Introduction; Mirroring And Parity; Disk Striping; Basics Of Ahci And Raid Technology - Compaq dc5850 - Microtower PC Use Manual

Introduction

A RAID (Redundant Array of Independent Disks) is a data storage scheme that uses two or more drives
accessed in combination to improve fault tolerance. Initially used with servers, desktop PCs are increas-
ingly using RAID controllers and extra ATA or SCSI disks. Newer system boards often have RAID control-
lers.
The HP Compaq dc5850 Business PC takes advantage of Serial Advanced Technology Attachment
(SATA) and the integration of RAID into AMD's RS780 and SB700 chipsets. The HP Compaq dc5850
Business PC products incorporate RAID drive support through factory configurations. This white paper
provides a basic overview of RAID technology, supported factory configurations of HP Compaq dc5850
Business PCs, and other supported RAID configurations.

Mirroring and Parity

Fault tolerance is achieved by mirroring or parity. Mirroring is 100% duplication of the data on two drives
(RAID 1). Parity is used to calculate the data in two drives and store the results on a third drive (RAID 5).
After a failed drive is replaced, the RAID controller automatically rebuilds the lost data from the other two
drives. RAID systems may have a spare drive (hot spare) ready and waiting to be the replacement for a
drive that fails.

Disk Striping

RAID improves performance by disk striping, which interleaves bytes or groups of bytes across multiple
drives, so more than one disk is reading and writing simultaneously.

Basics of AHCI and RAID Technology

Definitions

RAID Definitions
Table 1 Basic AHCI and
AHCI Advanced Host Controller Interface, a specification for hardware and software, is a register
interface for SATA, intended to add higher speed, NCQ and other features.
ATA Advanced Technology Attachment.
BIOS Basic Input/Output System, also known as system ROM.
Chipset Term used to define a collection of integrated components required to make a PC function.
HDD Hard disk drive.
IDE Integrated Drive Electronics.
MBR = Master Book Record
2