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22_StorageClass.md

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What is StorageClass?

  • A StorageClass defines how storage is dynamically provisioned in Kubernetes.

It tells Kubernetes:

  • What storage backend to use (EBS, NFS, Ceph, Azure Disk, CSI drivers, etc.)
  • What parameters to use (type, disk speed, filesystem)
  • What reclaim policy to apply (Retain/Delete)

When a PVC Requests storage, Kubernetes looks at the PVC’s storageClassName and automatically creates a matching PersistentVolume (PV) using the StorageClass.

📌 StorageClass = Blueprint for dynamic storage creation

Key Characteristics

1. Enables Dynamic Provisioning

Without StorageClass → PVs must be created manually (static provisioning). With StorageClass → PVs are automatically created when PVCs request them.

Highly useful for cloud and scalable setups.

2. Abstracts underlying storage technology

StorageClass hides backend details such as:

  • AWS EBS
  • Azure Disk
  • GCE Persistent Disk
  • vSphere
  • Ceph / RBD / CephFS
  • NFS
  • NetApp
  • CSI driver plugins PVC users don’t need to know which backend is used.

3. Defines storage parameters StorageClass defines how volumes should be created: example:

parameters:
  type: gp3
  fsType: ext4
  iops: "3000"

4. Controls the reclaim policy

Sets what happens to the PV when PVC is deleted:

  • Delete → delete underlying storage
  • Retain → keep storage for manual cleanup
reclaimPolicy: Delete

5. Sets volume binding mode

Defines when PV is provisioned:

  • Immediate
    • PV created right after PVC creation (default).
  • WaitForFirstConsumer
    • PV only created when Pod is scheduled, ensuring:
      • Correct node placement
      • High availability
      • Zonal/local storage placement Useful for zonal storage like AWS EBS.

6. Supports expansion (if enabled)

Some StorageClasses allow resizing PVCs

allowVolumeExpansion: true

StorageClass YAML Example (AWS EBS)

apiVersion: storage.k8s.io/v1
kind: StorageClass
metadata:
  name: gp3-storage
provisioner: ebs.csi.aws.com
parameters:
  type: gp3
  fsType: ext4
allowVolumeExpansion: true
reclaimPolicy: Delete
volumeBindingMode: WaitForFirstConsumer

Use Cases:

  • Automatic storage allocation for PVCs
  • Cloud-native workloads needing dynamic scaling
  • Databases requiring fast SSD or high IOPS
  • StatefulSet Pods (each Pod auto-gets PV)

Summary

Feature Description
What is StorageClass? Template describing dynamic storage provisioning
Purpose Automatically create PVs for PVCs
Defines Provisioner, parameters, reclaim policy, binding mode
Backend Any storage provider (cloud, CSI, Ceph, NFS, etc.)
Modes Immediate / WaitForFirstConsumer
Expansion Can allow PVC resizing
Common Use Databases, StatefulSets, cloud storage automation