Data Centers

Demystifying Uptime Institute's complex Tier-Rating system for data centers

The Uptime Institute's Tier-Rating system is sometimes criticized as being too complex and for having evaluation criteria that's unclear. This overview might provide some clarity.

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Every so often a squabble breaks out about Uptime Institute's Tier Ratings for data centers. Opponents feel the classification system is out-of-date and too complex.

Hector Diaz, the Denver AFCOM Chapter president, who also manages one million square feet of data-center space for a multinational enterprise, told Colleen Miller of Data Center Knowledge, that the Tier standards are often confusing, and "There needs to be more understanding conceptually."

Matt Stansberry, Director of Content and Publications at Uptime Institute, refutes the claims made by Diaz.

After reading both sides, it seems helpful to step back, look at the Tier-Rating system, and if certification is required decide whether it makes sense to get qualified by Uptime Institute or an independent professional commissioner backed by the Building Commissioning Association.

The test categories

A good place to start is to define tier rating. Colocation America's definition is succinct and understandable: "Data center tier standards objectify the design features of a particular facility based upon infrastructure design, capacities, functionalities, and operational sustainability."

Uptime Institute's Tier-Rating system comprises two categories: Tier Certification of Design Documents (TCDD) and Tier Certification of Constructed Facility (TCCF). TCDD involves the following steps:

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    Review of detailed design document package
  • Letter report of tier deficiencies and operational sustainability enhancements
  • Teleconference with project team, including project owner and Engineer-of-Record, to ensure comprehension of report findings
  • Review of revised design drawing package

Next is TCCF. Uptime Institute consultants come on site and determine if the data center's construction meets design specifications. Then the consultants put the data center through its paces, measuring whether it fulfills the desired tier's requirements. Services include:

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    On-site assessment of installed site infrastructure
  • Identify discrepancies between design and installed infrastructure
  • Confirm commissioning documents
  • Observe select demonstrations

The four tiers

The Uptime Institute slide below provides a quick glimpse at the differences between the four tiers.

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Image: Uptime Institute

The terms N and N+1 are not commonly used outside the data center; fortunately, it is one of the simpler concepts in the tier-rating system. If a data center requires two backup generators to meet workload requirements, three backup generators are required to meet the N+1 rating.

Next are simplified descriptions of each tier based on the Uptime Institute white paper Tier Standard: Topology. One important thing to remember about the Uptime Institute Tier Ratings is that each rating builds on the previous one.

Tier I (Basic Capacity): Tier I infrastructure includes a dedicated space for IT systems; an Uninterruptible Power Supply (UPS) to filter power fluctuations and outages; dedicated cooling equipment that runs 24/7; and a backup generator to power IT equipment during extended power outages.

Tier II (Redundant Capacity Components): Tier II facilities include redundant power and cooling components to provide maintenance opportunities and an increased margin of safety against IT process disruptions resulting from equipment failures. The redundant components include UPS modules, chillers, pumps, and engine generators.

Tier III (Concurrently Maintainable): A Tier III data center can maintain and replace equipment without shutting down. A redundant delivery path for power and cooling is added to the redundancy incorporated by Tier II so every component needed to support the IT environment can be shut down and maintained without impact on the overall IT operation.

Tier IV (Fault Tolerance): Tier IV adds the concept of Fault Tolerance to the site infrastructure, so when individual equipment failures or distribution interruptions occur, the data center's IT operation is not affected.

Besides complexity, another stigma following the Uptime Institute is its reticence about what constitutes its evaluation criteria. In their defense, the Uptime Institute offers the following resources:

Complex rules, but so are demands

After reading the white papers and Stansberry's explanation, it is obvious the Uptime Institute's Tier-Rating system is complex, but is it over-simplistic to think the complexity can be reduced and still maintain operational parameters expected of data centers, especially when customers are demanding 100% uptime?

About Michael Kassner

Information is my field...Writing is my passion...Coupling the two is my mission.

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