my-docs/Containerization-Orchestration/Kubernetes/Storage/Pv.md

Kubernetes Persistent Volumes (PV) Cheat Sheet

What is a Persistent Volume (PV)?

A Persistent Volume (PV) is a piece of storage in a Kubernetes cluster that can be:

• Pre-provisioned by an administrator, or
• Dynamically provisioned using a StorageClass.

PVs allow data to persist beyond the lifecycle of individual Pods.

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PV Storage Options

1. HostPath

• Mounts a file or directory from the host node’s filesystem into a Pod.
• Suitable only for local development or single-node clusters such as Minikube or Kind.
• Not recommended for production workloads.

2. NFS

• Network File System; allows multiple Pods and nodes to share storage.
• Recommended for shared or distributed environments.

3. Cloud Volumes

• AWS: awsElasticBlockStore
• GCP: gcePersistentDisk
• Azure: azureDisk or azureFile
• CSI Drivers: Preferred modern approach for all major clouds and on-prem solutions.

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Kubernetes Storage Architecture

1. Persistent Volume (PV) – Represents the actual storage resource, managed by the cluster admin or a dynamic provisioner.
2. Persistent Volume Claim (PVC) – A user request for storage with specific size and access requirements.
3. StorageClass – Defines how dynamic provisioning should occur (provisioner, reclaim policy, parameters).

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PV Lifecycle Phases

State	Description
Available	PV is ready to be bound.
Bound	PV is bound to a PVC.
Released	PVC was deleted; PV is unbound but data may still exist.
Failed	Automatic cleanup failed.

Reclaim Policies:

• Delete: Removes the underlying storage resource.
• Retain: Keeps data for manual recovery.
• Recycle: Deprecated (previously used to scrub the volume).

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PV Access Modes

Mode	Description
ReadWriteOnce (RWO)	One node can read/write.
ReadOnlyMany (ROX)	Many nodes can read.
ReadWriteMany (RWX)	Many nodes can read/write.
ReadWriteOncePod (RWOP)	Only one Pod can mount it with read/write access (Kubernetes ≥1.22).

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CLI Commands to Manage PVs & PVCs

# List all Persistent Volumes
kubectl get pv

# List all Persistent Volume Claims
kubectl get pvc -A

# Describe a specific PV or PVC
kubectl describe pv <pv-name>
kubectl describe pvc <pvc-name> -n <namespace>

# Delete a PV or PVC
kubectl delete pv <pv-name>
kubectl delete pvc <pvc-name> -n <namespace>

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Example: Deployment with hostPath Volume

apiVersion: apps/v1
kind: Deployment
metadata:
  name: app-1
  namespace: dev
spec:
  replicas: 3
  selector:
    matchLabels:
      app: nginx
  template:
    metadata:
      labels:
        app: nginx
    spec:
      containers:
        - name: nginx
          image: nginx
          ports:
            - containerPort: 80
          volumeMounts:
            - name: nginx-log
              mountPath: /var/log/nginx
      volumes:
        - name: nginx-log
          hostPath:
            path: /root/nginx/logs
            type: DirectoryOrCreate

Valid hostPath Types: DirectoryOrCreate, Directory, FileOrCreate, File, Socket, CharDevice, BlockDevice

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Example: Static Persistent Volume (PV)

Important: A PV must specify a volume source type (this was the cause of your validation error). For example, this corrected PV uses hostPath:

apiVersion: v1
kind: PersistentVolume
metadata:
  name: pv001
spec:
  capacity:
    storage: 128Mi
  accessModes:
    - ReadWriteMany
  persistentVolumeReclaimPolicy: Retain
  storageClassName: manual
  hostPath:
    path: /mnt/data/pv001

---

Example: Persistent Volume Claim (PVC)

apiVersion: v1
kind: PersistentVolumeClaim
metadata:
  name: pvc-2
  namespace: db
spec:
  accessModes:
    - ReadWriteOnce
  resources:
    requests:
      storage: 64Mi
  storageClassName: manual

To bind this PVC to a specific PV manually:

volumeName: pv001

---

NFS-Based Persistent Volume

Persistent Volume (PV)

apiVersion: v1
kind: PersistentVolume
metadata:
  name: pv-nfs-2
spec:
  capacity:
    storage: 128Mi
  accessModes:
    - ReadWriteMany
  persistentVolumeReclaimPolicy: Retain
  storageClassName: nginx-files
  mountOptions:
    - hard
    - nfsvers=4.2
  nfs:
    path: /root/Nginx_Files
    server: 192.168.6.160

Persistent Volume Claim (PVC)

apiVersion: v1
kind: PersistentVolumeClaim
metadata:
  name: pvc-1
  namespace: db
spec:
  volumeName: pv-nfs-2
  accessModes:
    - ReadWriteMany
  resources:
    requests:
      storage: 64Mi
  storageClassName: nginx-files

---

Static StorageClass for Pre-Provisioned Volumes

apiVersion: storage.k8s.io/v1
kind: StorageClass
metadata:
  name: nginx-files
provisioner: kubernetes.io/no-provisioner
volumeBindingMode: WaitForFirstConsumer
reclaimPolicy: Retain

---

Recommended Additions

1. Always include storageClassName to ensure predictable binding.

2. Set volumeBindingMode: WaitForFirstConsumer in StorageClasses for node-aware provisioning.

3. Avoid using hostPath in multi-node clusters; use NFS or CSI drivers.

4. Check events for troubleshooting PV/PVC binding:

   kubectl describe pvc <pvc-name> -n <namespace>
   

5. Automate cleanup with proper reclaim policies or storage lifecycle controllers.