Symptoms:

• vCenter is 7.0U3d build 19480866 or higher.
• ESXi is 7.0U3d build 19482537.
• When trying to enable the vSAN RDMA feature, you get the below error:

VMware vSAN 7.0.x

vSAN RDMA cannot be enabled when the feature 'largeScaleClusterSupport' is enabled.

As of version 7.0 U3d, 32+ nodes are supported by default, so this feature, 'largeScaleClusterSupport' is deprecated, and the option to disable/enable this feature was removed from the vCenter Web Client. If you had enabled 'largeScaleClusterSupport' feature previously, there is no way to disable it from the vCenter Web Client after upgrading to 7.0 U3d.

Prior to upgrading to 7.0 U3d

After upgrading to 7.0U3d


Disabling large cluster support from the ESXi command line won't resolve this either.

Upgrade both vCenter and ESXi to 7.0 U3f or higher and run the below powershell command to disable 'largeScaleClusterSupport'. After disabling this feature, you will be able to enable RDMA.

pwsh> Connect-VIServer -Server <vCenter-IP>
pwsh> Set-VsanClusterConfiguration -Configuration <ClusterName> -LargeClusterSupported 0

For more information about vSAN RDMA, see the below links:
vSAN 7 Update 2 RDMA Support
Designing the vSAN Network

Below link is Dell's KB for this issue regarding VxRail clusters:
Dell VxRail: vSAN RDMA is not supported in VxRail 7.0.37x releases

Impact/Risks:
When 'largeScaleClusterSupport' feature is enabled, vSAN RDMA cannot be enabled.