Amazon EBS provides the ability to save point-in-time snapshots of your volumes to Amazon S3. Amazon EBS Snapshots are stored incrementally: only the blocks that have changed after your last snapshot are saved, and you are billed only for the changed blocks. If you have a device with 100 GB of data but only 5 GB has changed after your last snapshot, a subsequent snapshot consumes only 5 additional GB and you are billed only for the additional 5 GB of snapshot storage, even though both the earlier and later snapshots appear complete.
When you delete a snapshot, you remove only the data not needed by any other snapshot. All active snapshots contain all the information needed to restore the volume to the instant at which that snapshot was taken. The time to restore changed data to the working volume is the same for all snapshots.
Snapshots can be used to instantiate multiple new volumes, expand the size of a volume, or move volumes across Availability Zones. When a new volume is created, you may choose to create it based on an existing Amazon EBS snapshot. In that scenario, the new volume begins as an exact replica of the snapshot.