Performance of RAID as a storage system for Internet image delivery

Redundant Array of Inexpensive Disks (RAID) vendors rely on multi-megabyte files and large numbers of physical disks to achieve the high transfer rates and Input/Output Operations Per Second (lOPS) quoted in the promotional literature. Practical image database applications do not always deliver such large files and cannot always afford the cost of the large numbers of disks required to match the vendors' performance claims. Because the user is often waiting on-line to view the images, applications deployed on the World Wide Web (WWW) are especially sensitive to keeping inline images relatively small. For such applications, the expected performance advantages of RAID storage may not be achieved. The Lister Hill National Center for Biomedical Communications houses three image datasets on a SPARCstorage Array RAID system. Applications deliver these images to users via the Internet using the WWW and other client/server programs. Although approximately 3% of the images exceed 1 MB in size, the average file size is less than 200 KB and approximately 60% of the files are less than 100 KB in size. A study was undertaken to determine the configuration of the RAID system that will provide the fastest retrieval of these image files and to discover general principles of RAID performance. Average retrieval times with single processes and with concurrent processes are measured and compared for several configurations of RAID levels 5and 0+1 . A few trends have emerged showing a tradeoff between optimally configuring the RAID for a single process or for concurrent processes.© (1996) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.