Kubeblocks Volume Expansion

Volume Expansion: Increase Storage

Overview

Volume expansion increases the persistent storage allocated to a KubeBlocks database cluster. This is an online operation — pods continue running while the underlying PVCs are resized.

Official docs: https://kubeblocks.io/docs/preview/user_docs/kubeblocks-for-mysql/cluster-management/expand-the-storage-of-a-mysql-cluster Full doc index: https://kubeblocks.io/llms-full.txt

Important: Volumes can only be expanded, never shrunk. Plan storage capacity carefully.

Prerequisites

The StorageClass must support volume expansion. Check:

kubectl get sc

Look for ALLOWVOLUMEEXPANSION = true in the output. If it shows false, the StorageClass does not support expansion and must be reconfigured by a cluster administrator:

kubectl get sc <storage-class-name> -o jsonpath='{.allowVolumeExpansion}'

Pre-Check

Before proceeding, verify the cluster is healthy and no other operation is running:

# Cluster must be Running
kubectl get cluster <cluster-name> -n <namespace> -o jsonpath='{.status.phase}'

# No pending OpsRequests
kubectl get opsrequest -n <namespace> -l app.kubernetes.io/instance=<cluster-name> --field-selector=status.phase!=Succeed

If the cluster is not Running or has a pending OpsRequest, wait for it to complete before proceeding.

Check current PVC sizes and StorageClass expansion support:

# Current PVC sizes
kubectl get pvc -n <namespace> -l app.kubernetes.io/instance=<cluster-name>

# StorageClass supports expansion
kubectl get sc -o custom-columns='NAME:.metadata.name,EXPANSION:.allowVolumeExpansion'

Workflow

- [ ] Step 1: Check current storage and StorageClass
- [ ] Step 2: Apply volume expansion OpsRequest
- [ ] Step 3: Monitor the operation
- [ ] Step 4: Verify new storage size

Step 1: Check Current Storage and StorageClass

Check current PVC sizes:

kubectl get pvc -n <namespace> -l app.kubernetes.io/instance=<cluster-name>

Check the cluster spec for storage configuration:

kubectl get cluster <cluster-name> -n <namespace> -o yaml | grep -A 6 volumeClaimTemplates

Verify StorageClass supports expansion:

kubectl get sc -o custom-columns='NAME:.metadata.name,PROVISIONER:.provisioner,EXPANSION:.allowVolumeExpansion'

Step 2: Apply Volume Expansion OpsRequest

OpsRequest Template

apiVersion: apps.kubeblocks.io/v1beta1
kind: OpsRequest
metadata:
  name: volumeexpand-<cluster-name>
  namespace: <namespace>
spec:
  clusterName: <cluster-name>
  type: VolumeExpansion
  volumeExpansion:
    - componentName: <component-name>
      volumeClaimTemplates:
        - name: <volume-name>
          storage: "<new-size>"

Volume Name Reference

Example: Expand MySQL Data Volume to 50Gi

Before applying, validate with dry-run:

kubectl apply -f - --dry-run=server <<'EOF'
apiVersion: apps.kubeblocks.io/v1beta1
kind: OpsRequest
metadata:
  name: volumeexpand-mysql-cluster
  namespace: default
spec:
  clusterName: mysql-cluster
  type: VolumeExpansion
  volumeExpansion:
    - componentName: mysql
      volumeClaimTemplates:
        - name: data
          storage: "50Gi"
EOF

If dry-run reports errors, fix the YAML before proceeding.

kubectl apply -f - <<'EOF'
apiVersion: apps.kubeblocks.io/v1beta1
kind: OpsRequest
metadata:
  name: volumeexpand-mysql-cluster
  namespace: default
spec:
  clusterName: mysql-cluster
  type: VolumeExpansion
  volumeExpansion:
    - componentName: mysql
      volumeClaimTemplates:
        - name: data
          storage: "50Gi"
EOF

