FreeNAS - How do you monitor disk/share usage?

I have a server running FreeNAS. It has a built in RAID card that is currently running 4 disks in RAID 10.

I have a LibreNMS server that uses SNMP to monitor all our network, virtual OSes, and physical machines. I just noticed that when monitoring a FreeNAS machine it does not show disk usage. Not even the OS that is running off a USB stick.

Is this just FreeNAS thing? If so how do you monitor your disk usage to know when disks are becoming full?

From what I recall of FreeNAS, you actually need to enable the SNMP service from the GUI. There's a HOST-RESOURCES-MIB that should show you what you're looking for. All MIBs are located under the /usr/local/share/snmp/mibs directory.

edit: Try a combination of these three OIDs (exact OID may vary on your system):

HOST-RESOURCES-MIB::hrStorageAllocationUnits.13
HOST-RESOURCES-MIB::hrStorageSize.13
HOST-RESOURCES-MIB::hrStorageUsed.13

You will need to multiply the hrStorageAllocationUnits into the hrStorageSize and hrStorageUsed to convert to bytes.