問46
頻出度★★☆
SLA のサービスレベルの項目は, 可用性, 信頼性, 性能などに分けられる。可用性に分類されるものはどれか。
平成23年度 秋期 ITパスポート試験 問46
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This question's explanation and your answers so far.
解説
問 46
Incorrectア
Online response time is the time from when a user performs an operation until the response comes back on the screen, and it is classified as performance. It measures how fast that processing is, on the premise that the service is running. Even if the response is slow, the service itself is still usable, so this is a viewpoint different from availability, which asks whether you can use the service when you want to. In an SLA it is agreed as a performance level in a form such as “a response time within 3 seconds in 95 percent or more of the cases”.
Incorrectイ
External connectivity is an item that shows how far the system can link and connect with other systems and external services, and it generally falls into the extensibility category (how easy it is to add functions or connect with others in the future). It expresses the range of partners and methods that can be connected, not the length of time the service is running. Therefore it does not serve as an indicator of availability.
- ウ
正解 Availability is the degree to which users can actually use a service when they want to use it. In an SLA (Service Level Agreement), items such as the uptime rate, the service hours provided, and the advance-notice period for planned outages are agreed on in order to measure this availability numerically. Choice ウ, “service hours”, defines the time band in which the service is provided — for example, 8:00 to 22:00 on weekdays and 24 hours on Sundays. The longer the service hours are, the more users can use the service whenever they like, so this is exactly an indicator of “can I use it when I want to” and is classified as availability. If you grasp availability as an indicator from the viewpoint of time — whether the service is running or stopped — you can separate it clearly from speed of response (performance), resistance to breaking and speed of recovery (reliability), and strength of protection (security). Therefore the correct answer is ウ.
Incorrectエ
The communication encryption level is an item that shows by which method and at what strength the data on the communication path is encrypted and protected, and it is classified as security. It is an agreement for ensuring the confidentiality of information, and strengthening the encryption does not increase the amount of time the service can be used. Availability (being usable), integrity, and confidentiality stand side by side as the three elements of information security and are separate viewpoints; this choice is an indicator on the confidentiality side.
ここがポイント
- An SLA (Service Level Agreement) is a document in which the provider and the user agree in numerical terms on the quality level of the service to be provided. Service level items are classified into availability, reliability, performance, extensibility, security, and so on, and availability is expressed by service hours (the time band of provision), the uptime rate, advance notice of planned outages, and the like.
- Memorize how the categories are divided by pairing them up: performance is online response time and batch processing time (speed); reliability is mean time to repair and the number of failures (resistance to breaking and ease of recovery); extensibility is external connectivity and customizability; security is the communication encryption level and access log management.
用語