Check manual page of esx_vsphere_hostsystem_mem_usage_cluster

VMware ESX vCenter: Total Physical RAM Usage of Clustered ESX Hosts
Distribution	official part of Check_MK
License	GPL
Supported Agents	vSphere

This check measures the total physical RAM usage for a cluster of hosts. This check is only applicable for clusters and cannot be inventorized. You need to create a manual check for it in WATO and assign it to a cluster host.