When attempting to remove a host from a vSphere Distributed Switch (vDS), an administrator observes the error message: The resource '16' is in use What are two reasons why this error would be…

VMkernel adapters (management, vMotion, vSAN, iSCSI, etc.) are host-level resources bound to vDS port groups. As long as any VMkernel adapter references the vDS, ESXi marks that resource as in use and blocks host removal.

Virtual machine vNICs connected to vDS port groups are also tracked as active port consumers. Each connected vNIC holds a port allocation on the vDS, so the switch resource remains in use until those VMs are migrated or disconnected.

Network I/O Control is a traffic-shaping policy configured on the vDS itself, not a host-bound resource, and its presence does not prevent a host from being removed.

Active traffic flowing through the vDS is a consequence of adapters being connected, not an independent resource lock - ESXi tracks adapter attachment, not packet flow, when evaluating whether a resource is in use.