Volume Cloning

Status and Releases

Overview

A Clone is defined as a duplicate of an existing Kubernetes Volume. For more information on cloning in Kubernetes see the concepts doc for Volume Cloning. A storage provider that allows volume cloning as a create feature, may choose to implement volume cloning via a control-plan CSI RPC call.

For details regarding the kubernetes API for volume cloning, please see kubernetes concepts.

Implementing Volume cloning functionality

To implement volume cloning the CSI driver MUST:

1. Implement checks for csi.CreateVolumeRequest.VolumeContentSource in the plugin's CreateVolume function implementation.
2. Implement CLONE_VOLUME controller capability.

It is the responsibility of the storage plugin to either implement an expansion after clone if a provision request size is greater than the source, or allow the external-resizer to handle it. In the case that the plugin does not support resize capability and it does not have the capability to create a clone that is greater in size than the specified source volume, then the provision request should result in a failure.

Deploying volume clone functionality

The Kubernetes CSI development team maintains the external-provisioner which is responsible for detecting requests for a PVC DataSource and providing that information to the plugin via the csi.CreateVolumeRequest. It's up to the plugin to check the csi.CreateVolumeRequest for a VolumeContentSource entry in the CreateVolumeRequest object.

There are no additional side-cars or add on components required.

Enabling Cloning for CSI volumes in Kubernetes

Volume cloning was promoted to Beta in version 1.16 and GA in 1.18, and as such is enabled by defult for kubernetes versions >= 1.16

In Kubernetes 1.15 this feature was alpha status and required enabling the appropriate feature gate:

--feature-gates=VolumePVCDataSource=true

Example implementation

A trivial example implementation can be found in the csi-hostpath plugin in its implementation of CreateVolume.