DATA CENTER TIERS | 1, 2, 3 & 4 Explained with Downloads

Introduced by the Uptime Institute, Data Center Tiers classify the reliability of IT infrastructure based on uptime and availability. These tiers range from Tier 1 (Basic Capacity) to Tier 4 (Fault Tolerant) and play a pivotal role in safeguarding continuous operations for businesses and organizations. The Uptime tiers cover:

Tier I: Basic Capacity

• Offers fundamental capacity with no redundancy.
• Prone to potential downtime risks due to single points of failure.
• Suitable for small businesses or non-critical applications.

Tier II: Redundant Site Infrastructure

• Provides redundant components, minimizing the risk of downtime, however
• However, scheduled maintenance activities might still cause disruptions.

Tier III: Concurrently Maintainable

• Designed to allow maintenance and upgrades without disrupting ongoing operations.
• Equipped with redundant components and multiple distribution paths.
• Ideal for businesses seeking increased uptime for critical applications.

Tier IV: Fault-Tolerant Infrastructure

• Offers unparalleled fault tolerance.
• Features fully redundant systems, ensuring uninterrupted operation even in the face of a single point of failure.
• Best suited for mission-critical operations and organizations demanding near-zero downtime.

Selecting the appropriate tier ensures seamless functioning and protects against potential disruptions. With this classification system, we can confidently make informed decisions to support our organization’s specific needs.

🔗 There is a Tier V Standard, but not Classified by Uptime, for more information on that and who developed it, see our article | TIER V Platinum Data Center | What is it?

🔗 Please note this article is not about Data Center Levels, for that please refer to 'DATA CENTER | 0, 1, 2, 3, 4, 5, 6 Levels of Commissioning'

🟩 Who Would Use the Tier System?

The Tier system finds its relevance among many individuals and organizations; each can use its benefits, including:

• Owners of Data Centers looking to build new facilities,
• Owners of Data Centers looking at expanding an existing facility,
• Data Center Operators looking for an evaluation of an existing facility,
• Data Center Customers, such as companies utilizing a third-party data center/co-location space, must complete due diligence surveys, etc.

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💾 Click the button below to download a free copy of the high-level table and graphics seen throughout this article.

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🟩 What is ‘Uptime’?

‘Uptime’ basically means ‘Availability’ and is the most critical aspect of data center operations, as it refers to the facility’s reliability and ability to maintain the quantity of time a data center is available and online, being able to provide services to its customers without downtime or disruption.

A high level of ‘Uptime’ or ‘Availability’ is essential to ensure that our mobile phones, computers, and connected devices are served via the cloud and networks with the internet, software programs, email, work files, financial transactions, e-commerce, location, texts, and calls etc.

🔗 To read more on obtaining Uptime Tier Ratings, see our article: UPTIME TIER RATINGS | The Simple Steps to Obtain them

🟩 What is the Data Center Tier Classification System?

There are two types of Data Center Tier Classification Systems, design and operational, with the objectives of both being to create a uniform and standardized approach for assessing and categorizing data center establishments and their infrastructure performance and uptime/availability.

‘ Infrastructure’ means equipment, systems, or services critical to the operation of the data spaces.

For example, mechanical, electrical, water, emergency power, and security systems.

🚀 This article will concentrate on the ‘Design’ Element

🟧 Understanding the Design/Topology

Under the design classification, a facility’s potential infrastructure performance or uptime is evaluated based upon four levels of performance, referred to as Tier 1 – Basic Capacity | Tier 2 – Redundant Capacity | Tier 3 – Concurrently Maintainable | and Tier 4 – Fault Tolerant, with each higher tier incorporating all of the features of the previous one.

🚀 In the Tier rating system for data centers, it’s essential to understand that the primary power source is not the utility power but the generator system. The utility power is considered as an economical backup option, and any disruptions from it are not considered a failure.

