Monitor FreeNAS disk using PRTG Network Monitor

In the following post I will show how to monitor FreeNAS volumes using Paessler PRTG Network Monitor.

Currently I’m using FreeNAS version 11.3-U2 and Paessler PRTG Network Monitor version 20.3.0.

SNMP OID: 1.3.6.1.4.1.50536.1.1.1.1

First let’s find what is the allocation size unit, for this we will need to run snmpget for OID: 1.3.6.1.4.1.50536.1.1.1.1.3.1

We can use either SNMP Tester utility (can be download from Paessler site) or do snmpwalk on Linux machine.

Here we can see I get 4096, write down this value as we will need it later on.

Now we will use OID 1.3.6.1.4.1.50536.1.1.1.1.4.1 to get the size of the volume:

As you can see the value is: 1946157056, multiple this value in the allocation size unit (4096) will give us 7,971,459,301,376, divide it by 1,000,000,000 and you will get the volume size in GigaByte: 7971, which is 8TB – my current volume size.

Use OID: 1.3.6.1.4.1.50536.1.1.1.1.5.1 to get the used size, and OID: 1.3.6.1.4.1.50536.1.1.1.1.6.1 the get the free available size. Again, we will need to multiple the values in the allocation unit size and divide the result in 1,000,000,000 the get it in GBytes.

Now open PRTG desktop and add new sensor to your FreeNAS device, in the search line type “OID” and select SNMP Custom:

Type in the sensor name (Volume Use), and the OID value: 1.3.6.1.4.1.50536.1.1.1.1.5.1:

Scroll down, type Channel Name (Used In GB), Unit string (GBytes), in multiplication type the allocation unit (4096) and in Division type 1,000,000,000:

Click Save.

Repeat the same for OID 1.3.6.1.4.1.50536.1.1.1.1.6.1 to get the free available size in GBytes:

Click save.

Now you got 2 new sensors, one which show how much GByte are used and the other how much free GBytes you got for your FreeNAS.