Parallel Access Volumes (PAV) allow to define more than one Unit Control Block (UCB) per logical disk volume. The operation system, therefore, performs more than one I/O operation to that volume at a time.
One of the problems with mechanical storage disks, is that they are single threading. Only one process can access the data on a disk at a time. OS/390 managed this by allocating a Unit Control Block (UCB) to each storage device. If several applications wanted to access a device at the same time, then the IO operations were queued at the CPU by the IO supervisor. In performance terms, this is called IOSQ delay.
IOSQ is an especial problem for disks with several very active datasets, and storage administrators allocated busy databases, RACF files, HSM control files, Page & Spool datasets etc. on their own dedicated volumes. This required careful monitoring, and manual effort to change.
IBM -- Enterprise Storage Server Model 800
Dramatically improve performance in z/OS environment and improve system admin time: By reducing or eliminating IOSQ time on single z/OS or OS/390 images. Parallel Access Volumes provide the ability to eliminate almost all IOSQ time, a major contributor to response time.
Sun StorEdge 9900 Parallel Access Volumes
Conventional methods for accelerating access to active volumes of information involve labor-intensive performance tuning and the reallocation and splitting of data across multiple volumes. Sun StorEdge 9900 Parallel Access Volumes (PAV) software allows multiple applications running on a host server to access the same information simultaneously. Multiple Allegiance (MA) software extends this capability to applications running on multiple servers.
PAV can provide substantially faster host access to the data stored in Sun StorEdge 9900 series systems. The Workload Manager (WLM) host software function helps the host to utilize the PAV functionality of the Sun StorEdge 9900 series systems, which support both static and dynamic PAV functionality.