How to find GCP Persistent Disk Usage?

Question

I have a GCP Persistent Disk associated with a pod in a GKE cluster. How do I find the disk usage for the persistent disk ? Is there any GCP commands which will be help me find the disk usage ?

Thanks a lot for your answers.

Answer 1

TL;DR

You can use the utilization (percentage of used space) of a certain volume mount for a Pod with following metric:

• kubernetes.io/pod/volume/utilization

The description states:

The fraction of the volume that is currently being used by the instance. This value cannot be greater than 1 as usage cannot exceed the total available volume space.

You can use this metric to monitor specific volume mounts that are backed by Persistent Disk.

Disclaimer!

Please remember that this method requires some tailoring to suit specific use cases. I've included an example below. I've also added a monitoring api query to extract the same information.

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Using the kubernetes.io/pod/volume/utilization metric

Assuming that you have a GKE cluster with:

• 3 PVC's that are backed by PD's with 100GB of space each
• 3 Pods where each of them is using single PVC
  • ubuntu-ten - where there is 10GB stored on mounted PVC
  • ubuntu-twenty - where there is 20GB stored on mounted PVC
  • ubuntu-thirty - where there is 30GB stored on mounted PVC

You can follow:

• GCP Cloud Console (Web UI) -> Monitoring -> Metrics explorer

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Querying the API

As asked in the comments under another answer:

Is there any examples for the monitoring API to retrieve the disk usage?

Yes they are. You can query the monitoring API for data by using MQL (Monitoring Query Language).

You will need to have query from example used earlier (volume_utilization). You can extract such query by going into Query Editor (it's on last image).

fetch k8s_pod
| metric 'kubernetes.io/pod/volume/utilization'
| filter
    (resource.cluster_name == 'CLUSTER_NAME'
     && resource.pod_name =~ 'ubuntu.*')
    && (metric.volume_name == 'volume-data')
| group_by 1m, [value_utilization_mean: mean(value.utilization)]
| every 1m

To query the API you can use Try this API feature available in GCP documentation:

• Cloud.google.com: Monitoring: API: Ref_v3: Rest: V3: Projects.timeseries: Query

Query created with the help of this tool:

curl --request POST \
  'https://monitoring.googleapis.com/v3/projects/PROJECT-NAME/timeSeries:query?key=[YOUR_API_KEY]' \
  --header 'Authorization: Bearer [YOUR_ACCESS_TOKEN]' \
  --header 'Accept: application/json' \
  --header 'Content-Type: application/json' \
  --data '{"query":"fetch k8s_pod| metric '"'"'kubernetes.io/pod/volume/utilization'"'"'| filter(resource.cluster_name == '"'"'CLUSTER-NAME'"'"'&& resource.pod_name =~ '"'"'ubuntu.*'"'"')&& (metric.volume_name == '"'"'volume-data'"'"')| group_by 1m,[value_utilization_mean: mean(value.utilization)]| every 1m"}' \
  --compressed

In the response you should get the information about the utilization of volumes used by Pods.

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Additional resources:

• Cloud.google.com: Kubernetes Engine: Persistent Volumes: Persistent Volume Claims
• Cloud.google.com: Monitoring

Answer 2

You cannot see the disk usage via a prepared command. But, you can check it via Stackdriver Monitoring (Google Cloud Operations Suite) with the metric named container/disk/bytes_used: documentation. You can use Monitoring APIs if you need to automatize it.

Please notice that you must enable Stackdriver on your cluster before. If you haven't, follow the documentation.