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CSI volume snapshots

Container Storage Interface (CSI) snapshots capture point-in-time copies for data protection and recovery. Snapshots enable restoring volumes to previous states or creating new volumes from existing data using VolumeSnapshot, VolumeSnapshotContent, and VolumeSnapshotClass objects.

Overview of CSI volume snapshots

A snapshot represents the state of the storage volume in a cluster at a particular point in time. Volume snapshots can be used to provision a new volume.

OKD supports Container Storage Interface (CSI) volume snapshots by default. However, a specific CSI driver is required.

Familiarity with persistent volumes is suggested. For information about persistent volumes, see "Persistent volumes".

With CSI volume snapshots, a cluster administrator can:

  • Deploy a third-party CSI driver that supports snapshots.

  • Create a new persistent volume claim (PVC) from an existing volume snapshot.

  • Take a snapshot of an existing PVC.

  • Restore a snapshot as a different PVC.

  • Delete an existing volume snapshot.

With CSI volume snapshots, an app developer can:

  • Use volume snapshots as building blocks for developing application- or cluster-level storage backup solutions.

  • Rapidly rollback to a previous development version.

  • Use storage more efficiently by not having to make a full copy each time.

Be aware of the following when using volume snapshots:

  • Support is only available for CSI drivers. In-tree and FlexVolumes are not supported.

  • OKD only includes select CSI drivers. For CSI drivers that are not provided by an OKD Driver Operator, it is recommended to use the CSI drivers provided by the Kubernetes community or known storage vendors. Follow the installation instructions furnished by the CSI driver provider. For information about Kubernetes CSI drivers, see "Kubernetes CSI Developer Documentation".

  • CSI drivers may or may not have implemented the volume snapshot functionality. CSI drivers that have provided support for volume snapshots will likely use the csi-external-snapshotter sidecar. See documentation provided by the CSI driver for details.

CSI snapshot controller and sidecar

Container Storage Interface (CSI) snapshots require two components: a controller deployed by OKD to the control plane, and a vendor-provided sidecar with the CSI driver. The controller manages VolumeSnapshot bindings while the sidecar triggers create and delete operations.

The CSI snapshot controller and sidecar provide volume snapshotting through the OKD API. These external components run in the cluster.

The external controller is deployed by the CSI Snapshot Controller Operator.

External controller

The CSI snapshot controller binds VolumeSnapshot and VolumeSnapshotContent objects. The controller manages dynamic provisioning by creating and deleting VolumeSnapshotContent objects.

External sidecar

Your CSI driver vendor provides the csi-external-snapshotter sidecar. This is a separate helper container that is deployed with the CSI driver. The sidecar manages snapshots by triggering CreateSnapshot and DeleteSnapshot operations. Follow the installation instructions provided by your vendor.

About the CSI Snapshot Controller Operator

You can manage volume snapshots in OKD by using the CSI Snapshot Controller Operator’s custom resource definitions (CRDs) for snapshot requests, storage, and configuration.

The Container Storage Interface (CSI) Snapshot Controller Operator runs in the openshift-cluster-storage-operator namespace. It is installed by the Cluster Version Operator (CVO) in all clusters by default.

The CSI Snapshot Controller Operator installs the CSI snapshot controller, which runs in the openshift-cluster-storage-operator namespace.

Volume snapshot CRDs

During OKD installation, the CSI Snapshot Controller Operator creates the following snapshot custom resource definitions (CRDs) in the snapshot.storage.k8s.io/v1 API group:

VolumeSnapshotContent

A snapshot taken of a volume in the cluster that has been provisioned by a cluster administrator.

Similar to the PersistentVolume object, the VolumeSnapshotContent CRD is a cluster resource that points to a real snapshot in the storage back end.

For manually pre-provisioned snapshots, a cluster administrator creates a number of VolumeSnapshotContent CRDs. These carry the details of the real volume snapshot in the storage system.

The VolumeSnapshotContent CRD is not namespaced and is for use by a cluster administrator.

VolumeSnapshot

Similar to the PersistentVolumeClaim object, the VolumeSnapshot CRD defines a developer request for a snapshot. The CSI Snapshot Controller Operator runs the CSI snapshot controller, which handles the binding of a VolumeSnapshot CRD with an appropriate VolumeSnapshotContent CRD. The binding is a one-to-one mapping.

The VolumeSnapshot CRD is namespaced. A developer uses the CRD as a distinct request for a snapshot.

VolumeSnapshotClass

The VolumeSnapshotClass CRD allows a cluster administrator to specify different attributes belonging to a VolumeSnapshot object. These attributes may differ among snapshots taken of the same volume on the storage system, in which case they would not be expressed by using the same storage class of a persistent volume claim.

