Mastering Kubernetes Persistent Storage: PV, PVC, and CSI Explained

Why HostPath is insufficient

HostPath provides persistent storage but stores data on the node itself, making it suitable only for read‑only scenarios. When a Pod is rescheduled, its data would be lost, so network storage is required.

Kubernetes storage abstraction: PV and PVC

Kubernetes solves this problem by introducing PersistentVolumes (PV) and PersistentVolumeClaims (PVC), decoupling storage from the underlying infrastructure. Users request storage just like CPU or memory.

PV : Describes a persistent storage volume, typically defining a directory on a host such as an NFS mount.

PVC : Describes the desired storage attributes for a Pod, such as size and access mode.

Administrators configure the network storage type and provide corresponding PV specifications. Users simply create a PVC and reference it in a Pod’s volume definition.

Using network storage with CSI

Kubernetes offers the Container Storage Interface (CSI) that allows vendors to develop custom storage plugins, enabling support for block, file, or object storage.

Example: Defining a PersistentVolume

<code>apiVersion: v1
kind: PersistentVolume
metadata:
  name: pv-example
spec:
  accessModes:
  - ReadWriteMany
  capacity:
    storage: 10Gi
  csi:
    driver: nas.csi.everest.io
    fsType: nfs
    volumeAttributes:
      everest.io/share-export-location: nas01-mycloud.com:/share-96314776
    volumeHandle: 68e4a4fd-d759-444b-8265-20dc66c8c502
</code>

Create the PV and inspect it:

<code>$ kubectl create -f pv.yaml
persistentvolume/pv-example created

$ kubectl get pv
NAME        CAPACITY   ACCESS MODES   RECLAIM POLICY   STATUS    CLAIM
pv-example  10Gi       RWX            Retain           Available
</code>

Understanding PV status fields

RECLAIM POLICY Retain means the PV remains after the PVC is released. STATUS Available indicates the PV is ready for binding.

Example: Creating a PersistentVolumeClaim

<code>apiVersion: v1
kind: PersistentVolumeClaim
metadata:
  name: pvc-example
spec:
  accessModes:
  - ReadWriteMany
  resources:
    requests:
      storage: 10Gi
  volumeName: pv-example
</code>

Create the PVC and verify its binding:

<code>$ kubectl create -f pvc.yaml
persistentvolumeclaim/pvc-example created

$ kubectl get pvc
NAME          STATUS  VOLUME       CAPACITY   ACCESS MODES   STORAGECLASS   AGE
pvc-example   Bound   pv-example   10Gi       RWX
</code>

The PVC is bound to the PV, and the PV status changes to Bound with CLAIM default/pvc-example, illustrating that PVs are cluster‑wide resources while PVCs are namespace‑scoped.