In Kubernetes v1.15, SIG Storage continued work to [enable migration of in-tree volume plugins](https://github.com/kubernetes/enhancements/issues/625) to the Container Storage Interface (CSI). SIG Storage worked on bringing CSI to feature parity with in-tree functionality, including functionality like resizing, inline volumes, and more. SIG Storage introduces new alpha functionality in CSI that doesn't exist in the Kubernetes Storage subsystem yet, like volume cloning.