Veeam Backup for Microsoft Azure produces the following types of backup chains:
If you configured a backup policy to create image-level backups, every backup session will produce a new backup in a backup repository. A sequence of backups produced during a set of backup sessions makes up a backup chain.
For more information on how Veeam Backup for Microsoft Azure creates backups, see How Backup Works.
The backup chain can include backups of the following types:
- Full backups
Veeam Backup for Microsoft Azure always creates a full backup upon the initial backup policy session. Such a full backup contains complete information about backed-up Microsoft Azure VMs and is considered the first restore point in a backup chain.
- Incremental backups
Veeam Backup for Microsoft Azure creates incremental backups during subsequent backup policy sessions. Such incremental backups keep only changes that have occurred since the preceding backup and are considered subsequent restore points in a backup chain.
When Veeam Backup for Microsoft Azure performs incremental backup, it needs to know what data blocks have changed since the previous job session. To get the list of changed data blocks, Veeam Backup for Microsoft Azure uses the changed block tracking mechanism (CBT). CBT increases the speed and efficiency of incremental backups.
Veeam Backup for Microsoft Azure CBT uses REST API to determine the changed metadata regions in Veeam Backup for Microsoft Azure virtual disks. CBT compares two snapshots: a snapshot of the current virtual disks environment with the snapshot that was obtained during the previous backup. Only the changed metadata regions that the API detects are backed up and written to backup repository. After the backup completes, the current snapshot will become the previous snapshot for comparison in the next backup operation. Only one snapshot per VM will be retained for comparison.
The following is an example of a backup chain consisting of six restore points in total:
- A full backup (an initial restore point).
- Five incremental backups (subsequent restore points).
If you configured a backup policy to create cloud-native snapshots, every backup session will create a new snapshot for every Microsoft Azure VM added to the backup policy. The created snapshot includes point-in-time snapshots of virtual disks attached to the processed Microsoft Azure VM. To create snapshots, Veeam Backup for Microsoft Azure uses native Microsoft Azure capabilities.
For more information on how Veeam Backup for Microsoft Azure creates snapshots, see How Backup Works.