One of the most quoted portions of the standard is . . . → Read More: Collocation Facilities And The Myth Of The Tiered Data Center]]> A number of years ago the ANSI/TIA-942-2005 came out as “the” Telecommunications Infrastructure Standard for Data Centers.  Its purpose was to provide requirements and guidelines when designing a data center and to encourage planning for the data center earlier in the property development process.

One of the most quoted portions of the standard is the “Tiered Reliability”, which was intended as a means for determining specific data center needs required to lessen the time a data center was taken off-line.  The tier breakdown assists designers with a method to quantify certain aspects and to objectively compare one center to another.

Tier I – Basic Components

• single path for power and cooling with no redundant components (N)
• susceptible to disruptions from both planned maintenance activities and unplanned events
• may or may not have back up generator, UPS (uninterrupted power supply) or raised floor
• 99.671% availability – 28.8 hours (statistically) of annual downtime

Tier II – Redundant Maintainable

• single path for power and cooling with redundant components (N+1)
• less susceptible to planned and unplanned disruptions.  Planned infrastructure maintenance may require a processing shutdown
• includes generator, UPS, and raised floors
• 99.749% availability – 22.0 hours (statistically) of annual downtime

Tier III – Concurrently Tolerant

• multiple paths for power and cooling with only one active at any time (active/passive – N+1)
• planned infrastructure maintenance can be performed without disruption.  Unplanned events may cause disruptions
• includes raised floor, generator, UPS with each power and cooling path capable of carrying the full data center load
• 99.982% availability – 1.6 hours (statistically) of annual downtime

Tier IV – Fault Tolerant

• multiple active power and cooling distribution paths including redundant components (2(N+1) S+S) for example each path has UPS in an N+1 configuration
• can sustain planned maintenance activities and at least  one unplanned event without a critical impact on load
• includes raised floors, multiple generators, multiple UPS and other multiple distribution components
• 99.995% availability – 0.4 hours (statistically) of annual downtime

The standards went a long way to elevate the need for specific elements in the data center and the best practices for their usage.  Unfortunately, once the marketing spin took off, numerous collocation vendors began touting their facilities as a Tier III or Tier IV without regard for the full spectrum of component requirements or the processes supporting those components.  In addition the design standards cover other elements including:

• cable and fiber designs
• network distribution
• rack and cabinets layout
• space utilization and pathways
• air flow design

Many commercial collocation facilities claiming higher fault tolerance, achieve this mark by maintaining a lower power density requirement on their tenants driving up customer costs and reducing cabinet layout efficiencies. Even when the power plant supports high electrical draws, floor load ratings may limit the cabinet’s capacity.  Other times, best practices must be completely rethought, for example the best hot and cold aisle layout will fail to achieve design goals if the collocation facility locates the client in a cage space which does not support air flow management. Of course occasionally collocation customers themselves lower the reliability by failing to incorporate proper redundancy practices within their private suite or cage space.

Each business has unique up-time, cost, networking and processing density goals in mind when they establish a data center.  In order to reach those goals, a balance between requirements and design standards must be struck.  While the tiered data center may be an over used marketing myth, the ANSI/TIA-942-2005 provides a solid base template.  This template, along with skilled engineering and management practices can go a long way to facilitate a data center build out that delivers on technical design goals at an agreed upon business price point.