Parallel Access Volumes (PAV) allow z/OS to start more than 1 I/O to each System z 3390 image. This way most queueing can be eliminated, and overall I/O throughput can be improved significantly.
PAV uses ‘alias’ addresses are used to start the additional I/Os. The ‘alias’ addresses need to be configured by the installation. Two different modes are supported in z/OS:
- With Static PAVs the alias assignment is fixed, so you need to manually assign a certain number of aliases to each volume for which you want to reduce queueing.
- With Dynamic PAVs the alias assignment will be more dynamic, you simply assign a pool of addresses to each LCU. z/OS will assign the aliases where they are most useful to reduce queuing and to help meet the service objectives of your installation.
- With HyperPAV the alias assignment occurs for each individual I/O request for each LPAR accessing the Disk Subsystem. This mechanism is by far the most efficient.
When HyperPAV cannot be used, dynamic PAV (shown in the image) is the preferred option to use, as it will automate the alias management.
You do need to know how many aliases to assign to each volume. How many are needed depends mostly on the activity of the volume, where larger volumes (“3390 Model 54”) are more likely to show a high I/O rate. IntelliMagic Vision for z/OS provides recommendations on the number of aliases required for both HyperPAV and Dynamic PAV configurations.