// +optional
  optional NFSVolumeSource nfs = 5;

  // rbd represents a Rados Block Device mount on the host that shares a pod's lifetime.
  // More info: https://examples.k8s.io/volumes/rbd/README.md
  // +optional
  optional RBDPersistentVolumeSource rbd = 6;

  // iscsi represents an ISCSI Disk resource that is attached to a

- CephRBD volume plugin ( `kubernetes.io/rbd`) was removed in this release. And its csi migration support was also removed, so the `rbd` volume type became non-functional. Alternative is to use RBD CSI driver (https://github.com/ceph/ceph-csi/) in your Kubernetes Cluster. A re-deployment of your application is required to use the new driver if you were using `kubernetes.io/rbd` volume plugin before upgrading cluster version to 1.31+. ([#124546](https://git...

- This release enables in-tree RBD migration to CSI driver with a couple of feature gates.  These featuregates are alpha in this release.

  - `CSIMigrationRBD`: when enabled, it will redirect traffic from in tree rbd plugin ( kubernetes.io/rbd )  to CSI driver ( rbd.csi.ceph.com) , default to `false` now.
  - `IntreePluginRBDUnregister`: Disables the RBD in-tree driver

  The feature gates can be enabled by:

 - Deprecated support for CSI migration of `Ceph RBD volumes`. Users who were relying on Kubernetes' ability
  to migrate to an out-of-tree storage driver should complete that migration before the support for it is removed. ([#118303](https://github.com/kubernetes/kubernetes/pull/118303), [@carlory](https://github.com/carlory))
 - RBD volume plugin (`kubernetes.io/rbd`) has been deprecated in this release

          * 'node.kubernetes.io/memory-pressure=:NoSchedule' if MemoryPressure is true
          * 'node.kubernetes.io/out-of-disk=:NoSchedule' if OutOfDisk is true
* rbd: default image format to v2 instead of deprecated v1 ([#51574](https://github.com/kubernetes/kubernetes/pull/51574), [@dillaman](https://github.com/dillaman))

### Bug or Regression

- Address a bug in rbd migration translation plugin ([#106878](https://github.com/kubernetes/kubernetes/pull/106878), [@humblec](https://github.com/humblec)) [SIG Storage]