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Understanding RAID
RAID is a well-established technology, and stands for Redundant Array of Independent
Disks, which is a way of protecting your data in case of a disk failure. High-quality reference
material about RAID is widely available on the Internet at sites like Wikipedia
(http://en.wikipedia.org/wiki/RAID), which is the source of the following information.
RAID is used as an umbrella term for computer data storage schemes that can combine and
replicate data among multiple hard disk drives. The different schemes and architectures are
named by the word RAID followed by a number, as in RAID 0, RAID 1, and so on. RAID is
designed to meet one of two key goals: increased data reliability or increased I/O
performance. When multiple physical disks are set to use RAID technology, they are said to
be in a RAID array. This array distributes data across multiple disks, but the array is seen by
the operating system and computer user as one single disk.
RAID Basics
RAID redundancy is achieved by either writing the same data to multiple drives (known as
mirroring), or writing extra data (known as parity data) across the array, calculated such that
the failure of one (or more, depending on the type of RAID) disks in the array will not result in
loss of data. A failed disk can be replaced by a new one, and the lost data can be
reconstructed from the remaining data and the parity data.
Organizing disks into a redundant array decreases the usable storage capacity.
For instance,
•
a 2-disk RAID 1 array loses half of the total capacity that would have otherwise been
available using both disks independently.
•
a RAID 5 array with several disks loses the capacity of one disk. Other types of RAID
arrays are arranged so they are faster to write to, and read from, than a single disk.
RAID Levels
There are various RAID combinations that give various levels of protection against data loss,
capacity, and speed. RAID levels 0, 1, and 5 are the most commonly found, and cover most
requirements.
•
RAID 0 (striped disks) distributes data across several disks in a way that gives
improved speed and no lost capacity, but all data on all disks will be lost if any one
disk fails. Although such an array has no actual redundancy, it is customary to call it
RAID 0.
•
RAID 1 (mirrored settings/disks) duplicates data across every disk in the array,
providing full redundancy. Two (or more) disks each store exactly the same data, at
the same time, and at all times. Data is not lost as long as one disk survives. Total
capacity of the array equals the capacity of the smallest disk in the array. At any given
instant, the contents of each disk in the array are identical to those of every other disk
in the array.
ReadyNAS for Business RAIDiator 4.2.17
Understanding RAID
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