ITPEC FE Morning April 2018 Question 15

Source exam: ITPEC FE Morning April 2018Topic: Computer Systems & Hardware

ITPEC FE Morning April 2018 — Question 15 of 80

System Availability (MTBF & MTTR) — identify correct behavior of the availability formula.

Formula: A = MTBF / (MTBF + MTTR)

  • •MTBF (Mean Time Between Failures) — average uptime between failures
  • •MTTR (Mean Time To Repair) — average time to fix a failure

Analysis of each statement:

  • •(a) Wrong — same MTTR but different MTBF gives different availability: 100/105 ≠ 200/205
  • •(b) Correct — reducing MTTR with constant MTBF decreases the denominator → availability increases
  • •(c) Wrong — increasing MTBF with constant MTTR improves availability (numerator grows faster than denominator)
  • •(d) Wrong — same sum does not mean same availability: 90/100 = 0.9 vs 50/100 = 0.5

Key rule: To improve availability — either increase MTBF (fail less often) or decrease MTTR (fix faster).

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