🟨 Equipment, Components, and Systems Covered

The are many types of equipment and components that the Tiers relate to and should be considered when designing or commissioning a data center, some common ones being:

◻️ Mechanical Equipment

◻️ BMS/Control Equipment

◻️ Electrical Equipment

◻️ Plumbing and Drainage Equipment

◻️ IT Equipment and Services

◻️ Security Equipment and Systems

🔗 Below we will talk about 'redundancy' - we have written an article covering this in more depth see | Data Center Redundancy | N, N+1, N+2, 2N & 2N+1 Explained 

🟩 Tier 1, 2, 3 & 4 Requirements Summarized

This table provides a high-level overview of the Tier requirements for each certification that are described in more detail below:

🟩 Tier 1 – Basic Capacity

Tier 1 is the lowest tier rating, offering the most fundamental capacity level with no cooling or electrical equipment redundancy.

Key points about a Tier 1 data center:

• Provides basic capacity without redundancy.
• No built-in redundancy for system components.
• Expected uptime of 99.671% annually [with a potential offline time of up to 29 hours].
• Suitable for small business owners who prefer independent IT systems without relying on general building infrastructure.
• Offers limited resilience.

In summary, a Tier 1 data center is a simple and cost-effective option for businesses that require basic IT capacity but can tolerate minor downtime.

🟧 General Requirements

Although it is the lowest in tier ratings, there are still some expectations that need to be met to be awarded the certificate:

• Sufficient capacity – there is sufficient capacity within the system to meet the system’s requirements.
• An uninterruptible power supply (UPS) for power sags – outages, and spikes, maintaining the overall service of the data center and servers.
• A dedicated area for IT systems – so no installing the servers in the corner of an office,
• Dedicated cooling equipment – that can run outside of office hours so it is not affected by time clocks and office user interference,
• Make-up Water – where evaporative cooling is used, the makeup water should have an onsite storage facility of 12 hours for backup.
• An engine generator – for power outages, with a minimum of 12 hours of fuel backup. Uptime also notes that a ‘fuel cell’ can be used.

🚀 The Engine Generator at [N] demand for this Tier CAN restrict the consecutive hours of run time based on the manufacturer’s requirements.

🟧 Tier 1 Data Center Graphic

Below is a typical graphic of a Tier 1 Power and Cooling Infrastructure; these can differ from project to project depending on the design and installation, so only provided as an example.

🟧 Benefits of Designing and Installing a Tier 1 System

The Tier 1 data center has some great benefits for a client, compared to a facility not designed in line with a standard and using general office infrastructure.

Below is a list of eight that we can think of:

🟧 Considerations When Designing and Installing a Tier 1 System

If comparing against having the data center infrastructure running from a local/ordinary office-type power and cooling system, there are not many considerations, as the upgrade is positive.

The only items that would need to be considered are:

🟩 Tier 2 – Redundant Site Infrastructure Capacity

Tier 2 data centers build upon the Tier 1 design, offering additional redundant critical power and cooling capacity to ensure higher safety margins and increased uptime/availability.

Key points about Tier 2 data centers:

• Enhanced Capacity: Tier 2 data centers provide greater capacity than Tier 1 design.
• Redundancy in Critical Components: Critical power and cooling components are redundant, bolstering reliability.
• Non-Redundant Distribution Paths: While components have redundancy, distribution paths do not.
• Expected Uptime: Tier 2 data centers aim for 99.741% uptime in a year, with a possible offline duration of up to 22 hours.
• Ideal for Small to Medium Businesses: Owners seeking enhanced protection for their IT systems, especially critical equipment, find Tier 2 suitable.

In summary, Tier 2 data centers offer improved redundancy and uptime compared to Tier 1, making them a valuable choice for businesses seeking increased reliability without reaching the highest levels of data center design complexity.

