Subtract two values with graphite possible?

Grafana Graphite
1

Hello, i have following problem:
I already show the Windows Server File Share Quota Status on he Grafana Dashboard. I use the pie chart plugin from the plugin library.
The workflow how grafana gets the values are following: icinga2 (check_drivesize via NSClient++) → performance-data → graphite → grafana.
From the check_drive plugin i get only the used and the total value. This means i use two metric lines. One is total and the other is used.
The problem here is that to show the graph correctly i would need the “used” and “free” value but i dont have the free one right now.
So my thinking was that a workaround could be that i subtract used from the total value. Is this possible in grafana?

Edit: Same problem like here: https://community.grafana.com/t/disk-usage-as-percentage-of-used-disk/1499/3

Thank you!

2

There is a graphite function called substract i think

3

I could not find a function called “substract” do you have a link or example for me?

4

It’s called diffSeries

5

If you’re looking for a solution that fully works in grafana, look at my other post: Disk usage as percentage of used disk - #4 by bjgocraft

6

Yes, it’s possible to calculate the “free” value in Grafana by subtracting the “used” value from the “total” value. You can achieve this by using Grafana’s query editor to create a new metric.

Here’s a brief outline of how to do it:

  1. Open your Grafana panel where you want to display the data.
  2. Go to the query editor for your data source.
  3. Add a new metric that performs the calculation:
  • If you’re using Graphite, your query could look something like this:

total - used

  • For Prometheus, you can use:

total_metric - used_metric

  1. Create the pie chart using the new “free” value along with the “used” value.