Promise Technology 66 Pro user manual Block Striping with Parity Drive RAID

SuperTrak66™ User's Manual Appendix A

Block Striping with Parity Drive (RAID 3)

RAID level 3 organizes data across the physical drives of the array, and stores parity information on to a drive dedicated to this purpose. This organization allows increased performance by accessing multiple drives simultaneously for each operation, as well as fault tolerance by providing parity data. In the event of a hard drive failure, data can be re-calculated by the RAID system based on the remaining drive data and the parity information.

The adjustable block size of the RAID 3 array allows for performance-tuning based on the typical I/O request sizes for your system. The block size must be set at the time it is created and cannot be adjusted dynamically. Generally, RAID Level 3 tends to exhibit lower random write performance due to the heavy workload going to the dedicated parity drive for parity recalculation for each I/O.

The capacity of a RAID 3 array is the smallest drive size multiplied by the number of drives less one. Hence, a RAID 3 array with (4) 1.0 GB hard drives will have a capacity of 3.0GB. An array with (2) 1.2GB hard drives and (1) 1.0GB hard drive will have a capacity of 2.0GB.

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