Data center tiers

There are a number of nationally and internationally recognized standards for ensuring the quality, availability, and security of data centers. Among the most important standards are the Tier Classification Standard issued by the Uptime Institute, the Telecommunications Industry Association’s TIA-942 standard, DIN EN50600, and the recently introduced ISO/IEC 22237 standard. These data center tier classification systems provide information about the centers’ fire safety, maintenance and uptime, among other things.

From your personal cloud with email and office apps to small businesses to international corporations — pretty much everyone relies on secure data centers, cloud computing, and software-defined data centers. The more connected our social and professional worlds become, the more important it is to ensure security in data centers, prevent server failures, and maintain the availability of system resources. That’s why there are official international standards and classifications that allow you to judge a data center’s suitability for your business.

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Overview of the standards and classifications

There are four systems commonly used to evaluate data centers:

  • Uptime Institute’s Tier Classification System
  • Telecommunications Industry Association’s TIA-942 standard
  • DIN standards
  • ISO/IEC standards

All of these systems provide a reliable basis for evaluating the planning, implementation, and launch of new data centers, as well as for optimizing and developing the performance and security existing data centers.


Data centers are of critical importance for businesses. Not every company needs its own server sites. Check out our article “What is a data center?” to learn about the different types of data centers.

Uptime Institute’s Tier Classification System

Uptime Institute’s Tier Classification System is one of the most prominent standards and classifies data centers using a hierarchical system. The four tiers indicate where a data center stands regarding uptime, security, and redundancy.

The levels touch on external factors like connectivity and the hierarchy of data centers in international networks, as well as internal factors like security measures and data center downtime.

The system is progressive, meaning that each higher tier also includes the requirements of the tiers below it. Below we’ll look in detail at the requirements for each data center tier.

Tier 1 data centers

  • No redundancy
  • Single path for power and cooling
  • No fault tolerance, not concurrently maintainable
  • Limited cooling capacity: 220-230 watts per square meter
  • Expected 99.67% uptime (maximum 28.8 hours of downtime per year)
  • Suited for: Small companies and startups with low budgets and limited IT requirements. Not used very often

Tier 2 data centers

  • Partial redundancy for cooling and power
  • One path for power
  • Low fault tolerance, not concurrently maintainable
  • Simple cooling capacity: 430-540 watts per square meter
  • Expected 99.75% uptime (maximum 22 hours of downtime per year)
  • Suited for: Simple IT processes that require good performance but aren’t mission critical. Not used very often.

Tier 3 data centers

  • Reliable redundancy for different components: two servers, multiple paths for cooling and power
  • Good fault tolerance, concurrently maintainable
  • Good cooling capacity: 1,070-1,620 watts per square meter
  • Expected 99.98% uptime (maximum 1.6 hours of downtime per year)
  • Suited for: Recommended minimum level for businesses with high standards for seamless IT processes, e-commerce, and mission-critical processes

Tier 4 data centers

  • Complete redundancy for all parts of the system, including power and cooling
  • Very high fault tolerance, no single points of failure
  • Very good cooling capacity: over 1,620 watts per square meter
  • Expected 99.991% uptime (maximum .8 hours of downtime per year)
  • Suited for: Large companies with internationally connected computing networks, 24/7 system availability, and highly mission-critical IT processes

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Telecommunications Industry Association’s TIA-942 standard

The TIA-942 standard is another data center classification system that’s frequently used in the US. Released in 2005, it was among the first standards specifically geared towards data centers. It covers site selection and layout of the space, cabling infrastructure, and environmental considerations and includes a tiered reliability system based on Uptime’s. The standard is particularly relevant to the design and implementation of new data centers.

International standards: ISO/IEC 22237 and DIN EN 50600

In addition to the two American-based data center standards we’ve discussed, there are also international standards like DIN EN 50600 and ISO/IEC 22237. The DIN EN 50600 is a European standard that primarily focusses on physical security in data centers. The ISO/IEC 22237 was recently introduced by the International Organization for Standardization (ISO) and International Electrotechnical Commission (IEC) and borrows heavily from the DIN EN 50600. It’s valid internationally and is expected to replace Uptime’s tier classification for data centers as well as DIN EN 50600.


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What’s covered in the ISO/IEC 22237?

The ISO/IEC 22237 adopts the most important points from the DIN EN 50600 and expands on them using recent findings on sustainability and energy efficiency. It also integrates a four-tiered system for classifying quality and uptime. It’s thus not only a valuable tool for developers and planners but also a way to build trust with investors and end users. The standard consists of seven main points:

  • ISO/IEC 22237-1 (EN 50600-1): General concepts
  • ISO/IEC TS 22237-2 (EN 50600-1): Building construction
  • ISO/IEC 22237-3 (EN 50600-2): Power distribution
  • ISO/IEC 22237-4 (EN 50600-3): Environmental control
  • ISO/IEC TS 22237-5 (EN 50600-4): Telecommunications cabling infrastructure
  • ISO/IEC TS 22237-6 (EN 50600-5): Security systems
  • ISO/IEC TS 22237-7 (EN 50600-3-1): Management and operational information

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Is quality testing mandatory for data centers?

Standards, tiers, and certifications are not mandatory ⁠— data centers participate voluntarily in them. There are also independent organizations that review data centers’ compliance with standards. This makes it even more important for investors, consumers, and end users to look out for a transparent indication of which tier a data center belongs to. It’s also in the interest of those running data centers to increase their credibility with standards and certifications.

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