問65
頻出度★★★
フェールセーフの説明として, 適切なものはどれか。
平成21年度 春期 ITパスポート試験 問65
テクノロジ系システム構成要素 › システムの評価指標
This question's explanation and your answers so far.
解説
問 65
- ア
正解 The correct answer is ア. Fail-safe, just as its name says, is a reliability design idea: even if something fails, it should fall to the safe side. It starts from the premise that equipment and systems will break down sooner or later and that people will inevitably make operating errors, and builds in beforehand an automatic shift to the state that is least harmful and not dangerous. Familiar examples: a traffic light turns every direction red when it breaks down, an oil heater puts out its own flame when it is knocked over, and a railway signalling system stops the train when it detects an abnormality. All of these are fail-safe behavior, and what they share is that they put being safe ahead of keeping running. Choice ア, “Even if a failure or operating error occurs, the system is designed to maintain safety”, states exactly this idea, so it is appropriate.
Incorrectイ
Cutting off the part where a fault occurred and continuing to run with only the healthy parts so that the whole system is not affected is the idea of fail-soft (keep operating even at reduced performance) and fault tolerance (keep functions available through redundancy even when a fault occurs). What it gives priority to is continued operation, not safety, so its purpose differs from that of fail-safe.
Incorrectウ
Preventing an organization's internal network from being intruded from outside describes security measures typified by a firewall. It is not reliability design about how a system should behave when it breaks down, but a defense against the threat of unauthorized access, so it is not a description of fail-safe.
Incorrectエ
Accepting only data that matches specific conditions describes validation checks or filtering applied to input data. It is a mechanism that blocks incorrect data at the entrance, which is a different matter from designing a system to shift to the safe side when a failure occurs.
ここがポイント
- Fail-safe = a design idea that moves the system into a safe state even when a failure or an operating error occurs. The point is not to make it unbreakable, but to make it harmless when it does break.
- Distinguishing similar terms is a frequent exam point. Fail-soft / fault tolerant = keep operating even when a fault occurs (availability first); fool-proof = make an incorrect operation impossible in the first place (preventing operating mistakes); fail-safe = secure safety when a fault occurs (safety first).
用語