PersistentVolumes & StorageClasses

Understand the Kubernetes storage layer: PVs, PVCs, and dynamic provisioning.

Time: ~10 minutes Difficulty: Intermediate

What You Will Learn

• PersistentVolume (PV): a piece of storage in the cluster
• PersistentVolumeClaim (PVC): a request for storage by a pod
• StorageClass: dynamic provisioning without pre-creating PVs
• Access modes: ReadWriteOnce, ReadOnlyMany, ReadWriteMany
• Reclaim policies: Retain vs Delete
• Data persistence across pod restarts

Deploy

Check available StorageClasses

kubectl get storageclasses

Minikube provides a standard StorageClass backed by hostPath.

Static provisioning (manual PV)

Navigate to the demo directory:

cd demos/persistent-volumes

kubectl apply -f manifests/namespace.yaml
kubectl apply -f manifests/static-pv.yaml

Check the PV and PVC:

kubectl get pv
kubectl get pvc -n storage-demo

The PVC should be Bound to the PV.

Dynamic provisioning (automatic PV)

kubectl apply -f manifests/dynamic-pvc.yaml

kubectl get pvc -n storage-demo
kubectl get pv

A new PV is automatically created by the standard StorageClass and bound to the PVC.

Use the Storage

Write data

kubectl apply -f manifests/writer-pod.yaml
kubectl logs writer -n storage-demo -f

The writer appends a log entry every 5 seconds to /data/log.txt on the PVC.

Delete the writer and verify data persists

kubectl delete pod writer -n storage-demo

# Data is still on the PVC
kubectl run verify --rm -it --image=busybox:1.36 -n storage-demo \
  --overrides='{"spec":{"volumes":[{"name":"d","persistentVolumeClaim":{"claimName":"dynamic-pvc"}}],"containers":[{"name":"v","image":"busybox:1.36","command":["cat","/data/log.txt"],"volumeMounts":[{"name":"d","mountPath":"/data"}]}]}}'

The data survives pod deletion because it lives on the PVC, not in the container.

Read data with the reader pod

kubectl apply -f manifests/reader-pod.yaml
kubectl logs reader -n storage-demo

What is Happening

manifests/
  namespace.yaml      # storage-demo namespace
  static-pv.yaml      # Manual PV (hostPath) + PVC with label selector
  dynamic-pvc.yaml    # PVC using standard StorageClass (PV auto-created)
  writer-pod.yaml     # Writes to dynamic-pvc
  reader-pod.yaml     # Reads from manual-pvc

Storage hierarchy:

StorageClass (how to provision)
    |
    v
PersistentVolume (a piece of storage)
    |
    v (bound)
PersistentVolumeClaim (a request for storage)
    |
    v (mounted)
Pod

Access modes:

Mode	Short	Description
ReadWriteOnce	RWO	One node can mount read-write
ReadOnlyMany	ROX	Many nodes can mount read-only
ReadWriteMany	RWX	Many nodes can mount read-write

Reclaim policies:

Policy	What Happens When PVC Is Deleted
Retain	PV keeps data, admin must clean up manually
Delete	PV and underlying storage are deleted
Recycle	Deprecated. Was rm -rf /volume/*

Experiment

1. Check what backing storage the dynamic PV uses:

   kubectl get pv -o wide
   kubectl describe pv <pv-name>

2. Delete the PVC and check the PV reclaim behavior:

   kubectl delete pvc dynamic-pvc -n storage-demo
   kubectl get pv

   Dynamic PVs with Delete policy are removed. Static PVs with Retain stay.

3. List StorageClass details:

   kubectl describe storageclass standard

Cleanup

kubectl delete namespace storage-demo
kubectl delete pv manual-pv --ignore-not-found

Further Reading

See docs/deep-dive.md for a detailed explanation of CSI drivers, volume snapshots, volume expansion, topology-aware provisioning, and production storage patterns.

Next Step

Move on to Vault to learn production secret management with HashiCorp Vault.