xDev Asia

PersistentVolume, PersistentVolumeClaim, StorageClass hands-on. Dynamic provisioning, reclaim policies, volume modes and access modes for CKA.

Persistent Volumes, PVCs and StorageClass — Static and Dynamic Provisioning

1. PV & PVC Lifecycle

Static Provisioning:
  Admin creates PV → Developer creates PVC → K8s binds PVC to matching PV

Dynamic Provisioning:
  Developer creates PVC (with storageClassName) → StorageClass auto-creates PV

Binding criteria:
  ✓ accessMode match
  ✓ storage size: PV >= PVC requested
  ✓ storageClass match (or "")
  ✓ volumeMode match

2. Creating PV and PVC

# PersistentVolume (static, hostPath for lab)
apiVersion: v1
kind: PersistentVolume
metadata:
  name: pv-data
spec:
  capacity:
    storage: 5Gi
  accessModes:
    - ReadWriteOnce
  persistentVolumeReclaimPolicy: Retain
  storageClassName: manual
  hostPath:
    path: /mnt/data    # Lab only; use NFS/EBS in production

---
# PersistentVolumeClaim
apiVersion: v1
kind: PersistentVolumeClaim
metadata:
  name: pvc-data
spec:
  accessModes:
    - ReadWriteOnce
  resources:
    requests:
      storage: 2Gi
  storageClassName: manual

Reclaim Policy	Behavior when PVC is deleted
Retain	PV keeps data, phase = Released (admin must delete manually)
Delete	PV and storage backend are deleted automatically
Recycle (deprecated)	Deletes files, PV ready for new PVC

Exam tip: PV phase lifecycle: Available (no PVC) → Bound (PVC bound) → Released (PVC deleted, Retain policy) → Failed. A Released PV cannot bind to a new PVC until the admin manually edits the PV to remove .spec.claimRef.

3. StorageClass

apiVersion: storage.k8s.io/v1
kind: StorageClass
metadata:
  name: fast
  annotations:
    storageclass.kubernetes.io/is-default-class: "true"  # Default SC
provisioner: kubernetes.io/aws-ebs
parameters:
  type: gp3
  iopsPerGB: "10"
reclaimPolicy: Delete
allowVolumeExpansion: true
volumeBindingMode: WaitForFirstConsumer  # Delay until Pod scheduled

volumeBindingMode	Behavior
Immediate	PV provisioned immediately when PVC is created
WaitForFirstConsumer	Delayed until Pod is scheduled (ensures same zone)

4. Pod Using PVC

apiVersion: v1
kind: Pod
metadata:
  name: app-pod
spec:
  containers:
  - name: app
    image: nginx
    volumeMounts:
    - name: data-volume
      mountPath: /var/data
  volumes:
  - name: data-volume
    persistentVolumeClaim:
      claimName: pvc-data    # Reference PVC name

5. Cheat Sheet

Task	Command
List PVs	`kubectl get pv`
List PVCs	`kubectl get pvc -n NAMESPACE`
PVC status	`kubectl describe pvc NAME`
List StorageClasses	`kubectl get storageclass`
Expand PVC	Edit PVC spec.resources.requests.storage (SC must allow)

6. Practice Questions

Q1: A PVC is stuck in "Pending" state. A PV with 10Gi exists. The PVC requests 5Gi with ReadWriteMany, but the PV only supports ReadWriteOnce. What happens?

A) The PVC binds to the PV and uses RWO
B) The PVC remains Pending — no PV matches the requested access mode ✓
C) Kubernetes auto-converts the PV access mode
D) The Pod using the PVC starts but cannot write

Explanation: PVC binding requires all criteria to match: storage size (PV >= PVC), access mode, storageClass, and volumeMode. If the PV only supports RWO but PVC needs RWX, they won't bind.

Q2: A PVC bound to a PV is deleted. The PV has reclaimPolicy: Retain. What is the PV's state?

A) The PV is deleted
B) The PV transitions to Available and can be reused
C) The PV transitions to Released — data is preserved but PV can't be rebound automatically ✓
D) The PV is immediately provisioned for another PVC

Explanation: Retain policy preserves the PV and its data. The PV enters Released state. To reuse it, an admin must manually delete the old claimRef (kubectl patch pv myPV -p '{"spec":{"claimRef":null}}') to return it to Available.

Q3: In a cloud environment, WaitForFirstConsumer volumeBindingMode is recommended over Immediate. Why?

A) It reduces storage costs
B) It ensures the volume is provisioned in the same availability zone as the scheduled Pod ✓
C) It allows multiple Pods to share the volume
D) It speeds up Pod startup time