Example: Expand PostgreSQL Data Volume to 100Gi

Before applying, validate with dry-run:

kubectl apply -f - --dry-run=server <<'EOF'
apiVersion: apps.kubeblocks.io/v1beta1
kind: OpsRequest
metadata:
  name: volumeexpand-pg-cluster
  namespace: default
spec:
  clusterName: pg-cluster
  type: VolumeExpansion
  volumeExpansion:
    - componentName: postgresql
      volumeClaimTemplates:
        - name: data
          storage: "100Gi"
EOF

If dry-run reports errors, fix the YAML before proceeding.

kubectl apply -f - <<'EOF'
apiVersion: apps.kubeblocks.io/v1beta1
kind: OpsRequest
metadata:
  name: volumeexpand-pg-cluster
  namespace: default
spec:
  clusterName: pg-cluster
  type: VolumeExpansion
  volumeExpansion:
    - componentName: postgresql
      volumeClaimTemplates:
        - name: data
          storage: "100Gi"
EOF

Example: Expand Kafka Data and Metadata Volumes

Before applying, validate with dry-run:

kubectl apply -f - --dry-run=server <<'EOF'
apiVersion: apps.kubeblocks.io/v1beta1
kind: OpsRequest
metadata:
  name: volumeexpand-kafka-cluster
  namespace: default
spec:
  clusterName: kafka-cluster
  type: VolumeExpansion
  volumeExpansion:
    - componentName: kafka-combine
      volumeClaimTemplates:
        - name: data
          storage: "100Gi"
        - name: metadata
          storage: "20Gi"
EOF

If dry-run reports errors, fix the YAML before proceeding.

kubectl apply -f - <<'EOF'
apiVersion: apps.kubeblocks.io/v1beta1
kind: OpsRequest
metadata:
  name: volumeexpand-kafka-cluster
  namespace: default
spec:
  clusterName: kafka-cluster
  type: VolumeExpansion
  volumeExpansion:
    - componentName: kafka-combine
      volumeClaimTemplates:
        - name: data
          storage: "100Gi"
        - name: metadata
          storage: "20Gi"
EOF

Expand Multiple Components

spec:
  volumeExpansion:
    - componentName: kafka-broker
      volumeClaimTemplates:
        - name: data
          storage: "200Gi"
    - componentName: kafka-controller
      volumeClaimTemplates:
        - name: data
          storage: "50Gi"

Step 3: Monitor the Operation

Watch the OpsRequest:

kubectl get ops volumeexpand-<cluster-name> -n <namespace> -w

Success condition: .status.phase = Succeed | Typical: 1-5min | If stuck >10min: kubectl describe ops volumeexpand-<cluster-name> -n <namespace>

Expected progression: Pending → Running → Succeed.

Watch PVC resize:

kubectl get pvc -n <namespace> -l app.kubernetes.io/instance=<cluster-name> -w

Step 4: Verify New Storage Size

After the OpsRequest succeeds, confirm PVC sizes:

kubectl get pvc -n <namespace> -l app.kubernetes.io/instance=<cluster-name>

Check the CAPACITY column reflects the new size.

Also verify from inside a pod:

kubectl exec -it <cluster-name>-<component>-0 -n <namespace> -- df -h /data

Troubleshooting

OpsRequest fails with "volume expansion not supported":

• The StorageClass does not allow expansion. Check: kubectl get sc <name> -o jsonpath='{.allowVolumeExpansion}'
• Ask the cluster admin to enable it: kubectl patch sc <name> -p '{"allowVolumeExpansion": true}'

PVC resize stuck in FileSystemResizePending:

• Some storage providers require a pod restart to complete the filesystem resize. KubeBlocks handles this automatically, but it may take a few minutes.
• Check PVC conditions: kubectl describe pvc <pvc-name> -n <namespace>

Cannot shrink volumes:

• This is a Kubernetes limitation. Volumes can only be expanded, never shrunk.
• If smaller storage is needed, create a new cluster with the desired size and migrate data.

Expansion for log or metadata volumes:

• Some addons define additional volumes (e.g., Kafka's metadata volume). Use the correct volume name from the reference table above.

For complete volume name reference across all addons, additional OpsRequest examples (Redis, MongoDB, Elasticsearch, Milvus), and StorageClass expansion support by cloud provider, see reference.md.

For general agent safety conventions (dry-run, status confirmation, production protection), see safety-patterns.md.