Backups (Microsoft Hyper-V)

The Virtual Server Agent on the Hyper-V hosts can back up the virtual machines on the Hyper-V Server or Hyper cluster depending on the configuration settings on the virtualization client, backup set, and subclient components.

When a virtual machine is discovered during backup, a client for the VM is created in the CommCell Console if one does not already exist. If a virtual machine with spaces or special characters in its name is discovered during backup, the spaces or special characters are replaced with underscores ('_') when creating the VM client name that is displayed in the CommCell Console. The VM name with spaces or special characters is still displayed on the Virtual Machine Status tab for the backup job, in the backup job summary, and in reports that include the VM name. The following special characters are replaced:

[ \ \ | ` ~ ! @ # $ % ^ & * + = < > ? , { } ( ) : ; ' \ " \ \ s / ]

What Gets Backed Up

  • Virtual machines (powered on or powered off)
  • VHD and VHDX files
  • Snapshot files
  • Configuration files for the virtual machines
  • Metadata required for granular recovery of files (NTFS and ext3 volumes only)
  • VHDX formatted hard disks with sector size of 4K bytes without metadata
  • Hyper-V replica VMs that are stopped

What Does Not Get Backed Up

  • Pass-through disks
  • Hard links (only for disk-level backup)
  • Virtual machine smart paging files
  • Certain virtual machines in which Volume Shadow Copy Service (VSS) fails to create a shadow
  • Devices residing in a guest virtual machine over iSCSI or vHBA
  • Hyper-V replica VMs that are running
  • Page and swap files (Hyper-V Integration Services must be installed on guest VMs)
  • VM folders with compression enabled.

    When VM folders with compression enabled reside on a virtual machine, the backup of that virtual machine fails. However, manual snapshots of the virtual machine complete.

Hyper-V Server 2016 and More Recent Versions

  • Backups of shared VHD, VHDX or VHD Set files are not supported. Checkpoint operations fail when backing up VMs that are configured with shared disks.
  • Backups use a production checkpoint operation to perform an application-consistent backup. In some cases, the production checkpoint might not be created successfully (for example, because VSS operations are unable to present dynamic disks). In such cases, the backup continues as a crash-consistent backup, completes with errors, and displays the JPR "Production checkpoint failed for the VM."

    To prevent these backups from completing with errors, to the host Hyper-V server, add the ignoreQuiesceGuestErrors additional setting as shown in the following table.

    For instructions on adding additional settings from the CommCell Console, see Add or Modify an Additional Setting.











  • If pass-through disks are configured on Hyper-V virtual machines that are being backed up, those disks are not backed up and the backup job goes pending with the JPR, "Pass-through disks are not supported."

    Note: If you perform an out-of-place restore for a virtual machine that was configured with pass-through disks, and the source VM remains in place, the restored VM might fail to start. To start the restored VM, remove the pass-through disks manually.

Shared VHDX Files

  • Backups of shared VHDX files are only supported for streaming backups with the Hyper-V Server 2012 R2. IntelliSnap backups are not supported.
  • To back up shared VHDX files, on the Backup Options tab of the subclient properties, select the Perform application consistent backup option before performing a backup for the subclient. Although you must specify the application consistent backup option, shared VHDX disk files can only be backed up in a crash consistent format (a Microsoft limitation).

    Note: When performing crash consistent backups, Virtual Server Agent backups cannot collect file and folder metadata for clustered virtual machines that use shared VHDX files. To restore files and folder, use live browse from a VSA backup, or deploy a file system agent to perform backups and restores for the VMs.

  • When you back up shared VHDX disk files, the files cannot reside in the root of the cluster shared volume (CSV) due to permission constraints. To back up shared VHDX disk files successfully, be sure that the files reside in a folder within the CSV.
  • When you restore a VM that includes a shared VHDX disk file, only the ACLs for the restored VM are restored, not the ACLs for other VMs that refer to the disk. After the restore, you might need to reset the ACLs and modify the security properties for the disk to include all VMs that shared the disk.
  • If multiple VMs that refer to a shared VHDX are restored, each gets its own copy of the disk.

Application Aware Backups

See Application Aware Backups for the Virtual Server Agent.

Backup Types

You can perform the following types of backups, either immediately or on a schedule:

  • Full backups: Back up the entire virtual machine. This is the most comprehensive backup.
  • Incremental backups: Back up virtual machine data that has changed since the most recent backup.
  • Differential backups: Back up virtual machine data that has changed since the most recent full backup.
  • Synthetic Full backups: Consolidate virtual machine data from the most recent full backup with subsequent incremental and differential backups.

Backup Job Management

  • If some parts of a virtual machine backup job are not completed successfully, the job status is "Completed w/ one or more errors." You can view the Job Details dialog box and select the Virtual Machine Status tab to check the status of specific VMs.
  • If the status for a specific virtual machine is "Partial Success," some information for the VM was successfully backed up, but other information was not. Failed items for a VM contribute to the Failed Objects count in the Backup Job Summary Report.
  • A VM is only included in a backup of failed VMs if the VM is marked as Failed in the Virtual Machine Status tab. VMs that complete with partial success are not included as failed VMs.

Controlling Metadata Collection and Granular Recovery

By default, file and folder metadata is collected during backups. Metadata collection is required for recovery of guest files and folders from virtual machines.

If you do not need to recover file and folder information for some virtual machines, you can configure backups to disable the granular recovery option.


Last modified: 5/21/2021 8:15:40 PM