Users Guide

Understanding RAID concepts

Storage Management uses the Redundant Array of Independent Disks (RAID) technology to provide Storage Management capability.

Understanding Storage Management requires an understanding of RAID concepts, as well as some familiarity with how the RAID

controllers and operating system view disk space on your system.

Related concepts

What is RAID?

Organizing Data Storage For Availability And Performance

Choosing RAID Levels And Concatenation

Comparing RAID Level And Concatenation Performance

Topics:

• What is RAID?

• Organizing Data Storage For Availability And Performance

• Choosing RAID Levels And Concatenation

• Comparing RAID Level And Concatenation Performance

• No-RAID

What is RAID?

RAID is a technology for managing the storage of data on the physical disks that reside or are attached to the system. A key aspect of

RAID is the ability to span physical disks so that the combined storage capacity of multiple physical disks can be treated as a single,

extended disk space. Another key aspect of RAID is the ability to maintain redundant data which can be used to restore data in the event

of a disk failure. RAID uses different techniques, such as striping, mirroring, and parity, to store and reconstruct data. There are different

RAID levels that use different methods for storing and reconstructing data. The RAID levels have different characteristics in terms of

read/write performance, data protection, and storage capacity. Not all RAID levels maintain redundant data, which means for some RAID

levels lost data cannot be restored. The RAID level you choose depends on whether your priority is performance, protection, or storage

capacity.

NOTE:

The RAID Advisory Board (RAB) defines the specifications used to implement RAID. Although RAB defines the

RAID levels, commercial implementation of RAID levels by different vendors may vary from the actual RAID

specifications. An implementation of a particular vendor may affect the read and write performance and the degree of

data redundancy.

Hardware and software RAID

RAID can be implemented with either hardware or software. A system using hardware RAID has a RAID controller that implements the

RAID levels and processes data reads and writes to the physical disks. When using software RAID provided by the operating system, the

operating system implements the RAID levels. For this reason, using software RAID by itself can slow the system performance. You can,

however, use software RAID along with hardware RAID volumes to provide better performance and variety in the configuration of RAID

volumes. For example, you can mirror a pair of hardware RAID 5 volumes across two RAID controllers to provide RAID controller

redundancy.

RAID concepts

RAID uses particular techniques for writing data to disks. These techniques enable RAID to provide data redundancy or better

performance. These techniques include:

• Mirroring — Duplicating data from one physical disk to another physical disk. Mirroring provides data redundancy by maintaining two

copies of the same data on different physical disks. If one of the disks in the mirror fails, the system can continue to operate using the

18 Understanding RAID concepts