Persistent Storage

Containers are ephemeral — when a pod restarts, its filesystem is lost. Persistent storage decouples data from the container lifecycle. This lesson covers PersistentVolumes, PersistentVolumeClaims, StorageClasses, CSI drivers, and backup strategies.

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The Storage Stack

┌──────────────────────────────────────┐
│          Pod                         │
│  ┌──────────────────────────────┐    │
│  │   Container                  │    │
│  │   volumeMount: /data         │    │
│  └──────────────┬───────────────┘    │
└─────────────────┼────────────────────┘
                  │
┌─────────────────▼────────────────────┐
│  PersistentVolumeClaim (PVC)         │
│  "I need 50Gi of fast SSD storage"   │
└─────────────────┬────────────────────┘
                  │  binds to
┌─────────────────▼────────────────────┐
│  PersistentVolume (PV)               │
│  "50Gi SSD volume, provisioned"      │
└─────────────────┬────────────────────┘
                  │  backed by
┌─────────────────▼────────────────────┐
│  StorageClass                        │
│  "gp3-ssd" → CSI Driver → Cloud API │
└──────────────────────────────────────┘

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PersistentVolumes and PersistentVolumeClaims

PersistentVolume (PV)

A PV represents a piece of storage in the cluster, provisioned by an administrator or dynamically via a StorageClass.

apiVersion: v1
kind: PersistentVolume
metadata:
  name: database-pv
spec:
  capacity:
    storage: 100Gi
  accessModes:
    - ReadWriteOnce
  persistentVolumeReclaimPolicy: Retain
  storageClassName: fast-ssd
  csi:
    driver: ebs.csi.aws.com
    volumeHandle: vol-0abc123def456789

PersistentVolumeClaim (PVC)

A PVC is a request for storage by a user.

apiVersion: v1
kind: PersistentVolumeClaim
metadata:
  name: postgres-data
spec:
  accessModes:
    - ReadWriteOnce
  storageClassName: fast-ssd
  resources:
    requests:
      storage: 50Gi

Using a PVC in a Pod

apiVersion: v1
kind: Pod
metadata:
  name: postgres
spec:
  containers:
    - name: postgres
      image: postgres:16
      volumeMounts:
        - name: data
          mountPath: /var/lib/postgresql/data
  volumes:
    - name: data
      persistentVolumeClaim:
        claimName: postgres-data

Access Modes

Mode	Abbreviation	Description
ReadWriteOnce	RWO	Single node can mount read-write
ReadOnlyMany	ROX	Many nodes can mount read-only
ReadWriteMany	RWX	Many nodes can mount read-write
ReadWriteOncePod	RWOP	Single pod can mount read-write (K8s 1.27+)

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StorageClasses

StorageClasses enable dynamic provisioning — PVs are created automatically when a PVC is submitted.

apiVersion: storage.k8s.io/v1
kind: StorageClass
metadata:
  name: fast-ssd
provisioner: ebs.csi.aws.com
parameters:
  type: gp3
  iops: "5000"
  throughput: "250"
  encrypted: "true"
reclaimPolicy: Retain
volumeBindingMode: WaitForFirstConsumer
allowVolumeExpansion: true

Reclaim Policies

Policy	Behaviour When PVC Is Deleted
Retain	PV and data are kept (manual cleanup)
Delete	PV and underlying storage are deleted
Recycle	Data is scrubbed, PV made available again

Production tip: Use Retain for databases. You do not want accidental PVC deletion to destroy production data.

Volume Binding Modes