IBM ATA 133, User Manual

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Chapter 2 Introduction to RAID 3
2 Introduction to RAID
RAID (Redundant Array of Independent Disks) is an array (group) of multiple
independent hard drives that provide high performance and fault tolerance. A RAID disk
subsystem improves I/O (input/output) performance and reliability. The RAID array
appears to the host computer as a single storage unit or as multiple logical units. I/O is
expedited because several disks can be accessed simultaneously.
RAID systems improve data storage reliability and fault tolerance compared to single-
drive computers. Data loss resulting from a hard drive failure can be prevented by
reconstructing missing data from the remaining hard drives.
RAID Benefits
RAID has gained popularity because it improves I/O performance, and increases storage
subsystem reliability. RAID provides data security through fault tolerance and redundant
data storage.
Improved I/O Although hard drive capabilities have improved drastically, actual performance has
improved only three to four times in the last decade. Computing performance has
improved over 50 times during the same time period. RAID allows you to access several
disks simultaneously.
Increased Reliability
The electromechanical components of a disk subsystem operate more slowly, require
more power, and generate more noise and vibration than electronic devices. These factors
reduce the reliability of data stored on disks. RAID systems improve data storage
reliability and fault tolerance compared to single-drive computers. The additional drives
make it possible to prevent data loss from a hard drive failure. You can reconstruct
missing data from the remaining data.
In This Chapter
Table 2-1 lists the topics discussed in this chapter.
Table 2-1. Topics in This Chapter
Major Topic Subtopic
RAID Overview
Disk Striping
Disk Mirroring
Disk Spanning
RAID Terminology
Physical Drive
Physical Drive States
Array
Array
States
Fault Tolerance
Logical Drive
Disk Rebuild
Hot Spares
Consistency Check
Configuration Strategies
Selecting a RAID Level
Assigning RAID Levels