General Design Considerations

The design and operation of Internet data centers the art of compromise. One way to simplify the choices is to group the requirements in to different levels.



Level I

Level II

Level III

Level IV

Level V


Grade C

Grade B

Grade A

Grade AA

Grade AAA


Single site data processing facility, limited off-site impact due to failure

Corporate data processing center, end-office telecommunications office, local impact due to failure

Toll-office telecommunication facility, Internet collocation center, regional impact due to failure

International financial or airline communication facility, national impact due to failure

Critical military communications center, One-of-a-kind control center, international impact due to failure

Size (substitute measurement for "importance")

Less than 2,500 square feet

2,500 to 80,000 square feet

80,000 to 150,000 square feet

more than 150,000 square feet

Specialized requirements

General design

Meets minimum local building code requirements. System is able to withstand the temporary loss of off-site commercial utility power.

Meets code enhanced requirements such as NEBS, Factory Mutual, UL, etc. System is able to withstand a failure of a single active component with minimal impact to critical loads.

Meets requirements for essential facilities. System is able to withstand a failure of a single active component. Planned maintenance without impacting any critical load. Maintenance may affect fault tolerance.

Systems are able withstand a single, worst-case infrastructure failure without impacting any critical load.  Planned maintenance activity without impacting any critical load or fault tolerance.

Design for maximum probable event. Systems are designed to supply services continually during any scheduled or unscheduled, natural or man-made disruption.

Program elements

The design shall eliminate or reduce the probability of events that can cause injury or death to personnel or damage to or loss of equipment or property. Systems of high complexity or peculiarity shall be identified and minimized.

Standardized design to minimize use of custom or unusual components. Individual system and subsystem test and checkout requirements shall be developed to ensure safe and normal operation of the system.

Reliability, availability and maintainability requirements shall be implemented during design to maximize the availability of the systems.

Consolidated systems test program covering all phases of testing to develop confidence in the systems and provide for interim and final acceptance of equipment and complete systems.

Human factors engineering will ensure that reliability, availability and safety are not degraded through human activities during operation or maintenance.  The design incorporates, within program constraints, the highest level of inherent safety.

Reliability, availability and survivability (design)






Estimate of real-world availability annualized over facility lifetime


-26 hours


-13 hours


-2.6 hours


-10.5 minutes


-5.25 minutes


Probable design threat considerations

Loss of commercial power

Component failure, accidental fire

Severe weather (blizzard, thunderstorm, high winds, flooding), intrusion, simple human error

Natural hazards (earthquake, hurricane, volcanic eruption, wildfires), individual attacker, civil unrest, nearby explosion

Regional disaster (industrial or nuclear accident), war, trained attackers, bombing, stand-off weapons

Life-cycle cost analysis

Initial cost is the primary factor

5 to 15 year occupancy

10-30 year occupancy

20-50 year occupancy

Permanent occupancy, 25 years or longer.


The author does not ensure anyone using the information against any liability arising from that use. Users of the information should make independent investigation of the validity of that information for their particular use. This reference is published with the undertanding its author is supplying information but is not attempting to render engineering or other professional services. If such services are required, the assistance of an appropriate professional should be sought.
Copyright © 2002 Sean Donelan