RAID Overview

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As you might imagine, it can become increasingly difficult to manage a system as you add more and more disk drives. Instead of adding tens or hundreds of individual disk drives, many users prefer to use RAID (Redundant Array of Independent Disks). You can implement RAID by using software and existing I/O components, or you can purchase hardware RAID devices. In this section, you will learn about what RAID is and how it works.

As the name implies, RAID takes two or more disk drives and creates an array of disks. To the operating system, this array appears as one logical disk. This logical disk is also known as a disk volume because it is a collection of disks that appears as one. To the user, to the application, and even to Microsoft Windows 2000 (if hardware RAID is used), the array appears as one disk. In many cases, however, this single logical disk is much larger than any disk you could purchase. Not only does RAID allow you to create large logical disk drives, but many RAID levels (configurations) provide disk fault tolerance as well. Fault tolerance allows the RAID logical disk to survive (tolerate) the loss of one or more individual disk drives. In the next few sections, you will learn how this is possible and about the characteristics of various RAID levels.

As was mentioned earlier, RAID can be implemented by using software; in fact, Windows 2000 comes with RAID software. However, this chapter is concerned mostly with hardware-based RAID because of the additional features that it provides. In the next two sections, you will learn about some of these features and the characteristics of the various RAID levels.