SNMP Filesystemstats update only on restart


Feb 27, 2024

I'm monitoring our TrueNAS-Core System via SNMP in check_mk. Until now I've tought, everything is fine since the monitoring didn't show up anything ;-)

Last week I needed to power down the NAS due some construction work on the electricity. So far everything fine. After restarting the NAS my monitoring rised a warning for one of the Filesystems. Then I noticed a quite large step in the graph and wordered what has happen:
It seems, that the SNMP-Service always shows the same value until it is restarted (either the service or the whole system)

As you can see in the Reporting of TrueNAS, the used and free space is moving on a weekly basis up and down.
The values reported via SNMP are a flat-line until the restart last friday. Then the line remains on the higer level:

First, i was not sure if the issue comes from TrueNAS or from check_mk, but I was able to isolate it to TrueNAS:

1. I receive the raw snmp-values with an SNMP-Client like FrameFlow SNMP-Browser,
2. I change e.g. the size of the filesystem
3. Raw SNMP-values remain at their values
4. Restart
5. Raw SNMP-values changes

In my case the OIDs are

Does anyone know how to resolve this issue?

Thank you in advance
Best regards