Cloning a virtual machine disk into a new data volume

Cloning a virtual machine disk into a new data volume

You can clone the persistent volume claim (PVC) of a virtual machine disk into a new data volume by referencing the source PVC in your data volume configuration file.

Cloning operations between different volume modes are supported, such as cloning from a persistent volume (PV) with volumeMode: Block to a PV with volumeMode: Filesystem.

However, you can only clone between different volume modes if they are of the contentType: kubevirt.

When you enable preallocation globally, or for a single data volume, the Containerized Data Importer (CDI) preallocates disk space during cloning. Preallocation enhances write performance. For more information, see Using preallocation for data volumes.

Prerequisites

Users need additional permissions to clone the PVC of a virtual machine disk into another namespace.

About data volumes

DataVolume objects are custom resources that are provided by the Containerized Data Importer (CDI) project. Data volumes orchestrate import, clone, and upload operations that are associated with an underlying persistent volume claim (PVC). You can create a data volume as either a standalone resource or by using the dataVolumeTemplate field in the virtual machine (VM) specification.

VM disk PVCs that are prepared by using standalone data volumes maintain an independent lifecycle from the VM. If you use the dataVolumeTemplate field in the VM specification to prepare the PVC, the PVC shares the same lifecycle as the VM.

After a PVC is populated, the data volume that you used to create the PVC is no longer needed. OKD Virtualization enables automatic garbage collection of completed data volumes by default. Standalone data volumes, and data volumes created by using the dataVolumeTemplate resource, are automatically garbage collected after completion.

Cloning the persistent volume claim of a virtual machine disk into a new data volume

You can clone a persistent volume claim (PVC) of an existing virtual machine disk into a new data volume. The new data volume can then be used for a new virtual machine.

When a data volume is created independently of a virtual machine, the lifecycle of the data volume is independent of the virtual machine. If the virtual machine is deleted, neither the data volume nor its associated PVC is deleted.

Prerequisites

Determine the PVC of an existing virtual machine disk to use. You must power down the virtual machine that is associated with the PVC before you can clone it.
Install the OpenShift CLI (oc).

Procedure

Examine the virtual machine disk you want to clone to identify the name and namespace of the associated PVC.

Create a YAML file for a data volume that specifies the name of the new data volume, the name and namespace of the source PVC, and the size of the new data volume.

For example:

apiVersion: cdi.kubevirt.io/v1beta1
kind: DataVolume
metadata:
  name: <cloner-datavolume> (1)
spec:
  source:
    pvc:
      namespace: "<source-namespace>" (2)
      name: "<my-favorite-vm-disk>" (3)
  pvc:
    accessModes:
      - ReadWriteOnce
    resources:
      requests:
        storage: <2Gi> (4)

1	The name of the new data volume.
2	The namespace where the source PVC exists.
3	The name of the source PVC.
4	The size of the new data volume. You must allocate enough space, or the cloning operation fails. The size must be the same as or larger than the source PVC.

Start cloning the PVC by creating the data volume:
```
$ oc create -f <cloner-datavolume>.yaml
```
Data volumes prevent a virtual machine from starting before the PVC is prepared, so you can create a virtual machine that references the new data volume while the PVC clones.

CDI supported operations matrix

This matrix shows the supported CDI operations for content types against endpoints, and which of these operations requires scratch space.

Content types	HTTP	HTTPS	HTTP basic auth	Registry	Upload
KubeVirt (QCOW2)	✓ QCOW2 ✓ GZ ✓ XZ	✓ QCOW2* ✓ GZ ✓ XZ	✓ QCOW2 ✓ GZ ✓ XZ	✓ QCOW2 □ GZ □ XZ	✓ QCOW2 ✓ GZ ✓ XZ
KubeVirt (RAW)	✓ RAW ✓ GZ ✓ XZ	✓ RAW ✓ GZ ✓ XZ	✓ RAW ✓ GZ ✓ XZ	✓ RAW □ GZ □ XZ	✓ RAW ✓ GZ ✓ XZ*

✓ Supported operation

□ Unsupported operation

* Requires scratch space

** Requires scratch space if a custom certificate authority is required