C7 TIER CLASSIFICATIONS
Tier classifications provide a basis for comparing or describing the functionality, capacity, and cost of a data center’s overall architecture. Tier classifications focus on the availability of the entire facility including power, connectivity and cooling components.
Tier classifications also describe the degree to which the facility is resilient to failures of mechanical, electrical and plumbing (MEP) systems. Resilience to failures is provided by redundancy and architecture of the overall facility design. A Tier-1 facility is the least resilient and a Tier-4 is the most resilient. C7′s data center facilities are Tier-3. Below is a description of the difference between each rating.
Tier-1 – Basic Data Center
Tier-1 facilities have no redundant capacity components. This type of facility provides basic power and cooling with no excess capacity for backup or failover. There is no redundancy in the MEP distribution paths.
In a Tier-1 facility, unplanned outage or failure of a capacity component or distribution element will impact systems and customers. Maintenance needed for the MEP infrastructure to replace components or do utility work impacts the facility just as if there were an unplanned outage.
Tier-1 sites typically experience two separate 12-hour site-wide shutdowns per year for repair work. Additionally, Tier-1 sites typically experience 1.2 equipment or distribution component failures on average each year. This equates to 28.8 hours of downtime per year, or 99.67% availability.
Tier-2 – Redundant Data Center
A Tier-2 data center has redundant capacity components, but only a single non-redundant distribution path serving the data processing equipment. The benefit of this level is that any redundant capacity component can be removed from service on a planned basis without causing the data processing to be shut down.
Tier-2 sites average one unplanned outage per year, and schedule three maintenance activities over a two-year period. The annual impact to operations is 22 hours of downtime per year, or 99.75% availability.
Tier-3 – Redundant Data Center with Concurrent Maintenance
A Tier-3 data center has redundant capacity components and multiple independent distribution paths serving the data processing footprint. There is sufficient MEP capacity to meet the needs of the data processing systems even when one of these redundant MEP components has been removed from the infrastructure. Tier-3 data center can support maintenance activities and some unplanned events without interruption to the computing systems.
Because of concurrent maintenance capability provided by Tier-3 facilities, no annual shutdowns for routine maintenance are required. Tier-3 data centers have unplanned events totaling only 1.6 hours per year. Tier-3 sites deliver 99.98% availability.
Tier-4 – Fault-Tolerant Data Center
Tier-4 sites have multiple, independent, and physically separate systems that each have redundant capacity components and multiple, independent, diverse and active distribution paths supporting all data processing. In a Tier-4 data center, any single failure of an MEP component or distribution path has no negative impact to the data processing systems.
Facility-related failures that impact the data processing equipment are statistically reduced to 0.8 hours per year at Tier-4 sites which yields 99.99% availability.
A Note About Tier Classifications
If any single system in a Tier-n data center does not meet the Tier-n requirements, then the facility, as a whole, is not Tier-n. With this in mind, fractional tier ratings such as 2+ or 3.5 have no meaning in a tiered classification context and should not exist.