On - https://docs.okd.io/latest/backup_and_restore/application_backup_and_restore/installing/installing-oadp-kubevirt.html

see the NOTE:
```
When you restore a backup of VMs, you might notice that the Ceph storage capacity allocated for the restore is higher than expected. This behavior is observed only during the kubevirt restore and if the volume type of the VM is block.
Use the rbd sparsify tool to reclaim space on target volumes. For more details, see Reclaiming space on target volumes.
```

This link is broken and returns a 404