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Veeam Backup & Replication 9.5 Update 4
User Guide for Microsoft Hyper-V

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:

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.

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