SK0-004 · Question #123
Historical data shows that on average, a server is likely to fail once every nine months. A company has purchased 24x7, four hour hardware response to replace a server's failed hardware…
The correct answer is A. The company's MTTR is ten hours. MTTR (Mean Time To Repair) is the total time required to restore service, which here is the hardware response time plus the post-replacement restoration time: 4 + 6 = 10 hours.
Question
Historical data shows that on average, a server is likely to fail once every nine months. A company has purchased 24x7, four hour hardware response to replace a server's failed hardware. Additionally, the company can restore a server to its operational status within six hours from the time the failed hardware has been replaced. Which of the following describes this scenario?
Options
- AThe company's MTTR is ten hours.
- BIndividual servers have 99.999% uptime.
- CService can be restored within four hours.
- DThe operational SLA is six hours.
How the community answered
(21 responses)- A76% (16)
- B14% (3)
- C5% (1)
- D5% (1)
Why each option
MTTR (Mean Time To Repair) is the total time required to restore service, which here is the hardware response time plus the post-replacement restoration time: 4 + 6 = 10 hours.
MTTR is calculated as the total elapsed time from failure to full restoration of service. In this scenario, the 24x7 four-hour hardware response covers physical replacement, and the additional six hours covers software/configuration restoration - summing to a total MTTR of ten hours. This correctly applies the MTTR formula to the combined repair and restoration durations.
99.999% uptime (five nines) allows only about 5.26 minutes of downtime per year, which is incompatible with a 10-hour MTTR on a 9-month MTBF cycle.
Four hours represents only the hardware replacement SLA; the server is not operational until an additional six hours of restoration work is completed.
Six hours describes only the post-hardware-replacement restoration window, not the total MTTR, which must also include the four-hour hardware response time.
Concept tested: Calculating MTTR from hardware response and restoration times
Source: https://learn.microsoft.com/en-us/azure/well-architected/reliability/metrics
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