diff --git a/setup/start/collectd/du.py b/setup/start/collectd/du.py
index 5fa679bb1..e0fa890ff 100644
--- a/setup/start/collectd/du.py
+++ b/setup/start/collectd/du.py
@@ -3,6 +3,7 @@ import collectd,os,subprocess,sys,re,time
 # https://www.programcreek.com/python/example/106897/collectd.register_read
 
 PATHS = [] # { name, dir, exclude }
+# there is a pattern in carbon/storage-schemas.conf which stores values every 12h for a year
 INTERVAL = 60 * 60 * 12 # twice a day. change values in docker-graphite if you change this
 
 def du(pathinfo):