Created by Uptime Institute, Data Center Tier Classification distinguishes 4 levels/tiers of data centers based on the ability of the centers’ infrastructure to provide a certain level of website performance throughout the year. The more redundant components and distribution paths a data center has, the higher the website availability that can be sustained.

The most reliable data center is a Tier 4 certified one; the least – beingTier 1. In the table below, you can see the specifications of a data center that meets the Tier 1,2 3 or 4 standard.

Tier 1 Tier 2 Tier 3 Tier 4
Number of power & cooling distribution paths 1 1 1 Active +1 Alternative 2 Active
Redundant components No Only for power and cooling Only for power and cooling For each component that supports IT operations
The Operational Impact Planned* and unplanned* activities will influence website availability Planned and unplanned activities will influence website availability Planned activities will not influence website availability, but unplanned will influence Planned and unplanned activities will not influence website availability
Yearly Downtime (hours) 28.8 22.0 1.6 0.8
Expected Site Availability (%) 99.67 99.75 99.98 99.99

*Planned: repair, replacement, addition of infrastructure components, etc.

*Unplanned: outage, operational errors, etc.

Not every business needs a Tier 4 data center. If your website has medium to high traffic and requires 24/7 availability, Tier 3 and 4 data centers would be more than sufficient. However, some small companies can find it reasonable to save some money on data center reliability if website downtime doesn’t cause significant loss of money and customer loyalty.