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

Transaction Consistency

When you back up or replicate a running VM, you need to quiesce, or ‘freeze’ the VM to bring its file system and application data to a consistent state. If the VM is not quiesced, Veeam Backup & Replication will produce a crash-consistent backup or replica. The crash consistent backup or replica does not preserve data integrity of open files and transactional applications on the VM. Restore from a crash-consistent backup or replica is essentially equivalent to booting the VM after it was manually reset.

A crash-consistent backup or replica may be sufficient for VMs that run applications with low quantity of transactions. If you process VMs with highly transactional applications, you should instruct Veeam Backup & Replication to quiesce the VM and create a transactionally consistent backup or replica. Restore from transactionally consistent backups or replicas guarantees safety of application data.

Veeam Backup & Replication offers two options for creating consistent backups and replicas:

Application-aware processing (based on Microsoft VSS). This option is recommended for VMs running applications that support Microsoft VSS.
Microsoft Hyper-V guest quiescence. This option is recommended for VMs running applications that do not support Microsoft VSS, for example, Linux VMs.

To create consistent backups for such VMs, applications should be prepared using special pre-freeze and post-thaw scripts that you should create and store on the backup server beforehand. When the job starts, Veeam Backup & Replication will upload these scripts to the appropriate folders on VM guest. For more information, see Pre-Freeze and Post-Thaw Scripts.