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Chapter 3. Expanding persistent volumes

3.1. Enabling volume expansion support

Before you can expand persistent volumes, the StorageClass must have the allowVolumeExpansion field set to true.

Procedure

  • Edit the StorageClass and add the allowVolumeExpansion attribute. The following example demonstrates adding this line at the bottom of the StorageClass’s configuration. 

    apiVersion: storage.k8s.io/v1
kind: StorageClass
...
parameters:
  type: gp2
reclaimPolicy: Delete
allowVolumeExpansion: true 1
    1
    Setting this attribute to true allows PVCs to be expanded after creation.

3.2. Expanding Persistent Volume Claims (PVC) 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 involves expanding volume objects in the cloud provider, 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.

Prerequisites

  • The controlling StorageClass must have allowVolumeExpansion set to true.

Procedure

  1. Edit the PVC and request a new size by editing spec.resources.requests. For example, the following expands the ebs PVC to 8 Gi. 

    kind: PersistentVolumeClaim
apiVersion: v1
metadata:
  name: ebs
spec:
  storageClass: "storageClassWithFlagSet"
  accessModes:
    - ReadWriteOnce
  resources:
    requests:
      storage: 8Gi 1
    1
    Updating spec.resources.requests to a larger amount will expand the PVC.

  2. Once the cloud provider object has finished resizing, the PVC is set to FileSystemResizePending. The following command is used to check the condition: 

    $ oc describe pvc <pvc_name>
  3. When the cloud provider object has finished resizing, the persistent volume object reflects the newly requested size in PersistentVolume.Spec.Capacity. At this point, you can create or recreate a new pod from the PVC to finish the file system resizing. Once the pod is running, the newly requested size is available and the FileSystemResizePending condition is removed from the PVC.

3.3. Recovering from Failure when Expanding Volumes

If expanding underlying storage fails, the OpenShift Container Platform administrator can manually recover the Persistent Volume Claim (PVC) state and cancel the resize requests. Otherwise, the resize requests are continuously retried by the controller without administrator intervention.

Procedure

  1. Mark the persistent volume (PV) that is bound to the PVC with the Retain reclaim policy. This can be done by editing the PV and changing persistentVolumeReclaimPolicy to Retain.
  2. Delete the PVC. This will be recreated later.
  3. To ensure that the newly created PVC can bind to the PV marked Retain, manually edit the PV and delete the claimRef entry from the PV specs. This marks the PV as Available.
  4. Re-create the PVC in a smaller size, or a size that can be allocated by the underlying storage provider.
  5. Set the volumeName field of the PVC to the name of the PV. This binds the PVC to the provisioned PV only.
  6. Restore the reclaim policy on the PV.
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