Storage

You can use the SIR command to verify whether PAV support is active on your system.

Performance Considerations

Dependent on your workload and applications, there can be a significant performance improvement in I/O throughput and response time when using PAV. There will be no benefit on a single application basis. Due to the PAV load balancing algorithm a performance improvement will be achieved when running multiple applications issuing I/O against the same volume.

Attention Routine Commands

There are two Attention Routine (AR) commands that are useful when using PAV—SIR and VOLUME.

The SIR SMF,VSE,cuu command will display the maximum concurrently queued I/O requests on a given volume (i.e., cuu). For example, an installation might have a situation where there are two I/O requests waiting for a third request to be completed, causing performance degradation. By using the SIR SMF,VSE,cuu command, this problem could be quickly identified and potentially resolved by using PAV aliases.

The VOLUME command is another helpful command when using PAV support. The VOLUME command makes it easy to quickly see information about a particular volume, and has been enhanced to mark a base volume with PAV active by adding a *B in the “code” field. The DETAIL option for the VOLUME command shows the PAV-aliases for a given PAV-base.

Latest News

There are significant improvements for PAV support in z/VSE released with the following APARs: DY47396 for z/VSE 4.3 and DY47501 for z/VSE 5.1. PAV support is automatically included in z/VSE 5.2.

Summary

The use of the PAV feature can deliver significant z/VSE performance improvement when I/O operations are started against the same volume. By reducing I/O contention, organizations can increase the quantity of workload processed in a given time period, deliver better average response time throughout the entire day and help to elongate the use of the current mainframe system in use. If you are experiencing storage I/O bottlenecks, the use of PAV is worth considering.

References

• Hints and Tips for z/VSE 5.1 ftp://public.dhe.ibm.com/eserver/zseries/zos/vse/pdf3/zvse51/hintcmm2.pdf
• z/VSE Parallel Access Volume White Paper ftp://public.dhe.ibm.com/eserver/zseries/zos/vse/pdf3/White_Paper_PAV.pdf

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