레이드 RAID 방법

Redundant Arrays of Inexpensive Disks, as named by the inventors and commonly referred to as RAID, is a technology that supports the integrated use of two or more hard-drives in various configurations for the purposes of achieving greater performance, reliability through redundancy, and larger disk volume sizes through aggregation. RAID is also sometimes referred to as "Redundant Arrays of Inexpensive Drives" or "Redundant Arrays of Independent Disks/Drives". RAID is an umbrella term for computer data storage schemes that divide and replicate data among multiple hard disk drives. RAID's various designs balance or accentuate two key design goals: increased data reliability and increased I/O (input/output) performance.

Norman Ken Ouchi at IBM was awarded a 1978 U.S. patent 4,092,732[1] titled "System for recovering data stored in failed memory unit." The claims for this patent describe what would later be termed RAID 5 with full stripe writes. This 1978 patent also mentions that disk mirroring or duplexing (what would later be termed RAID 1) and protection with dedicated parity (that would later be termed RAID 4) were prior art at that time.

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.[2] This specification suggested a number of prototype RAID levels, or combinations of drives. Each had theoretical advantages and disadvantages. Over the years, different implementations of the RAID concept have appeared. Most differ substantially from the original idealized RAID levels, but the numbered names have remained. This can be confusing, since one implementation of RAID 5, for example, can differ substantially from another. RAID 3 and RAID 4 are often confused and even used interchangeably.

A number of standard schemes have evolved which are referred to as levels. There were five RAID levels originally conceived, but many more variations have evolved, notably several nested levels and many non-standard levels (mostly proprietary).

RAID combines physical hard disks into a single logical unit by using either special hardware or software. Hardware solutions often are designed to present themselves to the attached system as a single hard drive, and the operating system is unaware of the technical workings. Software solutions are typically implemented in the operating system, and again would present the RAID drive as a single drive to applications.

There are three key concepts in RAID: mirroring, the copying of data to more than one disk; striping, the splitting of data across more than one disk; and error correction, where redundant data is stored to allow problems to be detected and possibly fixed (known as fault tolerance). Different RAID levels use one or more of these techniques, depending on the system requirements. The main aims of using RAID are to improve reliability, important for protecting information that is critical to a business, for example a database of customer orders; or where speed is important, for example a system that delivers video on demand TV programs to many viewers.

RAID 0은 데이터 스트립핑을 하면서 패리티 체크는 하지 않음.

RAID 1은 미러링. 패리티 체크 없음.

스티리핑을 하면서 패리티 체크를 하고 이를 여러 디스크에 분산해서 저장하는 경우.

[참고자료]
위키피디아

• Page name: RAID
• Author: Wikipedia contributors
• Publisher: Wikipedia, The Free Encyclopedia.
• Date of last revision: 2 February 2008 18:28 UTC
• Date retrieved: 3 February 2008 13:47 UTC
• Permanent link: http://en.wikipedia.org/w/index.php?title=RAID&oldid=188638023
• Page Version ID: 188638023