Block Generation

If you choose a repository with immutability settings enabled as the target location for image-level backups, Veeam Backup for AWS creates an immutable backup chain in the repository instead of a regular backup chain. Immutable backup chains are built the same way as the chains of standard and archived EC2 and RDS backups, which means that each immutability chain is composed of a set of backups produced during a sequence of backup sessions, and that the same retention policies apply to these chains. The only difference is that objects in immutable backup chains can be neither removed nor modified until the immutability period is over. Therefore, every time Veeam Backup for AWS creates a new incremental backup containing modified data blocks, the retention period of the dependent unchanged data blocks (in the preceding incremental and full backups) is supposed to be extended. This can cause a substantial increase in I/O operations and associated costs incurred by Amazon S3.

To reduce the number of requests to the repository, thus to save traffic and to reduce transaction costs, Veeam Backup for AWS leverages the Block Generation mechanism. A generation is a period of up to 25 days that extends the retention period configured for backups composing the immutable backup chain. This means that the retention period is not explicitly extended for each dependent data block every time Veeam Backup for AWS creates a new incremental backup in the chain within one generation (during these 25 days).

How Block Generation Works

Block Generation works in the following way:

1. During the first backup session, Veeam Backup for AWS creates a full backup in a backup repository and adds 25 days to its retention period. The full backup becomes a starting point in the first generation of the immutable backup chain.
2. 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 backups in the backup repository. The content of each incremental backup depends on the content of the full backup and the preceding incremental backups in the immutable backup chain. Veeam Backup for AWS adds <25 - N> days to the retention period of these backups, where N is the number of days since the first backup in the generation was created.

As a result, all backups within one generation will have the same retention date, and will not be removed by the retention policy before this date.

3. On the 26th day a new block generation period is initiated, Veeam Backup for AWS creates a new incremental backup and adds 25 days to its retention period. This backup becomes a starting point in the second generation of the immutable backup chain. The new generation is automatically applied to all dependent data blocks from the preceding backups.
4. Veeam Backup for AWS repeats step 2 for the second generation.
5. Veeam Backup for AWS continues keeping dependent data blocks immutable by applying new generations to these blocks, thus continuously extending their retention period.

Block Generation Example

Consider the following example. You want a backup policy to create image-level backups of your critical workloads once a week starting from March 1, and to keep the backed-up data immutable for 30 days. In this case, you do the following:

1. In the policy target settings, you set the Enable backups toggle to On, and select a backup repository with immutability enabled as the target location for the created backups.
2. In the weekly scheduling settings, you select an hour and a day when backups will be created (for example, 7:00 AM; Monday), and specify the number of days for which Veeam Backup for AWS will retain the created backups (30 days).

According to the specified scheduling settings, Veeam Backup for AWS will create image-level backups in the following way:

1. On March 1, a backup session will start at 7:00 AM to create the full backup in the immutable backup chain. Veeam Backup for AWS will add 25 days to the retention period specified in the backup policy settings. Thus, the retention period of the backup will be prolonged to 55 days, and the immutability expiration date will become April 25.
2. On March 8, Veeam Backup for AWS will create a new incremental backup at 7:00 AM and add 24 days to the retention period specified in the backup policy settings. Thus, the retention period of the incremental backup will be prolonged to 54 days, and the retention date will become April 25.
3. On March 15-22, Veeam Backup for AWS will continue creating incremental backups and extending their retention period so that the retention date will still remain April 25.
4. On March 29, Veeam Backup for AWS will create a new backup at 7:00 AM. During the backup session, Veeam Backup for AWS will initiate a new block generation period, and apply the new generation to the newly created backup and all dependent data blocks. The retention period of this backup will be prolonged to 30 days, and the immutability expiration date will become May 23.

Then, all data blocks of the preceding backups whose retention period has not been extended will be removed by a retention session due to the immutability period expiration.