Data center metrics and standards guide
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There's a reason why data center designers aren't allowed to self-assess Uptime, TIA, LEED or other certificat...
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The Uptime Institute's tier levels aim to describe what you do and do not get in terms of data center redundancy and how much downtime to expect. Uptime's tiers are the de facto method of specifying the reliability or availability level to which a data center is designed and built.
However, Uptime tier levels are interpreted differently by data center designers. So-called self-certification designates a facility by a tier level that actual performance history rarely supports. Legitimate data center design certification comes only from The Uptime Institute, following a rigorous review.
Other data center design certifications operate in the same manner, such as LEED's (Leadership in Energy and Environmental Design's) Gold, Silver and Platinum tiers for facilities. Designers can compute the LEED points that they believe the project has accumulated, but validation and actual LEED certification come only from the U.S. Green Building Council.
Why it isn't what they say it is
The Uptime Institute awards a tier level based on the weakest link in the infrastructure systems. Therefore, even a facility with power and cooling component redundancy at the Tier IV level -- dual uninterruptible power supplies, chillers, power distribution units, computer room air handlers and so on -- and dual, active electrical distribution paths also at the Tier IV level will receive only Uptime Tier II certification if it has one pipe path.
Many data center designers are upset by this rigid and proprietary approach. A designer might assess the single pipe as sufficiently robust for the mission-critical workloads in the data center; the second path wasn't really needed to achieve the reliability target. Therefore, to the designer, the data center deserves the Tier IV Uptime ranking.
Data center designers often make what they consider informed compromises about redundancy based on budgets, space constraints or previous failure histories. For example, a history of cooling failures in a location known to have highly reliable power can cause the data center operator to push for stringent cooling redundancy but balk at the cost of equivalent redundancy in the power systems. This leads to Tier III Plus or Near Tier IV data center design claims, which the Uptime Institute unequivocally does not recognize. A facility is only as good as its weakest link. Uptime certifications do take into consideration what is really necessary to achieve the target availability and which modifications are allowable within a tier level.
TIA vs. Uptime Institute
Different data center design certifications were invented in attempts to supplant Uptime's tiers, but none really caught on.
The Telecommunications Industries Association (TIA) 942-A standard provides tier information as an annex, but it was designed to cover data center cabling. Annex F of the standard elaborates on the basic Uptime Institute definitions. To clearly state which certification the data center design follows, Uptime tiers are designated in Roman numerals (tiers I, II, III and IV) and TIA tiers in Arabic numerals (tiers 1, 2, 3 and 4).
The TIA standard takes a prescriptive approach that differs from Uptime's certifications. The TIA 942-A Annex provides charts of characteristics that qualify a data center for a given tier level in architectural, electrical, mechanical (cooling) and telecommunications (cabling). Unlike the Uptime Institute, TIA allows data center designs to classify each subgroup separately. A given data center could have a Tier 1 architecture, Tier 2 electrical designs, a Tier 2 mechanical setup and Tier 4 cabling infrastructure. This approach makes it easier for designers to meet varied criteria and to assess and classify the robustness of each part of the data center infrastructure. However, TIA tiers don't provide a realistic prediction of the reliability and availability of the data center as a whole. The Uptime Institute considers the TIA-942-A partial classifications illegitimate and of no value to determining long-term reliability and downtime.
What a design certification requires
Achieving a tier level just requires redundant components -- extra power supplies, air conditioners and pumps, right? Nothing could be further from the truth. Redundant components don't add reliability if they don't have a proper physical location in the facility and if attention hasn't been paid to how they're connected, installed and labeled.
The key differentiator between a Tier I or Tier II design and a Tier III or Tier IV design is concurrent maintainability: the data center operator's ability to perform maintenance on all system components without affecting the computing systems.
Redundant components are frequently installed in ways that still leave the facility prone to failure. Installation choices can also limit the facility's ability to take an infrastructure component or pathway out of service for maintenance without affecting the critical computing load. Other common mistakes include locating controls and valves where they are difficult to access in an emergency, or poorly labeling or inconsistently arranging these components. Uninformed design decisions trap operators into creating failures that would not have otherwise occurred.
The TIA 942-A standard warns, "It is important to understand that certain intentional or accidental events, or acts of nature, pose a risk to the operation of data centers. It is important for the data center designer, administrator and manager to both assess and try to mitigate the risk to their facilities these events pose, as well as make contingency plans."
Making certification-quality choices
Whether a data center design is certified to Uptime or TIA tier levels, true mission-critical design and construction requires collaboration with a knowledgeable team to avoid pitfalls.
If tier systems eventually meet their demise by losing validity or usefulness, it will likely be from how they are used or misused. If too many data centers touted as Tier III or Tier IV fail, particularly if they are hosting high-profile cloud services with widespread user impact, the tier designations could lose meaning for data center operators and their business customers.
It is possible to build a data center that meets a given level of performance without undertaking the complex process of certification from Uptime, TIA, LEED's U.S. Green Building Council or some other group. However, expect to pay for in-depth expertise on tier-level design, more detailed design documents and intense construction supervision, which generally washes out the time and cost savings of skipping the certification steps. A thorough peer review can act much like a certification process, ferreting out downtime risks but dealing more flexibly with the realities of design conditions than the rigid certification requirements do.
The Uptime Institute demands goals that result in realistic budgets before design begins, and an understanding of the increased downtime that can be expected if budgets are reduced. This is why any claim to tier ranking without rigorous formal certification is illegitimate. Whether you carry through with certification or not, tier rankings do provide a common basis of communication that everyone in the industry understands in principle.
Robert McFarlane is a principal in charge of data center design at Shen Milsom and Wilke LLC, with more than 35 years of experience. An expert in data center power and cooling, he helped pioneer building cable design and is a corresponding member of ASHRAE TC9.9. McFarlane also teaches at Marist College's Institute for Data Center Professionals.