Software Support

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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 Links
What Is RAID?
Organizing Data Storage For Availability And Performance
Choosing RAID Levels And Concatenation
Comparing RAID Level And Concatenation Performance
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 unaffected disk. Both sides of the mirror contain the
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