Enabling Expansion of Persistent Volume Claims

Volume expansion is a Technology Preview feature, and hence, is not enabled by default in your OpenShift Container Platform 3.9 cluster. There may be other reasons that OpenShift Container Platform administrators wish to enable this feature for certain use cases.

For more information on Red Hat Technology Preview features support scope, see https://access.redhat.com/support/offerings/techpreview/.

To allow expansion of persistent volume claims (PVC) by OpenShift Container Platform users, OpenShift Container Platform administrators must create or update a StorageClass with allowVolumeExpansion set to true. Only PVCs created from that class are allowed to expand.

Apart from that, OpenShift Container Platform administrators must enable the ExpandPersistentVolumes feature flag and turn on the PersistentVolumeClaimResize admission controller. Refer to Admission Controllers for more information on the PersistentVolumeClaimResize admission controller.

To enable the feature gate, set ExpandPersistentVolumes to true across the system:

  1. Configure node-config.yaml on all nodes in the cluster:

    # cat /etc/origin/node/node-config.yaml
    ...
    kubeletArguments:
    ...
      feature-gates:
      - ExpandPersistentVolumes=true
    # systemctl restart atomic-openshift-node
  2. Enable the ExpandPersistentVolumes feature gate on the master API:

    # cat /etc/origin/master/master-config.yaml
    ...
    kubernetesMasterConfig:
      apiServerArguments:
      ...
      feature-gates:
      - ExpandPersistentVolumes=true
    
    # systemctl restart atomic-openshift-master-api

Expanding GlusterFS-Based Persistent Volume Claims

Expanding GlusterFS volumes is easiest. Once the OpenShift Container Platform administrator has created a StorageClass with allowVolumeExpansion set to true, you can create a PVC from that class, and afterwards, whenever needed, you can edit the PVC and request a new size.

For example:

kind: PersistentVolumeClaim
apiVersion: v1
metadata:
  name: gluster-mysql
spec:
  storageClass: "storageClassWithFlagSet"
  accessModes:
    - ReadWriteOnce
  resources:
    requests:
      storage: 8Gi (1)
1 You can request an expanded volume by updating spec.resources.requests.

Expanding Persistent Volume Claims with a File System

Expanding PVCs based on volume types that need file system resizing (such as GCE PD, EBS, and Cinder) is a two-step process. This process usually involves expanding volume objects in the CloudProvider, and then expanding the file system on the actual node.

Expanding the file system on the node only happens when a new pod is started with the volume.

The following process assumes that the PVC was previously created from a StorageClass with allowVolumeExpansion set to true:

  1. Edit the PVC and request a new size by editing spec.resources.requests. Once the CloudProvider object has finished resizing, the PVC is set to FileSystemResizePending.

  2. Type the following command to check the condition:

  oc describe pvc <pvc_name>

When the CloudProvider object has finished resizing, the persistent volume (PV) object reflects the newly requested size in PersistentVolume.Spec.Capacity. At this point, you can create or re-create a new pod from the PVC to finish the file system resizing. Once the pod is running, the newly requested size is available and FileSystemResizePending condition is removed from the PVC.