The VolumeSnapshotClass CRD defines the parameters for the csi-external-snapshotter sidecar to use when creating a snapshot. This allows the storage back end to know what kind of snapshot to dynamically create if multiple options are supported.

Dynamically provisioned snapshots use the VolumeSnapshotClass CRD to specify storage-provider-specific parameters to use when creating a snapshot.

The VolumeSnapshotContentClass CRD is not namespaced and is for use by a cluster administrator to enable global configuration options for their storage back end.

For Google Cloud Platform (GCP) persistent disk (PD) storage CSI, there is a non-default VolumeSnapshotClass, named csi-gce-pd-vsc-images, that uses the snapshot-type: images parameter. When using KubeVirt, this allows you to create VMs from "golden images" (templates saved as snapshots).

If you want to use the images volume snapshot class for dynamic snapshot provisioning, you can either:

  • Make the images volume snapshot class the default by changing the snapshot.storage.kubernetes.io/is-default-class annotation to true. Also, for the normal default volume snapshot class, csi-gce-pd-vsc, be sure to change this parameter to false.

  • When creating the snapshot object, be sure to set volumeSnapshotClassName to csi-gce-pd-vsc-images.

    For information about creating volume snapshots, see "Dynamically creating a volume snapshot" and "Statically creating a volume snapshot".

    Example images volume snapshot class YAML file
    apiVersion: snapshot.storage.k8s.io/v1
kind: VolumeSnapshotClass
metadata:
  name: csi-gce-pd-vsc-images
driver: pd.csi.storage.gke.io
parameters:
  snapshot-type: images

  • metadata.name:csi-gce-pd-vsc-images: Specifies the name for the non-default images volume snapshot class.

  • parameters: snapshot-type: images: Defines the snapshot as a "golden image" or a bootable template, rather than the standard disk backup.

Volume snapshot provisioning

You can provision volume snapshots in OKD using either dynamic provisioning to create new snapshots on-demand or static provisioning to reference pre-existing snapshots.

Dynamic provisioning

Instead of using a preexisting snapshot, you can request that a snapshot be taken dynamically from a persistent volume claim. Parameters are specified using a VolumeSnapshotClass CRD.

Static provisioning

As a cluster administrator, you can manually pre-provision a number of VolumeSnapshotContent objects. These carry the real volume snapshot details available to cluster users.

Dynamically creating a volume snapshot

To create a point-in-time backup of a persistent volume claim (PVC), dynamically provision a volume snapshot by defining a VolumeSnapshotClass and VolumeSnapshot that automate the snapshot creation.

When you create a VolumeSnapshot object, OKD creates a volume snapshot.

Prerequisites

  • Logged in to a running OKD cluster.

  • A PVC created using a CSI driver that supports VolumeSnapshot objects.

  • A storage class to provision the storage back end.

  • No pods are using the persistent volume claim (PVC) that you want to take a snapshot of.

    Creating a volume snapshot of a PVC that is in use by a pod can cause unwritten data and cached data to be excluded from the snapshot. To ensure that all data is written to the disk, delete the pod that is using the PVC before creating the snapshot.
Procedure

  1. Create a file with the VolumeSnapshotClass object described by the following YAML:

    Example volumesnapshotclass.yaml
    apiVersion: snapshot.storage.k8s.io/v1
kind: VolumeSnapshotClass
metadata:
  name: csi-hostpath-snap
driver: hostpath.csi.k8s.io
deletionPolicy: Delete

    driver is the name of the CSI driver that is used to create snapshots of this VolumeSnapshotClass object. The name must be the same as the Provisioner field of the storage class that is responsible for the PVC that is being snapshotted.

    Depending on the driver that you used to configure persistent storage, additional parameters might be required. You can also use an existing VolumeSnapshotClass object.

  2. Create the object you saved in the previous step by entering the following command:

    $ oc create -f volumesnapshotclass.yaml

  3. Create a VolumeSnapshot object:

    Example volumesnapshot-dynamic.yaml
    apiVersion: snapshot.storage.k8s.io/v1
kind: VolumeSnapshot
metadata:
  name: mysnap
spec:
  volumeSnapshotClassName: csi-hostpath-snap
  source:
    persistentVolumeClaimName: myclaim

    • spec.volumeSnapshotClassName: Specifies the request for a particular class by the volume snapshot. If the volumeSnapshotClassName setting is absent and there is a default volume snapshot class, a snapshot is created with the default volume snapshot class name. But if the field is absent and no default volume snapshot class exists, then no snapshot is created.

