RAIDRAID

Redundant Array of Redundant Array of Inexpensive DisksInexpensive Disks

HistoryHistory

Single Large Expensive Disk (SLED)Single Large Expensive Disk (SLED) IBM and Berkeley UniversityIBM and Berkeley University RAID levels 0-5RAID levels 0-5

Why RAID?Why RAID?

Redundancy, fault toleranceRedundancy, fault tolerance Increased capacityIncreased capacity Increased performanceIncreased performance

MirroringMirroring

The easiest way to The easiest way to get high get high availabilityavailability

Half the sizeHalf the size Higher read Higher read

performance performance

Disk One

Data A

Data B

Data C

Data D

Disk Two

Mirror A

Mirror B

Mirror C

Mirror D

StripingStriping

Higher Higher performanceperformance

Distributed across Distributed across disksdisks

Work in parallelWork in parallel

Disk One

Data A

Data C

Data E

Data G

Disk Two

Data B

Data D

Data F

Data H

ParityParity

Improve the Improve the availabilityavailability

Less waste of Less waste of spacespace

Disk One

Data A

Data C

Data E

Data G

Disk Two

Data B

Data D

Data F

Data H

Disk Three

Check A+B

Check C+D

Check E+F

Check G+H

RAID 0RAID 0

StripingStriping Highest Highest

performanceperformance Lower availabilityLower availability

Disk One

Data A

Data C

Data E

Data G

Disk Two

Data B

Data D

Data F

Data H

RAID 1RAID 1

MirroringMirroring High availabilityHigh availability Low computing Low computing

powerpower

Disk One

Data A

Data B

Data C

Data D

Disk Two

Mirror A

Mirror B

Mirror C

Mirror D

RAID 2, 3, 4RAID 2, 3, 4

ParityParity High performanceHigh performance High availabilityHigh availability Disk One

Data A

Data D

Data G

Data J

Disk Two

Data B

Data E

Data H

Data K

Disk Three

Data C

Data F

Data I

Data L

Disk Four

Check A-C

Check D-F

Check G-I

Check J-L

RAID 5RAID 5

ParityParity with with distributiondistribution

Higher Higher performance than performance than level 1-4level 1-4

High High availabilityavailability Most used RAID Most used RAID

levellevel

Disk One

Data A

Data D

Data G

Check J-L

Disk Two

Data B

Data E

Check G-I

Data K

Disk Three

Data C

Check D-F

Data I

Data L

Disk Four

Check A-C

Data F

Data H

Data J

Combinations of Combinations of different levelsdifferent levels

Combine two levels and get the Combine two levels and get the advantages from bothadvantages from both

Either hardware driven, software Either hardware driven, software driven or a combination of bothdriven or a combination of both

Examples: Examples: 0+1, 1+0, 0+3, 3+0, 0+1, 1+0, 0+3, 3+0, 0+5, 5+0, 1+5, and 5+1.0+5, 5+0, 1+5, and 5+1.

Alternatives to RAIDAlternatives to RAID

Single Large Expensive DiskSingle Large Expensive Disk (SLED) (SLED) Redundant Array of Distributed Redundant Array of Distributed

DisksDisks (RADD) (RADD) More alternatives: More alternatives: 2D-RADD, C-2D-RADD, C-

RAID, RO WB-optimistic and RO WB-RAID, RO WB-optimistic and RO WB-pessimisticpessimistic

The EndThe End

First RAID system. Second RAID system.