Requirement for volume expansion by the operator

Does the feature of volume auto expansion requires a csi-compliant driver?

Can you elaborate a little more please, it's not clear what you are asking about in relation to Elasticsearch.

This PR introduced the option of expanding the underlying (PVC) volume of the statefulsets' nodes.

However, in k8s-terms, and if I am not mistaken, automatic volume expansion I think requires a csi-compliant storage class.

So I am asking whether the underlying storage class from which the PVCs of the statefulsets should be based on csi.

Ok given this is ECK specific, I have moved the topic.

So I am asking whether the underlying storage class from which the PVCs of the statefulsets should be based on csi.

The storage class needs to support volume expansion (allowVolumeExpansion: true ). Whether the underlying volume driver is based on CSI or not does not matter much. I think a few cloud-provider storage classes are not based on CSI but still allow volume expansion.