I/O activity

Input?output operations are generally the most significant factor in any performance equation. A reduction of I/O, either real or physical, often generates the most significant payback in any tuning exercise.

Many techniques are available to both eliminate I/O and to achieve optimum performance for physical I/O. Some of those techniques are discussed in this book. If you have a very high workload, consider any performance enhancing options, either hardware or software, available to you. However, we recommend you do not use software that alters the physical organization of a data set, because this can have detrimental effects on your HCL Workload Automation for Z data and availability.

The number of real I/Os can be reduced by removing any unnecessary processing and modifying VSAM cluster definitions.

Performance of physical I/Os can be optimized by utilization of DASD hardware facilities.

The duration of a physical I/O is very dependent on the performance of the I/O subsystem, which is influenced greatly by careful placement of data to reduce channel, path, and control unit contention.