Compaq Infortrend RAID Functions, An Introduction, Logical Volume, 1 Logical Drive, Chapter

Chapter

1	RAID Functions:
	An Introduction

Redundant Arrays of Independent Disks, or RAID, offers the following advantages: Availability, Capacity, and Performance. Choosing the right RAID level and drive failure management can increase Capacity and Performance, subsequently increasing Availability. Infortrend's external RAID controllers provide complete RAID functionality and enhanced drive failure management.

1.1Logical Drive

Figure 1 - 1 Logical Drive

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The advantages mentioned above are achieved by creating “logical drives.” A logical drive is an array of independent physical drives. The logical drive appears to the host as a contiguous volume, the same as a local hard disk drive does.

The following section describes the different methods to create logical arrays of disk drives, such as spanning, mirroring and data parity. These methods are referred to as “RAID levels.”

Logical Drive

1.2Logical Volume

What is a logical volume?

The concept of a logical volume is very similar to that of a logical drive. A logical volume is the combination of one or several logical drives. These logical drives are combined into a larger capacity using the RAID 0 method (striping). When data is written to a logical volume, it is first broken into data segments and then striped across different logical drives in a logical volume. Each logical drive

Functional Description 1-1