Be careful when you are channging SNMP Performance Cycle Interval from Collectors. When you first create a device or a new perfomance template with SNMP datapoint Zenoss creates new RRD files for them. It sets RRD minimal heartbeat to 3 times your SNMP Performance Cycle Interval. This means that if you later increase the value for SNMP Performance Cycle Interval you may get discontinuous graphs. This is because RRD ignores data if it is not updated within minimal heartbeat RRD.

You might see this problem when you increase your SNMP Performance Cycle Interval for performance reasons you risk "breaking" your graphs. Luckily there are two remedies:

1. The problem can be fixed by deleting RRD files, once Zenoss recreates them the minimal_heartbeat is correct
2. Command: rrdtool tune can be used to change minimal_heartbeat, for example set minimal_heartbeat to 120 seconds for load rrd:

rrdtool tune laLoadInt15_laLoadInt15.rrd -h ds0:120

RRDTool documentation clarifies the heartbeat functionality: http://oss.oetiker.ch/rrdtool/doc/rrdcreate.en.html (look for title: The HEARTBEAT and the STEP)