Expanding persistent volumes | Storage

Enabling volume expansion support
Expanding CSI volumes
Expanding FlexVolume with a supported driver
Expanding persistent volume claims (PVCs) with a file system
Recovering from failure when expanding volumes

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 by running the following command:
```
$ oc edit storageclass <storage_class_name> (1)
```
1 Specifies the name of the storage class.

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.

Expanding CSI volumes

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

OKD supports CSI volume expansion by default. However, a specific CSI driver is required.

OKD 4.9 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 Technology Preview Features Support Scope.

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 OKD.

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.

Because OKD does not support installation of FlexVolume plugins on control plane 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 object must have allowVolumeExpansion set to true.

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.

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.

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>
```
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.

Recovering from failure when expanding volumes

If expanding underlying storage fails, the OKD 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

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.
Delete the PVC. This will be recreated later.
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.
Re-create the PVC in a smaller size, or a size that can be allocated by the underlying storage provider.
Set the volumeName field of the PVC to the name of the PV. This binds the PVC to the provisioned PV only.
Restore the reclaim policy on the PV.