Compaq ProLiant 1000 I/O Performance Tuning of Compaq Servers - Page 4

I/O Performance Tuning of Compaq Servers 4 Introduction Perhaps the most common term when maximizing server performance is bottleneck. Invariably, one component in a system will be stressed more than others and, as a result, the performance of the entire system will be limited when the limits of that device have been reached. A bottleneck is not always a single device, and in some cases, it's not a device at all. Often, an entire subsystem or simply a less than optimal configuration limits performance. Given any configuration, there are bottlenecks and, usually, the limiting factor can not be eliminated completely. Maximizing performance for a server involves careful analysis and reconfiguration to reduce the effect of the bottlenecks. In order to identify and reduce the impact of the most stressed component, you must know the hardware present and normal operating conditions for your server. As you will see, an important factor in tuning a server is the server mix. The server mix is the ratio that expresses the amount of server requests that are: • random vs. sequential • small vs. large block transfers • reads vs. writes By understanding what data is requested,and how often, you can decide which components are most likely to become a bottleneck in your environment. For instance, a lightly-loaded server that performs all random, small file transfers will most likely incur a delay as the drives seek to find the requested data; the bus on this server remains relatively idle. On the other hand, large, contiguous file transfers need only position the drive heads initially to begin streaming data to the client; these requests are more likely to run into a bus saturation limitation. Perhaps a more obvious factor in server performance is the server itself. In every server environment, there are variables that must be considered regardless of configuration and operation. For instance, physical drive delays as the heads are positioned over the data are present in every computer. Performance tuning seeks to reduce the effect of individual delays on overall system performance. This document will give general recommendations for reducing the effect of any given delay and the role that some of the new technology can play. I/O Performance and Recommendations Dynamic systems, such as a network, operate within a set of boundary conditions. These boundary conditions describe the limitations imposed by the individual components of the system. Optimization of your system for maximum performance involves • Knowledge of the components and their relationships • Discovery of current performance through measurements and analysis • Adaptation to increase performance. The operating realm is a solution of the boundary conditions. In a graphical form, as in Figure 1, the solution for each operating parameter is a polygon. While the system can operate anywhere within the polygon, the boundaries of the polygon are where the system usually operates. In particular the modes of a solution are usually at an apex of the polygon. ECG044.0399