volumes to be manually provisioned by a cluster administrator before use. With
this feature, volume plugins that support it (GCE PD, AWS EBS, and Cinder) can
automatically provision a PersistentVolume to bind to an unfulfilled
PersistentVolumeClaim.
  * Run multiple schedulers in parallel, e.g. one or more custom schedulers
alongside the default Kubernetes scheduler, using pod annotations to select

  * This is something to pay close attention to if you’ve been using Kubernetes for a while, because it changes the default behavior of PersistentVolumeClaim objects on these clouds.
  * Marking a StorageClass as default makes it so that even a PersistentVolumeClaim without a StorageClass specified will trigger dynamic provisioning (instead of binding to an existing pool of PVs).

- Better pod events ("waiting for ephemeral volume controller to create the persistentvolumeclaim"" instead of "persistentvolumeclaim not found") when using generic ephemeral volumes. ([#104605](https://github.com/kubernetes/kubernetes/pull/104605), [@pohly](https://github.com/pohly))

### **Storage**

*   [stable] `PersistentVolume` and `PersistentVolumeClaim` objects must now have a capacity greater than zero.
*   [stable] Mutation of `PersistentVolumeSource` after creation is no longer allowed
*   [alpha] Deletion of `PersistentVolumeClaim` objects that are in use by a pod no longer permitted (if alpha feature is enabled).
*   [alpha] Container Storage Interface

- Migrated the volume attach/detach controller (within `kube-controller-manager`) to use [contextual logging](https://k8s.io/docs/concepts/cluster-administration/system-logs/#contextual-logging).
  Migrated the `PersistentVolumeClaim` protection controller (within `kube-controller-manager`) to use [contextual logging](https://k8s.io/docs/concepts/cluster-administration/system-logs/#contextual-logging).

- Raw Block Support: Allow volumes to be surfaced as block devices inside containers instead of just mounted filesystems.
- Volume Cloning: Duplicate a PersistentVolumeClaim and underlying storage volume using the Kubernetes API via CSI.
- CSIDriver Kubernetes API Object: Simplifies CSI driver discovery and allows CSI Drivers to customize Kubernetes behavior.

* pvc.Spec.Resources.Requests min and max can be enforced with a LimitRange of type "PersistentVolumeClaim" in the namespace ([#30145](https://github.com/kubernetes/kubernetes/pull/30145), [@markturansky](https://github.com/markturansky))

- Implemented a queueing hint for PersistentVolumeClaim/Add event in the `CSILimit` plugin. ([#124703](https://github.com/kubernetes/kubernetes/pull/124703), [@utam0k](https://github.com/utam0k)) [SIG Scheduling and Storage]

- Fixed a bug where Kubernetes would apply a default StorageClass to a PersistentVolumeClaim,
  even when the deprecated annotation `volume.beta.kubernetes.io/storage-class` was set. ([#116089](https://github.com/kubernetes/kubernetes/pull/116089), [@cvvz](https://github.com/cvvz)) [SIG Apps and Storage]

### Apps

- Users can now specify a DataSource/Kind of type `PersistentVolumeClaim` in their PVC spec.  This can then be detected by the external csi-provisioner and plugins if capable. ([#76913](https://github.com/kubernetes/kubernetes/pull/76913), [@j-griffith](https://github.com/j-griffith))