🟧 General Requirements

A Tier 2 Classified Data Center should include the following within its design, installation, and maintenance, as a minimum:

• Components can be removed from service – When required via planned maintenance or operational issues, components can be removed from its service without impact on the critical environment it serves. Achieved by introducing redundancy into parts of the design.
• Single non-redundant distribution path – removing a distribution path from service for maintenance or operationally will generally require shutting down the critical environment it serves.
• Uninterruptible power supply (UPS) – power sags, outages, and spikes, maintaining the overall service of the data center and servers and allowing some maintenance with no impact to the data center operations,
• Redundant UPS capacity [N+1] – allowing for some operational failures and maintenance with no impact on the data center operations,
• A dedicated area for IT systems – so no installing the servers in the corner of an office,
• Dedicated cooling equipment – that can run outside of office hours, so it is not affected by time clocks and office user interference,
• Redundant chiller capacity [N+1] – allowing for some operational failures and maintenance with no impact on the data center operations,
• Redundant heat rejection capacity [N+1] – allowing for some operational failures and maintenance with no impact on the data center operations,
• Redundant pump capacity [N+1] – allowing for some operational failures and maintenance with no impact on the data center operations,
• Redundant cooling unit capacity [N+1] – allowing for some operational failures and maintenance with no impact on the data center operations,
• Redundant chiller control capacity [N+1] – allowing for some operational failures and maintenance with no impact on the data center operations,
• Make-up Water – where evaporative cooling is used, the makeup water should have an onsite storage facility of 12 hours for backup.
• An engine generator – for power outages, with a minimum of 12 hours of fuel backup during regular operation. Uptime also notes that ‘fuel cells’ can be used.
• Redundant engine generator capacity [N+1] – allowing for some operational failures and maintenance with no impact on the data center operations,
• Redundant generator fuel system capacity [N+1] – allowing for some operational failures and maintenance with no impact on the data center operations,

🚀 The Engine Generator at [N] demand for this Tier CAN restrict the consecutive hours of run time based on the manufacturer’s requirements.

🟧 Tier 2 Data Center Graphic

Below is a typical graphic of a Tier 2 Power and Cooling Infrastructure; these can differ from project to project depending on the design and installation, so only provided as an example.

🟧 Benefits of Designing and Installing a Tier 2 System

Combined with the Tier 1 infrastructure, a Tier 2 data center will provide some additional benefits:

🟧 Considerations When Designing and Installing a Tier 2 System

When conducting a comparison between Tier 1 and Tier 2 designs, it is important to consider various factors.

🟩 Tier 3 – Concurrently Maintainable

Tier 3 data centers represent an improvement over Tier 2 design, offering additional redundancy in critical power, cooling capacity/components, and independent distribution paths [backbones] that ensure continuous service even when one path is unavailable.

This redundancy allows maintenance or removal of any component serving critical areas without impacting ongoing operations.

Key Features of Tier 3 Data Center Design:

• Enhanced Capacity: Tier 3 design increases capacity compared to Tier 2 data centers.
• Comprehensive Redundancy: Redundancy is integrated into all aspects, including critical power, cooling components, and distribution paths.
• High Uptime Expectation: Tier 3 data centers aim for 99.982% uptime throughout the year, allowing for a possible offline duration of up to 1.6 hours.
• Ideal for Medium to Large Businesses: It suits medium to large business owners seeking protection from IT system disruptions, especially during maintenance or switching of distribution paths.

In summary, Tier 3 data center design is an advanced and reliable option that ensures businesses experience minimal downtime and offers excellent protection for critical IT operations.

🚀 An ELECTRICAL POWER Backbone/Distribution Path is considered as the path from the on-site power generation system [generator/fuel cell], to the input of the critical UPS equipment serving the IT equipment or mechanical equipment.

🚀 A MECHANICAL Backbone/Distribution Path is considered as the pipework and infrastructure for transporting the chilled water from the critical areas via CRAH/CRAC or Fan Walls etc, to the atmosphere via Pumps, Air Cooled or Water Cooled Chillers, and Cooling Towers [Chilled Water System and Condenser Water System].

