問73
頻出度★★☆
複数のコンピュータを連携させ, 全体を 1 台の高性能のコンピュータであるかのように利用する。連携しているコンピュータのどれかに障害が発生した場合には, ほかのコンピュータに処理を肩代わりさせることで, システム全体として処理を停止させないようにするものはどれか。
平成21年度 春期 ITパスポート試験 問73
テクノロジ系システム構成要素 › システムの構成
This question's explanation and your answers so far.
解説
問 73
- ア
正解 The correct answer is ア. The word cluster originally means a mass of many things gathered together, like a bunch of grapes, and a cluster system is a configuration in which multiple computers are linked over a network so that, to users, the whole looks as if it were a single high-performance computer. The first half of the stem, using the whole as if it were one high-performance computer, is exactly this definition. The action in the second half, having other computers take over the processing when one of the linked computers fails so that the system as a whole does not stop, is called failover: the computers (nodes) that make up the cluster monitor one another to see whether they are alive, and the remaining healthy nodes take over the processing of the failed node. Cluster systems include a load-balancing type that raises performance by sharing the processing among many nodes, and a high-availability (HA) type that keeps operating by taking over on failure. Because this question touches on performance in the first half and on availability in the second half, it corresponds uniquely to the description of a cluster system. Another advantage over introducing a single dedicated large machine is that performance can be extended simply by adding nodes (scale-out).
Incorrectイ
A dual system prepares two identically configured systems, runs the same processing on both at the same time, and compares their results at fixed intervals (cross-checking) to detect errors. Disconnecting a system that has failed and continuing with the remaining one does resemble the description in this question, but because the two systems perform the same processing redundantly, they do not deliver the processing power of two machines. Its purpose is to ensure the correctness and reliability of the processing results, so it does not match the performance-oriented statement about using the whole as if it were a single high-performance computer.
Incorrectウ
A duplex system prepares two systems, a primary (active) system and a secondary (standby) system. Normally only the primary carries out the real processing, while the secondary either stands by or handles other work such as batch jobs. Switching to the secondary and continuing the processing when the primary fails does correspond to the availability part of the statement, but in normal operation only one side is doing the real processing, so it does not satisfy the first condition of bundling multiple computers and using them as one high-performance computer. Depending on how the standby side waits, it is further divided into hot standby, warm standby, and cold standby, which differ in the time needed to switch over.
Incorrectエ
A multiprocessor system mounts multiple processors (CPUs) inside a single computer and raises performance by sharing the processing among them. Its aim of improving performance is close to the first half of the statement, but what it describes happens entirely inside one computer; it is not the configuration of linking multiple computers together that the stem refers to. In addition, the availability mechanism in the second half, where other computers take over the processing when a failure occurs, is not part of the definition of this term.
ここがポイント
- Cluster system = a configuration in which multiple computers (nodes) are linked over a network so that the whole looks like a single high-performance computer. The action in which other nodes take over the processing of a failed node is called failover; clusters come in a load-balancing type that raises performance and a high-availability (HA) type that aims to keep the system running.
- Redundant configurations for higher reliability are told apart by their purpose and by how each system is used. Dual system = two systems run the same processing simultaneously and their results are compared; duplex system = the primary does the processing while the secondary stands by and takes over on failure; multiprocessor system = several CPUs mounted inside one computer. The deciding points are whether it involves multiple computers or is contained within a single computer, and whether all systems are doing the real processing during normal operation.
用語