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What is PersistentVolume?

A PersistentVolume (PV) is a piece of storage in a Kubernetes cluster that has been provisioned by an administrator or dynamically created using a StorageClass.

It is a cluster-level resource, not tied to any specific Pod or namespace.

Think of it as a storage disk that exists independently of Pods.

Pods use PVs through PersistentVolumeClaims (PVCs).

Key Characteristics:

1. Cluster-wide storage resource

  • PV lives at the cluster scope, not inside a namespace.
  • It is created and managed independently of Pods.

2. Decoupled from Pod lifecycle

  • PVs outlive Pods
  • When a Pod dies or is rescheduled, its data remains intact
  • Ideal for stateful applications like databases

PVCs allow Pods to request storage without knowing the underlying details.

3. Supports multiple storage backends

PVs can represent many types of storage:

  • NFS
  • CephFS / RBD
  • AWS EBS
  • GCE Persistent Disk
  • Azure Disk
  • iSCSI
  • Local storage
  • GlusterFS
  • CSI drivers (Container Storage Interface)

4. Uses access modes

Each PV declares supported access modes:

  • ReadWriteOnce (RWO)
    • Only one node can mount it at a time (most common).
  • ReadOnlyMany (ROX)
    • Multiple nodes can read it.
  • ReadWriteMany (RWX)
    • Multiple nodes can read/write at the same time (for shared storage).

5. Capacity PV specifies the amount of storage, e.g.:

resources:
  requests:
    storage: 10Gi

6. Reclaim policies

Controls what happens when PVC is deleted:

  • Retain
    • Keep PV and data (manual cleanup required).
  • Delete
    • Delete PV and underlying storage.
  • Recycle (Deprecated)
    • Simple scrub & reuse.

7. Static or Dynamic Provisioning

  • Static PV
    • Admin creates PVs manually.
  • Dynamic PV
    • StorageClass auto-creates PV on demand.

Use Cases

  • Databases (MySQL, PostgreSQL, MongoDB, Cassandra)
  • StatefulSet applications
  • Log storage
  • Persistent cache
  • File uploads / shared file systems

YAML Definition

apiVersion: v1
kind: PersistentVolume
metadata:
  name: pv-example
spec:
  capacity:
    storage: 5Gi
  accessModes:
    - ReadWriteOnce
  persistentVolumeReclaimPolicy: Retain
  hostPath:
    path: "/mnt/data"

Summary

Feature Description
What is PV? Cluster-wide storage resource
Purpose Provide persistent, reliable storage for Pods
Lifecycle Independent of Pods
Backends NFS, EBS, Ceph, CSI, local storage
Access Modes RWO, ROX, RWX
Reclaim Policy Retain/Delete
Provisioning Static or dynamic (StorageClass)
Use Cases Databases, StatefulSets, CNFs needing state