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  1. Home
  2. NetBackup™ for Hyper-V Administrator's Guide
  3. Introduction
  4. Basic phases in a NetBackup backup of a Hyper-V virtual machine
NetBackup™ for Hyper-V Administrator's Guide

Basic phases in a NetBackup backup of a Hyper-V virtual machine

The following tables describe the phases of the NetBackup backup process for the two Hyper-V backup methods: VSS and WMI.

Table: VSS backup method: Phases of NetBackup for Hyper-V backup

Phase

Description

Phase 1

The NetBackup primary server initiates the backup.

Phase 2

The NetBackup client on the Hyper-V host initiates a snapshot.

Phase 3

On Windows 2012 hosts: The VSS Hyper-V writer quiesces the Windows virtual machine (places the data in a consistent state) and creates the snapshot on the host volume. If the Hyper-V writer cannot quiesce the virtual machine, the virtual machine is placed in the Saved state before creation of the snapshot.

On Windows hosts: The Hyper-V writer quiesces the Windows virtual machine and creates a .avhd or .avhdx snapshot on the host volume.

Phase 4

On Windows 2012 hosts: If the virtual machine was placed in the Saved state, Hyper-V returns the virtual machine to its original state.

Phase 5

The NetBackup client on the Hyper-V host reads the data from the snapshot of the virtual machine and transfers the data to the media server. The media server writes the data to the NetBackup storage unit.

Phase 6

The NetBackup client on the Hyper-V host deletes the host volume snapshot.

Table: WMI backup method: Phases of NetBackup for Hyper-V backup

Phase

Description

Phase 1

The NetBackup primary server initiates the backup.

Phase 2

The NetBackup client on the Hyper-V host initiates a virtual machine snapshot (checkpoint).

Phase 3

On Windows 2016 or later hosts, the NetBackup client on the Hyper-V host creates a virtual machine snapshot (checkpoint).

  • If the Hyper-V policy Consistency level option is set to Application consistent or Application consistent then crash consistent: The VSS integration services component inside the guest OS attempts to quiesce the virtual machine.

  • If the Hyper-V policy Consistency level option is set to Crash consistent: The virtual machine is not quiesced.

If the backup uses block-level incremental backup (BLIB), the snapshot is converted to a reference point. Resilient change tracking (RCT) is used to perform faster backup of the virtual machines by moving only the blocks that have changed between backups.

As a result of the virtual machine snapshot (checkpoint), the .avhd or .avhdx files are created for the virtual machine. All subsequent writes from the virtual machine go to these files.

Note:

The Consistency level option is set on the policy's Hyper-V tab, under Advanced.

Phase 4

The NetBackup client reads the data directly from the virtual machine files on the Hyper-V host and transfers the data to the media server. The media server writes the data to the storage unit.

Phase 5

The NetBackup client on the Hyper-V host deletes the virtual machine snapshot (checkpoint). As a result, the.avhd or .avhdx files that were created during the backup are merged back into the original virtual machine disks.

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