    • spec.source.persistentVolumeClaimName: Specifies the name of the PersistentVolumeClaim object bound to a persistent volume. This defines what you want to create a snapshot of. Required for dynamically provisioning a snapshot.

  4. Create the object you saved in the previous step by entering the following command:

    $ oc create -f volumesnapshot-dynamic.yaml
Verification

  1. After the snapshot has been created in the cluster, additional details about the snapshot are available.

    To display details about the volume snapshot that was created, run the following command:

    $ oc describe volumesnapshot mysnap

    The following example displays details about the mysnap volume snapshot:

    Example volumesnapshot.yaml
    apiVersion: snapshot.storage.k8s.io/v1
kind: VolumeSnapshot
metadata:
  name: mysnap
spec:
  source:
    persistentVolumeClaimName: myclaim
  volumeSnapshotClassName: csi-hostpath-snap
status:
  boundVolumeSnapshotContentName: snapcontent-1af4989e-a365-4286-96f8-d5dcd65d78d6
  creationTime: "2020-01-29T12:24:30Z"
  readyToUse: true
  restoreSize: 500Mi

    • status.boundVolumeSnapshotContentName: This parameter is the pointer to the actual storage content that was created by the controller.

    • status.creationTime: Specifies the time when the snapshot was created. The snapshot contains the volume content that was available at this indicated time.

    • status.readyToUse: Specifies the readiness of the snapshot. If the value is set to true, the snapshot can be used to restore as a new PVC. If the value is set to false, the snapshot was created. However, the storage back end needs to perform additional tasks to make the snapshot usable so that it can be restored as a new volume. For example, Amazon Elastic Block Store data might be moved to a different, less expensive location, which can take several minutes.

  2. To verify that the volume snapshot was created, enter the following command:

    $ oc get volumesnapshotcontent

    The pointer to the actual content is displayed. If the boundVolumeSnapshotContentName field is populated, a VolumeSnapshotContent object exists and the snapshot was created.

  3. To verify that the snapshot is ready, confirm that the VolumeSnapshot object has readyToUse: true.

Statically creating a volume snapshot

To make a pre-existing storage snapshot available in OKD, manually create a volume snapshot that references the existing snapshot content by name.

Prerequisites

  • Logged in to a running OKD cluster.

  • A PVC created using a CSI driver that supports VolumeSnapshot objects.

  • A storage class to provision the storage back end.

  • No pods are using the persistent volume claim (PVC) that you want to take a snapshot of.

    Creating a volume snapshot of a PVC that is in use by a pod can cause unwritten data and cached data to be excluded from the snapshot. To ensure that all data is written to the disk, delete the pod that is using the PVC before creating the snapshot.
Procedure

  1. Create a file with the VolumeSnapshotClass object described by the following YAML:

    Example volumesnapshotclass.yaml
    apiVersion: snapshot.storage.k8s.io/v1
kind: VolumeSnapshotClass
metadata:
  name: csi-hostpath-snap
driver: hostpath.csi.k8s.io
deletionPolicy: Delete

    driver is the name of the CSI driver that is used to create snapshots of this VolumeSnapshotClass object. The name must be the same as the Provisioner field of the storage class that is responsible for the PVC that is being snapshotted.

    Depending on the driver that you used to configure persistent storage, additional parameters might be required. You can also use an existing VolumeSnapshotClass object.

  2. Create the object you saved in the previous step by entering the following command:

    $ oc create -f volumesnapshotclass.yaml

  3. Provide a value for the volumeSnapshotContentName parameter as the source for the snapshot:

    Example volumesnapshot-manual.yaml
    apiVersion: snapshot.storage.k8s.io/v1
kind: VolumeSnapshot
metadata:
  name: snapshot-demo
spec:
  source:
    volumeSnapshotContentName: mycontent

    spec.source.volumeSnapshotContentName is required for pre-provisioned snapshots.

  4. Create the object you saved in the previous step by entering the following command:

    $ oc create -f volumesnapshot-manual.yaml
Verification

After the snapshot has been created in the cluster, additional details about the snapshot are available.

  1. To display details about the volume snapshot that was created, enter the following command:

    $ oc describe volumesnapshot mysnap

    The following example displays details about the mysnap volume snapshot:

    Example volumesnapshot.yaml
    apiVersion: snapshot.storage.k8s.io/v1
kind: VolumeSnapshot
metadata:
  name: mysnap
spec:
  source:
    persistentVolumeClaimName: myclaim
  volumeSnapshotClassName: csi-hostpath-snap
status:
  boundVolumeSnapshotContentName: snapcontent-1af4989e-a365-4286-96f8-d5dcd65d78d6
  creationTime: "2020-01-29T12:24:30Z"
  readyToUse: true
  restoreSize: 500Mi

    • status.boundVolumeSnapshotContentName: Specifies the pointer to the actual storage content that was created by the controller.

