How do PersistentVolumes and PersistentVolumeClaims work?

PVs are cluster-scoped storage resources. PVCs are namespaced requests for size, access mode and optionally a StorageClass. The binding can be static, where an admin creates the PV, or dynamic, where a provisioner creates one from a StorageClass. Pods reference the PVC, not the PV.

• ReadWriteOnce is mounted read-write by a single node, not necessarily a single pod
• ReadOnlyMany and ReadWriteMany depend on the underlying driver
• Reclaim policy Retain keeps data after the PVC is deleted; Delete removes it
• A PVC is bound to one PV and usually cannot be shrunk
• StatefulSets use volumeClaimTemplates to create one PVC per pod

apiVersion: v1
kind: PersistentVolumeClaim
metadata:
  name: data
spec:
  accessModes:
    - ReadWriteOnce
  storageClassName: fast-ssd
  resources:
    requests:
      storage: 20Gi
---
apiVersion: v1
kind: Pod
metadata:
  name: app
spec:
  containers:
    - name: app
      image: registry.example.com/app:2.0.0
      volumeMounts:
        - name: data
          mountPath: /data
  volumes:
    - name: data
      persistentVolumeClaim:
        claimName: data

Access modes are a common source of confusion. Many block storage drivers only support ReadWriteOnce, so multiple replicas cannot safely share the same volume. Choose storage based on the access pattern, latency, durability and snapshot requirements, not just capacity.