Mass Storage and I/O - II RAID: Redundant Array of Inexpensive Disks - - PDF document

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CSC 4103 - Operating Systems Spring 2008

Tevfik Koar

Louisiana State University

April 10th, 2008

Lecture - XIX

Mass Storage and I/O - II

RAID Structure

• As disks get cheaper, adding multiple disks to the same

system provides increased storage space, as well as increased reliability and performance.

• RAID: Redundant Array of Inexpensive Disks

– multiple disk drives provides reliability via redundancy.

• RAID is arranged into six different levels.

RAID (cont)

• RAID schemes improve performance and improve the

reliability of the storage system by storing redundant data.

– Mirroring (shadowing): duplicate each disk

• Simplest but most expensive approach

– Block interleaved parity uses much less redundancy. – Data Striping: splitting each bit (or block) of a file across multiple disks.

RAID Levels RAID Level 0

5

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RAID Level 0

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RAID Level 1

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RAID Level 1

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RAID Level 2

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RAID Level 2

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RAID Level 3

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RAID Level 3

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RAID Level 4

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RAID Level 4

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RAID Level 5

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RAID Level 5

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RAID Level 6

• Similar to RAID 5, but uses dual distributed parity
• more reliability versus less data space

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Hierarchical Storage Management (HSM)

• A hierarchical storage system extends the storage

hierarchy beyond primary memory and secondary storage to incorporate tertiary storage — usually implemented as a jukebox of tapes or removable disks.

• Usually incorporate tertiary storage by extending the

file system.

– Small and frequently used files remain on disk. – Large, old, inactive files are archived to the jukebox.

• HSM is usually found in supercomputing centers and
• ther large installations that have enormous volumes of

data.

Hierarchical Storage Management