is to guide a design topology that will deliver high levels of availability–as dictated by the owner's business case. Uptime Institute Tiers evaluates data centers by their capability to allow maintenance and to withstand a fault. Uptime Institute Tiers is not available in checklist form. To avoid further confusion, Uptime Institute recommends Roman numbers (I, II, III, IV) to signify Tier-based projects."

Jonathan Jew, co-author of the previously referenced article on TIA-942 as well as co-editor of the standard's in-development revision TIA-942-A and partner with data center design firm J&M Consultants (, backs up TUI's stance on Tiers and TIA-942. "The TIA-942 Tiering scheme was initially developed based on the concept of four tiers originally developed by TUI because we wanted to acknowledge that their scheme was in fact the most widely used for evaluating data center reliability and they had very useful definitions associated with each Tier," he says.

"While TIA has remained with prescriptive definitions for each Tier, TUI has decided to move to a functional approach. In the TIA scheme we might recommend a certain design solution, while TUI would be more open to various solutions as long as the result provided the desired level of availability.

"The TIA's scheme is open to evaluate the relative security and availability levels of a data center," he continues. "However, just selecting the right pieces does not guarantee the desired level of availability. It still requires competent engineers to design a system that functions properly."

The TUI's approach is proprietary and is the organization's intellectual property. Jew further says, "Because TUI's system is based on function rather than components, their system can't be completely put down in table form." He adds that both approaches are useful. While TUI's is the more complex of the two and requires more analysis, TIA's also requires a qualified engineer to put the pieces together for proper functioning despite the fact that the TIA method is open and standards-based.

Designations and specifications

Since 2009 TUI has offered the Accredited Tier Designer designation for data center design professionals. TUI describes the program as "a comprehensive training course for design professionals to enhance their understanding of the practical application of the Tiers, including misconceptions and common misapplications. An ATD designation will be awarded upon successful completion of an exam." TUI adds that for design professionals, the ATD designation is "a substantial differentiator," especially for data center projects that specify a Tier objective.

The actual specifications for what makes a data center anything from a Tier I to a Tier IV facility are spelled out in TUI's document "Data Center Site infrastructure Tier Standard: Topology." The nuts-and-bolts definitions of Tier I through Tier IV take up barely more than two pages of the document, yet time has shown they have significant implications on data center design and administration. Acknowledging that reality, TUI published an introduction that is not part of the Tier specs but is part of the overall document. Within the introduction, the group explains the document is a restatement of content previously published as a TUI white paper entitled "Tier Classifications Define Site Infrastructure Performance."

The introduction takes the opportunity to provide other commentary that leans toward the myth-busting approach it has taken at other times. Specifically, TUI says, "The Tier topology rating for an entire site is constrained by the rating of the weakest subsystem that will impact site operation. For example, a site with a robust Tier IV UPS configuration combined with a Tier II chilled water system yields a Tier II site rating."

In mid-2010 TUI introduced another specification, "Tier Standard: Operational Sustainability." According to the organization, this specification addresses a facility's management behaviors and risks that affect long-term data center uptime by aligning the infrastructure's capabilities (as defined by the Tier classification system) with its ongoing management.

TUI's vice president Julian Kudritzki commented at the time, "The Institute's Tier classification system ensures a data center facility is designed and built to deliver uptime in accordance with its business requirements. 'Operational Sustainability' ensures the site is managed to sustain that level of availability over the long-term."

TUI explains the specification is structured around the three most influential elements of a data center's ongoing performance in the following prioritized order: management and operations, building characteristics and site location.

The Uptime Institute, developer of the Tier classification system, has spent time and effort educating data center professionals about what the system is and isn't. It has also produced services and documents seeking to further the cause of the Tier classification system. While TIA-942 has helped the design and installation of data center physical infrastructure, The Uptime Institute has taken significant measures to spread awareness that there is more to achieving a Tier rating than simply complying with TIA-942.

Patrick McLaughlin is chief editor of Cabling Installation & Maintenance.

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