What must be true to expand a PersistentVolumeClaim in Kubernetes?

To expand a PersistentVolumeClaim (PVC) in Kubernetes, it is essential that the StorageClass associated with the PVC is configured with the allowVolumeExpansion parameter set to true. This setting enables the functionality to increase the allocated storage size for the PVC after it has been created.

When allowVolumeExpansion is set to true, it signals that the volume backing the PVC can be resized. This is crucial because Kubernetes needs to support dynamic resizing of volumes, which is often managed at the storage backend level. Without this configuration, any attempts to expand the PVC will not proceed, leading to an error.

In contrast, while it's a good practice to back up data before resizing operations, the existence of a backup is not a strict requirement to expand a PVC, nor does it influence the capability to perform the expansion itself. The state of the volume (whether it is empty or not) also does not impact the ability to resize the PVC, as expansions can occur on in-use volumes. Additionally, there is no inherent requirement to restart the associated Pod when a PVC is expanded, as Kubernetes can handle such changes dynamically under the right conditions.