CAS-001 · Question #72
There have been some failures of the company's customer-facing website. A security engineer has analyzed the root cause to be the WAF. System logs show that the WAF has been down for 14 total hours…
The correct answer is C. 4 hours. MTTR (Mean Time To Repair) measures the average time to recover from unplanned failures. Scheduled maintenance is excluded because it is planned, not a failure event. Total unplanned downtime = 14 hours − 2 hours (scheduled maintenance) = 12 hours. Number of unplanned incidents…
Question
There have been some failures of the company's customer-facing website. A security engineer has analyzed the root cause to be the WAF. System logs show that the WAF has been down for 14 total hours over the past month in four separate situations. One of these situations was a two hour scheduled maintenance activity aimed to improve the stability of the WAF. Which of the following is the MTTR, based on the last month's performance figures?
Options
- A3 hours
- B3.5 hours
- C4 hours
- D4.666 hours
How the community answered
(58 responses)- A7% (4)
- B14% (8)
- C76% (44)
- D3% (2)
Explanation
MTTR (Mean Time To Repair) measures the average time to recover from unplanned failures. Scheduled maintenance is excluded because it is planned, not a failure event. Total unplanned downtime = 14 hours − 2 hours (scheduled maintenance) = 12 hours. Number of unplanned incidents = 4 − 1 = 3. MTTR = 12 hours ÷ 3 incidents = 4 hours. Note: MTBF (Mean Time Between Failures) uses the total number of failures including maintenance; MTTR specifically focuses on repair of failures, making it 4 hours.
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