Promise Technology 66 Pro - Manual (Page 129)

SuperTrak66™ User's Manual Appendix A
A-5
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.