User's Manual

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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.
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