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Understanding PersistentVolumeClaims (PVC) in Kubernetes

category: DevOps
tags: kubernetes, storage, pvc, persistent-volumes, containers

Main Topic 1

PersistentVolumeClaims (PVCs) are how pods request and use persistent storage in Kubernetes. PVCs abstract the details of the underlying storage, enabling decoupled, dynamic provisioning.

Subtopic A: Key Components

• PersistentVolume (PV) – A piece of storage in the cluster provisioned by an admin or dynamically.
• PersistentVolumeClaim (PVC) – A request for storage by a user/pod.
• PVCs define how much storage is needed and the access mode.
• Kubernetes matches the claim with a suitable PV.
• Mounting the Volume – Once claimed, the volume can be mounted into a container using volumeMounts.

Subtopic B: Why Use PVCs?

• Data Persistence – Data survives pod restarts or rescheduling.
• Separation of Concerns – Devs request storage without needing to know where it comes from.
• Managed Storage – Cloud volumes, NFS, and other backends are supported via PVs.

Main Topic 2

In Context

You declare the volume in your pod spec like this:

volumes:
  - name: my-volume
    persistentVolumeClaim:
      claimName: my-pvc

And then mount it like this:

volumeMounts:
  - name: my-volume
    mountPath: /app/data

This means:
- Kubernetes will look for a PersistentVolumeClaim named my-pvc
- It will mount that volume inside the container at /app/data

Code Example (if applicable)

apiVersion: v1
kind: Pod
metadata:
  name: my-pod
spec:
  containers:
    - name: my-container
      image: nginx
      volumeMounts:
        - name: my-volume
          mountPath: /app/data
  volumes:
    - name: my-volume
      persistentVolumeClaim:
        claimName: my-pvc

Commands (if applicable)

# Create a PVC
kubectl apply -f my-pvc.yaml

# Check PVC status
kubectl get pvc

# Describe the bound volume
kubectl describe pvc my-pvc

Key Concepts Summary

• PV (Persistent Volume) – Cluster-managed storage resource
• PVC (Persistent Volume Claim) – User request for PV
• Volume Mount – Path where the claimed volume is made available to the container

Best Practices / Tips

1. Use PVCs over hostPath – Portability and safety in multi-node clusters
2. Set storageClass in PVC – For dynamic provisioning
3. Monitor PVC status – Ensure it's Bound before using it

Common Issues / Troubleshooting

Problem 1: PVC Stuck in Pending

• Symptom: PVC status remains Pending
• Cause: No available PV matches the request
• Solution: Create a PV manually or fix the storageClass and size

Problem 2: Data Not Persisting After Pod Restart

• Symptom: Data is lost on pod restart
• Cause: emptyDir volume was used instead of PVC
• Solution: Ensure persistentVolumeClaim is specified in volume definition

Type	Use Case	Persistent?
emptyDir	Temporary scratch space per pod	❌ No
hostPath	Mount a directory from the node's filesystem	✅* (node-bound)
PVC (via PV)	Durable storage across pod reschedules/restarts	✅ Yes

References / Further Reading

• https://kubernetes.io/docs/concepts/storage/persistent-volumes/
• https://kubernetes.io/docs/tasks/configure-pod-container/configure-persistent-volume-storage/
• https://www.mirantis.com/blog/introduction-to-kubernetes-persistent-volumes/

Last updated: 2025-08-26 20:00 UTC