Dell Automation Platform: Qcow2 file backup failed on NFSV4 windows-based server

In Dell Automation Platform 1.0.0.0, NFS backup is supported for application data protection.

If the users execute below command on a file path mounted from a Windows NFSv4 server.

qemu-img convert -f raw -O qcow2 -t none nbd+unix:///vda?socket=/var/tmp/vm_rbjscx_sock.sock /home/eceuser/nfs_shared_win/vm_rbjscx-2025-04-23_03-53-51.qcow2

User observes below error.
qemu-img: /home/eceuser/nfs_shared_win/vm_rbjscx-2025-04-23_03-53-51.qcow2: error while converting qcow2: Image is not in qcow2 format

This issue arises when using NFSv4 mounts from a Windows server. The same operation works flawlessly when using NFSv3 from the same Windows server and also functions correctly with both NFSv3 and NFSv4 on Ubuntu NFS server.

The root cause is linked to incompatibility between the Windows implementation of NFSv4 and the expectations of Qemu-img, particularly regarding file locking/layout handling. Qemu-img relies on accurate and consistent file read operations, and any deviation in protocol behavior can lead it to misinterpret the file format. This issue has been documented in https://bugzilla.redhat.com/show_bug.cgi?id=1891673 

It is recommended to configure the Windows server to export the share using NFSv3 instead of NFSv4. 

Environment-specific observation:

• Works: NFSv3 on Windows server
• Works: NFSv3 and NFSv4 on Ubuntu server
• Fails: NFSv4 on Windows server