Chapter 2 Introduction to RAID
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2 Introduction to RAID
RAID (Redundant Array of Independent Disks) is an array of multiple independent hard disk
drives that provide high performance and fault tolerance. A RAID disk subsystem improves I/O
performance. The RAID array appears to the host computer as a single storage unit or as multiple
logical units. I/O is faster because drives can be accessed simultaneously. RAID improves data
storage reliability and fault tolerance. You can prevent data loss caused by drive failure by
reconstructing missing data from the remaining data and parity drives.
RAID Overview
The following topics are discussed:
• RAID levels on page 6
• Consistency check on page 6
• Fault tolerance on page 6
• Disk striping on page 7
• Disk mirroring on page 8
• Disk spanning on page 8
• Parity on page 10
• Hot spares on page 11
• Disk rebuilds on page 12
• Logical drives on page 13
• Hot swap on page 13
• SCSI drive states on page 13
• Logical drive states on page 13
• Disk array types on page 14
• Enclosure management on page 14
