Introduction; Raid Basics - MSI P4M900M2 Series User Manual

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Introduction

This section gives a brief introduction on the RAID-related background knowledge and
a brief introduction on VIA SATA RAID Host Controller. For users wishing to install their
VIA SATA RAID driver and RAID software, proceed to Driver and RAID Software
Installation section.

RAID Basics

RAID (Redundant Array of Independent Disks) is a method of combining two or more
hard disk drives into one logical unit. The advantage of an Array is to provide better
performance or data fault tolerance. Fault tolerance is achieved through data redundant
operation, where if one drives fails, a mirrored copy of the data can be found on
another drive. This can prevent data loss if the operating system fails or hangs. The
individual disk drives in an array are called "members". The configuration information of
each member is recorded in the "reserved sector" that identifies the drive as a member.
All disk members in a formed disk array are recognized as a single physical drive to the
operating system.
Hard disk drives can be combined together through a few different methods. The
different methods are referred to as different RAID levels. Different RAID levels
represent different performance levels, security levels and implementation costs. The
RAID levels which the VIA VT8237A / VT8237S SATA RAID Host Controller supports are
RAID 0 and RAID 1. The table below briefly introduced these RAID levels.
RAID Level No. of Drives
RAID 0
(Striping)
RAID 1
(Mirroring)
RAID 0 (Striping)
RAID 0 reads and writes sectors of data interleaved between multiple drives. If
any disk member fails, it affects the entire array. The disk array data capacity is equal
to the number of drive members times the capacity of the smallest member. The striping
block size can be set from 4KB to 64KB. RAID 0 does not support fault tolerance.
RAID 1 (Mirroring)
RAID 1 writes duplicate data onto a pair of drives and reads both sets of data in
parallel. If one of the mirrored drives suffers a mechanical failure or does not respond,
the remaining drive will continue to function. Due to redundancy, the drive capacity of
the array is the capacity of the smallest drive. Under a RAID 1 setup, an extra drive
called the .spare drive. can be attached. Such a drive will be activated to replace a
failed drive that is part of a mirrored array. Due to the fault tolerance, if any RAID 1 drive
fails, data access will not be affected as long as there are other working drives in the
array.
A-2
Capacity
2 Smallest size * 2
2 Smallest size
Benefits
Highest performance without
data protection
Data protection