Data Center Categories
TIER 1 to TIER 4: "The Uptime Institute created the data center Tier classification levels over 25 years ago, and today, they remain the international standard for data center performance".
Tier 1 - "Basic Capacity" / Least expensive
Uptime: 99.671% (28.8 hours of downtime annually).
Single path for power (via UPS) and cooling with limited redundancy and backup components.
Physical security arrangements should be put into practice. The data center should be well-maintained and free of excessive humidity or temperature extremes.
The data center must be completely shutdown to perform maintenance.
Tier 2 - "Redundant Capacity" / Cost-conscious
Uptime: 99.741% (22.7 hours of downtime annually).
Single path for power (via UPS) and cooling with limited redundancy and backup components.
Raised floor.
Engine generators. Energy storage. Chillers. Cooling units. UPS modules. Pumps. Heat rejection equipment. Fuel tanks. Fuel cells. The distribution path of Tier II serves a critical environment, and the components can be removed without shutting it down. Like a Tier I facility, unexpected shutdown of a Tier II data center will affect the system.
Tier 3 - "Concurrently Maintainable"
Uptime: 99.982% (95 minutes of downtime annually).
N+1 Redundancy: Multiple paths for power and cooling and systems in place to update and maintain it without taking it offline. Tier 3 data centers can also stay operational during most repairs and maintenance projects; in other words, they are mostly "fault-tolerant."
N+1 fault tolerance, with 72 hours of outage protection (in other words, Tier 3 facilities provide the amount of redundancy required for operation, expressed as n, plus one backup)
A Tier 3 data center is concurrently maintainable with redundant components as a key differentiator, with redundant distribution paths to serve the critical environment. Unlike Tier I and Tier II, these facilities require no shutdowns when equipment needs maintenance or replacement. The components of Tier III are added to Tier II components so that any part can be shut down without impacting IT operation.
Tier 4 - "Fault Tolerant"
Uptime: 99.995% (26 minutes of downtime annually).
A Tier 4 data center is built to be completely fault tolerant and has redundancy for every component. Tier 4 data centers offer unsurpassed uptime guarantees and exceptional redundancy in cooling, power, and infrastructure. Require continuous cooling to make the environment stable.
2N+1 redundancy (e.g., two times the amount of power/infrastructure needed for operation, plus one backup) with 96 hours of outage protection.
For enterprises that must host mission-critical servers, a tier 4 service is the most appropriate solution.
A Tier 4 data center has several independent and physically isolated systems that act as redundant capacity components and distribution paths. The separation is necessary to prevent an event from compromising both systems. The environment will not be affected by a disruption from planned and unplanned events. However, if the redundant components or distribution paths are shut down for maintenance, the environment may experience a higher risk of disruption if a failure occurs.
NOTE: All of the IT equipment must have a fault-tolerant power design to be compatible.