VERITAS Volume Manager 3.1 Reference Guide

Chapter 3 111
Disk Arrays
Disk Array Overview
Volume Manager’s implementations of RAID is described in the
Introduction to” Volume Manager” chapter of the VERITAS Volume
Manager Administrator’s Guide.
RAID-0
Although it does not provide redundancy, striping is often referred to as a
form of RAID, known as RAID-0. The Volume Manager’s implementation
of striping is described in the “Introduction to Volume Manager” chapter
of the VERITAS Volume Manager Administrator’s Guide. RAID-0 offers
a high data transfer rate and high I/O throughput, but suffers lower
reliability and availability than a single disk.
RAID-1
Mirroring is a form of RAID, which is known as RAID-1. The Volume
Manager’s implementation of mirroring is described in the “Introduction
to Volume Manager” chapter of the VERITAS Volume Manager
Administrator’s Guide. Mirroring uses equal amounts of disk capacity to
store the original plex and its mirror. Everything written to the original
plex is also written to any mirrors. RAID-1 provides redundancy of data
and offers protection against data loss in the event of physical disk
failure.
RAID-2
RAID-2 uses bitwise striping across disks and uses additional disks to
hold Hamming code check bits. RAID-2 is described in a University of
California at Berkeley research paper entitled A Case for Redundant
Arrays of Inexpensive Disks (RAID) , by David A. Patterson, Garth
Gibson, and Randy H. Katz (1987).
RAID-2 deals with error detection, but does not provide error correction.
RAID-2 also requires large system block sizes, which limits its use.
RAID-3
RAID-3 uses a parity disk to provide redundancy. RAID-3 distributes
the data in stripes across all but one of the disks in the array. It then
writes the parity in the corresponding stripe on the remaining disk. This
disk is the parity disk.
Figure 3-2, “RAID-3 Disk Array,” shows a RAID-3 disk array.