How to measure z/VSE I/O performance ?
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There are several ways to measure the I/O performance of your z/VSE workload. The best tools are provided by performance monitor products from z/VSE vendors.
Just for getting some information about the I/O behavior of your system, you may use the SIR command.
With the SIR console (Attention Routine = AR) command you can get some characteristics of your workload, such as z/VSE supervisor call usage (SIR MON command) and I/O data.
You can retrieve I/O data with the SIR SMF command. The data comes from the Subsystem Measurement Facility of you IBM Z processor or the I/O Supervisor.
The SIR SMF output might help to identify the cause of I/O performance problems. We recommend to activate SIR SMF for a shorter time period to avoid the overflow of I/O counters. You can activate the I/O measurement with SIR MON=ON and stop measurement with SIR SMF=OFF. With SIR SMF you can display the counters as long as the I/O measurement is active.
Before you start a measurement period, activate SIR SMF.
The SIR SMF output displays the I/O count, the queued, connect, disconnect and total I/O time in milliseconds per start subchannel (I/O).
You can get the output for all disk devices or a specific one (SIR SMF=<cuu> or SIR SMF,<cuu>).
If you have Parallel Access Volume (PAV) devices and PAV is activated (SYSDEF SYSTEM,PAV=START), you will see the I/O counters for the base and alias devices too. With z/VSE 6.2 you may also retrieve the zHPF (high performance FICON) counters, if zHPF is activated (SYSDEF SYSTEM,ZHPF=START).
You can find a more detailed description with examples in the Hints and Tips for z/VSE 6.2 book. You can download that book here.