Cloning a virtual machine by using a data volume template

Cloning a virtual machine by using a data volume template

You can create a new virtual machine by cloning the persistent volume claim (PVC) of an existing VM. By including a dataVolumeTemplate in your virtual machine configuration file, you create a new data volume from the original PVC.

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.

Creating a new virtual machine from a cloned persistent volume claim by using a data volume template

You can create a virtual machine that clones the persistent volume claim (PVC) of an existing virtual machine into a data volume. Reference a dataVolumeTemplate in the virtual machine manifest and the source PVC is cloned to a data volume, which is then automatically used for the creation of the virtual machine.

When a data volume is created as part of the data volume template of a virtual machine, the lifecycle of the data volume is then dependent on the virtual machine. If the virtual machine is deleted, the data volume and associated PVC are also 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 you want to clone to identify the name and namespace of the associated PVC.

Create a YAML file for a VirtualMachine object. The following virtual machine example clones my-favorite-vm-disk, which is located in the source-namespace namespace. The 2Gi data volume called favorite-clone is created from my-favorite-vm-disk.

For example:

apiVersion: kubevirt.io/v1
kind: VirtualMachine
metadata:
  labels:
    kubevirt.io/vm: vm-dv-clone
  name: vm-dv-clone (1)
spec:
  running: false
  template:
    metadata:
      labels:
        kubevirt.io/vm: vm-dv-clone
    spec:
      domain:
        devices:
          disks:
          - disk:
              bus: virtio
            name: root-disk
        resources:
          requests:
            memory: 64M
      volumes:
      - dataVolume:
          name: favorite-clone
        name: root-disk
  dataVolumeTemplates:
  - metadata:
      name: favorite-clone
    spec:
      storage:
        accessModes:
        - ReadWriteOnce
        resources:
          requests:
            storage: 2Gi
      source:
        pvc:
          namespace: "source-namespace"
          name: "my-favorite-vm-disk"

1	The virtual machine to create.

Create the virtual machine with the PVC-cloned data volume:
```
$ oc create -f <vm-clone-datavolumetemplate>.yaml
```

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