Performance aspects of RAID architectures

RAID (Redundant Array of Inexpensive Disks) concept was introduced to provide high performance I/O subsystem by striping data across multiple low cost disk drives and storing parity information on one of the disks to generate the original data in case of a disk failure. However, only CPU and disk drives were considered in the evaluation of system architecture of the original RAID investigation. Later, more studies to address RAID performance have been reported but they fail to provide an approach to complete evaluation of RAID I/O subsystems. This paper attempts to provide an approach to comprehensive evaluation of RAID architectures. It considers the complete I/O subsystem consisting of CPU, operating system, data bus, I/O controller, controller cache, disk paths and SCSI disk drives. Analytical models are developed to analyze the performance of different RAID designs. The main conclusions of the paper are: (1) Performance of I/O subsystems depends on data management in the cache (CPU, Storage Controller and Disk) and disk, and (2) RAID architectures provide high data availability but NOT necessarily high performance.