Question

A system has 99.99% uptime and has a mean-time-between-failure of 1 day. how fast the system does has to repair itself in order to reach this availability goal?

1. 9 seconds
2. 10 seconds
3. 11 seconds
4. 12 seconds

Answer 1

To achieve 99.99% availability with a MTBF of 1 day, the system must have a MTTR of less than 9 seconds, which corresponds closest to the listed answer of 9 seconds.

Step-by-step explanation:

Availability of a system is calculated using the formula: Availability = (MTBF / (MTBF + MTTR)) x 100%, where MTBF is Mean Time Between Failures, and MTTR is Mean Time To Repair. The question states the system has 99.99% availability and a MTBF of 1 day (1440 minutes).

To find MTTR, we rearrange the formula: 99.99% = (1440 / (1440 + MTTR)) implies MTTR = (1440 / 99.99%) - 1440. Plugging in the values: MTTR = (1440 / 0.9999) - 1440 which results in MTTR being approximately 0.144 minutes, or 8.64 seconds.

Since the system must repair itself in less than 9 seconds to achieve 99.99% availability, the closest answer listed in the question is 9 seconds.