Working with RBD snapshots

Ceph extends full support to snapshots, which are point-in-time, read-only copies of an RBD image. You can preserve the state of a Ceph RBD image by creating snapshots and restoring the snapshot to get the original data.

How to do it…

Let's see how a snapshot works with Ceph.

1. To test the snapshot functionality of Ceph, let's create a file on the block device that we created earlier:

   # echo "Hello Ceph This is snapshot test" > /mnt/ceph-disk1/snapshot_test_file

   
2. Create a snapshot for the Ceph block device:

   Syntax: rbd snap create <pool-name>/<image-name>@<snap-name>

   # rbd snap create rbd/rbd1@snapshot1 --name client.rbd
   

3. To list the snapshots of an image, use the following:

   Syntax: rbd snap ls <pool-name>/<image-name>

   # rbd snap ls rbd/rbd1 --name client.rbd
   

   
4. To test the snapshot restore functionality of Ceph RBD, let's delete files from the filesystem:

   # rm -f /mnt/ceph-disk1/*
   

5. We will now restore the Ceph RBD snapshot to get back the files that we deleted in the last step. Please note that a rollback operation will overwrite the current version of the RBD image and its data with the snapshot version. You should perform this operation carefully:

   Syntax: rbd snap rollback <pool-name>/<image-name>@<snap-name>

   # rbd snap rollback rbd/rbd1@snapshot1 --name client.rbd
   

6. Once the snapshot rollback operation is completed, remount the Ceph RBD filesystem to refresh the filesystem state. You should be able to get your deleted files back:

   # umount /mnt/ceph-disk1
   # mount /dev/rbd1 /mnt/ceph-disk1
   # ls -l /mnt/ceph-disk1
   

   
7. When you no longer need snapshots, you can remove a specific snapshot using the following syntax. Deleting the snapshot will not delete your current data on the Ceph RBD image:

   Syntax: rbd snap rm <pool-name>/<image-name>@<snap-name>

   # rbd snap rm rbd/rbd1@snapshot1 --name client.rbd
   

8. If you have multiple snapshots of an RBD image and you wish to delete all the snapshots with a single command, then use the purge sub command:

   Syntax: rbd snap purge <pool-name>/<image-name>

   # rbd snap purge rbd/rbd1 --name client.rbd