This one looks like is meant to be an internal communication message, i.e., between Storage Manager Agent and Storage Manager server. "mod.sys.na.NetApp" is the module on the agent that is responsible for collecting data. I am guessing 21 is the device ID of the NetApp storage that the module has an issue connecting to. In the web console, if you hover over the console links for your NetApp devices, you will see the URL in the status bar of your browser. You may want to check if deviceID 21 is one of your netapp devices assigned to this agent. You can also tell if you were to open windows explorer on the agent machine, browse to the <install folder>/systemic/mod.sys.na.NetApp_1.0 and open the xml file with the same name as the module.
But the disk status change one should ideally contain the netapp name.
