What are the three tiers defined in the TIA-942 standard?

The three tiers defined in the TIA-942 standard are accurately captured in the first choice: Tier I (basic), Tier II (redundant), and Tier III (concurrently maintainable).

Tier I is characterized by a basic level of infrastructure that includes a single path for power and cooling, without any redundancy. This means that if any disruption occurs, the entire data center would go down, making it a less reliable option for data center operations.

Tier II introduces redundancy into the infrastructure by providing an additional capacity component that can serve as a backup. In this tier, there is still a single path but with the capacity for some redundancy in critical systems, allowing for a higher level of system reliability compared to Tier I.

Tier III is recognized for its capability to operate concurrently maintainable systems. This means that all critical components have redundancy, and any system can be taken offline for maintenance without impacting the overall functionality of the data center. This tier supports continuous operation, greatly improving reliability and uptime.

Understanding these tiers is essential for data center design as they provide a framework for assessing the availability and reliability levels necessary to meet various operational requirements.