Storage

A StorageClass describes a 'class' of storage offered by the cluster (e.g. fast SSD vs slow HDD). It defines how PersistentVolumes are dynamically provisioned, so administrators do not have to pre-create PVs by hand. Users select a class by name in their PVC.

provisioner (the volume plugin/CSI driver that creates the volume), parameters (driver-specific options like disk type or filesystem), and reclaimPolicy (Delete or Retain). It may also set volumeBindingMode and allowVolumeExpansion.

It names the volume plugin or CSI driver responsible for creating the underlying storage (e.g. ebs.csi.aws.com, pd.csi.storage.gke.io, rancher.io/local-path). The special value kubernetes.io/no-provisioner means no dynamic provisioning is performed.

Delete and Retain. The default is Delete, meaning the underlying PV (and backing storage) is removed when the bound PVC is deleted. PVs dynamically provisioned by the class inherit this reclaim policy.

It controls when volume binding and dynamic provisioning happen. Immediate binds/provisions as soon as the PVC is created. WaitForFirstConsumer delays binding until a Pod using the PVC is scheduled, so topology constraints (zone, node) of the consuming Pod are respected.

With Immediate, a volume may be provisioned in a zone where no node can run the Pod, causing scheduling failures. WaitForFirstConsumer defers provisioning until the scheduler picks a node, so the volume is created in the right topology (zone/region) matching the Pod's placement.