Implementing a Statically Adaptive Software RAID System

by Matt McCormick

Current RAID systems are limited by the performance of the slowest disk drive in the array. This paper proposes several new techniques for mapping data to the different drives in such a way that the higher performance disks receive a greater share of a files data than the lower performing disks. The techniques presented here statically determine the mapping strategy for the entire RAID. This determination is made at the creation of the RAID and remains the same through-out the life of the device. Preliminary studies show a modest 7% improvement for reading and writing large files (256 MB) in their entirety. More suprising is the reduction in bandwidth due to system overhead. The SCSI bus in the system studied is capable of maintaining 80 MB/s of traffic, but our results show a maximum read bandwidth of 65 MB/s and a maximum write bandwidth of only 45 MB/s.
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