Database Reference
In-Depth Information
Level 1—Mirrored
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Keeps 2 identical copies of data
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Write block on one disk followed by write block on second disk
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Does not stripe data across disks
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Most expensive
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No improvement in reading data
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RAID system consists of 4 data disks and 4 check disks
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Effective space utilization 50%
Level 0 + 1—Striped and Mirrored
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Combines features of Levels 0 and 1
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RAID system consists of 4 data disks and 4 check disks
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Effective space utilization 50%
Level 2—Error-Correcting Codes
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Single-bit striping
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Even small unit of read requires reading all 4 disks
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Good for large workloads, not for small
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RAID system consists of 4 data disks and 3 check disks
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Effective space utilization 57%
Level 3—Bit-Interleaved Parity
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Only 1 check disk needed
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Need to identify failed disk through disk controller
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Performance similar to Level 2
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Most expensive
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No improvement in reading data
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RAID system consists of 4 data disks and 1 check disk
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Effective space utilization 80%
Level 4—Block-Interleaved Parity
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Block as striping unit
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Check disk written for each data write
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RAID system consists of 4 data disks and 1 check disk
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Effective space utilization 80%
Level 5—Block-Interleaved Distributed Parity
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Improves on Level 4
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Parity blocks distributed uniformly over all disks
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