public double diskOverhead(VespaFlavor flavor, NodeResources resources, boolean real, boolean exclusive) {
        if ( flavor.realResources().storageType() != NodeResources.StorageType.local) return 0;
        double hostDiskOverhead = reservedSpacePolicy.getPartitionSizeInBase2Gb(NodeType.host, ! exclusive);
        double diskShare = resources.diskGb() /
                           ( flavor.advertisedResources().diskGb() - ( real ? hostDiskOverhead : 0) );
        return hostDiskOverhead * diskShare;
    }
Returns the disk overhead resulting if the given advertised resources are placed on the given node

@param real true if the resources are in real values, false if they are in advertised
node-repository/src/test/java/com/yahoo/vespa/hosted/provision/autoscale/awsnodes/AwsResourcesCalculator.java