4.4.5.6. Read Only Volume

How to Create a Read-Only NVMesh Volume & Populate it with Data

This example describes how to create an NVMesh volume for use as a ReadOnlyMany Persistent Volume.
We will go over creating a Volume, populating it with data and then turn it into a ReadOnlyMany Volume.

*The following example uses volumeMode: Filesystem but the same applies for volumeMode: Block.

Create a Storage Class with reclaimPolicy: Retain.

kind: StorageClass
apiVersion: storage.k8s.io/v1
metadata:
  name: nvmesh-concatenated-retained
provisioner: nvmesh-csi.excelero.com
parameters:
  # set here the desired VPG
  vpg: DEFAULT_CONCATENATED_VPG
# set reclaimPolicy to retain so that the PV will not be deleted when it's PVC is deleted
reclaimPolicy: Retain
allowVolumeExpansion: true
volumeBindingMode: Immediate

Create a PVC for populating the volume with data.
This will create a new volume with accessMode ReadWriteOnce so we can write data into the volume.

kind: PersistentVolumeClaim
apiVersion: v1
metadata:
  name: claim-populate-vol-with-data
spec:
  accessModes:
    - ReadWriteOnce
  resources:
    requests:
      storage: 1Gi
  storageClassName: nvmesh-concatenated-retained
  volumeMode: Filesystem

Create a pod to write the data to the volume.

Example: This pod will create a file with data.

apiVersion: v1
kind: Pod
metadata:
  name: populate-vol-with-data
spec:
  restartPolicy: OnFailure
  containers:
    - name: write-to-volume
      image: centos:7
      command: ["/bin/bash", "-c", "echo some-data > /data/data.txt"]
      volumeMounts:
        - name: data-volume
          mountPath: /data/
  volumes:
    - name: data-volume
      persistentVolumeClaim:
        claimName: claim-populate-vol-with-data

*When the Pod is finished, delete the pod and also delete any workload using the PVC.

kubectl delete pod populate-vol-with-data

Delete the PVC.
As we used the storage-class with reclaimPolicy: retain, the PV will not be deleted by this action.

kubectl delete pvc claim-populate-vol-with-data

Edit the PersistentVolume Object.

Run this to find the PV created by the Claim:

kubectl get pv -o=custom-columns=NAME:.metadata.name,PVC:.spec.claimRef.name | grep claim-populate-vol-with-data

Edit the PV object by running:

kubectl edit pv <pv name>

Perform the following changes:

kind: PersistentVolume
apiVersion: v1
metadata:
  name: pvc-f89b81c9-1c23-40c0-b3a7-eb70525c25ea
spec:
  capacity:
    storage: 1Gi
  csi:
    ...
  accessModes:
    # change ReadWriteOnce to ReadOnlyMany
    # - ReadWriteOnce
    - ReadOnlyMany
  # Remove claimRef so that the PV can be bounded again to a new PVC
  #claimRef:
  #  ...
  persistentVolumeReclaimPolicy: Retain
  storageClassName: nvmesh-concatenated-retained
  volumeMode: Filesystem

Create a PVC with ReadOnlyMany.

kind: PersistentVolumeClaim
apiVersion: v1
metadata:
  name: claim-rom
spec:
  accessModes:
    - ReadOnlyMany
  resources:
    requests:
      storage: 1Gi
  storageClassName: nvmesh-concatenated-retained
  volumeMode: Filesystem

Create a pod to read the data.

Example Pod:
This pod will read the data.txt file and then try to delete the file printing the exit code (reading should succeed and deletion should fail).

apiVersion: v1
kind: Pod
metadata:
  name: read-data
spec:
  restartPolicy: OnFailure
  containers:
    - name: read-data
      image: centos:7
      cmd: ["/bin/bash", "-c" ,"cat /data/data.txt ; rm /data/data.txt; echo exit_code=$?"]
      volumeMounts:
        - name: data-volume
          mountPath: /data/
  volumes:
    - name: data-volume
      persistentVolumeClaim:
        claimName: claim-rom