===== Five Nines =====
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**Five Nines** is the term used for describing the [[dido:public:ra:xapend:xapend.a_glossary:a:availability|availability]] of a computer or a service at 99.999 percent of the time it is required. In other words, the system or service is only unavailable for 5.39 minutes throughout the year for planned or unplanned [[dido:public:ra:xapend:xapend.a_glossary:d:downtime|downtime]]. Five nines is recommended and required for [[dido:public:ra:xapend:xapend.a_glossary:m:missioncritical|mission-critical]] requirements and for certain areas such as e-commerce. However, five nines availability has always been a challenge for a service or network and is often impossible to guarantee. 

<table>
<caption>Five nines in terms of availability</caption>

^ Number of Nines  ^  percent  ^  Availability Per Year   ^
^  1               ^   9% | 332+ days of downtime per year |
^  2               ^   99% | 3 days, 15 hours and 40 minutes downtime per year |
^  3               ^   99.9% | 8 hours, 46 minutes downtime per year |
^  4               ^   99.99% | 52 minutes, 36 seconds downtime per year |
^  5               ^   99.999% | 5 minutes, 15 seconds or less of downtime in a year |

</table>
    
Source: [[https://www.techopedia.com/definition/14235/five-nines | Five Nines ]]