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I'm trying to understand a vSphere cluster where there are 20+ VMs on each host, almost all of them in unique vlans from each other.

To have vMotion work successfully between the hosts does each vlan need to have a VMotion enabled VMKernel or will the 'main' VMotion VMKernel on each host be enough?

The documentation doesn't suggest that one per vlan is necessary but that's the way this one is configured and I thought I'd check before I started removing them.

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In order to have vMotion working successfully, one VMkernel adapter per host is sufficient. However, one adapter per physical network interface would result in faster vMotion operations because vSphere would instruct hosts to use multiple network connections for parallel transfer of the virtual machine state (reference: KB2007467). There is no need for one VMkernel adapter per VLAN.

If an Enterprise Plus license is available in the cluster, it is recommended to configure VLANs as distributed port groups (dvPortGroups) of an unique vNetwork Distributed Switch (vDS) (KB1010555), because:

  • Creation of a new dvPortGroup on the vDS would make a new VLAN instantly available to all VMs on hosts that are members of that vDS; and
  • vDS health check, when enabled (KB2032878), would issue alarms when a particular VLAN tag configured in a dvPortGroup is absence from a host's physical network interface. That is very useful to avoid communication loss on a VM that depends on such VLAN.

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