Monitoring Hard Disk Space

Monitoring hard disk space solves at least two purposes: it can be used to generate alerts or trigger corrective actions if a system runs out of free space. It can also be used as a statistical tool to monitor disk space utilization over time.

In our tutorial, we configure a simple disk space monitor and define a rule that stores the results into a text file that can be analysed later. Of course, we could have added trigger conditions for alerts and such. We have not done this, to keep things simple.

As always, we create the needed rule set first. In our sample, we call it “DiskSpace”. Please note that this time we actually create a “Rule Set”, not just an additional rule in the “Defaults” rule set. The reason is that for our purpose, it is much easier to define a specialised rule set and then bind this specialised rule set to the disk space monitor. If we would use the generic “Defaults” rule set, we had to make sure that our filter conditions would only match when an event of type disk space monitor would come in. In addition, it would require more processing time, as all rules and condition filters would be processed – a process that is not needed as we deal with a specific case. As such, it is more appropriate to define a specific rule set, which is then only used for the disk space monitor. What is appropriate in your environment depends on your needs. There is no general rule.

Inside the new rule, we create a filter condition that evaluates to true only if the reported diskspace has less than 20 gigabytes of free space. So we log date only when we potentially have constrained disk space. The filter looks as follows:


Monitoring Hard Disk Space - Figure 1

To create this filter, select “Disk Space Monitor”, then “Disk Space Left” when pressing the “Add Filter” button.

We use the “Write to File” action in this sample. The action is called “Write DiskSpace” as can be seen below. We could also have used other actions, including emailing, to alert an administrator or start a script to delete temporary files.


Monitoring Hard Disk Space - Figure 2

Please note: you should make sure that the base name is different from other “write to file” actions. Otherwise data might get mixed up in the files.

Having created the new rule set, we now need to create the disk space monitor service itself. It is the part of the software that actively goes out and monitors the disk space. To create it, right-click “Services” and select “Add Service”. Below “File System monitoring” you find “Diskspace Monitor” as seen below:


Monitoring Hard Disk Space - Figure 3

We name the service “Diskspace Monitor” in our sample. Leave the default settings. Please note that when you select the new service, it is typically bound to the “Defaults” rule set. We need to change this, as we have created the specific “Disk Space Monitor” rule set. Change the “Rule Set to Use” to update it to the new binding.


Monitoring Hard Disk Space - Figure 4

Save the configuration and restart the service. After a few moments, the disk space log file should fill up (if there is less than 20 GB of free space on the monitored system). In notepad, it looks like follows:


Monitoring Hard Disk Space - Figure 5