I/O priorities are also recognized at the I/O controller level. To ensure that all connected systems utilize the same ranges of I/O priorities consistently it is recommended that you enable I/O priority groups in the service definitions of all active systems and sysplexes sharing I/O controllers as soon as you exploit I/O priority groups in one sysplex. In other words, you may have to enable I/O priority groups even if no service class is assigned to I/O priority group HIGH in the service definition.
Enabling I/O priority groups requires to specify yes for I/O priority management.