Raid Levels And Linear Support - Red Hat LINUX 7.2 - OFFICIAL LINUX CUSTOMIZATION GUIDE Manual

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An example of a Hardware RAID device would be one that connects to a SCSI controller and presents
the RAID arrays as a single SCSI drive. An external RAID system moves all RAID handling "intelli-
gence" into a controller located in the external disk subsystem. The whole subsystem is connected to
the host via a normal SCSI controller and appears to the host as a single disk.
RAID controllers also come in the form of cards that act like a SCSI controller to the operating system
but handle all of the actual drive communications themselves. In these cases, you plug the drives
into the RAID controller just like you would a SCSI controller, but then you add them to the RAID
controller's configuration, and the operating system never knows the difference.
4.3.2 Software RAID
Software RAID implements the various RAID levels in the kernel disk (block device) code. It offers
the cheapest possible solution, as expensive disk controller cards or hot-swap chassis
Software RAID also works with cheaper IDE disks as well as SCSI disks. With today's fast CPUs,
Software RAID performance can excel against Hardware RAID.
The MD driver in the Linux kernel is an example of a RAID solution that is completely hardware
independent. The performance of a software-based array is dependent on the server CPU performance
and load.
For information on configuring Software RAID in the Red Hat Linux installation program, refer to
the Chapter 5, Software RAID Configuration.
For those interested in learning more about what Software RAID has to offer, here is a brief list of the
most important features:
• Threaded rebuild process
• Fully kernel-based configuration
• Portability of arrays between Linux machines without reconstruction
• Backgrounded array reconstruction using idle system resources
• Hot-swappable drive support
• Automatic CPU detection to take advantage of certain CPU optimizations

4.4 RAID Levels and Linear Support

RAID supports various configurations, including levels 0, 1, 4, 5, and linear. These RAID types are
defined as follows:
1 A hot-swap chassis allows you to remove a hard drive without having to power-down your system.
Chapter 4:Redundant Array of Independent Disks (RAID)
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are not required.