Hyper-V FLR request failure.

SUMMARY

Hyper-V FLR request failure.

ISSUE

Purpose

How to address a Hyper-V file-level recovery (FLR) error.

Description

Hyper-V FLR request fails if the file name and configured disk name are different for the vhd/vhdx file.

Cause

Sometime after the Hyper-V VM is configured, the VHD file name is changed with a different CASE but not a different name. For example, the VM was configured with the disk named externaldisk.vhd, and initially the VHD file name that contains this disk is stored on the server with the same name. At some point a change is made to the file name on the server to ExternalDisk.vhd.  For Hyper-V on a windows system this has no affect because windows is not case sensitive in file names.  However, after the VM is backed up and a request is made to do an FLR the FLR process will fail because the DPU is running a Linux operating system which IS case sensitive, so to the DPU the configured file name externaldisk.vhd is different than the physical file name ExternalDisk.vhd.
This problem can also manifest itself after a Hyper-V VM has been restored.  In some cases the disk name is converted to all caps in the restore process, thus creating this problem.

Resolution

If this situation occurs an FLR cannot be done, however the VM can still be restored. To confirm this problem check the log cmc_vdisk_mount_createhv.log and in the log file verify that the file name pulled from the GUID.xml file for the vhd/vhdx is the same, including case, as the file pulled from the CTAR.

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