🟧 General Requirements

A Tier 3 Classified Data Center should include the following within its design, installation, and maintenance, as a minimum:

• Components can be removed from service – Every component that provides the capacity to the IT critical areas can be removed from service with zero impact on the environment it serves,
• Concurrently maintainable – Every component that provides the capacity to the IT critical areas can be removed from service with zero impact on the environment it serves,
• Sufficient capacity – sufficient capacity is available for critical environments when any component is removed from service,
• Redundant distribution paths – removing a distribution path from service for maintenance or operationally will not require shutting down the critical environment it serves; this includes valving arrangements,
• Critical IT equipment dual-powered – IT equipment must be dual-powered to ensure zero interruption during power failures. Can use transfer switches [STS/ATS],
• Uninterruptible power supply (UPS) – power sags, outages, and spikes, maintaining the overall service of the data center and servers and allowing some maintenance with no impact to the data center operations,
• Redundant UPS capacity [N+1] – allowing for some operational failures and maintenance with no impact on the data center operations,
• A dedicated area for IT systems – so no installing the servers in the corner of an office,
• Dedicated cooling equipment – that can run outside of office hours, so it is not affected by time clocks and office user interference,
• Redundant chiller capacity [N+1] – allowing for some operational failures and maintenance with no impact on the data center operations,
• Redundant heat rejection capacity [N+1] – allowing for some operational failures and maintenance with no impact on the data center operations,
• Redundant pump capacity [N+1] – allowing for some operational failures and maintenance with no impact on the data center operations,
• Redundant cooling unit capacity [N+1] – allowing for some operational failures and maintenance with no impact on the data center operations,
• Redundant chiller control capacity [N+1] – allowing for some operational failures and maintenance with no impact on the data center operations,
• Make-up water – where evaporative cooling is being used, the makeup water should have an onsite storage facility of 12 hours for backup,
• Make-up water – systems to be concurrently maintainable,
• An engine generator – for power outages, with a minimum of 12 hours of fuel backup during regular operation. Uptime also notes that ‘fuel cells’ can be used,
• Engine generator – to be rated for continuous usage,
• Redundant engine generator capacity [N+1] – allowing for some operational failures and maintenance with no impact on the data center operations,
• Engine generator concurrently maintainable – meets the requirements throughout and proven via testing,
• Redundant generator fuel system capacity [N+1] – allowing for some operational failures and maintenance with no impact on the data center operations,

🚀 The Engine Generator at [N] demand for this Tier is NOT ALLOWED to have restricted consecutive run hours and restrict the consecutive hours of run time based on the manufacturer’s requirements.

🟧 Tier 3 Data Center Graphic

Below is a typical graphic of a Tier 3 Power and Cooling Infrastructure; these can differ from project to project depending on the design and installation, so only provided as an example.

🟧 Benefits of Designing and Installing a Tier 3 System

Combined with the Tier 1 and 2 infrastructure, a Tier 3 data center will provide some additional benefits similar to those shown for Tier 2:

🟧 Considerations When Designing and Installing a Tier 3 System

When conducting a review of a Tier 3 design versus a Tier 2, there are several points that should be considered.

🟩 Tier 4 – Fault Tolerant Infrastructure

A Tier 4 data center is designed to provide the highest level of reliability and uptime for critical IT infrastructure. Building upon the Tier 3 design, Tier 4 incorporates fault tolerance throughout the entire system.

Key Features of a Tier 4 Data Center:

• Fault Tolerance Everywhere: Every system, distribution path, and component serving the IT spaces are equipped with redundancy, ensuring operations remain unaffected even if a component or path fails or undergoes maintenance.
• Enhanced Capacity: Compared to Tier 3, Tier 4 data centers offer increased capacity and can handle more complex and demanding business requirements.
• Exceptional Uptime: Tier 4 data centers aim for an expected uptime of 99.995% for the year, allowing only up to 26.3 minutes of possible offline time.
• Ideal for Complex Businesses: A Tier 4 data center is the top choice for large and complex businesses seeking the most stringent protection against disruptions in their IT systems. Its unmatched fault tolerance and redundancy ensures unparalleled peace of mind for critical operations.

