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Hyper-V Backup Crashes at Exactly 10GB (Not a Repo/Target Issue)

Iris Smith 0 Reputation points
2026-03-13T13:41:48.5+00:00

I've got two VMs living on this Hyper-V box, but one of them is being super stubborn with backups. Basically, Veeam keeps failing on just this one specific virtual machine. It'll hum along and transfer about 10GB of data perfectly fine, and then just inexplicably bomb out. I’ve already spent way too much time going back and forth with Veeam support on this with zero luck.

I tried running a native Windows Server Backup on the host but it did the exact same thing, spit out a super vague 'Incorrect function' error message. I thought maybe my NAS was timing out or dropping the connection, so I repointed the backup destination to a local drive directly on the host. Exact same crash happened. Any idea why this one specific VM keeps hitting a brick wall at exactly 10 gigs?

Windows for business | Windows 365 Enterprise
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  1. Harry Phan 18,120 Reputation points Independent Advisor
    2026-03-13T14:56:30.75+00:00

    Hi Iris,

    When backups consistently fail at the 10GB mark across both Veeam and native Windows Server Backup, the issue is almost certainly tied to the underlying VSS snapshot process for that VM rather than the backup software or destination. The “Incorrect function” error is a generic VSS failure, usually triggered when the VM has a corrupt checkpoint chain or a problematic integration service.

    You can start by checking the Hyper-V host’s Event Viewer under Applications and Services Logs > Microsoft > Windows > Hyper-V-VMMS > Admin for VSS-related errors at the time of failure. On the affected VM, verify that Hyper-V Integration Services are installed and up to date, and confirm that the Volume Shadow Copy service is enabled and running. Also inspect the VM’s .avhdx chain in C:\ProgramData\Microsoft\Windows\Hyper-V\Virtual Hard Disks for inconsistencies; a broken differencing disk will cause snapshot creation to fail once the backup hits a certain size. If corruption is suspected, merge checkpoints manually and recreate a clean baseline. If everything checks out but the error persists, the VM’s VSS writers may be failing: run vssadmin list writers inside the guest and look for any in a failed state. A failed writer will block backups beyond a certain threshold, and repairing that service or application is required before backups succeed.

    If you find it's helpful, please give it a thump up or accept the answer, very much appreciate it :)

    Harry.

    1 person found this answer helpful.

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