public static int compare(DiskSpeed a, DiskSpeed b) {
            if (a == any) a = slow;
            if (b == any) b = slow;

            if (a == slow && b == fast) return -1;
            if (a == fast && b == slow) return 1;
            return 0;
        }
Compares disk speeds by cost: Slower is cheaper, and therefore before.
Any can be slow and therefore costs the same as slow.
config-provisioning/src/main/java/com/yahoo/config/provision/NodeResources.java