Application-consistent backups on Hyper-V VMs

Beginning in version 8.84, the Hyper-V Agent can create application-consistent backups of Microsoft SQL Server, Exchange, SharePoint and Active Directory on Windows virtual machines (VMs) in Hyper-V environments.

Note: A Hyper-V Agent backup is not sufficient for an authoritative restore of Active Directory objects. For an authoritative restore, a System State backup with the Windows Agent is required.

In an application-consistent backup, pending application transactions are written to disk before the data is backed up. This minimizes the amount of work required to restore the application. If application-consistency is not enabled in a backup job, the backups are crash-consistent. In a crash-consistent backup, pending application transactions are rolled back and manual steps are required to ensure that applications are completely restored.

To create application-consistent backups on Hyper-V VMs, you must provide credentials that have admin access to VMs. You can provide guest VM credentials with admin access to multiple VMs in a backup job and/or provide credentials for specific VMs. If you provide credentials for a specific VM, the guest VM credentials for multiple VMs will never be used to connect to that VM.

If you enable application-consistent backups in a backup job but an application-consistent backup cannot be created for a VM, the Hyper-V Agent creates a crash-consistent backup for the VM. To check whether each VM backup is application-consistent or crash-consistent, view the backup log.

An application-consistent backup cannot be created in the following cases:

• The guest VM credentials are incorrect.

• The VM is not in a running state (e.g., is powered off, paused or migrating).

• The VM is running on a Hyper-V host with an operating system where application-consistent backups are not supported.

• The VM is running on a Hyper-V host where the Host service is not installed.

• The VM has a guest operating system where application-consistent backups are not supported.

• The VM configuration version is earlier than 6.2.

• The Backup (volume shadow copy) integration service is not enabled for the VM.

• A VSS writer on the host cannot connect to the VM.

• A VSS writer on the VM is not available or is in a bad state.

  Note: To determine whether VSS writers required for an application-consistent backup are available on a VM (e.g., the SQL writer for a SQL Server backup), check the backup log. The backup log lists VSS writers on each VM and indicates the status of each writer.

For a list of supported Hyper-V host and guest operating systems, see the Hyper-V Agent release notes. Release notes for current product versions are available here.

Log truncation in application-consistent backups

When performing application-consistent backups, the Hyper-V Agent can truncate SQL Server, Exchange and SQL transaction logs for SharePoint Server. This prevents the transaction logs from taking up a significant amount of disk space and reducing system performance. There are no logs to truncate when performing application-consistent backups of Domain Controllers with Active Directory.

Note: The Hyper-V Agent can truncate transaction logs for the default SQL Server instance and for all Exchange Server databases. The Hyper-V Agent cannot truncate logs for named SQL Server instances.

To truncate transaction logs on a VM after an application-consistent backup, you must enable log truncation in the backup job.

To check whether log truncation was successful on each VM after a backup, view the backup logs.

Note: If you also back up databases using another tool (e.g., native SQL Server backup), use only one tool for truncating logs.