What is the Difference Between Data Center Tiers and Classifications?

"Data center tier classifications are designated as Tiers 1 through 4 for the main purpose of defining the uptime of the data center. Each tier also measures the data center’s performance, investment, and return on investment.

A Tier 1 data center typically is well-suited for a small business, where as a Tier 2 data center is most likely the best fit for a medium-sized business. A Tier 3 data center is an excellent choice for a larger company. Since a Tier 4 data center is the strongest and most robust of all tiers with the least probability of failure, it is therefore the best choice for a multi-million dollar business. Additionally, Tiers 3 and 4 are capable of sustaining power outages of 72-hours (for Tier 3) and 96-hours (for Tier 4), where as Tiers 1 and 2 are not.

Data Center Availability is also defined within each of the four tiers and is greater with each tier:

Tier 1: Guaranteeing 99.671% availability.
Tier 2: Guaranteeing 99.741% availability.
Tier 3: Guaranteeing 99.982% availability.
Tier 4: Guaranteeing 99.995% availability.
Annual Downtime for each data center tier are as follows:

Tier 1: Annual downtime due to site is 28.8 hours
Tier 2: Annual downtime due to site is 22.0 hours
Tier 3: Annual downtime due to site is 1.6 hours
Tier 4: Annual downtime due to site is 0.04 hours

Overall, a higher data center tier offers greater availability and less annual downtime."