my-rook-config/deploy/examples/monitoring/externalrules.yaml

# Copied from /deploy/charts/rook-ceph-cluster/prometheus/, CR header added, and indentation increased on the groups
apiVersion: monitoring.coreos.com/v1
kind: PrometheusRule
metadata:
  labels:
    prometheus: rook-prometheus
    role: alert-rules
  name: prometheus-ceph-rules
  namespace: rook-ceph # namespace:cluster
spec:
  groups:
    - name: persistent-volume-alert.rules
      rules:
        - alert: PersistentVolumeUsageNearFull
          annotations:
            description: PVC {{ $labels.persistentvolumeclaim }} on cluster {{ $labels.cluster }} utilization has crossed 75%. Free up some space or expand the PVC.
            message: PVC {{ $labels.persistentvolumeclaim }} on cluster {{ $labels.cluster }} is nearing full. Data deletion or PVC expansion is required.
            severity_level: warning
            storage_type: ceph
          expr: |
            (kubelet_volume_stats_used_bytes * on (cluster,namespace,persistentvolumeclaim) group_left(storageclass, provisioner) (kube_persistentvolumeclaim_info * on (cluster,storageclass)  group_left(provisioner) kube_storageclass_info {provisioner=~"(.*rbd.csi.ceph.com)|(.*cephfs.csi.ceph.com)"})) / (kubelet_volume_stats_capacity_bytes * on (cluster,namespace,persistentvolumeclaim) group_left(storageclass, provisioner) (kube_persistentvolumeclaim_info * on (cluster,storageclass)  group_left(provisioner) kube_storageclass_info {provisioner=~"(.*rbd.csi.ceph.com)|(.*cephfs.csi.ceph.com)"})) > 0.75
          for: 5s
          labels:
            severity: warning
        - alert: PersistentVolumeUsageCritical
          annotations:
            description: PVC {{ $labels.persistentvolumeclaim }} on cluster {{ $labels.cluster }} utilization has crossed 85%. Free up some space or expand the PVC immediately.
            message: PVC {{ $labels.persistentvolumeclaim }} on cluster {{ $labels.cluster }} is critically full. Data deletion or PVC expansion is required.
            severity_level: error
            storage_type: ceph
          expr: |
            (kubelet_volume_stats_used_bytes * on (cluster,namespace,persistentvolumeclaim) group_left(storageclass, provisioner) (kube_persistentvolumeclaim_info * on (cluster,storageclass)  group_left(provisioner) kube_storageclass_info {provisioner=~"(.*rbd.csi.ceph.com)|(.*cephfs.csi.ceph.com)"})) / (kubelet_volume_stats_capacity_bytes * on (cluster,namespace,persistentvolumeclaim) group_left(storageclass, provisioner) (kube_persistentvolumeclaim_info * on (cluster,storageclass)  group_left(provisioner) kube_storageclass_info {provisioner=~"(.*rbd.csi.ceph.com)|(.*cephfs.csi.ceph.com)"})) > 0.85
          for: 5s
          labels:
            severity: critical