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
   metadata:
     name: <snapshot_name>
   spec:
     volumeSnapshotClassName: topolvm-snapclass
     source:
       persistentVolumeClaimName: test-claim-thin
   EOF

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   where:

   kind

   Specifies the type of VolumeSnapshot object to create.

   metadata.name

   Specifies the name that you specify for the snapshot.

   volumeSnapshotClassName

   Specifies the desired name of the VolumeSnapshotClass object.

   persistentVolumeClaimName

   Specifies 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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4. When the volumeSnapshot object is in a ReadyToUse state, you can restore the state as a volume for future PVCs. Restart the pod or scale the replica count back up to the desired number.

5. After you have created the volume snapshot, you can remount the source PVC to a new pod.

   Important

   Volume snapshots are located on the same devices as the original data. To use the volume snapshots as backups, move the snapshots to a secure location.

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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   • Replace <namespace> and <snapshot_name> with the namespace and snapshot name you used.

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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   • Replace <retrieved_volume_identity> with the volume identity.

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_volume_identity>

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   • Replace <retrieved_volume_identity> with the volume identity.

     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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   • Replace <retrieved_snapshot_handle> with the device name.

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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   • Replace <destination> with the path to the secure location.

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:

   Example volumesnapshotclass.yaml file

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

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   • deletionPolicy: 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.

     Note

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

     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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   • 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:

   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.