This technote provides a discussion of capped and uncapped shared pool partitions with respect to DLPAR and the Advanced POWER Virtualization feature of p5 servers.
A partition that is capped and a partition that is uncapped with a weight of 0 are functionally identical. In terms of performance, you get exactly the same result (utilization can only go up to the partition's entitled capacity, not higher), but weighting can be changed from within the partition in workload-managed LPAR groups, whereas capped/uncapped state cannot. If partition capping is an area you would like to change from within a partition using workload management software in the future, an uncapped partition with a weight of 0 should be selected. The HMC is dynamically able to change a partition from capped to uncapped, and to change the weight.
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