IPA FE Subject A sample Question 13

Topic: System Component

A question IPA Japan published in 基本情報技術者試験 科目A サンプル問題 問13, translated into English. ITPEC is based on the same exams.

There is a system that operates a virtualized machine environment on 20 physical machines. Under the operating conditions below, at least how many physical machines must stop for the system to go into degraded operation?

[Operating conditions]

(1)When a physical machine stops, the virtual machines that were running on it are run equally on all the other physical machines, and the resources they were using are distributed in the same way.(2)When there are 20 physical machines, the resources used are 70% on every physical machine.(3)If the resources used on one physical machine exceed 90%, the whole system goes into degraded operation.(4)Conditions other than (1) through (3) do not need to be considered.

Explanation

5 machines — find the fewest stopped machines that push the load on each remaining machine over 90%.

Total load: 20 machines × 70% = 1400% of one machine’s resources. Stopping machines does not reduce this load; it is spread evenly over the machines still running.

StoppedRunningLoad per machine
2181400 ÷ 18 ≈ 77.8%
3171400 ÷ 17 ≈ 82.4%
4161400 ÷ 16 = 87.5%
5151400 ÷ 15 ≈ 93.3%

Degraded operation starts only when the load exceeds 90%. With 4 machines stopped it is 87.5%, still within the limit; with 5 stopped it is 93.3%.

Answer (d)

Why not others:

  • •(a) 2 and (b) 3 — the load per machine is still about 82% or less
  • •(c) 4 — 87.5% is close to 90% but does not exceed it

Key rule: Keep the total load constant and divide it by the machines left: 1400 ÷ (20 − x) > 90 gives 20 − x < 15.6, so x ≥ 5.

System Component · AI-written, may contain errors

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This question comes from the past questions IPA Japan publishes, translated into English by ITPEC Practice. ITPEC Practice is an independent study tool and is not affiliated with IPA or ITPEC. See the original paper (PDF) or Report an issue.