Storage SLOs

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Storage Operations


This SLO measures the percentage of failed storage operations, reported by kubelets and the controller-manager. The error rate is a general indicator of the health of the storage provider, but might not show you the root cause of the issue.

There are two types of alerts that fire if we expect to miss the configured objective.

  • A ticket alert means that the error rate is slightly higher than the objective. If we don’t intervene at some point after receiving this alert, we can expect to miss the objective. However no immediate, urgent action is necessary. A ticket alert should have a label severity: warning.

  • A page alert means that the error rate is significantly higher than the objective. Immediate action is necessary to not miss the objective. A page alert should have a label severity: critical and should page on-call.

Steps for debugging

A high storage operations error rate can have many root causes. To narrow down the issue we first need to find out which operations and which providers are effected.

Connect to the Prometheus on the cluster and run the following query:

sum(rate(storage_operation_duration_seconds_count{volume_plugin=~"", status="fail-unknown"}[5m])) by (job, operation_name, volume_plugin, node)

This should return one or more time series. With these you should be able to narrow down the issue:

  • If all time series have the same volume_plugin label the issue is most likely caused by that provider. Look at the logs of that csi provider to investigate further.

  • If they have the same node label it might be an issue with one specific node.

  • If all have the same operation_name label then there is an issue with this specific operation. For volume_attach and volume_detach check if the controller-manager logs anything useful. For all other operations the kubelet might log more information.

  • If all time series have the same job label it might be an issue with the kubelet or the controller-manager, look at the respective logs.

This should give you a starting point to investigate the root cause. You should also check if there are other, related firing alerts and create/delete a test PVC to properly assess the impact of this alert.

We don’t have a lot of experience with this alert yet. If you had to debug this alert, please consider adding any insight, tips, or code snippets you gained to this runbook.


If this alert isn’t actionable, noisy, or was raised too late you may want to tune the SLO.

You have the option tune the SLO through the component parameters. You can modify the objective, disable the page or ticket alert, restrict the SLO to certain storage operations or volume plugins, or completely disable the SLO.

The example below will set the SLO set the objective to 99.25%, disable the page alert, and only consider the Syn-managed CephFS storage provider. This means this SLO won’t alert on-call anymore and won’t alert if there are issues with CSI plugins other than the Syn-managed CephFS CSI plugin.

      objective: 99.25
        volume_plugin: ""
          enabled: false
Disabling the SLO or changing the objective will also impact the SLO dashboard and SLA reporting. Only disable SLOs if they’re not relevant, not if the alerts are noisy.