    • status.creationTime: Specifies the time when the snapshot was created. The snapshot contains the volume content that was available at this indicated time.

    • status.readyToUse: If the value is set to true, the snapshot can be used to restore as a new PVC. If the value is set to false, the snapshot was created. However, the storage back end needs to perform additional tasks to make the snapshot usable so that it can be restored as a new volume. For example, Amazon Elastic Block Store data might be moved to a different, less expensive location, which can take several minutes.

  2. To verify that the volume snapshot was created, enter the following command:

    $ oc get volumesnapshotcontent

    The pointer to the actual content is displayed. If the boundVolumeSnapshotContentName field is populated, a VolumeSnapshotContent object exists and the snapshot was created.

  3. To verify that the snapshot is ready, confirm that the VolumeSnapshot object has readyToUse: true.

Deleting a volume snapshot

To clean up unneeded snapshots and free storage resources, delete volume snapshots by setting a deletion policy that controls whether the underlying content is retained or removed.

Procedure

  1. Specify the deletion policy that you require in the VolumeSnapshotClass object, as shown in the following example:

    Example volumesnapshotclass.yaml file
    apiVersion: snapshot.storage.k8s.io/v1
kind: VolumeSnapshotClass
metadata:
  name: csi-hostpath-snap
driver: hostpath.csi.k8s.io
deletionPolicy: Delete
# ...

    When deleting the volume snapshot, if deletionPolicy is set to Delete, the underlying snapshot is deleted along with the VolumeSnapshotContent object. If the Retain value is set, both the underlying snapshot and VolumeSnapshotContent object remain.

    If the Retain value is set and the VolumeSnapshot object is deleted without deleting the corresponding VolumeSnapshotContent object, the content remains. The snapshot itself is also retained in the storage back end.

  2. Delete the volume snapshot by entering the following command:

    $ oc delete volumesnapshot <volumesnapshot_name>

    Replace <volumesnapshot_name> with the name of the volume snapshot you want to delete.

    Example output
    volumesnapshot.snapshot.storage.k8s.io "mysnapshot" deleted

  3. If the deletion policy is set to Retain, delete the volume snapshot content by entering the following command:

    $ oc delete volumesnapshotcontent <volumesnapshotcontent_name>

    Replace <volumesnapshotcontent_name> with the content you want to delete.

  4. Optional: If the VolumeSnapshot object is not successfully deleted, enter the following command to remove any finalizers for the leftover resource so that the delete operation can continue:

    Only remove the finalizers if you are confident that there are no existing references from either persistent volume claims or volume snapshot contents to the VolumeSnapshot object. Even with the --force option, the delete operation does not delete snapshot objects until all finalizers are removed.

    		 
    $ oc patch -n $PROJECT volumesnapshot/$NAME --type=merge -p '{"metadata": {"finalizers":null}}'
    Example output
    volumesnapshotclass.snapshot.storage.k8s.io "csi-ocs-rbd-snapclass" deleted

    The finalizers are removed and the volume snapshot is deleted.

Restoring a volume snapshot

To recover previous data or reuse snapshot data, create a new persistent volume claim (PVC) that is pre-populated with content from an existing volume snapshot.

The VolumeSnapshot CRD content can be used to restore the existing volume to a previous state. After your VolumeSnapshot CRD is bound and the readyToUse value is set to true, you can use that resource to provision a new volume that is pre-populated with data from the snapshot.

Prerequisites

  • Logged in to a running OKD cluster.

  • A persistent volume claim (PVC) created using a Container Storage Interface (CSI) driver that supports volume snapshots.

  • A storage class to provision the storage back end.

  • A volume snapshot has been created and is ready to use.

Procedure

  1. Specify a VolumeSnapshot data source on a PVC as shown in the following:

    pvc-restore.yaml
    apiVersion: v1
kind: PersistentVolumeClaim
metadata:
  name: myclaim-restore
spec:
  storageClassName: csi-hostpath-sc
  dataSource:
    name: mysnap
    kind: VolumeSnapshot
    apiGroup: snapshot.storage.k8s.io
  accessModes:
    - ReadWriteOnce
  resources:
    requests:
      storage: 1Gi

    • spec.dataSource.name: Specifies the name of the VolumeSnapshot object representing the snapshot to use as source.

