For this server, there are 12 physical cores installed in the server but the FCO setting has been set to 4 so when the server is activated, only 4 of the 12 cores will be treated as installed. The remaining 8 cores will be logically removed (garded) and are not available for use. The service processor will try to balance the number of activated processor cores across the active processor chips. The FCO option is a very simple method of configuring your server to ensure compliance with software license limits. One drawback of this approach is if the Power hardware detects that a processor may fail, the previously garded processors are not available as hot spares. More information on FCO can be found at the following link.Another approach to enforcing software processor limits is the use of shared processor pools. A shared processor pool is a way to limit the amount of CPU consumption for a group of partitions. From the HMC if you select Virtual Resources, Shared Processor Pool Management you are presented with:
From this panel you can set a maximum limit on processor consumption for a group of partitions. You use the Partitions tab to indicate which partitions belong to specific shared processor pools. The shared processor pool approach is a bit more complicated than the FCO option but it allows all the cores in the server to be available in the rare case of a processor failure. Also, the maximum limit can be dynamically changed without requiring a server reboot. More information on shared processors pools can be found at the following link.Hardware Based Processor Limits (Capacity On Demand)Hardware based processor limits, also referred to as COD, are limits on the number of physical processors available for applications. When there are unlicensed cores, the Hypervisor will specifically choose individual cores to be licensed and unlicensed. The hypervisor will put the unlicensed cores into a state that reduces the overall energy consumption of the server. When a server is initially powered on or a customer runs a Dynamic Platform Optimizer (DPO) operation, the hypervisor treats all cores as licensed, makes the optimal assignment of processors and memory based on the configuration of the various partitions and then marks unused cores as unlicensed. Having dark cores in the server allows the hypervisor to optimize the resource assignments yielding improved application performance. Also, similar to dark memory, dark cores can be used as spares in the unlikely event of a processor failure. In summary, the PowerVM Capacity On Demand feature not only reduces the initial cost of ownership but allows customers to concurrently grow their hardware resources over time. There are also performance and reliability benefits available on servers that have dark resources. More information about COD can be found at Power Systems Capacity On Demand.
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