Chapter 1 Introduction to disk array (RAID)
1.1 Disk array (RAID)
Individual hard disk, either SCSI or IDE type, is subject to the matching problems between revolution
speed of driving motor and transmission interface. Transmission speed of an Ultra 160 SCSI or ATA100
IDE hard disk may have a limit of 30MB/Sec at the bandwidth of 100MHz. With limited lifespan any
disk failure may lead to the disaster of system broken and data loss. Both are critical to any network
environment. A new device, the so called Redundant Arrays of Inexpensive / Independent Disks (RAID)
is then created by combining several independent disks into a hard disk group for better transmission
and storage performance.
A disk array combines two or more than two physical disk drives into a virtual/logical disk system with
on-line, fast access, large capacity and fault tolerant features by Striping, Mirroring and Parity Checking
mechanism. A disk array then may continue its normal operation without causing any system failure or
data loss when any one drive in the array is out of work.
In short the RAID technique improves efficiency and data integrity for any network configuration.
1.2 Functions of disk array
•
Enhance storage capacity
•
Improve data access speed
•
Reduce cost
•
Inherent fault tolerance
•
Hot swap
•
Auto data rebuilding
•
Hot spare
•
On-line capacity expansion
1.3 Terminology
The following terms are used in this Manual:
RAID
Redundant Array of Independent Disks
PD
Physical Disk
RG
Raid Group
VD
Virtual Disk
LUN
Logical Unit Number
GUI
Graphic User Interface
WT
Write-Through
Introduction to disk array (RAID)
5
