storage-class

Storge Class

Introduction

Storage Class

• A StorageClass provides a way for administrators to describe the classes of storage they offer.
• Different classes might map to quality-of-service levels, or to backup policies, or to arbitrary policies determined by the cluster administrators.
• The Kubernetes concept of a storage class is similar to “profiles” in some other storage system designs.

StorageClass objects

Each StorageClass contains the fields:

• provisioner : is responsible for the creation of the actual storage resource (e.g., a persistent volume) when a PersistentVolumeClaim (PVC) requests it.
• parameters : The parameters field in a StorageClass allows for fine-tuning of the provisioned storage volumes according to the requirements and capabilities of the underlying storage provider.
• reclaimPolicy :
  • The reclaimPolicy in Kubernetes is an important attribute of a PersistentVolume (PV) that dictates what happens to the physical storage resource when the PV is released (i.e., when its associated PersistentVolumeClaim (PVC) is deleted).
  • The reclaimPolicy can be set to one of the following values:
    • Retain:
      • This policy allows for manual reclamation of the resource.
      • When the PVC is deleted, the PV remains and its status becomes Released.
      • A cluster administrator can manually reclaim the resource, making it available for reuse.
      • Note:
        • In case of pilot and production it is suggested to change the reclaim policy to retain, to avoid pvc getting deleted unintentionally.
        • Or create one more storage class with reclaimPolicy with default value as retain and use it for deployments holding crucial non transactional data.
    • Delete:
      • This policy automatically deletes the associated storage resource when the PVC is deleted.
      • For dynamically provisioned volumes, the underlying storage resource (such as an AWS EBS volume or a GCE PD) will be deleted.
    • Recycle:
      • This policy is deprecated as of Kubernetes v1.11.
      • It used to delete the contents of the volume and make it available again for a new claim.
      • The recommended approach now is to use external storage providers or scripts for similar functionality.

Default StorageClass

• StorageClass can be specified as default for k8 cluster.
• When a PVC does not specify a storageClassName, the default StorageClass is used.
• If storageclass.kubernetes.io/is-default-class annotation is set to true on more than one StorageClass in k8s cluster, and PersistentVolumeClaim is created with no storageClassName set, k8s uses the most recently created default StorageClass.

Volume expansion

• PersistentVolumes can be configured to be expandable.
• This allows you to resize the volume by editing the corresponding PVC object, requesting a new larger amount of storage.

Storage Class Setup

Repo contains steps to setup below mentioned Storage classes for k8 cluster.

• NFS
• Longhorn
• CEPH CSI
• EBS
• EFS