What does a five-nines requirement in a service agreement refer to?

Question

Options

• ACompliance with a particular section of PCI DSS
• BUnplanned downtime less than .001% of the service term
• CFive layers of redundancy in the network design
• DFuture-proof solution designed to last five or more years

• A
  5% (3)
• B
  90% (54)
• C
  2% (1)
• D
  3% (2)

Explanation

Five-nines (99.999%) availability means a system is permitted only about 5.26 minutes of unplanned downtime per year - which is less than 0.001% of the year, making B correct. The term comes from writing out 99.999% uptime, which contains five nines.

• A is wrong because five-nines is an uptime/availability metric, not a PCI DSS compliance standard.
• C is wrong because five-nines specifies an availability target, not a specific network architecture; redundancy may be a means to achieve it, but five layers isn't the definition.
• D is wrong because five-nines has nothing to do with product lifespan or future-proofing - it strictly measures service availability.

Memory tip: Count the nines in 99.999% - there are five of them. Each additional nine reduces allowable downtime by roughly a factor of 10 (four-nines = ~52 min/year, five-nines = ~5 min/year), so more nines = stricter uptime requirement.

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