Data Center Quality Tiers - What Tier Levels Are There

The English word Tier is commonly used in computer science and information technology and can have different meanings and contexts depending on the situation. Literally translated, it simply means "level", "layer", "tier" or "rank" and refers to a specific position in a hierarchical model where lower positions are directly dependent on those above them. The concept of Tier is universal and is used for designations in hardware, network protocols and layers, as well as in information technology. When combined with servers and data centres, Tier has two different contexts. It refers to both the connectivity or operator of the infrastructure based on its position within the global network, as well as the quality levels in a data centre, which can be partially secured through certifications.

Certifications play a subordinate role in this model - the individual tiers do not depend on them because they guarantee their availability and the permanent provision of capacities for data centres, providers, and other major customers on a contractual basis. This scale also does not reflect any direct quality levels - typically, the (theoretically) available bandwidth significantly exceeds the needs of the subordinate level and surpasses their hardware capacities in a data centre. The model rather defines the concept of transcontinental and national companies that have a nationwide network in a country. Examples of Tier 1 include Deutsche Telekom in Germany, NTT in Japan, AT&T, Verizon, and Level 3 Communications in the USA, or Orange in France. Tier 2 includes subordinate, nationally operating providers such as Vodafone or Swisscom and large data centres directly connected to Tier 1. Tier 3 encompasses regional providers with no or limited proprietary fibre network, distributing resources and lines as resellers or connecting individual regional data centres.

What are tiers as quality levels in data centres?

Within a data centre, tiers serve as one of the possible designations for quality levels reflecting the availability guaranteed by the operator through certifications. The scale uses a calendar year as a reference frame, in which a system such as a virtual or dedicated server may be down for a maximum period of time. This timeframe covers all potential reasons and explicitly excludes events such as maintenance, software administration, hardware damage, and often cases of "force majeure" - such as natural disasters or power interruptions. Four different levels of availability for a data centre are distinguished:

• Tier 1 guarantees a minimum availability of 99.671 percent or a maximum downtime of 28.8 hours per year
• Tier 2 guarantees a minimum availability of 99.749 percent or a maximum downtime of 22.7 hours per year
• Tier 3 guarantees a minimum availability of 99.982 percent or a maximum downtime of 1.6 hours per year
• Tier 4 guarantees a minimum availability of 99.995 percent or a maximum downtime of 26.3 minutes per year

Data center certifications are carried out by both the operators themselves and independent institutes, which, for example, verify compliance with important standards such as the DIN EN 50600, which came into effect in 2019. In addition, some providers and portals on the internet conduct their own certifications by regularly checking and statistically evaluating the accessibility of data centers using automated scripts. Official certifications based on international standards by independent companies and organizations are only carried out at a data center upon the explicit request of the operator and are not legally required, but are done solely on a voluntary basis. These certifications also include general standards for commercial enterprises such as ISO 9001, which describes quality management, or ISO 14000 ff, which provides guidelines for environmental management, CO2 emissions, and the use of renewable energies.

What alternative systems for quality levels in data centres exist?

One disadvantage of the Tier model is that its certifications primarily consider availability or uptime and contain few other criteria. For this reason, other classifications have now been established that determine the quality levels for a data centre in a more complex context. For example, the Federal Office for Information Security (BSI) has its own analysis model and awards certifications to verified data centres. It includes six different quality levels that also reflect availability:

• VK 0 represents availability up to 95 percent or a maximum of two to three weeks of downtime per year
• VK 1 represents availability between 95 percent and 99 percent or a maximum of 90 hours of downtime per year
• VK 2 represents availability between 99 percent and 99.9 percent or a maximum of 9 hours of downtime per year
• VK 3 represents availability between 99.9 percent and 99.99 percent or a maximum of 60 minutes of downtime per year
• VK 4 represents availability between 99.99 percent and 99.999 percent or a maximum of 5 minutes of downtime per year
• VK 5 represents 100 percent availability and allows no downtime 24/7/365 over a year

Another popular classification for quality levels in data centres is the Trusted Site Infrastructure (TSI) developed by TÜV, which was first released in 2001 and has since gained significant importance. It is now one of the most common independent certifications for data centres and has been complemented with TSI.EN50600 to also issue certifications for the new Euro standard. It also considers the physical security of data centres based on distances from hazardous operations such as petrochemical facilities, flood-prone areas, airports, and other risk factors. Certifications by TSI have four different levels for data centres:

• Level 1 "medium availability" with basic protection for operating data centres
• Level 2 "advanced availability" with redundant structures for power supply, network connectivity, and climate control
• Level 3 "high availability" with 24/7/365 permanent operational control, secured and redundant supply, and fire control
• Level 4 "very high availability" for dedicated data centres with comprehensive pre-emptive security and maintenance tolerances

The demands on a data centre have changed significantly in recent years and now require standards that in the past were only found in critical facilities such as police, fire departments, military, or energy supply. This has led to the establishment of independent certifications for data centres like TSI and DIN EN 50600, even though there is no legal obligation to do so.

Photo: Gerd Altmann on Pixabay