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

Crash-Consistent Backup

Crash-consistent backup is Veeam’s proprietary method of creating crash-consistent VM images. A crash-consistent image can be compared to the state of a VM that has been manually reset. Unlike offline backup, crash-consistent backup does not require any downtime of a VM.

Crash-Consistent Backup Important!

Crash-consistent backup does not preserve data integrity of open files of transactional applications on the VM guest OS and may result in data loss.

The procedure of crash-consistent backup depends on the Microsoft Hyper-V Server version:

Microsoft Hyper-V Server 2012 R2 and Earlier

Crash-consistent backup is performed in the following way:

  1. Veeam Backup & Replication interacts with the Hyper-V host VSS Services and requests backup of a specific VM.
  2. The Hyper-V host VSS Writer notifies the VSS provider that volume snapshots can be taken.
  3. The Hyper-V host VSS provider creates a snapshot of the requested volume.
  4. The volume snapshot is presented to Veeam Backup & Replication. Veeam Backup & Replication reads VM files from the volume snapshot using one of two backup modes — on-host backup or off-host backup. After the backup is completed, the snapshot is deleted.

Crash-Consistent Backup 

Microsoft Hyper-V Server 2016

Crash-consistent backup of VMs on Microsoft Hyper-V 2016 relies on production checkpoints. Crash-consistent backup is performed in the following way:

  1. Veeam Backup & Replication requests a production checkpoint of a specific VM.
  2. A production checkpoint is created in the crash-consistent state. Every virtual disk of a VM receives a temporary AVHDX file. All new writes are redirected to temporary AVHDX files.
  3. Further activities depend on the backup mode:

The volume snapshot is mounted to the offhost backup proxy and presented to Veeam Backup & Replication. Veeam Backup & Replication reads VM data from the volume snapshot. After the backup job completes, the volume snapshot is deleted.

Crash-Consistent Backup 

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