Your Kubernetes installation must either have a default storage class specified
(see https://kubernetes.io/docs/concepts/storage/storage-classes/ and https://kubernetes.io/docs/tasks/administer-cluster/change-default-storage-class/)
or you must specify the storage class for the Consul servers:
```yaml
server:
storageClass: your-class
```
See the [Helm reference](/docs/k8s/helm#v-server-storageclass) for that setting for more information.