Microsoft Volume Shadow Copy Service (VSS) snapshots might not be deleted after backups for a Windows Server 2012 R2 operating system
Article ID: HPV0024 Microsoft has identified an issue in which leftover snapshots might result in greater disk space usage.
After backup operations for a Windows Server 2012 R2 machine, you might see an increase in disk space usage. The machine could be a virtual or physical machine.
Disk space issues might be caused by snapshot files that were not removed after previous backup operations. Microsoft has identified this as a known issue.
See the Microsoft support article "Snapshots are not deleted after you perform a backup operation by using VSS in Windows Server 2012 R2": https://support.microsoft.com/en-us/kb/3060678.