I/O priority recommendations

Channel subsystem I/O priority queuing is used by z/OS® WLM component to dynamically manage the priority of I/O operations for given workloads based on the performance goals for these workloads as specified in the WLM policy.

Channel subsystem I/O priority queuing is used by z/VM® to manage the priority of I/O operations performed by guests. The VM Resource Manager adjusts guest I/O priorities based on the performance goals of the associated workloads. It is recommended that you establish a range of I/O priorities for z/VM logical partitions that is sufficient to enable effective discrimination among guest I/O requests of different importance.

In order to provide WLM the greatest flexibility in managing I/O requests across members of an LPAR cluster, it is highly recommended that you establish the same range of priorities for each member of an LPAR cluster. A range of eight priorities (from minimum to maximum) is optimum. If a range greater than eight is specified, only the top eight will be utilized by WLM.

Non-WLM managed LPs should be assigned I/O priorities according to their importance relative to the LPs that are members of LPAR clusters. Unless it is running z/VM (in which case the recommendations above should be followed), a non-WLM managed LP should be assigned equal values for minimum and maximum I/O priorities.