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.

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 does not ship with any CSI drivers. It is recommended to use the CSI drivers provided by community or storage vendors. Follow the installation instructions provided by the CSI driver.

OpenShift Container Platform 4.4 supports version 1.1.0 of the CSI specification.

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/.

Expanding FlexVolume with a supported driver

When using FlexVolume to connect to your backend 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 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.

Because OpenShift Container Platform does not support installation of FlexVolume plugins on master nodes, it does not support control-plane expansion of FlexVolume.

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 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.

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.