CBT Impact on Snapshot Retention
If CBT is available, Veeam Backup for AWS does not remove the cloud-native snapshot used as a source for image-level backup from the snapshot chain until the next image-level backup session completes. Therefore, at some point you may discover that Veeam Backup for AWS ignores retention policy settings and keeps an additional restore point in the snapshot chain.
Consider the following example. You configured a backup policy to create cloud-native snapshots of your critical workloads 6 times a day (at 7:00 AM, 9:00 AM, 11:00 AM, 1:00 PM, 3:00 PM, and 5:00 PM) and to keep 2 daily snapshots in the snapshot chain. You also enabled creation of image-level backups 2 times a day (at 7:00 AM and 5:00 PM) and configured the retention policy settings to keep the backups in a backup repository for 7 days.
Veeam Backup for AWS will run the backup policy in the following way:
- At 7:00 AM, the first backup session will create a cloud-native snapshot, and then will use this snapshot to create a full image-level backup.
- From 9:00 AM to 3:00 PM, subsequent sessions will create only cloud-native snapshots.
- After the backup session runs at 11:00 AM, the length of the snapshot chain (3 restore points) will exceed the retention limit (2 restore points). The earliest snapshot, however, will not be removed as it will be used to track changed data at 5:00 PM when the next image-level backup creation is scheduled.
- After the backup session runs at 1:00 PM and 3:00 PM, Veeam Backup for AWS will remove the snapshots created at 9:00 AM and 11:00 AM. The length of the snapshot chain will remain 3 restore points.
- At 5:00 PM, the backup session will create a new cloud-native snapshot. Veeam Backup for AWS will compare this snapshot with the one created at 7:00 AM to identify changed data blocks. After that, the backup session will create an incremental image-level backup based on the data obtained during the snapshot comparison.
- After the snapshot comparison, Veeam Backup for AWS will apply the retention policy and remove from the chain the snapshot created at 7:00 AM (as it is no longer needed) and the snapshot created at 1:00 PM.