Windows Server Backup Fails: There is not enough disk space to create the volume shadow copy...

Solution 1:

Change your VSS for the system partition to use the C:\ at present it doesn't have enough space to create VSS for itself so fails the backup.

enter image description here

Solution 2:

Assign "System Reserved volume" I:

Run fsutil usn deletejournal /N /D I:

Remove drive Letter I:

Backup again

https://www.partitionwizard.com/partitionmagic/backup-not-enough-space.html