Volume Resizing and Expansion

Overview

You can now resize an existing volume by editing the PersistentVolumeClaim (PVC) object. You no longer have to manually interact with the storage backend, or delete and recreate PV and PVC objects, to increase the size of a volume. Kubernetes will automatically expand the volume, using storage backend, and it will also expand the underlying file system in-use by the Pod, without requiring any downtime if the underlying storage provisioner can support it.

Prerequisites

• Before performing an expansion, make sure that the source volume (PV) is provisioned dynamically, by adding the underlying source storageClass. If not, volume expansion fails.

• Make sure that underlying storage driver allows for volume expansion. Check the respective storage provider's documentation to verify.

Method

Perform volume expansion by editing the existing PersistentVolumeClaim (PVC) object. You can expand the volume online or offline based on the specific storage driver support.

Online

Expands a PVC while the PVC is still in-use by the Pod.

• Pods referencing the resized volume do not need to be restarted. Instead, the file system will automatically be resized while in use as part of volume expansion.

Offline

Expanding a PVC which is not in-use by any Pod.

• If the underlying storage driver can only support offline expansion, users must take down their Pod before expanding the volume.

Expanding the CTE-PVC Volume

You can use either command: kubectl patch or kubectl edit to expand the volume size.

1. Using the kubectl patch command:

   kubectl patch pvc <CTE-PVC_Name> -n <Namespace> --type merge -p '{"spec":{"resources":{"requests":{"storage":"<New_Size>"}}}}'
   

   Example

   This example requests expansion to 5G:

   kubectl patch pvc cte-claim -n ns1 --type merge -p '{"spec":{"resources":{"requests":{"storage":"5Gi"}}}}'
   

2. Using the kubectl edit command:

   1. Type:

      kubectl edit pvc -n

   Example

   kubectl edit pvc cte-claim -n ns1
   

   1. Update the resource > request > storage field with the required size, for example 5Gi.

Validating volume expansion

The duration for volume expansion depends on the size of the new volume requested and the type of storage driver provisioner.

• You can verify it by viewing the cte-csi-controller-xxx log:

  kubectl logs cte-csi-controller-6f669d4b94-8xdcl -n kube-system cte-csi
  

• For more details, describe the CTE-PVC and sourcePVC. To verify this information, type:

  kubectl describe pvc <pvc_name> -n <Namespace>
  
  kubectl get pvc <pvc_name> -n <Namespace> -o yaml
  

• Watch the status.conditions field of the CTE-PVC, and sourcePVC, to see if the resize has completed.

• Refer to the storage driver documentation for more specific details.

Unsupported Functions

• Shrinking persistent volumes is not supported.

• Only dynamically provisioned PVCs whose storage class has the allowVolumeExpansion parameter set to true are expandable.