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Chapter 6. Expanding persistent volumes

To increase available storage capacity, expand persistent volumes in MicroShift. You can resize existing volumes to accommodate growing application data requirements without recreating storage resources.

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

Important

Shrinking persistent volumes (PVs) is not supported.

Prerequisites

  • The underlying CSI driver supports resize.

    For information about which CSI drivers support resizing, see under the Additional resources section "CSI drivers supported by Red Hat build of MicroShift".

  • Dynamic provisioning is used.

  • The controlling StorageClass object has allowVolumeExpansion set to true.

    For more information, see section Enabling volume expansion support.

Procedure

  • For the persistent volume claim (PVC), set .spec.resources.requests.storage to the desired new size.

Verification

  • To confirm that the resize is finished, look at the status.conditions field of the PVC . Red Hat build of MicroShift adds the Resizing condition to the PVC during expansion, which is removed after expansion completes.

6.3. Expanding local volumes
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To expand your Local Storage Operator (LSO) storage capacity and meet growing data needs, update the storage request in your persistent volume (PV) and persistent volume claim (PVC). This increases capacity for existing volumes without recreating them.

Procedure

  1. Expand the underlying devices. Ensure that appropriate capacity is available on these devices.
  2. Update the corresponding PV objects to match the new device sizes by editing the .spec.capacity field of the PV.
  3. For the storage class that is used for binding the PVC to PV, set the allowVolumeExpansion field to true.
  4. For the PVC, set .spec.resources.requests.storage to match the new size.

Result

Kubelet should automatically expand the underlying file system on the volume, if necessary, and update the status field of the PVC to reflect the new size.

To expand your storage capacity and meet growing data needs, you can resize existing volumes without recreating them.

Expanding persistent volume claims (PVCs) based on volume types that need file system resizing, such as Google Cloud Platform (GCP) persistent disk (PD), AWS Elastic Block Storage (EBS), and Cinder, is a two-step process. First, expand the volume objects in the cloud provider. Second, expand the file system on the node.

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

Prerequisites

  • The controlling storage class has the allowVolumeExpansion field set to true.

    For more information, see section Enabling volume expansion support.

Procedure

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

    Example PVC YAML file

    kind: PersistentVolumeClaim
apiVersion: v1
metadata:
  name: ebs
spec:
  storageClass: "storageClassWithFlagSet"
  accessModes:
    - ReadWriteOnce
  resources:
    requests:
      storage: 8Gi

    Where updating spec.resources.requests to a larger amount expands the PVC.

Verification

After the cloud provider object has finished resizing, the PVC is set to FileSystemResizePending.

  • Check the condition by running the following command: 

    $ oc describe pvc <pvc_name>

Next steps

When the cloud provider object has finished resizing, the PersistentVolume object reflects the newly requested size in PersistentVolume.Spec.Capacity. You can now create or recreate a new pod from the PVC to finish the file system resizing. After the pod is running, the newly requested size is available and the FileSystemResizePending condition is removed from the PVC.

If a resize request fails or remains in a pending state, you can try again by entering a different resize value in .spec.resources.requests.storage for the persistent volume claim (PVC). The new value must be larger than the original volume size.

If entering another smaller resize value in .spec.resources.requests.storage for the PVC does not work, use the following procedure to recover.

Procedure

  1. Mark the persistent volume (PV) that is bound to the PVC with the Retain reclaim policy. Change the persistentVolumeReclaimPolicy field to Retain.
  2. Delete the PVC.
  3. Manually edit the PV and delete the claimRef entry from the PV specification to ensure that the newly created PVC can bind to the PV marked Retain. This marks the PV as Available.
  4. Recreate 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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