What Is a Tier Standard? What Are Its Scope and Requirements?
The importance of information in today’s world is indisputable. As the volume of information grows, sharing it quickly, storing it securely, and ensuring its reliability become increasingly important. Delivering all of this without interruption requires the infrastructure in data centers to be maintained at defined levels.
The electrical, mechanical, and security systems in a data center vary according to the criticality of the data it processes and stores. In general, data centers are equipped with backup power supplies, redundant data communication links, climate control systems that cool the equipment inside the facility, fire suppression systems, and security systems that protect data from external threats in line with its security classification. A data center’s infrastructure reliability is confirmed at its target level once the standard it meets has been certified. Tier standards were created for this purpose: they determine a facility’s level on the basis of tests and inspections carried out by independent organizations.
What Is Tier?
Tier is a certification system developed by Uptime Institute to classify data centers, which have become essential in today’s world. There are four Tier levels: Tier I, II, III, and IV. Each level has its own characteristics and operating principles. Companies select the Tier level that suits their size and requirements to keep their data continuously available.
What Is the Tier Certification System?
Each Tier certificate reflects a specific operating model, level of energy consumption, expected failure rate, and approach to planned maintenance. Some Tier levels guarantee uninterrupted operation and data flow, while others are more susceptible to problems with power consumption or data flow. Tier certificates define the equipment and power paths a data center has. The four Tier standards and their requirements are as follows:
Tier I (Basic Capacity) Data Center Scope
Tier I certified data centers represent the lowest level of the Tier standards. They are used mainly by businesses that do not need large-scale data storage. Unlike other data centers, the equipment is housed in a room set aside for this purpose within an office environment. Because these facilities have limited operating capacity, they have no backup systems. Whenever data needs to be backed up or a change is made to the system, the hardware must be stopped in a planned manner and the system shut down. Once the system is down, the required changes, repairs, or upgrades are carried out, and the hardware is restarted in a planned manner. These data centers can experience 28.8 hours of downtime per year, which corresponds to an uptime rate of 99.676%. Tier I data centers are not prepared for outages lasting longer than 10 minutes.
Tier II (Redundant Capacity Components) Data Center Scope
Tier II certified data centers include redundant critical power and cooling components, which provide a greater safety margin against IT process interruptions caused by site infrastructure equipment failures. Redundant components include uninterruptible power supply (UPS) modules, chillers or pumps, and engine generators. While the components are designed with N+1 redundancy, the distribution paths are not expected to be redundant. Annual downtime for Tier II certified data centers is estimated at 22 hours, corresponding to an uptime rate of 99.741%. Thanks to their generators, these data centers can withstand 24-hour power outages.
Tier III (Concurrently Maintainable) Data Center Scope
Tier III certified data centers have concurrently maintainable infrastructure, with redundant components and redundant distribution paths serving the critical environment. The key differentiator is that the facility does not need to be shut down when equipment is maintained or replaced. Tier III adds redundant power and cooling distribution paths to the redundant critical components of Tier II, so that any component supporting the IT processing environment can be shut down and maintained without affecting IT operations. These data centers have an uptime rate of 99.982% and can withstand outages of up to 72 hours.
Tier IV (Fault Tolerant) Data Center Scope
Tier IV certified data centers have multiple independent, physically isolated systems that serve as redundant capacity components and distribution paths. Compartmentalization is required to prevent a single event from compromising both systems. The environment is not affected by disruptions caused by planned or unplanned events. However, if redundant components or distribution paths are taken offline for maintenance, the environment may face a higher risk of disruption should a failure occur.
Tier IV certified data centers add fault tolerance to the Tier III topology. If a piece of equipment fails or a distribution path is interrupted, IT operations are not affected. All IT equipment must have a fault-tolerant power design to be compatible with this topology. Tier IV data centers require continuous cooling to maintain a stable environment. These data centers experience only 0.8 hours of downtime per year, achieving an uptime rate of 99.999%.