3.3. Hardware RAID versus Software RAID

3.3.1. Hardware RAID

The hardware-based system manages the RAID subsystem independently from the host and presents to the host only a single disk per RAID array.

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 a SCSI controller, but then you add them to the RAID controller's configuration, and the operating system never knows the difference.

3.3.2. Software RAID

[1] are not required. 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 10 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

• 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