Intel 170 Servers Batch Performance, Effect of CPU Speed on Batch, Effect of Dasd Type on Batch

Chapter 3. Batch Performance

In a commercial environment, batch workloads tend to be I/O intensive rather than CPU intensive. The factors that affect batch throughput for a given batch application include the following:

yMemory (Pool size)

yCPU (processor speed)

yDASD (number and type)

ySystem tuning parameters

Batch Workload Description

The Batch Commercial Mix is a synthetic batch workload designed to represent multiple types of batch processing often associated with commercial data processing. The different variations allow testing of sequential vs random file access, changing the read to write ratio, generating "hot spots" in the data and running with expert cache on or off. It can also represent some jobs that run concurrently with interactive work where the work is submitted to batch because of a requirement for a large amount of disk I/O.

3.1 Effect of CPU Speed on Batch

The capacity available from the CPU affects the run time of batch applications. More capacity can be provided by either a CPU with a higher CPW value, or by having other contending applications on the same system consuming less CPU.

Conclusions/Recommendations

yFor CPU-intensive batch applications, run time scales inversely with Relative Performance Rating (CPWs). This assumes that the number synchronous disk I/Os are only a small factor.

yFor I/O-intensive batch applications, run time may not decrease with a faster CPU. This is because I/O subsystem time would make up the majority of the total run time.

yIt is recommended that capacity planning for batch be done with tools that are available for iSeries. For example, PATROL for iSeries - Predict from BMC Software, Inc. * (PID# 5620FIF) can be used for modeling batch growth and throughput. BATCH400 (an IBM internal tool) can be used for estimating batch run-time.

3.2 Effect of DASD Type on Batch

For batch applications that are I/O-intensive, the overall batch performance is very dependent on the speed of the I/O subsystem. Depending on the application characteristics, batch performance (run time) will be improved by having DASD that has:

yfaster average service times

yread ahead buffers

ywrite caches

Additional information on DASD devices in a batch environment can be found in Chapter 14, “DASD Performance”.

IBM i 6.1 Performance Capabilities Reference - January/April/October 2008
© Copyright IBM Corp. 2008	Chapter 3 - Batch Performance	39