The goal of this blueprint is to implement a driver for cinder. This will allow to create volume in local storage and back up point-in-time snapshots of your data to Swift for durable recovery. This snapshots are incremental backups, meaning that only the blocks on the volume that have changed since your last snapshot will be saved.
Even though the snapshots are saved incrementally, when you delete a snapshot, only the data not needed for any other snapshot is removed. So regardless of which prior snapshots have been deleted, all active snapshots will contain all the information needed to restore the volume. In addition, the time to restore the volume is the same for all snapshots, offering the restore time of full backups with the space savings of incremental.
All in a word, our solutions is local storage + qcow2 image + dependent snapshot + swift. This is like http://wiki.cloudstack.org/display/RelOps/Local+storage+for+data+volumes, but we have incremental snapshot than cloundstack.
If you are interested in this topic, please read the full specification: http://wiki.openstack.org/LocalStorageVolume