Difference between revisions of "RAID"
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==Types== | ==Types== | ||
| − | Different RAID schemes are referred to by labels of the form 'RAID n', where n is a digit; all produce a single virtual drive. RAID 2-6 all use an [[error-correcting code|ECC]], and are able to recover from damage to a single physical drive | + | Different RAID schemes are referred to by labels of the form 'RAID n', where 'n' is a digit; all produce a single virtual drive. RAID 2-6 all use an [[error-correcting code|ECC]], and are able to recover from damage to a single physical drive. In RAID 2-4, the ECC information is stored on a single other drive; in RAID 5 and 6, it is stored on multiple drives. |
The main ones are: | The main ones are: | ||
| − | * RAID 0 - a virtual drive is split across multiple physical drives; provides increased performance only | + | * RAID 0 - a virtual drive is striped (split) across multiple physical drives; provides increased performance only |
* RAID 1 - a virtual drive is mirrored across multiple physical drives; provides increased reliability only | * RAID 1 - a virtual drive is mirrored across multiple physical drives; provides increased reliability only | ||
* RAID 2 - a virtual drive is striped across multiple physical drives, a [[bit]] at a time | * RAID 2 - a virtual drive is striped across multiple physical drives, a [[bit]] at a time | ||
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* [https://www2.eecs.berkeley.edu/Pubs/TechRpts/1987/CSD-87-391.pdf A Case for Redundant Arrays of Inexpensive Disks (RAID)] | * [https://www2.eecs.berkeley.edu/Pubs/TechRpts/1987/CSD-87-391.pdf A Case for Redundant Arrays of Inexpensive Disks (RAID)] | ||
* [http://web.eecs.umich.edu/~michjc/eecs584/Papers/katz-2010.pdf RAID: A Personal Recollection of How Storage Became a System] | * [http://web.eecs.umich.edu/~michjc/eecs584/Papers/katz-2010.pdf RAID: A Personal Recollection of How Storage Became a System] | ||
| + | * [https://minnie.tuhs.org/cgi-bin/utree.pl?file=V6/usr/man/man4/rk.4 rk.4] - 'striping' in UNIX V6 | ||
[[Category: Device Basics]] | [[Category: Device Basics]] | ||
Latest revision as of 12:18, 7 September 2023
RAID (originally an acronym for 'redundant array of inexpensive disks'; later redefined to stand for 'redundant array of independent disks') is the name for a family of schemes to increase the reliability, performance or size of disk mass storage by using a number of drives in parallel.
The basic ideas pre-date the original definition of the term (below): early UNIX disk device drivers had split a single virtual drive across multiple physical drivers ('striping'); and mirrored disks (for reliability) had been used by Tandem.
Types
Different RAID schemes are referred to by labels of the form 'RAID n', where 'n' is a digit; all produce a single virtual drive. RAID 2-6 all use an ECC, and are able to recover from damage to a single physical drive. In RAID 2-4, the ECC information is stored on a single other drive; in RAID 5 and 6, it is stored on multiple drives.
The main ones are:
- RAID 0 - a virtual drive is striped (split) across multiple physical drives; provides increased performance only
- RAID 1 - a virtual drive is mirrored across multiple physical drives; provides increased reliability only
- RAID 2 - a virtual drive is striped across multiple physical drives, a bit at a time
- RAID 3 - a virtual drive is striped across multiple physical drives, a byte at a time
- RAID 4 - a virtual drive is striped across multiple physical drives, a block at a time
- RAID 5 - a virtual drive is striped across multiple physical drives, with distributed ECC
- RAID 6 - a virtual drive is striped across multiple physical drives, with replicated, distributed ECC
