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ID:-13103030 Section:-B
RAID is a data storage technology that combines multiple disk drive components into a logical unit for the purposes of data redundancy and performance improvement. Data is distributed across the drives in one of several ways, referred to as RAID levels, depending on the specific level of redundancy and performance required.
RAID is now used as an umbrella term for computer data storage schemes that can divide and replicate data among multiple physical drives: RAID is an example of storage virtualization and the array can be accessed by the operating system as one single drive.
History
The term RAID was first defined by David A. Patterson, Garth A. Gibson and Randy Katz at the University of California, Berkeley, in 1987. They studied the possibility of using two or more drives to appear as a single device to the host system and published a paper: "A Case for Redundant Arrays of Inexpensive Disks (RAID)" in June 1988 at the SIGMOD conference. Each of the five levels of RAID named in the paper was well established in the art prior to the paper's publications, for example:
Around 1983, DEC began shipping subsystem mirrored RA8X disk drives (now known as RAID 1) as part of its HSC50 subsystem.
Around 1988, the Thinking Machines DataVault used error correction codes (now known as RAID 2) in an array of disk drives. A similar approach was used in 1970s on the IBM 3330.
In 1977, Norman Ken Ouchi at IBM filed a patent disclosing what was subsequently named RAID 4.
In 1986, Clark et al. at IBM filed a patent disclosing what was subsequently named RAID 5.
Standard levels
Main article: Standard RAID levels
A number of standard schemes have evolved. These are called levels. Originally, there were five RAID levels, but many variations have evolved—notably several nested levels and many non-standard levels (mostly proprietary). RAID levels and their associated data formats are standardized by the Storage Networking Industry
RAID is a data storage technology that combines multiple disk drive components into a logical unit for the purposes of data redundancy and performance improvement. Data is distributed across the drives in one of several ways, referred to as RAID levels, depending on the specific level of redundancy and performance required.
RAID is now used as an umbrella term for computer data storage schemes that can divide and replicate data among multiple physical drives: RAID is an example of storage virtualization and the array can be accessed by the operating system as one single drive.
History
The term RAID was first defined by David A. Patterson, Garth A. Gibson and Randy Katz at the University of California, Berkeley, in 1987. They studied the possibility of using two or more drives to appear as a single device to the host system and published a paper: "A Case for Redundant Arrays of Inexpensive Disks (RAID)" in June 1988 at the SIGMOD conference. Each of the five levels of RAID named in the paper was well established in the art prior to the paper's publications, for example:
Around 1983, DEC began shipping subsystem mirrored RA8X disk drives (now known as RAID 1) as part of its HSC50 subsystem.
Around 1988, the Thinking Machines DataVault used error correction codes (now known as RAID 2) in an array of disk drives. A similar approach was used in 1970s on the IBM 3330.
In 1977, Norman Ken Ouchi at IBM filed a patent disclosing what was subsequently named RAID 4.
In 1986, Clark et al. at IBM filed a patent disclosing what was subsequently named RAID 5.
Standard levels
Main article: Standard RAID levels
A number of standard schemes have evolved. These are called levels. Originally, there were five RAID levels, but many variations have evolved—notably several nested levels and many non-standard levels (mostly proprietary). RAID levels and their associated data formats are standardized by the Storage Networking Industry