Using volume expansion

Autopilot Standard

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In Google Kubernetes Engine (GKE) version 1.24 or later, you can use the Kubernetes volume expansion feature to change a persistent volume's capacity after its creation.

For more information on volume expansion, see the open source Kubernetes documentation.

Prerequisites

Volume expansion has the following prerequisites:

• If the volume you want to resize is managed by a CSI Driver:
  • Ensure the GKE cluster version is 1.16 or later. If the cluster has Windows node pools, ensure the GKE cluster version is 1.18 or later. If you are using the managed GKE Filestore CSI driver, the cluster version must be 1.21 or later.
  • Check your storage vendor's documentation to verify your CSI driver supports volume expansion. The Compute Engine Persistent Disk CSI driver and the Filestore CSI driver support volume expansion.
• If the volume you want to resize is managed by an in-tree volume plugin:
  • Ensure the GKE cluster version is 1.11 or greater. While GKE cluster versions 1.11-1.14 support expansion of volumes managed by in-tree plugins, they require all Pods using the volume to be terminated and recreated to complete volume expansion.
  • Check your storage vendor's documentation to verify your in-tree volume plugin supports volume expansion (the Compute Engine Persistent Disk in-tree plugin does).
• You can't use volume expansion when using ReadOnlyMany access mode.

Using volume expansion

Note: To avoid errors using volume expansion, ensure that you complete the steps in this section in the right sequence.

To use volume expansion, perform the following tasks:

1. Add allowVolumeExpansion: true to your StorageClass, if your StorageClass doesn't already have the field. For example:

   apiVersion: storage.k8s.io/v1
   kind: StorageClass
   metadata:
     name: standard
   provisioner: my.driver
   ...
   allowVolumeExpansion: true
   

2. Request a change in volume capacity by editing your PersistentVolumeClaim's spec.resources.requests.storage field.

    kubectl edit pvc pvc-name
   

   For example, you could change the following PVC from having a 30 gibibyte (GiB) disk to having a 40 GiB disk.

   Before editing:

    # pvc-demo.yaml
    apiVersion: v1
    kind: PersistentVolumeClaim
    metadata:
      name: pvc-demo
    spec:
      accessModes:
        - ReadWriteOnce
      resources:
        requests:
          storage: 30Gi
   

   After editing:

    # pvc-demo.yaml
    apiVersion: v1
    kind: PersistentVolumeClaim
    metadata:
      name: pvc-demo
    spec:
      accessModes:
        - ReadWriteOnce
      resources:
        requests:
          storage: 40Gi
   

3. Verify the change by viewing PVC. To view your PVC, run the following command:

   kubectl get pvc pvc-name -o yaml
   

   Eventually, you should see the new volume in the status.capacity field. For example:

   ...
   spec:
     accessModes:
     - ReadWriteOnce
     resources:
       requests:
         storage: 40Gi
     storageClassName: standard
     volumeMode: Filesystem
     volumeName: pvc-078b7484-cc8d-4077-9bcb-2c17d8d4550c
   status:
     accessModes:
     - ReadWriteOnce
     capacity:
       storage: 40Gi
   ...
   

Note: Don't edit the capacity of the PersistentVolume object directly. If you edit the capacity of a PersistentVolume, and then change the size of the corresponding PersistentVolumeClaim to the same value, volume expansion won't happen. Kubernetes will assume that the backing volume was manually resized, and that no expansion is required.

If the capacity of a PersistentVolume is modified directly, this could lead the container file system to be incorrect. To fix these issues, see troubleshoot volume expansion changes.

Managing volume expansions in StatefulSets

If you need to increase the size of volumes used by Pods within a StatefulSet in Kubernetes, you should adjust the spec.resources.requests.storage field of the PersistentVolumeClaims (PVCs) associated with the Pods. Attempting to modify the volumeClaimTemplates field directly in the StatefulSet object will cause an error.

Additionally, if you increase the replica count of the StatefulSet, it will still create PVCs of the original size. To permanently change the size of the volumes provisioned for the Pods managed by the StatefulSet, you must delete and recreate the StatefulSet object with the updated size specified in the volumeClaimTemplates field. Unless your StatefulSet has PVC Auto-Deletion enabled, deleting your StatefulSet will only result in the deletion of the StatefulSet Pods, and won't delete their corresponding PVCs. For these PVCs to reflect the updated size, you must also delete and recreate the PVCs. Depending on the ReclaimPolicy of the PVCs, the underlying storage might also be deleted.

You can perform the following steps in order to keep the original Pods up and running while adjusting the StatefulSet to provision future replicas with the new volume size.

1. Save the existing StatefulSet to a file:

   kubectl get StatefulSet statefulset-name -o yaml > sts-backup.yaml
   

2. Remove the StatefulSet object from the cluster while keeping the Pods running as standalone Pods:

   kubectl delete sts statefulset-name --cascade=orphan
   

3. Edit the new volume storage size in the locally saved sts-backup.yaml file, specifically the value of spec.volumeClaimTemplates.spec.resources.requests.storage

4. Recreate the StatefulSet back in the cluster:

   kubectl apply -f sts-backup.yaml
   

What's next

• Learn more about volumes.
• Learn more about Resizing Persistent Volumes using Kubernetes.