As a DevOps engineer, you can expand a persistent block volume after its creation. In vSphere IaaS control plane, both types of clusters, Supervisors and Tanzu Kubernetes Grid, support offline and online volume expansion.

Note: You can expand only persistent block volumes. Currently, vSphere IaaS control plane does not support volume expansion for ReadWriteMany volumes.

Storage classes that appear in the vSphere IaaS control plane environment have allowVolumeExpansion set to true by default. This parameter makes it possible to modify the size of an offline or online volume.

A volume is considered to be offline when it is not attached to a node or pod. An online volume is a volume that is available on a node or pod.

The level of support of the volume expansion functionality depends on the vSphere version. You can expand volumes created in the earlier versions of vSphere when you upgrade your vSphere environment to appropriate versions that support expansions.

When you expand the volumes, keep in mind the following:
  • You can expand the volumes up to the limits specified by storage quotas. vSphere IaaS control plane supports consecutive resize requests for a persistent volume claim object.
  • All types of datastores, including VMFS, vSAN, vSAN Direct, vVols, and NFS, support volume expansion.
  • You can perform volume expansion for deployments or standalone pods.
  • You can resize statically provisioned volumes in a Supervisor and Tanzu Kubernetes Grid cluster if the volumes have storage classes associated with them.
  • You cannot expand volumes that are created as a part of a StatefulSet when you use the StatefulSet definition. Currently, Kubernetes does not support this functionality. As a result, your attempts to expand the volumes by increasing the storage size in the StatefulSet definition fail.
  • If a virtual disk that backs a volume has snapshots, it cannot be resized.
  • vSphere IaaS control plane does not support volume expansion for in-tree or migrated volumes.

Expand a Persistent Volume in Offline Mode

A volume is considered to be offline when it is not attached to a node or pod. Both types of clusters, Supervisors and Tanzu Kubernetes Grid clusters, support offline volume expansion.

Prerequisites

Make sure to upgrade your vSphere environment to an appropriate version that supports offline volume expansion.

Procedure

  1. Create a persistent volume claim (PVC) with a storage class.
    1. Define a PVC using the following YAML manifest as an example.
      In the example, the size of the requested storage is 1 Gi. 
      apiVersion: v1
kind: PersistentVolumeClaim
metadata:
  name: example-block-pvc
spec:
  accessModes:
  - ReadWriteOnce
  resources:
    requests:
      storage: 1Gi
  storageClassName: example-block-sc
    2. Apply the PVC to the Kubernetes cluster. 
      kubectl apply -f example-block-pvc.yaml
  2. Patch the PVC to increase its size.
    If the PVC is not attached to a node or being used by a pod, use the following command to patch the PVC. In this example, the requested storage increase is 2 Gi. 
    kubectl patch pvc example-block-pvc -p '{"spec": {"resources": {"requests": {"storage": "2Gi"}}}}'
    This action triggers an expansion in the volume associated with the PVC.
  3. Verify that the size of the volume has increased. 
    kubectl get pv
NAME                                       CAPACITY ACCESS MODES RECLAIM POLICY STATUS   CLAIM                       STORAGECLASS           REASON AGE
pvc-9e9a325d-ee1c-11e9-a223-005056ad1fc1   2Gi           RWO         Delete     Bound    default/example-block-pvc   example-block-sc              6m44s
    Note: The size of the PVC remains unchanged until the PVC is used by a pod.
    The following example shows that the PVC size hasn't changed. If you describe the PVC, you can see the FilesystemResizePending condition applied on the PVC. 
    kubectl get pvc
NAME                STATUS VOLUME                                     CAPACITY ACCESS MODES   STORAGECLASS       AGE
example-block-pvc   Bound  pvc-9e9a325d-ee1c-11e9-a223-005056ad1fc1   1Gi           RWO       example-block-sc   6m57s
  4. Create a pod to use the PVC.
    When the PVC is used by the pod, the filesystem is expanded.
  5. Verify that the size of the PVC has been modified. 
    kubectl get pvc
NAME                STATUS VOLUME                                    CAPACITY ACCESS MODES STORAGECLASS     AGE
example-block-pvc   Bound  pvc-24114458-9753-428e-9c90-9f568cb25788   2Gi         RWO      example-block-sc 2m12s
    The FilesystemResizePending condition has been removed from the PVC. Volume expansion is complete.

What to do next

A vSphere administrator can see the new volume size in the vSphere Client. See Monitor Persistent Volumes in the vSphere Client.

Expand a Persistent Volume in Online Mode

An online volume is a volume that is available on a node or pod. As a DevOps engineer, you can expand an online persistent block volume. Both types of clusters, Supervisors and Tanzu Kubernetes Grid clusters, support online volume expansion.

Prerequisites

Make sure to upgrade your vSphere environment to an appropriate version that supports online volume expansion.

Procedure

  1. Find the persistent volume claim to resize. 
    $ kubectl get pv,pvc,pod
NAME                                                        CAPACITY   ACCESS MODES   RECLAIM POLICY   STATUS      CLAIM               STORAGECLASS   REASON   AGE
persistentvolume/pvc-5cd51b05-245a-4610-8af4-f07e77fdc984   1Gi        RWO            Delete           Bound       default/block-pvc   block-sc                4m56s
 
NAME                              STATUS   VOLUME                                     CAPACITY   ACCESS MODES   STORAGECLASS   AGE
persistentvolumeclaim/block-pvc   Bound    pvc-5cd51b05-245a-4610-8af4-f07e77fdc984   1Gi        RWO            block-sc       5m3s
 
NAME            READY   STATUS    RESTARTS   AGE
pod/block-pod   1/1     Running   0          26s

    Note that the size of storage the volume uses is 1 Gi.

  2. Patch the PVC to increase its size.
    For example, increase the size to 2 Gi. 
    $ kubectl patch pvc block-pvc -p '{"spec": {"resources": {"requests": {"storage": "2Gi"}}}}'
persistentvolumeclaim/block-pvc edited
    This action triggers an expansion in the volume associated with the PVC.
  3. Verify that the size of both PVC and PV has increased. 
    $ kubectl get pvc,pv,pod
NAME                              STATUS   VOLUME                                     CAPACITY   ACCESS MODES   STORAGECLASS   AGE
persistentvolumeclaim/block-pvc   Bound    pvc-5cd51b05-245a-4610-8af4-f07e77fdc984   2Gi        RWO            block-sc       6m18s
 
NAME                                                        CAPACITY   ACCESS MODES   RECLAIM POLICY   STATUS      CLAIM               STORAGECLASS   REASON   AGE
persistentvolume/pvc-5cd51b05-245a-4610-8af4-f07e77fdc984   2Gi        RWO            Delete           Bound       default/block-pvc   block-sc                6m11s
 
NAME            READY   STATUS    RESTARTS   AGE
pod/block-pod   1/1     Running   0          101s

What to do next

A vSphere administrator can see the new volume size in the vSphere Client. See Monitor Persistent Volumes in the vSphere Client.