Veeam Agent backup job finished with "Disk is running low on free space" warning

A Veeam Agent backup job finishes with the warning:
Disk RECOVERY is running low on free space

There is a limit on space that must be free on each volume of the backup source. Veeam Agent requires free space to create a VSS snapshot of the backed-up volume. The limit depends on the size of the volume.

Volume Size (MB)	Free Space Limit (MB)
up to 524	52
525 to 1073	355
1074 to 2146	525
2147 and more	1073

During the backup job session, Veeam Agent checks volumes to ensure there is enough space for the job to run:

• If free space is less than the free space limit, the backup job fails.
• If free space is less than the free space limit multiplied by 2, the backup job finishes with a warning.

For example, if the volume size is less than 525 MBs and free space is 52 to 104 MBs, Veeam Agent finishes the backup job with a warning.

It is recommended to resolve the issue in one of the following ways:

• Free space on the volume.
• Increase the volume size.

As a workaround, you can create the following registry key to disable the warning: 

1. Run regedit.exe.
2. Locate the HKEY_LOCAL_MACHINE\SOFTWARE\Veeam\Veeam EndPoint Backup key.
3. Add the following value under the key:
   • Name: DisableVolumeFreeSpaceCheckWarning
   • Type: REG_DWORD
   • Value: 1
4. Go to Control Panel > System and Security > Administrative Tools > Services.
5. Restart the Veeam Agent for Microsoft Windows service. 

If free space on the backup source drops below the limit after the registry key update, the backup job still fails.