Chapter 7. Working with volume snapshots

Procedure

1. Prevent data from being written to the volume during snapshotting by using one of the two following steps:

   1. Delete the pod to ensure that no data is written to the volume during snapshotting by running the following command:

      $ oc delete my-pod

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   2. Scale the replica count to zero on a pod that is managed with a replication controller. Setting the count to zero prevents the instant creation of a new pod when one is deleted.

2. After all writes to the volume are halted, run a command similar to the example that follows. Insert your own configuration details.

   Example snapshot configuration

   # oc apply -f <<EOF
   apiVersion: snapshot.storage.k8s.io/v1
   kind: VolumeSnapshot 

   1

   
   metadata:
     name: <snapshot_name> 

   2

   
   spec:
     volumeSnapshotClassName: topolvm-snapclass 

   3

   
     source:
       persistentVolumeClaimName: test-claim-thin 

   4

   
   EOF

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   1

   Create a VolumeSnapshot object.

   2

   The name that you specify for the snapshot.

   3

   Specify the desired name of the VolumeSnapshotClass object.

   4

   Specify either persistentVolumeClaimName or volumeSnapshotContentName. In this example, a snapshot is created from a PVC named test-claim-thin.

3. Wait for the storage driver to finish creating the snapshot by running the following command:

   $ oc wait volumesnapshot/<snapshot_name> --for=jsonpath\='{.status.readyToUse}=true'

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Next steps

1. When the volumeSnapshot object is in a ReadyToUse state, you can restore it as a volume for future PVCs. Restart the pod or scale the replica count back up to the desired number.
2. After you have created the volume snapshot, you can remount the source PVC to a new pod.

Procedure

1. Get the name of the volume snapshot by running the following command:

   $ oc get volumesnapshot -n <namespace> <snapshot_name> -o 'jsonpath={.status.volumeSnapshotContentName}'

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2. Get the unique identity of the volume created on the storage backend by using the following command and inserting the name retrieved in the previous step:

   $ oc get volumesnapshotcontent snapcontent-<retrieved_volume_identity> -o 'jsonpath={.status.snapshotHandle}'

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3. Display the snapshots by using the unique identity of the volume you retrieved in the previous step to determine which one you want to backup by running the following command:

   $ sudo lvdisplay <retrieved_snapshot_handle>

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   Example output

   --- Logical volume ---
   LV Path                /dev/rhel/732e45ff-f220-49ce-859e-87ccca26b14c
   LV Name                732e45ff-f220-49ce-859e-87ccca26b14c
   VG Name                rhel
   LV UUID                6Ojwc0-YTfp-nKJ3-F9FO-PvMR-Ic7b-LzNGSx
   LV Write Access        read only
   LV Creation host, time rhel-92.lab.local, 2023-08-07 14:45:26 -0500
   LV Pool name           thinpool
   LV Thin origin name    a2d2dcdc-747e-4572-8c83-56cd873d3b07
   LV Status              available
   # open                 0
   LV Size                1.00 GiB
   Mapped size            1.04%
   Current LE             256
   Segments               1
   Allocation             inherit
   Read ahead sectors     auto
   - currently set to     256
   Block device           253:11

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4. Create a directory to use for mounting the LV by running the following command:

   $ sudo mkdir /mnt/snapshot

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5. Mount the LV using the device name for the retrieved snapshot handle by running the following command:

   $ sudo mount /dev/<retrieved_snapshot_handle> /mnt/snapshot

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6. Copy the files from the mounted location and store them in a secure location by running the following command:

   $ sudo cp -r /mnt/snapshot <destination>

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Procedure

1. Restore a snapshot by specifying the VolumeSnapshot object as the data source in a persistent volume claim by entering the following command:

   $ oc apply -f <<EOF
   apiVersion: v1
   kind: PersistentVolumeClaim
   metadata:
     name: snapshot-restore
   spec:
     accessModes:
     - ReadWriteOnce
     dataSource:
       apiGroup: snapshot.storage.k8s.io
       kind: VolumeSnapshot
       name: my-snap
     resources:
       requests:
         storage: 1Gi
     storageClassName: topolvm-provisioner-thin
   ---
   apiVersion: v1
   kind: Pod
   metadata:
     name: base
   spec:
     containers:
     - command:
         - nginx
   	    - -g
   	    - 'daemon off;'
       image: registry.redhat.io/rhel8/nginx-122@sha256:908ebb0dec0d669caaf4145a8a21e04fdf9ebffbba5fd4562ce5ab388bf41ab2
       name: test-container
       securityContext:
         allowPrivilegeEscalation: false
         capabilities:
           drop:
           - ALL
       volumeMounts:
       - mountPath: /vol
         name: test-vol
     securityContext:
       runAsNonRoot: true
       seccompProfile:
         type: RuntimeDefault
     volumes:
     - name: test-vol
       persistentVolumeClaim:
         claimName: snapshot-restore
   EOF

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Verification

1. Wait for the pod to reach the Ready state:

   $ oc wait --for=condition=Ready pod/base

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2. When the new pod is ready, verify that the data from your application is correct in the snapshot.

Procedure

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

   volumesnapshotclass.yaml

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

   1

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   1

   When deleting the volume snapshot, if the Delete value is set, 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>

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   Example output

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

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

   $ oc delete volumesnapshotcontent <volumesnapshotcontent_name>

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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:

   Important

   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}}'

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   Example output

   volumesnapshotclass.snapshot.storage.k8s.io "csi-ocs-rbd-snapclass" deleted

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   The finalizers are removed and the volume snapshot is deleted.