Since the filers are quite accesible through things like ssh, web interface and SNMP I didn’t think it would be hard. But, when doing a quick search I’ve found this excellent nagios plugin made by Sven Velt. It is available at http://people.teamix.net/~svelt/check_netappfiler/. It has saved me *lots* of time.
It even seems to be prepared to be used with pnp4nagios too. I haven’t tried this since I’m not using it.
One strange thing though… I can query all the filers with standard SNMP settings even with SNMP disabled on the filer(s). This has suprised me a bit. It might be a bug, but I’m not sure.