We played with stacked graphs, and that allowed us to display the total amount of item collections on a graph, but what if we would like to find out average load on a cluster, or total available disk space on a group of file servers, and not only display that on a graph, but also use it in triggers and notifications?
To find out what we can use in such a situation, go to Configuration | Hosts, select Linux servers in the Group dropdown and click on Items next to A Test Host, then click Create Item. Now we have to figure out what item type to use. Expand the Type dropdown and look for an entry named Zabbix aggregate. That's the one we need, so choose it and click Select next to the Key field. Currently the key is listed as grpfunc, but that's just a placeholder - click on it. We have to replace it with actual group key - one of grpsum, grpmin, grpmax, or grpavg. We'll calculate the average for several hosts, so change it to grpavg. This key, or group function, takes several...