User's Manual

Understanding RAID Concepts 35
3
Understanding RAID Concepts
Storage Management uses 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 your system’s RAID controllers and operating
system view disk space.
This sub-section describes basic storage concepts
including What Is RAID?, Organizing Data Storage for Availability and
Performance, and Choosing RAID Levels and Concatenation.
What Is RAID?
RAID is a technology for managing how data is stored on the physical disks
that reside in your system or are attached to it. 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 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 the RAB defines the RAID levels, commercial
implementation of RAID levels by different vendors may vary from the actual RAID
specifications. An implementation used by 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