4.4. CSI volume cloning
Volume cloning duplicates an existing persistent volume to help protect against data loss in OpenShift Container Platform. This feature is only available with supported Container Storage Interface (CSI) drivers. You should be familiar with persistent volumes before you provision a CSI volume clone.
4.4.1. Overview of CSI volume cloning
A Container Storage Interface (CSI) volume clone is a duplicate of an existing persistent volume at a particular point in time.
Volume cloning is similar to volume snapshots, although it is more efficient. For example, a cluster administrator can duplicate a cluster volume by creating another instance of the existing cluster volume.
Cloning creates an exact duplicate of the specified volume on the back-end device, rather than creating a new empty volume. After dynamic provisioning, you can use a volume clone just as you would use any standard volume.
No new API objects are required for cloning. The existing dataSource field in the PersistentVolumeClaim object is expanded so that it can accept the name of an existing PersistentVolumeClaim in the same namespace.
4.4.1.1. Support limitations
By default, OpenShift Container Platform supports CSI volume cloning with these limitations:
- The destination persistent volume claim (PVC) must exist in the same namespace as the source PVC.
- The source and destination storage class must be the same.
- Support is only available for CSI drivers. In-tree and FlexVolumes are not supported.
- OpenShift Container Platform does not include any CSI drivers. Use the CSI drivers provided by community or storage vendors. Follow the installation instructions provided by the CSI driver.
- CSI drivers might not have implemented the volume cloning functionality. For details, see the CSI driver documentation.
- OpenShift Container Platform 4.5 supports version 1.1.0 of the CSI specification.
4.4.2. Provisioning a CSI volume clone
When you create a cloned persistent volume claim (PVC) API object, you trigger the provisioning of a CSI volume clone. The clone pre-populates with the contents of another PVC, adhering to the same rules as any other persistent volume. The one exception is that you must add a dataSource that references an existing PVC in the same namespace.
Prerequisites
- You are logged in to a running OpenShift Container Platform cluster.
- Your PVC is created using a CSI driver that supports volume cloning.
- Your storage back end is configured for dynamic provisioning. Cloning support is not available for static provisioners.
Procedure
To clone a PVC from an existing PVC:
Create and save a file with the
PersistentVolumeClaimobject described by the following YAML:pvc-clone.yaml
apiVersion: v1 kind: PersistentVolumeClaim metadata: name: pvc-1-clone namespace: mynamespace spec: storageClassName: csi-cloning 1 accessModes: - ReadWriteOnce resources: requests: storage: 5Gi dataSource: kind: PersistentVolumeClaim name: pvc-1- 1
- The name of the storage class that provisions the storage back end. The default storage class can be used and
storageClassNamecan be omitted in the spec.
Create the object you saved in the previous step by running the following command:
$ oc create -f pvc-clone.yaml
A new PVC
pvc-1-cloneis created.Verify that the volume clone was created and is ready by running the following command:
$ oc get pvc pvc-1-clone
The
pvc-1-cloneshows that it isBound.You are now ready to use the newly cloned PVC to configure a pod.
Create and save a file with the
Podobject described by the YAML. For example:kind: Pod apiVersion: v1 metadata: name: mypod spec: containers: - name: myfrontend image: dockerfile/nginx volumeMounts: - mountPath: "/var/www/html" name: mypd volumes: - name: mypd persistentVolumeClaim: claimName: pvc-1-clone 1- 1
- The cloned PVC created during the CSI volume cloning operation.
The created
Podobject is now ready to consume, clone, snapshot, or delete your cloned PVC independently of its originaldataSourcePVC.
