Sizing for RHOCP clusters

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You can use the formula that is provided here to estimate the IFL demand to maintain an idle Red Hat® OpenShift® cluster that runs on IBM Z®.

The calculation covers the baseline IFL demand and should not be used for sizing workloads. Therefore, extra IFLs are needed to run workloads reliably. To keep the formula simple, it is tuned for z/VM® and KVM. The formula might overestimate the IFL demand for bare metal deployments, since virtualization introduces additional layers, which contribute to CPU consumption.

The IFL demand for sizing Red Hat OpenShift clusters based on the number of compute nodes follows a linear equation:

D_{I F L} = N * 0.06 \frac{I F L s}{N o d e} + 1.26 I F L s

where:

$N_{}$: Number of compute nodes

This results in the demand listed in the following table:

Table 1. IFL demand of varying cluster sizes
Number of compute nodes	IFL demand
5	+1.6
10	+1.9
25	+2.8
50	+4.3
100	+7.4

Note: For example, if you plan to scale out a cluster from 5 to 25 nodes, you need at least 1.2 extra IFLs to run the cluster.