: Backup & Restore

"Microsoft Hyper-V" items

This Protected Item type backs up Microsoft Hyper-V virtual machines. The underlying technology is VSS and is compatible with all versions of Hyper-V running on Windows Server, including Windows Server 2016.

This backup type is only applicable when running on Windows Server. Hyper-V on Windows Desktop is not supported by this Protected item type.

Anti-Cloud integrates with the Hyper-V VSS writer to perform a Hyper-V backup snapshot, including support for in-VM quiescence on supported guest operating systems.

Backing up a Hyper-V virtual machine includes, but is not limited to:

its configuration file
all attached virtual drives
the contents of memory (if the machine was running)
the full tree of saved checkpoints

You can select individual virtual machines for backup, or choose "All virtual machines".

Consistency and guest additions

The following information applies to all products that perform Hyper-V backup.

When backing up a guest VM, it's important to get a consistent state of the VM. There are some different ways this happens.

If the guest OS has all necessary Hyper-V integration services installed, then the host can request for the guest VM to take a VSS snapshot. The snapshot is then exposed to Hyper-V on the host for Anti-Cloud to back up. It shouldn't interrupt the guest OS. The VM backup is application-consistent. This is known as a "Production checkpoint".

If the host OS is running Server 2012 R2 or newer, but there are no integration services inside the guest OS, then Hyper-V will take a checkpoint of the VM; Anti-Cloud will back up the checkpoint; and then the checkpoint will be removed. This kind of checkpoint does not interrupt the guest OS. The VM backup is crash-consistent. This is known as a "Standard checkpoint".

You can also achieve this behavior by disabling "Production checkpoints" in the Hyper-V settings for the VM.

If the host OS is older than Server 2012 R2, and there are no integration services inside the guest OS, then the VM will be paused; Windows will take a VSS snapshot of Hyper-V's files in paused state; the VM will be resumed and Anti-Cloud will back up from the VSS snapshot. It would cause a short interruption to the guest OS. The VM backup is crash-consistent.

You can also achieve this behavior by disabling checkpoints in the Hyper-V settings for the VM.

Replica VM

The following information applies to all products that perform Hyper-V backup.

If you are using Hyper-V replication, you can back up your virtual machines from either the primary or replica host.

A backup taken on the primary VM host is application-consistent (if possible), by quiescing a VSS snapshot inside the VM guest; or crash-consistent otherwise. A backup taken on the secondary VM host is only ever crash-consistent, because the replica VM is not running in order for guest integration services to take a VSS snapshot.

Current versions of Hyper-V do not allow backing up a VM that is currently replicating. If a VM is found to be currently replicating at the time of backup, Anti-Cloud will retry the operation a few times. If you repeatedly see errors of the form The virtual machine '...' cannot start a backup operation because it is currently executing a conflicting operation. Try the backup again., and you are running backups from the replica VM host, you could consider

scheduling the backup job to run at a time when it's more likely that the VM replication is up-to-date; or
using Before / After commands in Anti-Cloud to temporarily stop VM replication while the backup job is running.

For more information about backing up a replica VM, see https://blogs.technet.microsoft.com/virtualization/2014/04/24/backup-of-a-replica-vm/

Pass-through disks

The following information applies to all products that perform Hyper-V backup.

Hyper-V supports passthrough disks, to attach a physical disk from the host directly into the guest VM. This unmounts it from the host OS.

Hyper-V itself does not support backing up passthrough disks (nor does it support replicating them). A Hyper-V backup of the guest machines can be taken from the host, but does not include any data from passthrough disks.

You can work around this issue by either

installing Anti-Cloud Backup & Restore inside the guest VM, and backing up the extra data at a file level (this will use an extra Device license); or
changing your passthrough disks to be a real disk containing a large .vhd or .vhdx file. The "New Virtual Disk Wizard" in Hyper-V Manager has an option to convert an existing disk to a .vhd or .vhdx file.

For more information about backing up passthrough disks in Hyper-V, see https://blogs.technet.microsoft.com/virtualization/2009/03/03/working-around-the-pass-through-limitations-of-the-hyper-v-vss-writer/

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