The scaling of the y-axis values is disabled for some sample manager. (See classes that inherits from org.ametys.runtime.plugins.core.administrator.jvmstatus.monitoring.sample.AbstractSampleManager)

In case of a very high y-axis max-value, the generation of the graph will fails :

Caused by: java.lang.ArrayIndexOutOfBoundsException: -1
	at org.rrd4j.graph.ValueAxis.draw(ValueAxis.java:98)
	at org.rrd4j.graph.RrdGraph.drawGrid(RrdGraph.java:193)
	at org.rrd4j.graph.RrdGraph.createGraph(RrdGraph.java:75)
	at org.rrd4j.graph.RrdGraph.<init>(RrdGraph.java:40)
	at org.ametys.runtime.plugins.core.monitoring.RRDGraphReader.generate(RRDGraphReader.java:102)
	at org.apache.cocoon.components.pipeline.impl.AbstractCachingProcessingPipeline.processReader(AbstractCachingProcessingPipeline.java:901)
	... 47 more

This is dues to the configuration of the graph definition graphDef.setUnitsExponent(0);. This line is present in the method _populateGraphDefinition of some sample manager (for example, the disk IO sample manager, or the http request sample manager)