This is an archive version of the document. To get the most up-to-date information, see the current version.

How Backup Works

During backup, Veeam Agent for Microsoft Windows performs the following operations:

Veeam Agent for Microsoft Windows creates a Microsoft VSS snapshot of the volume whose data you want to back up. The VSS snapshot helps make sure that the data on the volume is consistent and does not change at the moment of backup.

In the Free and Workstation product editions, the VSS snapshot type depends on the OS of the Veeam Agent computer. On Microsoft Windows Client OSes, Veeam Agent creates a copy-only VSS snapshot. On Microsoft Windows Server OSes, Veeam Agent creates a full VSS snapshot.
In the Server product edition, the VSS snapshot type depends on the specified application-aware processing settings. To learn more, see Application-Aware Processing.

Veeam Agent for Microsoft Windows does not create a VSS snapshot for the EFI system partition on GPT disks as its data does not change during backup. For the System Reserved and other system partitions, VSS snapshot can be created if there is enough free disk space on the partition.

How Backup Works Note:

By default, Microsoft Windows does not include offline Outlook Data Files (.ost) into a VSS snapshot. As a result, these files are not included into Veeam Agent backups, too.

Veeam Agent for Microsoft Windows reads data from the created VSS snapshot, compresses it and copies it to the target location.

For volume-level backup, Veeam Agent for Microsoft Windows copies data blocks of the whole volume.
For file-level backup, Veeam Agent for Microsoft Windows creates a volume inside the backup file in the target location. The content of the volume in the backup file is synchronized with the volume on the source: Veeam Agent for Microsoft Windows copies only those data that you have selected to back up.

During incremental backup, Veeam Agent for Microsoft Windows uses Changed Block Tracking (CBT) to retrieve only those data blocks that have changed since the previous backup session. To learn more, see Change Block Tracking.

In the target location, Veeam Agent for Microsoft Windows stores copied data to the backup file.

[For Microsoft Windows Server OS] If an application on the computer uses transaction logs to maintain the database consistency, Veeam Agent for Microsoft Windows automatically truncates transaction logs upon successful backup.

How Backup Works Important!

The Veeam Agent Service runs under the LocalSystem account. On Microsoft SQL Server 2012, this account does not have necessary permissions to truncate transaction logs. If you want Veeam Agent for Microsoft Windows to automatically truncate transaction logs, you need to manually add the LocalSystem account to a group that has the SQL Server System Administrator rights.

How Backup Works