Veeam Support Knowledge Base
Guest OS File restore fails with ‘The revision level is unknown’

Guest OS File restore fails with ‘The revision level is unknown’

KB ID:	2776
Product:	Veeam Backup & Replication \| 9.5 \| 10 \| 11 \| 12 \| 12.1 \| 12.2 \| 12.3 \| 12.3.1
Published:	2018-09-26
Last Modified:	2021-11-09

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Challenge

When attempting to restore files from a backup of a server that was running Windows 2016 (or 2019) and had Deduplication enabled for some (or all) of the drives, the restore fails with the following error:

Failed to restore "<filepath>" Error: Failed to read xx bytes from the file [\\?\C:\VeeamFLR\<vmname>\Volume#\<filename>] in async mode. 
Win32 error: The revision level is unknown.  Code: 1305

Navigating to the location shown in the error on the Mount Server, the file can be seen, but it cannot be copied. Attempting to copy and paste it another location causes the error:

Error 0x80070519: The revision level is unknown.

Cause

Experiencing this error means that the Mount Server has the required Deduplication role enabled, but the OS of the Mount Server is older than the OS of the VM that was backed up.

The OS requirement is also noted in the warning message that pops up as the Backup Browser opens after the restore is initiated.

Copying and restoring files from deduplicated volumes requires that the mount server associated with the source backup repository uses the same or later guest OS version.

Pop warning states Copying and restoring files from deduplicated volumes requires that the mount server associated with the source backup repository uses the same or later guest OS version.

Solution

To resolve this error, the mount server associated with the source backup repository must be using the same or later guest OS version as the VM that was backed up. Either (a) select a different Mount Server running the same or newer OS than the VM that was backed up, or (b) upgrade the existing Mount Server's OS.

More Information

Related article: Unable to mount disk: unsupported disk type

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