| HP XP for Compatible Parallel Access Volumes Software (PAV) and HP XP for Compatible Hyper PAV Software enable high performance concurrent access of mainframe volumes by permitting a mainframe host system to issue multiple I/O requests in parallel to individual logical devices within the HP XP Disk Array. Without PAV, mainframe systems can initiate only one I/O request per device at a time, and must wait for the I/O to complete before starting another I/O request to the same device. By utilizing alias addresses that all point to the same device as the base address, PAV enables the host system to start several I/O requests simultaneously to the same device, thus greatly improving performance.
The HP XP Disk Array supports static PAV, dynamic PAV, and Hyper PAV. With static PAV, the number of aliases assigned to each base device does not change. With dynamic PAV, high workload base devices can borrow idle PAV aliases from other base devices, increasing their I/O capability. Accesses to large volumes will also be enhanced as resources are applied to allow multiple simultaneous accesses to the volume. Workload Manager (WLM), mainframe host-based software, can be used to manage PAV so that the host is able to take best advantage of the performance enhancements available with dynamic PAV. Hyper PAV enhances the efficiency of PAV by selecting alias IDs from a pool and binding them to base IDs only for the duration of the I/O operation, thus reducing the number of required PAV aliases while maintaining or improving the IO performance available to Mainframe hosts. Hyper PAV can coexist with both static PAV and dynamic PAV.
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