<p>We are using Kubernetes 1.10.1 </p>

<p>I'm having a statefulset which has a single volumeClaim attached.</p>

<p>I would like to add an additional volumeClaim since resizing of an existing PV is still in beta and also not available in Kubernetes 1.10.</p>

<p>My change would basically just add an additional PVC (and of course also mount it which is not mentioned here):</p>

<pre><code>*** 1,10 ****
--- 1,19 ----
    volumeClaimTemplates:
    - metadata:
        name: data
      spec:
        accessModes:
        - ReadWriteOnce
        resources:
          requests:
            storage: 100Gi
 +   - metadata:
 +       name: data2
 +     spec:
 +       accessModes:
 +       - ReadWriteOnce
 +       resources:
 +         requests:
 +           storage: 100Gi
</code></pre>

<p>As result I get an error:</p>

<p><code>Error: UPGRADE FAILED: StatefulSet.apps "my-app" is invalid: spec: Forbidden: updates to statefulset spec for fields other than 'replicas', 'template', and 'updateStrategy' are forbidden.</code></p>

<p>Shouldn't at least adding additional PVCs be supported as long the existing ones are not being touched? Am I missing something here? I haven't found anything related to this in the documentation.</p>

<p>I don't know if there's any rationale on the design but the only reason why you would not want to update the storage template on a StatefulSet would be the stability of your application overall.</p>

<p>In any case, I agree that this should be allowed since you are adding an extra storage, I would argue that resizing your volumes should be allowed too when it's available. Opened <a href="https://github.com/kubernetes/kubernetes/issues/69041" rel="nofollow noreferrer">this</a> feature request.</p>
