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Hyper-V backup fails with the following error reported in the log: [hypervvss_assist] INTERNAL ERROR: <0001> assert error (this_disk.virtual_disk_snapshot_id.isempty()), hypervvss_targets.cpp This error occurs right after Avamar is fetching the virtual hard disk (VHD) list of one or several VMs: avhypervvss Info <41738>: Fetching VHD chain list for 'VM_NAME<VM_ID> Even if the avtar flag shown below is used, the backup ends with a "Failed" status instead of "Completed With Exceptions." --save-partial-backup
This issue is seen in a Full backup with a virtual machine (VM) creating on a differencing disk or checkpoint. Note: The differencing disk or checkpoint must be created using Hyper-V Manager. In such a case, this disk does not have a snapshot id associated with it. Here are the steps to reproduce the problem: Perform first backup of a VM with a differencing disk or checkpoint. The backup job succeeds Add one more differencing disk with Hyper-V Manager. Run backup. Observed behavior: Backup fails. Expected behavior: Backup should succeed.
Exclude the VM(s with the custom or user-created checkpoints. This can be done either using the dataset or using the "--excludelist" flag in the avhypervvss.cmd file (in the Avamar var folder). Alternatively, remove the checkpoint from the VM. This can be done either using Hyper-V Manager or from the following PowerShell command: Get-VMSnapshot -ComputerName "MyHyperVHost" -VMName "VM with Checkpoint” | Remove-VMSnapshot If neither of the above workarounds is feasible, then contact DELL support and reference this KB article.
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