🚀 An ELECTRICAL POWER Backbone/Distribution Path is considered as the path from the on-site power generation system [generator/fuel cell], to the input of the critical UPS equipment serving the IT equipment or mechanical equipment.

🚀 A MECHANICAL Backbone/Distribution Path is considered as the pipework and infrastructure for transporting the chilled water from the critical areas via CRAH/CRAC or Fan Walls etc to the atmosphere via Pumps, Air Cooled or Water Cooled Chillers, and Cooling Towers [Chilled Water System and Condenser Water System].

🟧 General Requirements

A Tier 4 Classified Data Center should include the following within its design, installation, and maintenance, as a minimum:

• Any Fault – any potential fault must be detected, isolated, and contained while maintaining ‘N’ capacity to the critical loads,
• Single failures – No failure of a component, distribution path, or system will impact the facility’s operation. This includes valving arrangements etc.
• Infrastructure ‘controls’ operation – upon failure, will provide an autonomous reaction to any failure, with no impact on the critical systems,
• Compartmentalized – Complementary systems and distribution paths should be physically isolated. For example, this means separate chilled water systems serving dual coil CRAHs.
• Components can be removed from service – Every component that provides the capacity to the IT critical areas can be removed from service with zero impact on the environment it serves,
• Concurrently maintainable – Every component that provides the capacity to the IT critical areas can be removed from service with zero impact on the environment it serves,
• Sufficient capacity – sufficient capacity is available for critical environments when any component is removed from service,
• Redundant distribution paths – removing a distribution path from service for maintenance or operationally will not require shutting down the critical environment it serves,
• Critical IT equipment is dual-powered – IT equipment is to be dual-powered to ensure zero interruption during power failures. Can use transfer switches [STS/ATS],
• Uninterruptible power supply (UPS) – power sags, outages, and spikes, maintaining the overall service of the data center and servers and allowing some maintenance with no impact to the data center operations,
• Redundant UPS capacity [N+1] – allowing for some operational failures and maintenance with no impact to the data center operations,
• A dedicated area for IT systems – so no installing the servers in the corner of an office,
• Dedicated cooling equipment – that has the ability to run outside of office hours, so is not affected by time clocks and office user interference,
• Redundant chiller capacity [N+1] – allowing for some operational failures and maintenance with no impact on the data center operations,
• Redundant heat rejection capacity [N+1] – allowing for some operational failures and maintenance with no impact on the data center operations,
• Redundant pump capacity [N+1] – allowing for some operational failures and maintenance with no impact on the data center operations,
• Redundant cooling unit capacity [N+1] – allowing for some operational failures and maintenance with no impact on the data center operations,
• Redundant chiller control capacity [N+1] – allowing for some operational failures and maintenance with no impact on the data center operations,
• Make-up water – where evaporative cooling is being used, the makeup water should have an onsite storage facility of 12 hours for backup,
• Make-up water – systems to be concurrently maintainable,
• An engine generator – for power outages, with a minimum of 12 hours of fuel backup during regular operation. Uptime also notes that a ‘fuel cells’ can be used,
• Engine generator – to be rated for continuous usage,
• Redundant engine generator capacity [N+1] – allowing for some operational failures and maintenance with no impact on the data center operations,
• Engine generator concurrently maintainable – meets the requirements throughout and proven via testing,
• Redundant generator fuel system capacity [N+1] – allowing for some operational failures and maintenance with no impact on the data center operations,

🚀 The Engine Generator at [N] demand for this Tier is NOT ALLOWED to have restricted consecutive run hours and restrict the consecutive hours of run time based on the manufacturer’s requirements.

🟧 Tier 4 Data Center Graphic

🟨 Power System

The below shows a typical graphic of a Tier 4 Power Infrastructure, these can differ from project to project dependent on the design and installation, so only provided as an example.

🟨 Cooling System

The below shows a typical graphic of a Tier 4 Cooling Infrastructure, these can differ from project to project dependent on the design and installation, so only provided as an example.

