AWS Backup retention in depth

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Hi everyone,

I have the following situation with 2 backup plans and 1 EC2 instance for both of them:

Backup plan 1:

  • Frequency : every 12 hours (starting at 5 AM) / Retention 30 days

Backup plan 2:

  • Frequency : every 24h (starting at 5 AM) / Retention 1 day
  • Copy backup to another region (same account)

I had the above configuration and it generated some high costs in transferring data from one region to another one.

Questions:

  1. How does retention works more exactly ? Let's say the backup takes 2h to finish. Retention will be 1 day since STARTING the backup (5AM) OR since it was successfully FINISHED (7AM) ?
  2. Backup plan 2 generated some high costs (regarding transferring data) and I want to double check if this is because the backup is expired before starting the incremental backup and now is forced to perform a FULL backup from scratch ?
  3. Since this is about same EC2 instance, on Backup Plan 2 shouldn't perform an incremental backup of the backup from Plan 1 (since it has the backup since 12h ago)? - or the incremental is separated on each Backup plan, regardless of having the same instances in both plans.
asked a year ago404 views
1 Answer
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[Question] How does retention works more exactly ? Let's say the backup takes 2h to finish. Retention will be 1 day since STARTING the backup (5AM) OR since it was successfully FINISHED (7AM) ?

[Answer] If the Backup creation/start time is December 6, 2022, 05:00:00 (UTC+00:00) and backup completion time is December 6, 2022, 06:16:10 (UTC+00:00) and the retention is 1 day then backup expiration would be December 7, 2022, 05:00:00 (UTC+00:00). So, expiration time is calculated from the Backup creation time rather than completion time.

Please note: AWS Backup randomizes its deletions within 8 hours following recovery point expiration to maintain performance. https://docs.aws.amazon.com/aws-backup/latest/devguide/deleting-backups.html

[Question 2] Backup plan 2 generated some high costs (regarding transferring data) and I want to double check if this is because the backup is expired before starting the incremental backup and now is forced to perform a FULL backup from scratch ?

[Answer 2] Whether a snapshot copy is incremental is determined by the most recently completed snapshot copy. When you copy a snapshot across Regions or accounts, the copy is an incremental copy if the following conditions are met:

The snapshot was copied to the destination Region or account previously.

The most recent snapshot copy still exists in the destination Region or account.

All copies of the snapshot in the destination Region or account are either unencrypted or were encrypted using the same KMS key.

If the most recent snapshot copy was deleted, the next copy is a full copy, not an incremental copy. Refer https://docs.aws.amazon.com/AWSEC2/latest/UserGuide/ebs-copy-snapshot.html

[Question 3] Since this is about same EC2 instance, on Backup Plan 2 shouldn't perform an incremental backup of the backup from Plan 1 (since it has the backup since 12h ago)? - or the incremental is separated on each Backup plan, regardless of having the same instances in both plans.

[Answer 3] Backup of the same EC2 instance created by either Plan 1 and Plan 2 will always be incremental. New backup created by either of the backup plan saves only the blocks that have changed since your last snapshot. https://docs.aws.amazon.com/AWSEC2/latest/UserGuide/ebs-creating-snapshot.html

AWS
answered a year ago

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