Data availability

Data availability is a term used by computer storage manufacturers and storage service providers (SSPs) to describe products and services that ensure that data continues to be available at a required level of performance in situations ranging from normal through "disastrous."

Anytime a server loses power, for example, it has to reboot, recover data and repair corrupted data. The time it takes to recover, known as the mean time to recover (MTR), could be minutes, hours or days.

Data Center Standards

The two organizations in the United States that publish data center standards are the Telecommunications Industry Association (TIA) and the Uptime Institute.

TIA - Data Center Standards

See wiki entry on TIA-942.

Uptime Institute - Data Center Tier Standards

Tier I Requirements

• Single non-redundant distribution path serving the IT equipment
• Non-redundant capacity components
• Basic site infrastructure with expected availability of 99.671%

Tier II Requirements

• Meets or exceeds all Tier I requirements
• Redundant site infrastructure capacity components with expected availability of 99.741%

Tier III Requirements

• Meets or exceeds all Tier I and Tier II requirements
• Multiple independent distribution paths serving the IT equipment
• All IT equipment must be dual-powered and fully compatible with the topology of a site’s architecture
• Concurrently maintainable site infrastructure with expected availability of 99.982%

Tier IV Requirements

• Meets or exceeds all Tier I, Tier II and Tier III requirements
• All cooling equipment is independently dual-powered, including chillers and heating, ventilating and air-conditioning (HVAC) systems
• Fault-tolerant site infrastructure with electrical power storage and distribution facilities with expected availability of 99.995%

The Uptime Institute’s tier system allows for the following minutes of downtime annually:

• Tier I (99.671% minimum uptime) (1729 minutes maximum annual downtime)
• Tier II (99.741% minimum uptime) (1361 minutes maximum annual downtime)
• Tier III (99.982% minimum uptime) (95 minutes maximum annual downtime)
• Tier IV (99.995% minimum uptime) (26 minutes maximum annual downtime)

See also

• Data Center Tiers Data center tiers