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RAID

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Introduction

RAID is a method of connecting multiple hard drives so that they function as a single hard drive. This can be used to achieve an increase in performance or reliability.

This is achieved in three different ways:

Hardware RAID

This is the original RAID method that most often has the greatest benefits for a RAID setup. Hardware RAID acts independently of any operating system, though a driver is still required by the operating system for it to function properly along side the hardware RAID controller.

BIOS / Onboard RAID

This type of RAID is properly called BIOS or Onboard RAID. This is because the data organization and RAID setup is controlled by the BIOS, motherboard, and firmware on the computer. This method also involves a piece of hardware that helps facilitate the RAID setup; however, that RAID controller does not contain a true RAID chip and therefore requires the assistance of the computer's BIOS; therefore, this type of raid is sometimes called "Fake RAID"

BIOS RAID is often falsely advertised as "hardware" RAID. This is far from the truth. While there is a piece of hardware involved in the RAID setup, that piece of hardware is incapable of properly redirecting data across a RAID array by itself. Thus, it is not true hardware RAID and it can not achieve the performance that a true hardware RAID can achieve. For example, Sager advertises its NP9262 Notebook as having "Hardware RAID-0 / 1 / 5 support." In reality, the Sager NP9262 comes with the Intel ICH8R RAID controller, which is nothing more than a BIOS RAID controller and pales in comparison to true hardware RAID. (See the Specifications tab on this page)

To install Gentoo onto a BIOS RAID setup, see HOWTO Gentoo Install on Bios (Onboard) RAID

Software RAID

Software RAID is dictated by a certain operating system. In Gentoo's case, Linux is used to create logical drives that treat multiple physical drives as a single drive. Thus, RAID is achieved. This is operating system specific and can not be used simultaneously by multiple differing operating systems.

To install Gentoo onto a software RAID setup, see HOWTO Install on Software RAID

Which Type of RAID do I Have?

If you are using software RAID, you all ready know it. The process to set up software RAID is completely user driven, so using such a setup should be very evident.

On the other hand, discerning between BIOS RAID and true hardware RAID can be more difficult. As stated, manufacturers often incorrectly distinguish (Or fail to distinguish) these two types of RAID. The best solution in this instance is to run the lspci command in a console. Look through the output of lspci and find your RAID controller. Then do a search on the Internet to see what information you can find about your RAID controller. True hardware RAID controller are often rather expensive (~$400+), so if you customized a computer, it is very likely that choosing a hardware RAID setup made a very noticeable change in the computer's price.

When figuring out what type of RAID you have, you can NOT trust what manufacturers advertise. As shown above, false advertising is indeed possible. The below resources may be helpful.

See Also

Linux *ATA Wiki

Linux ATA RAID FAQ's

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Last modified: Tue, 02 Sep 2008 23:20:00 +0000 Hits: 1,567