Few weeks i observed strange graphs for network usage produced by munin, i did not attach any importance to this. But few days ago when i seen again 600Mbit badwidth usage on host that had 10Mbit connection i remembered that before made some changes in munin.conf. I looked at config and found that changed directive ‘graph_period’ to ‘minute’ before(do not remember why). When i change it back to ‘second’, i got normal graphs.