If available, Cockpit uses the Performance Co-Pilot framework to gather metrics data about the system. This data is used to display graphs. Cockpit can use the PCP logging feature to display archived data about the system from a different point in time. If PCP is not available, then Cockpit gathers the metrics data itself, but archival features are not available.
Whether or not metrics are archived depends on whether the
pmcd.service systemd units
are running or not. The "Store Performance Data" button in Cockpit
will enable and start these services.
$ pmstat @ Sat Sep 26 15:30:10 2015 loadavg memory swap io system cpu 1 min swpd free buff cache pi po bi bo in cs us sy id 4.19 0 20710m 605148 6450m 0 0 0 2548 5688 14K 19 3 76 ...