It is important to monitor your disk space. Usually you set a value that gives you a warning when disk is something like 90% full. This is good but in Check MK you can make this better. You may and up with something like this. It will predict when the disk is about to get full.
The full documentation for the parameters could be found here:
To do this you will have to create a rule called “Filesystems (used space and growth)”
It looks like this. You may want to edit some other parameters here as well like levels and magic factors. I have used some. Trend is set to 24 hours. Levels on trends will warn if the growth exceeds 100000 MB / range for the last 24 hours. This will notify you if very large amounts of data is stored on disks. Typically this is some user uploading their personal film collection on the server or something other very stupid. Levels for the percentual growth per time range does the same based on the percent.
Levels on the time gives you a warning some days in advance. Also tick display time left to see this in the output.
You may also want to include some disks or some hosts. In Linux systems you may want to add other mountpoints as well.