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IT Service Management and Systems Audit

The SLA for a cloud service defines monthly availability = (scheduled service time − outage time due to failures) ÷ scheduled service time, where the scheduled service time is the total time in the month minus the time of planned maintenance announced in advance. If the monthly availability is at least 99.9%, there is no refund; if it is at least 99.0% but below 99.9%, 10% of the monthly fee is refunded; and if it is below 99.0%, 30% is refunded. Take a month as 30 days. In one month there were 120 minutes of planned maintenance and a total of 40 minutes of outages due to failures. Which of the following is the refund rate for this month?

  1. A0%
  2. B10%
  3. C30%
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Answer: A. 0%

The total time in a month is 30 × 24 × 60 = 43,200 minutes, and the scheduled service time, excluding the 120 minutes of planned maintenance, is 43,080 minutes. The monthly availability is (43,080 − 40) ÷ 43,080 ≈ 99.91%, which is at least 99.9%, so there is no refund (0%). Counting the planned maintenance as outage time as well, (43,200 − 160) ÷ 43,200 ≈ 99.63%, leads to the wrong conclusion of 10%. In an SLA, it is important to define clearly in advance how planned maintenance is treated and the formula for availability.

  • A. Correct. (43,080 − 40) ÷ 43,080 ≈ 99.91%, which is at least 99.9%.
  • B. This judgment uses an availability (about 99.63%) that counts the 120 minutes of planned maintenance as outage time and is based on the total of 43,200 minutes.
  • C. To fall below 99.0%, outages due to failures would have to exceed 430.8 minutes.
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