In this module, you’ll be introduced to data centre classifications based on the Uptime Institute Tiers. You’ll gain a clear understanding about the four Tiers and their significance in ensuring operational reliability and redundancy within data centre infrastructures.

Data centre classifications are defined by four Tiers established by the Uptime Institute. These tiers aren’t hierarchical but are tailored to different business needs, with each Tier encompassing the requirements of the lower ones. For instance, Tier IV includes all features of Tier III plus enhanced reliability and redundancy. Each Tier is given a level of redundancy which is represented as ‘N’. ‘N’ is the baseline capacity, meaning that a data centre would have everything it needs to operate as designed but with nothing in place to accommodate equipment failure or maintenance. Anything above N is additional security for the data centre. The Tier classification also considers operational sustainability, focusing on management practices and risk mitigation to support long-term business objectives.

Now, let’s look at each Tier.
Tier I: Tier I facilities provide power and cooling support for the full IT load but lack redundancy for critical systems, requiring complete shutdowns for maintenance or repairs. Key requirements include:
• An uninterruptible power supply (UPS) for power spikes and outages
• A designated space for IT systems
• An engine-generator
• Dedicated cooling equipment that runs outside office hours

With the highest allowable downtime, up to 28.8 hours per year, Tier I data centres have zero redundancy. This results in a 99.671% annual uptime – the lowest among Uptime Institute-graded facilities.

Tier II: Tier II data centres encompass all Tier I features and introduce additional backup options for heightened disruption protection. These data centres are equipped with:
• Extra engine generators
• Energy storage
• Chillers
• Raised floors
• UPS modules
• Pumps
• Heat rejection equipment
• Fuel tanks and cells
• Extra cooling units

Despite this, Tier II data centres still rely on a single distribution path for power and cooling, leaving them vulnerable to unexpected disruptions. Clients can expect up to 22 hours of downtime per year with 99.741% uptime. Redundancy in this tier is partial, and the system lacks fault tolerance.

Tier III: Most data centre companies ranked by the Uptime Institute hold a Tier III status. They offer concurrent maintainability with redundant power and cooling paths to avoid shutdowns during maintenance or replacements. They include N+1 redundancy which guarantees operations even with a component failure. Tier III facilities require a backup solution for at least 72 hours of operation post-outage, promising no more than 1.6 hours of downtime annually, equating to 99.982% uptime. They provide many Tier IV benefits but with slightly less comprehensive protection.

Tier IV: Tier IV data centres enhance Tier III designs with fault tolerance, featuring dual-powered equipment and multiple independent distribution paths. They require:
• Dual generators, UPS systems, and cooling systems for all components
• Independent distribution paths to avoid cascading failures
• Continuation of operations for at least 96 hours post-power outage without external power sources
• Physical isolation of redundant systems to prevent simultaneous compromise
These measures are critical for Tier IV’s advanced fault tolerance and uninterrupted operation.

Tier IV data centres use 2N or 2N+1 redundancy, meaning they have fully duplicated systems or double capacity with an extra backup, ensuring operations continue despite failures. They guarantee a maximum of 26.3 minutes of downtime per year, equating to 99.995% annual uptime. Although not promising 100% uptime due to potential maintenance-related issues, Tier IV facilities ensure customer operations remain unaffected due to multiple backup systems for critical services, a standard for maintaining their top-tier status.

Data centres require careful consideration of several essential factors for efficient operations, including:
• Speed and agility
• Uptime
• Circular economy
• Trust and reliability
• Security
• Tier rating
• Redundancy
• Power Usage Effectiveness (PUE) - PUE is the measure of a data centres’ energy efficiency. It is a ratio of the facilities total power consumption to the IT power consumption.
• Water Usage Effectiveness (WUE) - WUE is a sustainability metric developed by the Green Grid. It is a ratio of the water used in a data centre to the IT power consumption.

A dependable cooling system is crucial for data centres, emphasising the need for careful planning to ensure seamless operations without any issues.