Question 59 - 5V0-35.21 discussion

The reason why vRealize Operations reports that the cluster has 0 days remaining when the actual CPU overcommit ratio is less than the 4:1 configured value is that the CPU demand in the cluster is greater than the total CPU capacity. The allocation model is a method of calculating the capacity and utilization of resources based on the amount of resources that are allocated to the objects, such as virtual machines, clusters, or datastores. The allocation model allows the administrator to set the overcommit ratio for CPU, memory, or disk space, which is the ratio of the allocated resources to the available resources.The overcommit ratio determines how much the resources can be overcommitted without affecting the performance or availability of the objects1.

When the administrator enables the allocation model in a policy and sets the CPU overcommit ratio to 4:1 for all vSphere clusters in a vSphere datacenter, it means that the administrator allows the CPU resources to be allocated four times more than the available CPU resources in the clusters. For example, if a cluster has 100 GHz of CPU capacity, the administrator can allocate up to 400 GHz of CPU resources to the virtual machines in the cluster. However, this does not mean that the virtual machines can consume up to 400 GHz of CPU resources without any impact. The actual CPU consumption of the virtual machines depends on the CPU demand, which is the amount of CPU resources that the virtual machines require to run their workloads.The CPU demand can vary depending on the workload type, intensity, and pattern2.

If the CPU demand in the cluster is greater than the total CPU capacity, it means that the virtual machines are requesting more CPU resources than the cluster can provide. This can result in CPU contention, performance degradation, and SLA violations. In this case, vRealize Operations reports that the cluster has 0 days remaining, which means that the cluster has reached its maximum capacity and cannot accommodate any more CPU demand. The cluster has 0 days remaining even if the actual CPU overcommit ratio is less than the 4:1 configured value, because the overcommit ratio only reflects the allocated resources, not the consumed resources.The overcommit ratio does not guarantee that the cluster can support the CPU demand of the virtual machines, but only indicates the potential capacity of the cluster based on the allocation model1.

References:1:Allocation Model - VMware Docs2:Demand Model - VMware Docs