Acronis Cyber Protect 15 virtual machine backup not working when using shared mode virtual disks vhds

Case

When you apply and run an Acronis Cyber Protect backup against a virtual machine which is part of a guest cluster which makes use of virtual disk shared files of type .vhds (VHD Set), you run across the following error.

Activity succeeded with warnings. Activity ‘Preparing for backup of virtual machine’ succeeded with the following warning ‘Windows error: (0xC05CFF0A). The requested operation cannot be performed on the virtual disk as it is currently used in shared mode.

Or the error may state something along the lines of: “Failed to open virtual disk file ‘[diskname].vhds’. Unknown format of the virtual disk.”

The same error as above can occur in virtual machine backup of virtual machines which include a .vdhx shared disk.

Solution

The above error is by design when you are attempting a virtual machine backup to virtual machine which does not have an Acronis backup agent installed, as per https://kb.acronis.com/content/68573. According to Acronis, as of July 2022, VHDS (VHD set) format virtual disk is not yet supported for agentless backup by Acronis Cyber Protect 15. Support is planned for future versions of the product.

However the above issue can persist even if you have the Acronis backup agent installed on your source virtual machine.

This can create confusion, since a virtual machine with the Acronis Cyber Protect agent should support the .vhds file format. The tricky part is that for every virtual machine, Acronis Cyber Protect creates two records in its database. One record corresponds to the virtual machine object as seen from the hypervisor side. In this case

Acronis uses three icons to represent three different objects in its management server database, as shown below.

The following icon represents a virtual machine as seen and managed via the hypervisor guest services.

The following icon represents the virtual machine as seen and managed via the Acronis backup agent. This corresponds to the Acronis agentless backup method.

The following icon represents a hypervisor host machine, also managed via the Acronis backup agent for hypervisor hosts. The following icon represents the virtual machine as seen and managed via the Acronis backup agent. This corresponds to the Acronis agent-based backup method.

So imagine the scenario that you have a guest WFC cluster comprising at least one SQL Server cluster node (virtual machine), which uses the .vhds file format for its shared cluster virtual disks. In this case Acronis will create two records for each SQL server cluster node, as shown in the example below. There will be one record which corresponds to the agentless backup method and is represented by the virtual machine’s hostname. There will also be one record which corresponds to the agent-based backup method and is represented by the virtual machines fully qualified domain name (FQDN).

To take successful backups of the SQL cluster nodes (virtual machine backups), you must apply an Acronis VM backup plan to the agent-based virtual machine object (the one designated with the FQDN).

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