If you enable image-level backups for an EC2 backup policy, Veeam Backup for AWS creates a new backup file in a backup repository during every backup session. A sequence of backup files created during a set of backup sessions makes up a backup chain.
The backup chain includes backup files of the following types:
- Full — a full backup file stores a copy of the full EC2 image.
- Incremental — incremental backup files store incremental changes of EC2 images.
To create a backup chain for an EC2 instance protected by a backup policy, Veeam Backup for AWS implements the forever forward incremental backup method:
- During the first backup session, Veeam Backup for AWS copies the full EC2 image and creates a full backup file in the backup repository. The full backup file becomes a starting point in the backup chain.
- During subsequent backup sessions, Veeam Backup for AWS copies only those data blocks that have changed since the previous backup session, and stores these data blocks to incremental backup files in the backup repository. The content of each incremental backup file depends on the content of the full backup file and the preceding incremental backup files in the backup chain.
Full and incremental backup files act as restore points for backed-up EC2 instances that let you roll back instance data to the necessary state. To recover an EC2 instance to a specific point in time, the chain of backup files created for the instance must contain a full backup file and a set of incremental backup files dependent on the full backup file.
If some file in the backup chain is missing, you will not be able to roll back to the necessary state. For this reason, you must not delete individual backup files from the backup repository manually. Instead, you must specify retention policy settings that will let you maintain the necessary number of backup files in the backup repository. For more information, see EC2 Backup Retention.