Importing virtual machine images to block storage with data volumes

• Prerequisites
• About data volumes
• About block persistent volumes
• Creating a local block persistent volume
• Importing a virtual machine image to a block persistent volume using data volumes
• CDI supported operations matrix
• Additional resources

You can import an existing virtual machine image into your OKD cluster. OKD Virtualization uses data volumes to automate the import of data and the creation of an underlying persistent volume claim (PVC).

Prerequisites

• If you require scratch space according to the CDI supported operations matrix, you must first define a storage class or prepare CDI scratch space for this operation to complete successfully.

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). Data volumes are integrated with OKD Virtualization, and they prevent a virtual machine from being started before the PVC has been prepared.

About block persistent volumes

A block persistent volume (PV) is a PV that is backed by a raw block device. These volumes do not have a file system and can provide performance benefits for virtual machines by reducing overhead.

Raw block volumes are provisioned by specifying volumeMode: Block in the PV and persistent volume claim (PVC) specification.

Creating a local block persistent volume

Create a local block persistent volume (PV) on a node by populating a file and mounting it as a loop device. You can then reference this loop device in a PV manifest as a Block volume and use it as a block device for a virtual machine image.

Procedure

1. Log in as root to the node on which to create the local PV. This procedure uses node01 for its examples.

2. Create a file and populate it with null characters so that it can be used as a block device. The following example creates a file loop10 with a size of 2Gb (20 100Mb blocks):

   $ dd if=/dev/zero of=<loop10> bs=100M count=20

3. Mount the loop10 file as a loop device.

   $ losetup </dev/loop10>d3 <loop10>  (1) (2)

   1	File path where the loop device is mounted.
   2	The file created in the previous step to be mounted as the loop device.

4. Create a PersistentVolume manifest that references the mounted loop device.

   kind: PersistentVolume
   apiVersion: v1
   metadata:
     name: <local-block-pv10>
     annotations:
   spec:
     local:
       path: </dev/loop10> (1)
     capacity:
       storage: <2Gi>
     volumeMode: Block (2)
     storageClassName: local (3)
     accessModes:
       - ReadWriteOnce
     persistentVolumeReclaimPolicy: Delete
     nodeAffinity:
       required:
         nodeSelectorTerms:
         - matchExpressions:
           - key: kubernetes.io/hostname
             operator: In
             values:
             - <node01> (4)

   1	The path of the loop device on the node.
   2	Specifies it is a block PV.
   3	Optional: Set a storage class for the PV. If you omit it, the cluster default is used.
   4	The node on which the block device was mounted.

5. Create the block PV.

   # oc create -f <local-block-pv10.yaml>(1)

   1	The file name of the persistent volume created in the previous step.

Importing a virtual machine image to a block persistent volume using data volumes

You can import an existing virtual machine image into your OKD cluster. OKD Virtualization uses data volumes to automate the importing data and the creation of an underlying persistent volume claim (PVC). You can then reference the data volume in a virtual machine manifest.

Prerequisites

• A virtual machine disk image, in RAW, ISO, or QCOW2 format, optionally compressed by using xz or gz.

• An HTTP or s3 endpoint where the image is hosted, along with any authentication credentials needed to access the data source

• At least one available block PV.

Procedure

1. If your data source requires authentication credentials, edit the endpoint-secret.yaml file, and apply the updated configuration to the cluster.

   1. Edit the endpoint-secret.yaml file with your preferred text editor:

      apiVersion: v1
      kind: Secret
      metadata:
        name: <endpoint-secret>
        labels:
          app: containerized-data-importer
      type: Opaque
      data:
        accessKeyId: "" (1)
        secretKey:   "" (2)

      1	Optional: your key or user name, base64 encoded
      2	Optional: your secret or password, base64 encoded

   2. Update the secret by running the following command:

      $ oc apply -f endpoint-secret.yaml

2. Create a DataVolume manifest that specifies the data source for the image you want to import and volumeMode: Block so that an available block PV is used.

   apiVersion: cdi.kubevirt.io/v1beta1
   kind: DataVolume
   metadata:
     name: <import-pv-datavolume> (1)
   spec:
     storageClassName: local (2)
     source:
         http:
            url: <http://download.fedoraproject.org/pub/fedora/linux/releases/28/Cloud/x86_64/images/Fedora-Cloud-Base-28-1.1.x86_64.qcow2> (3)
            secretRef: <endpoint-secret> (4)
     pvc:
       volumeMode: Block (5)
       accessModes:
         - ReadWriteOnce
       resources:
         requests:
           storage: <2Gi>

   1	The name of the data volume.
   2	Optional: Set the storage class or omit it to accept the cluster default.
   3	The HTTP source of the image to import.
   4	Only required if the data source requires authentication.
   5	Required for importing to a block PV.

3. Create the data volume to import the virtual machine image by running the following command:

   $ oc create -f <import-pv-datavolume.yaml>(1)

   1	The file name of the data volume that you created in the previous step.

CDI supported operations matrix

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

✓ Supported operation

□ Unsupported operation

* Requires scratch space

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

Additional resources

• Configure preallocation mode to improve write performance for data volume operations.