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Chapter 6. Expanding persistent volumes

6.1. Enabling volume expansion support

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

Procedure

  • Edit the StorageClass object and add the allowVolumeExpansion attribute. The following example demonstrates adding this line at the bottom of the storage class 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.

6.2. Expanding CSI volumes

You can use the Container Storage Interface (CSI) to expand storage volumes after they have already been created.

OpenShift Container Platform supports CSI volume expansion by default. However, a specific CSI driver is required.

OpenShift Container Platform 4.6 supports version 1.1.0 of the CSI specification.

Important

Expanding CSI volumes is a Technology Preview feature only. Technology Preview features are not supported with Red Hat production service level agreements (SLAs) and might not be functionally complete. Red Hat does not recommend using them in production. These features provide early access to upcoming product features, enabling customers to test functionality and provide feedback during the development process.

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

6.3. Expanding FlexVolume with a supported driver

When using FlexVolume to connect to your back-end storage system, you can expand persistent storage volumes after they have already been created. This is done by manually updating the persistent volume claim (PVC) in OpenShift Container Platform.

FlexVolume allows expansion if the driver is set with RequiresFSResize to true. The FlexVolume can be expanded on pod restart.

Similar to other volume types, FlexVolume volumes can also be expanded when in use by a pod.

Prerequisites

  • The underlying volume driver supports resize.
  • The driver is set with the RequiresFSResize capability to true.
  • Dynamic provisioning is used.
  • The controlling StorageClass object has allowVolumeExpansion set to true.

Procedure

  • To use resizing in the FlexVolume plugin, you must implement the ExpandableVolumePlugin interface using these methods:

    RequiresFSResize
    If true, updates the capacity directly. If false, calls the ExpandFS method to finish the filesystem resize.
    ExpandFS
    If true, calls ExpandFS to resize filesystem after physical volume expansion is done. The volume driver can also perform physical volume resize together with filesystem resize.
Important

Because OpenShift Container Platform does not support installation of FlexVolume plugins on control plane nodes (also known as the master nodes), it does not support control-plane expansion of FlexVolume.

6.4. Expanding persistent volume claims (PVCs) 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 object 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. After the cloud provider object has finished resizing, the PVC is set to FileSystemResizePending. Check the condition by entering the following command: 

    $ oc describe pvc <pvc_name>
  3. When the cloud provider object has finished resizing, the PersistentVolume 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.

6.5. 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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