問13
頻出度★★★
外部のストレージサービスの利用を検討している。可用性の観点でサービスを評価する項目として, 適切なものはどれか。
平成23年度 秋期 ITパスポート試験 問13
テクノロジ系セキュリティ › 情報セキュリティ管理
This question's explanation and your answers so far.
解説
問 13
- ア
正解 The correct answer is ア. Availability means the degree to which a system or service can be used continuously, without stopping, whenever it is needed. It is the availability element among the three elements of information security (confidentiality, integrity, and availability). The typical measure of availability is the operating ratio, calculated as (total time - downtime) / total time; MTBF (mean time between failures) and MTTR (mean time to repair) are also used. Choice ア, the unplanned service downtime caused by emergency maintenance, is exactly the time during which users cannot use the service when they want to. The longer it is, the lower the operating ratio becomes and the more availability is damaged. When you choose an external storage service, you check the guaranteed operating ratio stated in the SLA (service level agreement) and the actual hours of unplanned downtime, so this is an appropriate item for evaluating availability.
Incorrectイ
The ease of understanding of a user interface is an evaluation item for usability, which shows how easy a system is to operate and to learn. Even if the screen is hard to understand, the service itself is still running; conversely, even if the screen is easy to understand, the service cannot be used once it stops. This is a different perspective from availability, which measures whether the service is running, so it is wrong.
Incorrectウ
The degree of freedom in setting access rights for stored data and for users is an evaluation item for confidentiality, that is, letting only authorized people use the information, and for access management. Among the three elements of information security it corresponds to confidentiality rather than availability, and it has nothing to do with how long the service can be used, so it is wrong.
Incorrectエ
The cost per unit of capacity is an evaluation item for cost, that is, how cheap the price is. It is an important axis of comparison when selecting a service, but a cheap service with frequent outages has low availability, and an expensive service is not necessarily highly available. An amount of money cannot be a measure of availability, so it is wrong.
ここがポイント
- Availability expresses the degree to which something can be used when it is needed, and it is evaluated with measures related to downtime: the operating ratio = (total time - downtime) / total time, MTBF and MTTR, and the guaranteed operating ratio in an SLA.
- Keep the three elements of information security apart (confidentiality = management of access rights, integrity = data is accurate and has not been tampered with, availability = the service does not stop and can be used), and do not confuse them with evaluation items on other axes such as usability or cost.
用語