Hi Kersi,
For Volume(NAS) using NMC you can create a Alert for events such as Volume Almost full, Volume Full, etc. In NMC navigate to Notifications->Alarms and Add a new Alaram. This wizard wil let you create alarm based on event/ severity and specify the recipient of alarm- email, SNMP trap receiver.
From command line you can try "dfm alarm create" to create an alarm.
You can either use global threshold levels or set these thresholds for individual volumes as well using CLI :
To get the various thersholds for given volume use:
#dfm volume get -q <storage system>:/<vol_name>
To set the values for "Volume Nearly Full Threshold ", for example:
#dfm volume set <storage system>:/<vol_name> volNearlyFullThreshold=75
For LUN(SAN) am not sure if you can create an alarm. This may be due to the fact that LUN space is managed by the host file system and not by DFM/OnCommand.
Regards,
-Amir