LSI Corporation
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12Gb/s MegaRAID SAS Software User Guide
March 2014
Chapter 2: Introduction to RAID
Components and Features
Chapter 2: Introduction to RAID
This chapter describes Redundant Array of Independent Disks (RAID), RAID functions and benefits, RAID components,
RAID levels, and configuration strategies. In addition, it defines the RAID availability concept, and offers tips for
configuration planning.
RAID Description
RAID is an array, or group, of multiple independent physical drives that provide high performance and fault tolerance.
A RAID drive group improves I/O (input/output) performance and reliability. The RAID drive group appears to the host
computer as a single storage unit or as multiple virtual units. I/O is expedited because several drives can be accessed
simultaneously.
RAID Benefits
RAID drive groups improve data storage reliability and fault tolerance compared to single-drive storage systems. Data
loss resulting from a drive failure can be prevented by reconstructing missing data from the remaining drives. RAID
has gained popularity because it improves I/O performance and increases storage subsystem reliability.
RAID Functions
Virtual drives are drive groups or spanned drive groups that are available to the operating system. The storage space
in a virtual drive is spread across all of the drives in the drive group.
Your drives must be organized into virtual drives in a drive group, and they must be able to support the RAID level that
you select. Some common RAID functions follow:
Creating hot spare drives
Configuring drive groups and virtual drives
Initializing one or more virtual drives
Accessing controllers, virtual drives, and drives individually
Rebuilding failed drives
Verifying that the redundancy data in virtual drives using RAID level 1, 5, 6, 10, 50, or 60 is correct
Reconstructing virtual drives after changing RAID levels or adding a drive to a drive group
Selecting a host controller on which to work
2.1
Components and Features
RAID levels describe a system for ensuring the availability and redundancy of data stored on large disk subsystems.
See
for detailed information about RAID levels. The following subsections describes the components of
RAID drive groups and RAID levels.
2.1.1
Drive Group
A drive group is a group of physical drives. These drives are managed in partitions known as virtual drives.
2.1.2
Virtual Drive
A virtual drive is a partition in a drive group that is made up of contiguous data segments on the drives. A virtual drive
can consist of these components:
an entire drive group
more than one entire drive group
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