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