Disks

Disks in virtual machines (VirtualDisk resources) are essential for writing and storing data. They ensure the proper functioning of applications and operating systems. The structure of these disks includes storage provided by the platform.

Depending on the storage properties, disks during creation and virtual machines during operation may exhibit different behaviors.

VolumeBindingMode properties:

Immediate — disk is created immediately after the resource is created (it is assumed that the disk will be available for attachment to a virtual machine on any cluster node).

WaitForFirstConsumer — disk is created only after it is attached to a virtual machine and will be created on the node where the virtual machine is launched.

AccessMode:

ReadWriteOnce (RWO) — access to the disk is granted to only one instance of a virtual machine. Live migration of virtual machines with such disks is not possible.

ReadWriteMany (RWX) — multiple access to the disk is allowed. Live migration of virtual machines with such disks is possible.

When a disk is created, the controller automatically determines the most optimal parameters supported by the storage.

To find the available storage options on the platform, run the following command:

kubectl get storageclass

Example output:

NAME                          PROVISIONER                           RECLAIMPOLICY   VOLUMEBINDINGMODE      ALLOWVOLUMEEXPANSION   AGE
i-linstor-thin-r1 (default)   replicated.csi.storage.deckhouse.io   Delete          Immediate              true                   48d
i-linstor-thin-r2             replicated.csi.storage.deckhouse.io   Delete          Immediate              true                   48d
i-linstor-thin-r3             replicated.csi.storage.deckhouse.io   Delete          Immediate              true                   48d
linstor-thin-r1               replicated.csi.storage.deckhouse.io   Delete          WaitForFirstConsumer   true                   48d
linstor-thin-r2               replicated.csi.storage.deckhouse.io   Delete          WaitForFirstConsumer   true                   48d
linstor-thin-r3               replicated.csi.storage.deckhouse.io   Delete          WaitForFirstConsumer   true                   48d
nfs-4-1-wffc                  nfs.csi.k8s.io                        Delete          WaitForFirstConsumer   true                   30d

Creating an empty disk

Empty disks are typically used for installing operating systems or storing data.

To create a disk use:

d8 k apply -f - <<EOF
apiVersion: virtualization.deckhouse.io/v1alpha2
kind: VirtualDisk
metadata:
  name: blank-disk
spec:
  # Disk storage settings.
  persistentVolumeClaim:
    # Replace with your StorageClass name.
    storageClassName: i-linstor-thin-r2
    size: 100Mi
EOF

After creation, the VirtualDisk resource can be in the following states:

• Pending: Waiting for readiness of all dependent resources required for disk creation.
• Provisioning: The disk creation process is ongoing.
• Resizing: The disk resizing process is ongoing.
• WaitForFirstConsumer: The disk is waiting for a virtual machine that will use it.
• Ready: The disk is created and ready for use.
• Failed: An error occurred during the creation process.
• Terminating: The disk deletion process is ongoing. This process may “hang” in this state if the disk is still attached to a virtual machine.

Until the disk reaches the Ready phase, the entire .spec block can be modified. Changing it will restart the disk creation process.

Check the disk’s status after creation:

d8 k get vd blank-disk

Example output:

NAME         PHASE     CAPACITY   AGE
blank-disk   Ready     100Mi      1m2s

Creating a disk from an image

Disks can be created and populated with data from previously created images such as ClusterVirtualImage and VirtualImage.

When creating a disk, you can specify its desired size, which must be equal to or greater than the unpacked size of the image. If the size is not specified, the disk will be created with the same size as the source disk image.

Using a previously created project image VirtualImage, here’s an example command to determine the size of the unpacked image:

d8 k get cvi ubuntu-22.04 -o wide

Example output:

NAME           PHASE   CDROM   PROGRESS   STOREDSIZE   UNPACKEDSIZE   REGISTRY URL                                                                       AGE
ubuntu-22.04   Ready   false   100%       285.9Mi      2.5Gi          dvcr.d8-virtualization.svc/cvi/ubuntu-22.04:eac95605-7e0b-4a32-bb50-cc7284fd89d0   122m

The required size is indicated in the UNPACKEDSIZE column and is 2.5Gi.

Create a disk from this image:

d8 k apply -f - <<EOF
apiVersion: virtualization.deckhouse.io/v1alpha2
kind: VirtualDisk
metadata:
  name: linux-vm-root
spec:
  # Disk storage parameters configuration.
  persistentVolumeClaim:
    # Specify a size greater than the unpacked image size.
    size: 10Gi
    # Substitute with your StorageClass name.
    storageClassName: i-linstor-thin-r2
  # The source from which the disk is created.
  dataSource:
    type: ObjectRef
    objectRef:
      kind: VirtualImage
      name: ubuntu-22.04
EOF

Now, create a disk without specifying its size:

d8 k apply -f - <<EOF
apiVersion: virtualization.deckhouse.io/v1alpha2
kind: VirtualDisk
metadata:
  name: linux-vm-root-2
spec:
  # Disk storage parameters configuration.
  persistentVolumeClaim:
    # Substitute with your StorageClass name.
    storageClassName: i-linstor-thin-r2
  # The source from which the disk is created.
  dataSource:
    type: ObjectRef
    objectRef:
      kind: VirtualImage
      name: ubuntu-22.04
EOF

Check the state of the disks after creation:

d8 k get vd

Example output:

NAME           PHASE   CAPACITY   AGE
linux-vm-root    Ready   10Gi       7m52s
linux-vm-root-2  Ready   2590Mi     7m15s

Resizing a disk

The size of disks can be increased even if they are already attached to a running virtual machine. Changes are made to the spec.persistentVolumeClaim.size field:

Check the size before the change:

d8 k get vd linux-vm-root

Example output:

NAME          PHASE   CAPACITY   AGE
linux-vm-root   Ready   10Gi       10m

Apply the changes:

kubectl patch vd linux-vm-root --type merge -p '{"spec":{"persistentVolumeClaim":{"size":"11Gi"}}}'

Check the size after the change:

d8 k get vd linux-vm-root

Example output:

NAME          PHASE   CAPACITY   AGE
linux-vm-root   Ready   11Gi       12m