Ondat Volume Guide

Follow the recipes on this page to create your first PVC (Persistent Volume Claim) using Ondat. Ondat implements dynamic provisioning, so the creation of a PVC will automatically provision a PV (PersistentVolume) that can be used to persist data written by a Pod.

Create the PersistentVolumeClaim

You can find the basic examples in the Ondat use-cases repository, in the 00-basic directory.

git clone https://github.com/storageos/use-cases.git storageos-usecases
cd storageos-usecases/00-basic

PVC definition

apiVersion: v1
kind: PersistentVolumeClaim
metadata:
  name: my-vol-1
spec:
  storageClassName: "storageos" # Ondat StorageClass
  accessModes:
    - ReadWriteOnce
  resources:
    requests:
      storage: 5Gi

The above PVC will dynamically provision a 5GB volume using the storageos StorageClass. This StorageClass was created during the Ondat install and triggers creation of a PersistentVolume by Ondat.

For installations with CSI, you can create multiple StorageClasses in order to specify default labels.

apiVersion: storage.k8s.io/v1
kind: StorageClass
metadata:
  name: ondat-replicated
provisioner: csi.storageos.com # Provisioner when using CSI
parameters:
  csi.storage.k8s.io/fstype: ext4
  storageos.com/replicas: "1" # Enforces 1 replica for the Volume
  csi.storage.k8s.io/secret-name: storageos-api
  csi.storage.k8s.io/secret-namespace: storageos

The above StorageClass has the storageos.com/replicas label set. This label tells Ondat to create a volume with a replica. Adding Ondat feature labels to the StorageClass ensures all volumes created with the StorageClass have the same labels. For simplicity’s sake this example will use unreplicated volumes.

apiVersion: v1
kind: PersistentVolumeClaim
metadata:
  name: my-vol-1
spec:
  storageClassName: "ondat-replicated" # Reference to the StorageClass
  accessModes:
    - ReadWriteOnce
  resources:
    requests:
      storage: 5Gi

You can also choose to add the label in the PVC definition rather than the StorageClass. The PVC definition takes precedence over the SC.

apiVersion: v1
kind: PersistentVolumeClaim
metadata:
  name: my-vol-1
  labels:
      storageos.com/replicas: "1"
spec:
  storageClassName: "storageos"
  accessModes:
    - ReadWriteOnce
  resources:
    requests:
      storage: 5Gi

The above PVC has the storageos.com/replicas label set. This label tells Ondat to add a replica for the volume that is created. For the sake of keeping this example simple an unreplicated volume will be used.

Move into the examples folder and create a PVC using the PVC definition above.

# from storageos-usecases/00-basic
kubectl create -f ./pvc-basic.yaml

You can view the PVC that you have created with the command below

$ kubectl get pvc
NAME         STATUS   VOLUME                                     CAPACITY   ACCESS MODES   STORAGECLASS   AGE
pvc-1        Bound    pvc-f8ffa027-e821-11e8-bc0b-0ac77ccc61fa   5Gi        RWO            storageos       1m

Create a pod that mounts the PVC created in step 2.

kubectl create -f ./pod.yaml

The command above creates a Pod that uses the PVC that was created in step 1.

apiVersion: v1
kind: Pod
metadata:
  name: d1
spec:
  containers:
    - name: debian
      image: debian:9-slim
      command: ["/bin/sleep"]
      args: [ "3600" ]
      volumeMounts:
        - mountPath: /mnt
          name: v1
  volumes:
    - name: v1
      persistentVolumeClaim:
        claimName: pvc-1

In the Pod definition above volume v1 references the PVC created in step 2, and is mounted in the pod at /mnt. In this example a debian image is used for the container but any container image with a shell would work for this example.

Confirm that the pod is up and running

$ kubectl get pods
NAME      READY   STATUS    RESTARTS   AGE
d1        1/1     Running   0          1m

Execute a shell inside the container and write some contents to a file
```
$ kubectl exec -it d1 -- bash
root@d1:/# echo "Hello World!" > /mnt/helloworld
root@d1:/# cat /mnt/helloworld
Hello World!
```
By writing to /mnt inside the container, the Ondat volume created by the PVC is being written to. If you were to kill the pod and start it again on a new node, the helloworld file would still be avaliable.

If you wish to see more use cases with actual applications, see our Use Cases documentation.