Snapshots & Cloning

Volume snapshots capture the state of a PersistentVolume at a point in time, allowing you to create backups, restore data, or clone volumes for testing. Volume cloning creates a new volume from an existing volume or snapshot, useful for quickly provisioning similar storage environments.

Volume Snapshots

A volume snapshot represents a point-in-time copy of the data in a PersistentVolume. Snapshots are created using the VolumeSnapshot API and can be used to restore the original volume or create new volumes from the snapshot.

VolumeSnapshot API

Volume snapshots use Kubernetes’ VolumeSnapshot API, which is part of the snapshot.storage.k8s.io API group. This API requires a CSI driver that supports snapshots and a snapshot controller running in your cluster.

Key resources:

• VolumeSnapshot - Represents a snapshot of a volume
• VolumeSnapshotClass - Defines snapshot parameters (similar to StorageClass)
• VolumeSnapshotContent - Represents the actual snapshot in the storage system

Creating a Snapshot

To create a snapshot, you need:

1. A VolumeSnapshotClass (defines how snapshots are created)
2. A VolumeSnapshot (references a PVC and VolumeSnapshotClass)

Example VolumeSnapshotClass:

apiVersion: snapshot.storage.k8s.io/v1
kind: VolumeSnapshotClass
metadata:
  name: csi-snapshot-class
driver: pd.csi.storage.gke.io  # CSI driver name
deletionPolicy: Delete  # Delete snapshot when VolumeSnapshot is deleted

Example VolumeSnapshot:

apiVersion: snapshot.storage.k8s.io/v1
kind: VolumeSnapshot
metadata:
  name: db-snapshot
spec:
  volumeSnapshotClassName: csi-snapshot-class
  source:
    persistentVolumeClaimName: database-pvc  # Snapshot this PVC

Snapshot Lifecycle

Restoring from a Snapshot

You can restore a volume from a snapshot by creating a new PVC that references the snapshot:

apiVersion: v1
kind: PersistentVolumeClaim
metadata:
  name: restored-db-pvc
spec:
  dataSource:
    name: db-snapshot
    kind: VolumeSnapshot
    apiGroup: snapshot.storage.k8s.io
  accessModes:
    - ReadWriteOnce
  storageClassName: fast-ssd
  resources:
    requests:
      storage: 100Gi  # Must be >= original volume size

The restored volume contains the data from the snapshot at the time it was created.

Volume Cloning

Volume cloning creates a new volume from an existing volume or snapshot. Cloning is faster than creating a snapshot and restoring, but requires both volumes to exist simultaneously.

Clone from Volume

Create a new PVC that references an existing PVC:

apiVersion: v1
kind: PersistentVolumeClaim
metadata:
  name: cloned-pvc
spec:
  dataSource:
    name: source-pvc  # Clone from this PVC
    kind: PersistentVolumeClaim
  accessModes:
    - ReadWriteOnce
  storageClassName: fast-ssd
  resources:
    requests:
      storage: 100Gi  # Must be >= source volume size

Important: The source PVC must be bound and in use for cloning to work. Some CSI drivers support cloning from idle PVCs.

Clone from Snapshot

Create a new PVC from a VolumeSnapshot:

apiVersion: v1
kind: PersistentVolumeClaim
metadata:
  name: cloned-from-snapshot
spec:
  dataSource:
    name: db-snapshot
    kind: VolumeSnapshot
    apiGroup: snapshot.storage.k8s.io
  accessModes:
    - ReadWriteOnce
  storageClassName: fast-ssd
  resources:
    requests:
      storage: 100Gi

Snapshot vs Cloning Comparison

Snapshots:

• Point-in-time copies
• Original volume unchanged
• Can be stored separately
• Useful for backups
• Can create multiple clones

Cloning:

• Direct copy of current state
• Faster than snapshot + restore
• Requires source volume to exist
• Useful for quick provisioning
• Single clone operation

Complete Example: Database Backup and Restore

Here’s a complete example showing how to backup and restore a database:

1. Create a snapshot:

apiVersion: snapshot.storage.k8s.io/v1
kind: VolumeSnapshotClass
metadata:
  name: db-snapshot-class
driver: pd.csi.storage.gke.io
deletionPolicy: Retain  # Keep snapshot even if VolumeSnapshot is deleted
---
apiVersion: snapshot.storage.k8s.io/v1
kind: VolumeSnapshot
metadata:
  name: db-backup-2024-01-15
spec:
  volumeSnapshotClassName: db-snapshot-class
  source:
    persistentVolumeClaimName: postgres-data

