問55
頻出度★★☆
複数のハードディスクに同じ内容を書き込み，信頼性を向上させる方式はどれか。
平成24年度 秋期 ITパスポート試験 問55
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 55
Incorrectア
Striping is a method (RAID0) that divides one piece of data into fixed-size pieces and writes them across multiple hard disks. Since reads and writes can be done in parallel, its purpose is to speed up access. Each disk holds a different fragment, so it does not write the same content, and because it has no redundancy, the failure of even one disk loses all of the data. Its reliability is in fact lower than that of a single disk.
Incorrectイ
Fragmentation is a phenomenon in which, as files are created and deleted over and over, one file ends up recorded in non-contiguous areas scattered across the disk. It is not a method for raising reliability. On the contrary, it increases head movement during reads and writes and becomes a cause of slower access; it is something to be cleared up by defragmentation (optimization).
Incorrectウ
Multi-core is a technology that mounts several computing cores inside one CPU (processor), with the aim of running several tasks in parallel to raise processing performance. It is a speed-up technology on the CPU side, not a way of writing to hard disks, and it has nothing to do with improving reliability against disk failure.
- エ
正解 The correct answer is エ, mirroring. Mirroring writes exactly the same content to two or more hard disks at the same time and always keeps a copy (a mirror); among RAID configurations it corresponds to RAID1. Even if one of the disks fails, the same data is still on the other one, so the system can keep running without being stopped, and once the failed disk is replaced its content can be rebuilt. This property of withstanding a device failure through duplicated writing is exactly what the question means by writing the same content to improve reliability. Note as well that because the same capacity is used on two disks, the usable effective capacity is about half of the total, and content deleted or altered by mistake is reflected on both disks too, so mirroring is not a substitute for a backup.
ここがポイント
- Mirroring (RAID1) writes the same data twice onto multiple hard disks to secure redundancy and thereby raise reliability, while striping (RAID0) divides data across multiple disks to make access faster. Telling them apart by their purpose — mirroring for reliability, striping for speed — is the basic skill in this area.
- RAID is the general term for technologies that group multiple hard disks together and handle them as if they were one, so as to raise reliability and performance. There are also configurations such as RAID5, which combines striping with parity to achieve both speed and fault tolerance, and RAID10 (RAID1+0), which uses mirroring and striping together.
用語