    • spec.dataSource.kind: Must be set to the VolumeSnapshot value.

    • spec.dataSource.apiGroup: Must be set to the snapshot.storage.k8s.io value.

  2. Create a PVC by entering the following command:

    $ oc create -f pvc-restore.yaml

  3. Verify that the restored PVC has been created by entering the following command:

    $ oc get pvc

    A new PVC such as myclaim-restore is displayed.

Changing the maximum number of snapshots for vSphere

Configure the maximum number of snapshots per volume globally or for specific datastore types to balance storage capacity and performance in your vSphere environment.

The default maximum number of snapshots per volume in vSphere Container Storage Interface (CSI) is 3. You can change the maximum number up to 32 per volume. However, be aware that increasing the snapshot maximum involves a performance trade off, so for better performance use only 2 to 3 snapshots per volume.

For more VMware snapshot performance recommendations, see "Best practices for using VMware snapshots in the vSphere environment".

Prerequisites

  • Access to the cluster with administrator rights.

Procedure

  1. Check the current secret by the running the following command:

    $ oc -n openshift-cluster-csi-drivers get secret/vsphere-csi-config-secret -o jsonpath='{.data.cloud\.conf}' | base64 -d
    Example output
    # Labels with topology values are added dynamically via operator
[Global]
cluster-id = vsphere-01-cwv8p

# Populate VCenters (multi) after here
[VirtualCenter "vcenter.openshift.com"]
insecure-flag           = true
datacenters             = DEVQEdatacenter
password                = "xxxxxxxx"
user                    = "xxxxxxxx@devcluster.openshift.com"
migration-datastore-url = ds:///vmfs/volumes/vsan:52c842f232751e0d-3253aadeac21ca82/

    In this example, the global maximum number of snapshots is not configured, so the default value of 3 is applied.

  2. Change the snapshot limit by running the following command:

    • Set global snapshot limit:

      $ oc patch clustercsidriver/csi.vsphere.vmware.com --type=merge -p '{"spec":{"driverConfig":{"vSphere":{"globalMaxSnapshotsPerBlockVolume": 10}}}}'

clustercsidriver.operator.openshift.io/csi.vsphere.vmware.com patched

      In this example, the global limit is being changed to 10 (globalMaxSnapshotsPerBlockVolume set to 10).

    • Set Virtual Volume snapshot limit:

      This parameter sets the limit on the Virtual Volumes datastore only. The Virtual Volume maximum snapshot limit overrides the global constraint if set, but defaults to the global limit if it is not set.

      $ oc patch clustercsidriver/csi.vsphere.vmware.com --type=merge -p '{"spec":{"driverConfig":{"vSphere":{"granularMaxSnapshotsPerBlockVolumeInVVOL": 5}}}}'
clustercsidriver.operator.openshift.io/csi.vsphere.vmware.com patched

      In this example, the Virtual Volume limit is being changed to 5 (granularMaxSnapshotsPerBlockVolumeInVVOL set to 5).

    • Set vSAN snapshot limit:

      This parameter sets the limit on the vSAN datastore only. The vSAN maximum snapshot limit overrides the global constraint if set, but defaults to the global limit if it is not set. You can set a maximum value of 32 under vSAN ESA setup.

      $ oc patch clustercsidriver/csi.vsphere.vmware.com --type=merge -p '{"spec":{"driverConfig":{"vSphere":{"granularMaxSnapshotsPerBlockVolumeInVSAN": 7}}}}'
clustercsidriver.operator.openshift.io/csi.vsphere.vmware.com patched

      In this example, the vSAN limit is being changed to 7 (granularMaxSnapshotsPerBlockVolumeInVSAN set to 7).

Verification

  • Verify that any changes you made are reflected in the config map by running the following command:

    $ oc -n openshift-cluster-csi-drivers get secret/vsphere-csi-config-secret -o jsonpath='{.data.cloud\.conf}' | base64 -d
    Example output
    # Labels with topology values are added dynamically via operator
[Global]
cluster-id = vsphere-01-cwv8p

# Populate VCenters (multi) after here
[VirtualCenter "vcenter.openshift.com"]
insecure-flag           = true
datacenters             = DEVQEdatacenter
password                = "xxxxxxxx"
user                    = "xxxxxxxx@devcluster.openshift.com"
migration-datastore-url = ds:///vmfs/volumes/vsan:52c842f232751e0d-3253aadeac21ca82/

[Snapshot]
global-max-snapshots-per-block-volume = 10

    The parameter global-max-snapshots-per-block-volume is now set to 10.

Additional resources