2. Restore from snapshot:

apiVersion: v1
kind: PersistentVolumeClaim
metadata:
  name: postgres-data-restored
spec:
  dataSource:
    name: db-backup-2024-01-15
    kind: VolumeSnapshot
    apiGroup: snapshot.storage.k8s.io
  accessModes:
    - ReadWriteOnce
  storageClassName: fast-ssd
  resources:
    requests:
      storage: 200Gi
---
apiVersion: apps/v1
kind: Deployment
metadata:
  name: postgres-restored
spec:
  template:
    spec:
      containers:
      - name: postgres
        image: postgres:14
        volumeMounts:
        - name: data
          mountPath: /var/lib/postgresql/data
      volumes:
      - name: data
        persistentVolumeClaim:
          claimName: postgres-data-restored

Use Cases

Backup and Recovery

Create regular snapshots for backup purposes:

apiVersion: snapshot.storage.k8s.io/v1
kind: VolumeSnapshot
metadata:
  name: daily-backup-$(date +%Y%m%d)
spec:
  volumeSnapshotClassName: backup-snapshot-class
  source:
    persistentVolumeClaimName: critical-data

Testing and Development

Clone production data for testing:

apiVersion: v1
kind: PersistentVolumeClaim
metadata:
  name: test-db-data
spec:
  dataSource:
    name: prod-db-snapshot
    kind: VolumeSnapshot
    apiGroup: snapshot.storage.k8s.io
  accessModes:
    - ReadWriteOnce
  storageClassName: standard
  resources:
    requests:
      storage: 100Gi

Data Migration

Use snapshots to migrate data between clusters or storage systems:

1. Create snapshot in source cluster
2. Export snapshot data
3. Import snapshot in destination cluster
4. Create PVC from snapshot

Snapshot Deletion Policy

VolumeSnapshotClass has a deletionPolicy field that controls what happens when a VolumeSnapshot is deleted:

• Delete - The snapshot in the storage system is deleted when the VolumeSnapshot is deleted
• Retain - The snapshot in the storage system is retained when the VolumeSnapshot is deleted (manual cleanup required)

apiVersion: snapshot.storage.k8s.io/v1
kind: VolumeSnapshotClass
metadata:
  name: backup-snapshot-class
driver: pd.csi.storage.gke.io
deletionPolicy: Retain  # Keep snapshot data even if VolumeSnapshot deleted

Checking Snapshot Status

Check snapshot status and details:

# List snapshots
kubectl get volumesnapshot

# Get snapshot details
kubectl describe volumesnapshot db-snapshot

# Check snapshot ready status
kubectl get volumesnapshot db-snapshot -o jsonpath='{.status.readyToUse}'

Best Practices

1. Regular snapshots - Create snapshots on a schedule for backups
2. Test restores - Regularly test restoring from snapshots
3. Use appropriate deletion policy - Retain for backups, Delete for temporary snapshots
4. Monitor snapshot storage - Snapshots consume storage space
5. Document snapshot procedures - Document how to create and restore snapshots
6. Use cloning for quick provisioning - Use cloning when you need copies quickly
7. Verify CSI driver support - Ensure your CSI driver supports snapshots/cloning
8. Size cloned volumes correctly - Cloned volumes must be >= source volume size

Limitations and Considerations

• CSI driver support - Not all CSI drivers support snapshots and cloning
• Storage costs - Snapshots consume storage space
• Performance impact - Creating snapshots may have a performance impact
• Size requirements - Cloned volumes must be at least as large as the source
• Consistency - Snapshots capture data at a point in time; application consistency may require coordination

Troubleshooting

Snapshot Stuck in Pending

If a snapshot is stuck in Pending:

1. Check VolumeSnapshotClass exists: kubectl get volumesnapshotclass
2. Verify CSI driver supports snapshots
3. Check snapshot controller is running: kubectl get pods -n kube-system | grep snapshot
4. Review VolumeSnapshot events: kubectl describe volumesnapshot <name>

Clone Fails

If cloning fails:

1. Verify source PVC is bound: kubectl get pvc <source-pvc>
2. Check if CSI driver supports cloning
3. Ensure cloned volume size >= source volume size
4. Review PVC events: kubectl describe pvc <cloned-pvc>

See Also

• PVs & PVCs - Creating and using persistent volumes
• CSI Persistent Volumes - Container Storage Interface
• Backup & Restore - Data backup and restore strategies