Promise Array Management
Block and Parity Striping (RAID 5)
RAID 5 calculates parity in order to achieve redundancy rather than writing a second copy of the data, like RAID 1. Parity is distributed across the physical drives along with the data blocks. In each case, the parity data is stored on a different disk than its corresponding data block.
RAID 5 makes efficient use of hard drives and is the most versatile RAID Level. It works well for file, database, application and web servers.
Distributed Parity
Data
Blocks
1a | 2a | 3a | a parity |
1b | 2b | b parity | 4b |
1c | c parity | 3c | 4c |
d parity | 2d | 3d | 4d |
Disk Drives
Figure 86. RAID 5 Stripes all Drives with Data and Parity Information
The capacity of a RAID 5 array is the smallest drive size multiplied by the number of drives, less one. Hence, a RAID 5 array with four 100 GB hard drives will have a capacity of 300 GB. An array with two 120 GB hard drives and one 100 GB hard drive will have a capacity of 200 GB.
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