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What is Availability
Availability means that data or any equipment are available at the time of its needs. Is expressed as a percentage of the available time.

Availability is a concept of security management in the organization. Availability means that data or any equipment are available at the time of its needs. Availability disruption is called undesirable destruction or unavailability. Availability is usually expressed as a percentage of time in a given period, usually a year. An indicative list of availability is given below:

  • 90% availability means loss of 36.5 days
  • 95% availability means loss of 18.25 days
  • 98% availability means loss of 7.30 days
  • 99% availability means loss of 3.65 days
  • 99.5% availability means loss of 1.83 days
  • 99.8.% availability means loss of 17.52 hours
  • 99.9% (“three nines”) availability means loss of 8.76 hours
  • 99.99% (“four nines”) availability means loss of 52.6 minutes
  • 99.999% (“five nines”) availability means loss of 5.26 minutes
  • 99.9999% (“six nines”) availability means loss of 31.5 seconds

Although it is usual to indicate availability in percentage, more accurate are indicators of system recovery time and to the amount of data that we can lose:

Solving availability in practice: Data unavailability is one of the risks that can affect any organization. Availability is one of the key requirements for each important information system. Many factors influence the availability, such as:

In case that part of the software or infrastructure is outsourced (such as hosting, webhosting), the responsibility for the availability of these components is transferred to suppliers. Then it should be appropriately treated the level of availability that the supplier must comply with. The availability is usually part of the Service Level Agreement (SLA).

Related terms and methods:

Related standards:

Related management field:

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Last update: 28.11.2015

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