🟧 Benefits of Designing and Installing a Tier 4 System

Combined with the Tier 1, 2 and 3 infrastructure, a Tier 4 data center will provide some benefits similar to those shown for the Tier 3:

🟧 Considerations When Designing and Installing a Tier 4 System

If a review is being conducted between a Tier 3 design Vs. a Tier 4, there are a few considerations need to be considered and planned for:

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🟩 Who is the ‘Uptime Institute’?

Founded in the mid-1990s by Ken Brill and grown into a respected authority in the industry, the ‘Uptime Institute’ is a leading global provider of data center common standards and best practices [Data Center Tier 1-4 Classification System] to help designers and operators create and optimize their facilities, focusing on performance, efficiency, and availability.

Today, the Uptime Institute has a global presence with offices in North America, Europe, and Asia. The organization is headquartered in New York, USA, and is a subsidiary of The 451 Group, a technology industry analyst firm.

🟩 What Services do they Provide?

Uptime provides four main types of services for the Data Center Industry:

• Infrastructure Services,
• Management and Operation Services,
• Strategic Management Services,
• Sustainability Services.

🟧 Infrastructure Services

The ‘Uptime Institute’ provides comprehensive assessments to clients focusing on the physical infrastructure [mechanical, electrical, water, security, emergency power, etc] within their data center, certifying them to their ‘Tier’ system from the Design Stage to Operations.

The services include third-party Tier Certification for clients building new facilities from design to operations.

🟧 Management and Operation Services

By completing a comprehensive evaluation of a client’s current staffing, maintenance, operational practices, and management protocols; validating existing practices, and issuing recommendations for improvement, the ‘Uptime Institute’ can provide its stamp of approval based on its Management and Operations (M&O) Program to demonstrate a client’s operational excellence for their internal requirements or external stakeholders.

🟧 Strategic Management Services [SCIRA-FSI]

Financial sector organizations use the SCIRA-FSI assessment service to assess the operational resilience of their critical infrastructure.

This service helps organizations meet the growing regulatory requirements and manage the complexity of hybrid IT infrastructures, providing a standardized approach, based on input from over 20 premier financial institutions worldwide, to assess and mitigate outages.

By using this service, financial organizations will better understand their operational resilience and take steps to address any potential risks, which aids in the reduction of risk for downtime, increasing operational efficiency, and providing third-party validation of their operations to internal and external stakeholders.

🟧 Sustainability Services

With growing concern over the environmental sustainability of data center operations, regulators, customers, partners, and investors are looking for ways to show that the digital infrastructure they rely on is being designed and operated sustainably.

The Sustainability Service has been created to provide support and guidance by ‘Uptime Institute’ that organizations may require to become more environmentally aware and reduce the impact of their IT infrastructure and operations on the environment, reducing greenhouse gases, power, water usage and recycling of equipment.

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⬜ Definition of Terms

Below is a high-level list of terms that are included within this article for reference in case you are unsure what they mean:

Tier – A level of performance that a data center is categorized into based on its infrastructure’s design and operational characteristics.

Uptime – The availability of a data center’s systems and the time it is operational and available for use, also known as ‘availability’.

Data Center – A facility that houses critical IT systems and equipment, including servers, storage, and networking equipment.

Basic Capacity – Refers to the lowest level of performance in the tier classification system, including the minimum design and operational requirements for power and cooling systems.

Redundant Capacity – Refers to the duplication of critical components within a data center infrastructure to ensure continued operation in the event of a failure or outage of components.

Concurrently Maintainable – The ability to maintain and upgrade system components and equipment without impacting the overall operation of the data center.

Fault Tolerant – The ability of a system to continue functioning, even if one or more components fail.

Infrastructure – The physical components of a data center, including power, cooling, servers, storage, and networking equipment.

Operations – The day-to-day management and maintenance of a data center, including monitoring, maintenance, and upgrades to the infrastructure.

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