Amazon EBS snapshots - Amazon Elastic Compute Cloud

Amazon EBS snapshots

You can back up the data on your Amazon EBS volumes to Amazon S3 by taking point-in-time snapshots. Snapshots are incremental backups, which means that only the blocks on the device that have changed after your most recent snapshot are saved. This minimizes the time required to create the snapshot and saves on storage costs by not duplicating data. Each snapshot contains all of the information that is needed to restore your data (from the moment when the snapshot was taken) to a new EBS volume.

When you create an EBS volume based on a snapshot, the new volume begins as an exact replica of the original volume that was used to create the snapshot. The replicated volume loads data in the background so that you can begin using it immediately. If you access data that hasn't been loaded yet, the volume immediately downloads the requested data from Amazon S3, and then continues loading the rest of the volume's data in the background. For more information, see Create Amazon EBS snapshots.

When you delete a snapshot, only the data unique to that snapshot is removed. For more information, see Delete an Amazon EBS snapshot.

Snapshot events

You can track the status of your EBS snapshots through CloudWatch Events. For more information, see EBS snapshot events.

Multi-volume snapshots

Snapshots can be used to create a backup of critical workloads, such as a large database or a file system that spans across multiple EBS volumes. Multi-volume snapshots allow you to take exact point-in-time, data coordinated, and crash-consistent snapshots across multiple EBS volumes attached to an EC2 instance. You are no longer required to stop your instance or to coordinate between volumes to ensure crash consistency, because snapshots are automatically taken across multiple EBS volumes. For more information, see the steps for creating a multi-volume EBS snapshot under Create Amazon EBS snapshots .

Snapshot pricing

Charges for your snapshots are based on the amount of data stored. Because snapshots are incremental, deleting a snapshot might not reduce your data storage costs. Data referenced exclusively by a snapshot is removed when that snapshot is deleted, but data referenced by other snapshots is preserved. For more information, see Amazon Elastic Block Store Volumes and Snapshots in the AWS Billing and Cost Management User Guide.

How incremental snapshots work

This section shows how an EBS snapshot captures the state of a volume at a point in time, and how successive snapshots of a changing volume create a history of those changes.

Relations among multiple snapshots of the same volume

The diagram in this section shows Volume 1 at three points in time. A snapshot is taken of each of these three volume states. The diagram specifically shows the following:

  • In State 1, the volume has 10 GiB of data. Because Snap A is the first snapshot taken of the volume, the entire 10 GiB of data must be copied.

  • In State 2, the volume still contains 10 GiB of data, but 4 GiB have changed. Snap B needs to copy and store only the 4 GiB that changed after Snap A was taken. The other 6 GiB of unchanged data, which are already copied and stored in Snap A, are referenced by Snap B rather than being copied again. This is indicated by the dashed arrow.

  • In State 3, 2 GiB of data have been added to the volume, for a total of 12 GiB. Snap C needs to copy the 2 GiB that were added after Snap B was taken. As shown by the dashed arrows, Snap C also references 4 GiB of data stored in Snap B, and 6 GiB of data stored in Snap A.

  • The total storage required for the three snapshots is 16 GiB.


        Snapshots capturing an initial volume state and two subsequent states after data has
          been changed.

Relations among incremental snapshots of different volumes

The diagram in this section shows how incremental snapshots can be taken from different volumes.

Important

The diagram assumes that you own Vol 1 and that you have created Snap A. If Vol 1 was owned by another AWS account and that account took Snap A and shared it with you, then Snap B would be a full snapshot.

  1. Vol 1 has 10 GiB of data. Because Snap A is the first snapshot taken of the volume, the entire 10 GiB of data is copied and stored.

  2. Vol 2 is created from Snap A, so it is an exact replica of Vol 1 at the time the snapshot was taken.

  3. Over time, 4 GiB of data is added to Vol 2 and its total size becomes 14 GiB.

  4. Snap B is taken from Vol 2. For Snap B, only the 4 GiB of data that was added after the volume was created from Snap A is copied and stored. The other 10 GiB of unchanged data, which is already stored in Snap A, is referenced by Snap B instead of being copied and stored again.

    Snap B is an incremental snapshot of Snap A, even though it was created from a different volume.


        Snapshots capturing an initial volume state and two subsequent states after data has
          been changed.

For more information about how data is managed when you delete a snapshot, see Delete an Amazon EBS snapshot.

Copy and share snapshots

You can share a snapshot across AWS accounts by modifying its access permissions. You can make copies of your own snapshots as well as snapshots that have been shared with you. For more information, see Share an Amazon EBS snapshot.

A snapshot is constrained to the AWS Region where it was created. After you create a snapshot of an EBS volume, you can use it to create new volumes in the same Region. For more information, see Create a volume from a snapshot. You can also copy snapshots across Regions, making it possible to use multiple Regions for geographical expansion, data center migration, and disaster recovery. You can copy any accessible snapshot that has a completed status. For more information, see Copy an Amazon EBS snapshot.

Encryption support for snapshots

EBS snapshots fully support EBS encryption.

  • Snapshots of encrypted volumes are automatically encrypted.

  • Volumes that you create from encrypted snapshots are automatically encrypted.

  • Volumes that you create from an unencrypted snapshot that you own or have access to can be encrypted on-the-fly.

  • When you copy an unencrypted snapshot that you own, you can encrypt it during the copy process.

  • When you copy an encrypted snapshot that you own or have access to, you can reencrypt it with a different key during the copy process.

  • The first snapshot you take of an encrypted volume that has been created from an unencrypted snapshot is always a full snapshot.

  • The first snapshot you take of a reencrypted volume, which has a different CMK compared to the source snapshot, is always a full snapshot.

Complete documentation of possible snapshot encryption scenarios is provided in Create Amazon EBS snapshots and in Copy an Amazon EBS snapshot.

For more information, see Amazon EBS encryption.