Storage classes

Kestrel provides two OpenStack Cinder storage classes: csi-cinder-sc-delete (the default; reclaim policy Delete) and csi-cinder-sc-retain (reclaim policy Retain). Both are block volumes and support ReadWriteOnce only. ReadWriteMany (shared) volumes are not offered through a storage class — open a ticket with RCS to have a per-tenant NFS volume provisioned. These are the only two storage classes allowed on the cluster; naming any other storageClassName is rejected at admission and the PVC stays Pending.

Deleting a PVC deletes your data

The default class, csi-cinder-sc-delete, uses reclaimPolicy: Delete. When you delete a PVC bound to it, the underlying Cinder volume is destroyed immediately. There is no automatic backup, no recycle bin, and no way to recover the data after deletion — you cannot self-service a restore. Treat PVC deletion as permanent data loss and back up anything you need to keep before removing the claim. If you need the volume to outlive its PVC, use csi-cinder-sc-retain instead (see below). See Shared resource pool for how quota exhaustion in one namespace can pressure you into hasty cleanup in another.

csi-cinder-sc-delete (default)

Property	Value
Provisioner	cinder.csi.openstack.org
Access modes	ReadWriteOnce (RWO)
Volume type	Block (Cinder volume)
Reclaim policy	Delete
Backup	None (tenant-accessible)

This is the cluster default — a PVC that omits storageClassName gets csi-cinder-sc-delete. Each volume is a Cinder block volume mounted into exactly one Pod at a time. Use this for any single-writer workload: databases, caches, processing pipelines, or any Pod that needs dedicated storage where it is acceptable for the volume to be destroyed when the claim is deleted.

RWO means the volume can be mounted by one node at a time. If you reschedule the Pod to a different node (e.g. during a rolling update), the volume detaches and reattaches — there is a brief unavailability window during the transition, but no data is lost.

csi-cinder-sc-retain

Property	Value
Provisioner	cinder.csi.openstack.org
Access modes	ReadWriteOnce (RWO)
Volume type	Block (Cinder volume)
Reclaim policy	Retain
Backup	None (tenant-accessible)

csi-cinder-sc-retain is identical to the default class except that deleting the PVC leaves the underlying Cinder volume in place. The PersistentVolume moves to Released rather than being deleted, so the data survives an accidental kubectl delete pvc. Use this for stateful data you cannot afford to lose to a mistaken claim deletion. Note that a Released volume is not automatically rebound to a new PVC — recovery requires manual intervention, so this is a safety net against deletion, not a self-service restore mechanism.

When to pick which

Scenario	Class
Single-Pod database or cache	csi-cinder-sc-delete
Processing pipeline with one writer	csi-cinder-sc-delete
Stateful data that must survive accidental PVC deletion	csi-cinder-sc-retain
Scratch or rebuildable data	csi-cinder-sc-delete
You are unsure	csi-cinder-sc-delete — it is the default

Shared (ReadWriteMany) volumes

Neither storage class supports ReadWriteMany — both are block volumes restricted to ReadWriteOnce. There is no storage class on Kestrel that provisions a shared, multi-writer volume. If multiple Pods need to read and write the same path concurrently, RCS can provision a per-tenant NFS volume and wire it in as a static PersistentVolume. Open a ticket to request one. See Persistent volumes in practice for the PV/PVC pattern once it has been provisioned.

What neither class provides

• Automatic backups. Neither class snapshots or replicates your data to an off-cluster location. If you need backups, build them into your workload (e.g. a CronJob that dumps to an external target).
• Shared (RWX) access. Both classes are block volumes limited to ReadWriteOnce. Shared access requires a per-tenant NFS volume from RCS (see above).
• Per-tenant encryption at rest. There is no per-PVC or per-tenant key — any at-rest protection is provided cluster-wide by the OpenStack storage layer, not tenant-scoped.

See Persistent volumes in practice for how to request a PVC using either class.