Performance study of a LAN based image server

The objective is to predict the performance of a practical multi-user system. A prototype distributed system of AT-class computers for multi-user retrieval of electronic document images is described. The prototype system is used as a testbed in which response times are measured, with auxiliary computers simulating additional users. An image server operating on a local-area-network (LAN) and retrieving files from write only read many optical disks includes three potential contributors to a slow receive time: large files, the optical disk drive interface and transmission over a LAN. The authors describe improved receive time achieved through an enhanced optical disk interface, and describe the quantitative effect of Ethernet traffic and multiple users on receive time. Careful selection or design of the optical disk subsystem will reduce the contribution of this component to overall receive time. Of particular importance is the ability of the subsystem to buffer data as it is read from the optical disk. The authors describe a single server system that should be able to support up to five users simultaneously with an average receive time of 0.9 s or less, or to eight users simultaneously with an average receive time of 1.6 s or less