Managing volumes

Resizing an NFS volume

Starting with v18.10, Trident supports volume resize for NFS PVs. More specifically, PVs provisioned on ontap-nas, ontap-nas-economy, and ontap-nas-flexgroup backends can be expanded.

Resizing Persistent Volumes using Kubernetes blog post describes the workflows involved in resizing a PV. Volume resize was introduced in Kubernetes v1.8 as an alpha feature and was promoted to beta in v1.11, which means this feature is enabled by default starting with Kubernetes v1.11.

Because NFS PV resize is not supported by Kubernetes, and is implemented by the Trident orchestrator externally, Kubernetes admission controller may reject PVC size updates for in-tree volume plugins that don’t support resize (e.g., NFS). The Trident team has changed Kubernetes to allow such changes starting with Kubernetes 1.12. Therefore, we recommend using this feature with Kubernetes 1.12 or later as it would just work.

While we recommend using Kubernetes 1.12 or later, it is still possible to resize NFS PVs with earlier versions of Kubernetes that support resize. This is done by disabling the PersistentVolumeClaimResize admission plugin when the Kubernetes API server is started:

kube-apiserver --disable-admission-plugins=PersistentVolumeClaimResize

With Kubernetes 1.8-1.10 that offer this feature as alpha, the ExpandPersistentVolumes Feature Gate should also be turned on:

kube-apiserver --feature-gates=ExpandPersistentVolumes=true --disable-admission-plugins=PersistentVolumeClaimResize

To resize an NFS PV, the admin first needs to configure the storage class to allow volume expansion by setting the allowVolumeExpansion field to true:

$ cat storageclass-ontapnas.yaml
apiVersion: storage.k8s.io/v1
kind: StorageClass
metadata:
  name: ontapnas
provisioner: netapp.io/trident
parameters:
  backendType: ontap-nas
allowVolumeExpansion: true

If you have already created a storage class without this option, you can simply edit the existing storage class via kubectl edit storageclass to allow volume expansion.

Next, we create a PVC using this storage class:

$ cat pvc-ontapnas.yaml
kind: PersistentVolumeClaim
apiVersion: v1
metadata:
  name: ontapnas20mb
spec:
  accessModes:
  - ReadWriteOnce
  resources:
    requests:
      storage: 20Mi
  storageClassName: ontapnas

Trident should create a 20MiB NFS PV for this PVC:

$ kubectl get pvc
NAME                    STATUS    VOLUME                                CAPACITY   ACCESS MODES   STORAGECLASS        AGE
ontapnas20mb            Bound     default-ontapnas20mb-c1bd7            20Mi       RWO            ontapnas            14s

$ kubectl get pv default-ontapnas20mb-c1bd7
NAME                         CAPACITY   ACCESS MODES   RECLAIM POLICY   STATUS    CLAIM                  STORAGECLASS       REASON    AGE
default-ontapnas20mb-c1bd7   20Mi       RWO            Delete           Bound     default/ontapnas20mb   ontapnas                     1m

To resize the newly created 20MiB PV to 1GiB, we edit the PVC and set spec.resources.requests.storage to 1GB:

$ kubectl edit pvc ontapnas20mb
# Please edit the object below. Lines beginning with a '#' will be ignored,
# and an empty file will abort the edit. If an error occurs while saving this file will be
# reopened with the relevant failures.
#
apiVersion: v1
kind: PersistentVolumeClaim
metadata:
  annotations:
    pv.kubernetes.io/bind-completed: "yes"
    pv.kubernetes.io/bound-by-controller: "yes"
    volume.beta.kubernetes.io/storage-provisioner: netapp.io/trident
  creationTimestamp: 2018-08-21T18:26:44Z
  finalizers:
  - kubernetes.io/pvc-protection
  name: ontapnas20mb
  namespace: default
  resourceVersion: "1958015"
  selfLink: /api/v1/namespaces/default/persistentvolumeclaims/ontapnas20mb
  uid: c1bd7fa5-a56f-11e8-b8d7-fa163e59eaab
spec:
  accessModes:
  - ReadWriteOnce
  resources:
    requests:
      storage: 1Gi
...

We can validate the resize has worked correctly by checking the size of the PVC, PV, and the Trident volume:

$ kubectl get pvc ontapnas20mb
NAME           STATUS    VOLUME                       CAPACITY   ACCESS MODES   STORAGECLASS       AGE
ontapnas20mb   Bound     default-ontapnas20mb-c1bd7   1Gi        RWO            ontapnas           6m

$ kubectl get pv default-ontapnas20mb-c1bd7
NAME                         CAPACITY   ACCESS MODES   RECLAIM POLICY   STATUS    CLAIM                  STORAGECLASS       REASON    AGE
default-ontapnas20mb-c1bd7   1Gi        RWO            Delete           Bound     default/ontapnas20mb   ontapnas             6m

$ tridentctl get volume default-ontapnas20mb-c1bd7 -n trident
+----------------------------+---------+------------------+----------+------------------------+--------------+
|            NAME            |  SIZE   |  STORAGE CLASS   | PROTOCOL |        BACKEND         |     POOL     |
+----------------------------+---------+------------------+----------+------------------------+--------------+
| default-ontapnas20mb-c1bd7 | 1.0 GiB | ontapnas         | file     | ontapnas_10.63.171.111 | VICE08_aggr1 |
+----------------------------+---------+------------------+----------+------------------------+--------------+