Storage Class

This lesson explains StorageClasses in Kubernetes: what they are, how they differ from static provisioning, and how to use them to enable dynamic provisioning of persistent storage. Overview

Static provisioning: you create cloud disks ahead of time, then create the matching PersistentVolume (PV) objects and PersistentVolumeClaims (PVCs).
Dynamic provisioning (StorageClass): Kubernetes creates the backing storage (cloud disk) automatically when a PVC requests a StorageClass; the PV is created and bound automatically.

Static provisioning

With static provisioning you manually create the backing disk in your cloud provider, then create a PV that references that disk, and finally create a PVC which binds to the PV. This process works but requires manual steps and coordination between cloud resources and Kubernetes manifests. Example: a manually-provisioned PV, a PVC that claims it, and a Pod that mounts the PVC:

apiVersion: v1
kind: PersistentVolume
metadata:
  name: pv-vol1
spec:
  accessModes:
    - ReadWriteOnce
  capacity:
    storage: 500Mi
  gcePersistentDisk:
    pdName: pd-disk
    fsType: ext4
---
apiVersion: v1
kind: PersistentVolumeClaim
metadata:
  name: myclaim
spec:
  accessModes:
    - ReadWriteOnce
  resources:
    requests:
      storage: 500Mi
---
apiVersion: v1
kind: Pod
metadata:
  name: random-number-generator
spec:
  containers:
    - name: alpine
      image: alpine
      command: ["/bin/sh","-c"]
      args: ["shuf -i 0-100 -n 1 >> /opt/number.out;"]
      volumeMounts:
        - mountPath: /opt
          name: data-volume
  volumes:
    - name: data-volume
      persistentVolumeClaim:
        claimName: myclaim

Before creating the PV manifest above you typically create the disk on Google Cloud (example using gcloud):

gcloud beta compute disks create pd-disk \
  --size=1GB \
  --region=us-east1

This manual process is called static provisioning. It works, but you must provision storage ahead of time and ensure PV definitions stay synchronized with the cloud disks.

Dynamic provisioning with StorageClass

StorageClasses enable dynamic provisioning: when a PVC is created that references a StorageClass, Kubernetes uses the provisioner defined in that StorageClass to create backing storage on the cloud provider. The provisioner creates the disk, a PV object is created automatically, and the PVC binds to that PV. A minimal example StorageClass for Google Compute Engine using the legacy in-tree provisioner:

apiVersion: storage.k8s.io/v1
kind: StorageClass
metadata:
  name: google-storage
provisioner: kubernetes.io/gce-pd

Once a StorageClass exists you no longer need to create PVs manually. Instead, reference the StorageClass in your PVC with storageClassName:

apiVersion: storage.k8s.io/v1
kind: StorageClass
metadata:
  name: google-storage
provisioner: kubernetes.io/gce-pd
---
apiVersion: v1
kind: PersistentVolumeClaim
metadata:
  name: myclaim
spec:
  accessModes:
    - ReadWriteOnce
  storageClassName: google-storage
  resources:
    requests:
      storage: 500Mi
---
apiVersion: v1
kind: Pod
metadata:
  name: random-number-generator
spec:
  containers:
    - name: alpine
      image: alpine
      command: ["/bin/sh","-c"]
      args: ["shuf -i 0-100 -n 1 >> /opt/number.out;"]
      volumeMounts:
        - mountPath: /opt
          name: data-volume
  volumes:
    - name: data-volume
      persistentVolumeClaim:
        claimName: myclaim

When you apply the PVC above, the StorageClass’s provisioner will create the disk in Google Cloud, create the corresponding PV, and bind the PVC to it. The PV still exists — it is just created automatically instead of by you. Quick comparison: static vs dynamic provisioning

Provisioning type	Who creates cloud disk	Who creates PV object	When is disk created
Static	Operator / admin	Operator / admin	Before PVC is applied
Dynamic (StorageClass)	Provisioner (cloud driver)	Provisioner (Kubernetes)	When PVC is created and requests a StorageClass

Note about provisioners and parameters

Different provisioners support different parameters and settings. For the legacy in-tree Google Persistent Disk provisioner you can choose disk type and replication mode, for example:

Parameter	Meaning	Example values
`type`	Disk type	`pd-standard`, `pd-ssd`
`replication-type`	Replication mode	`none`, `regional-pd`

Example StorageClass using parameters for the in-tree GCE provisioner:

apiVersion: storage.k8s.io/v1
kind: StorageClass
metadata:
  name: google-storage
provisioner: kubernetes.io/gce-pd
parameters:
  type: pd-standard
  replication-type: none

You can create multiple StorageClasses to represent different service levels (e.g., silver/gold/platinum), each using different disk types or replication settings:

apiVersion: storage.k8s.io/v1
kind: StorageClass
metadata:
  name: silver
provisioner: kubernetes.io/gce-pd
parameters:
  type: pd-standard
  replication-type: none
---
apiVersion: storage.k8s.io/v1
kind: StorageClass
metadata:
  name: gold
provisioner: kubernetes.io/gce-pd
parameters:
  type: pd-ssd
  replication-type: none
---
apiVersion: storage.k8s.io/v1
kind: StorageClass
metadata:
  name: platinum
provisioner: kubernetes.io/gce-pd
parameters:
  type: pd-ssd
  replication-type: regional-pd

Next time you create a PVC, specify the desired class in storageClassName and Kubernetes will dynamically provision the appropriate storage for you.

Consider modern clusters may use CSI drivers rather than the in-tree provisioners. For GKE, for example, the CSI provisioner name is pd.csi.storage.gke.io. Check your cluster documentation and use the appropriate provisioner for production clusters.

Links and references

Kubernetes Storage Concepts: https://kubernetes.io/docs/concepts/storage/
Persistent Volumes: https://kubernetes.io/docs/concepts/storage/persistent-volumes/
StorageClass documentation: https://kubernetes.io/docs/concepts/storage/storage-classes/
GKE PD CSI Driver: https://cloud.google.com/kubernetes-engine/docs/how-to/persistent-volumes/gce-pd-csi-driver

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Static provisioning

Dynamic provisioning with StorageClass

Note about provisioners and parameters

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Practice Lab

​Static provisioning

​Dynamic provisioning with StorageClass

​Note about provisioners and parameters

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Practice Lab

Static provisioning

Dynamic provisioning with StorageClass

Note about provisioners and parameters