Backup jobs are failing due to errors related to the Microsoft Volume Shadow Copy Service (VSS), indicating "Insufficient storage to create either the shadow copy storage file or other shadow copy data."

The issue arises from the Microsoft Volume Shadow Copy Services (VSS) during disk image backup, where it writes a volume shadow copy to a folder on the same volume during a backup job. This behavior can lead to problems such as insufficient disk space during volume backup. It is possible to customize the shadow storage location for each NTFS volume on a Windows server to use a different NTFS volume.

Note: This feature is only available on Microsoft Windows Server editions and not on desktop versions of the operating system. For Windows desktop versions (Windows 7, 8, 8.1, 10), the shadow copies of the volume are written to the same volume and cannot be changed.

The recommended solution is to create a separate drive dedicated to storing shadow copies (excluding page files). If this is not feasible, storing the shadow files on a drive containing page files is a better alternative than using the drive being backed up.

To configure the shadow copy location for each volume:

1. Browse to C:\Windows\System32 to access the command line as an administrator. Right-click on cmd.exe and select "Run as administrator."
2. Execute the following command: vssadmin add shadowstorage /for=<drive being backed up> /on=<drive to store the shadow copy> /maxsize=<percentage of disk space to allow to be used>. 
   
1. For example: If the VSS shadow copies of D: drive will be stored on the C: drive and allowed to use up to 90% of the free disk space on the C: drive, the command would look like: vssadmin add shadowstorage /for=d: /on=c: /maxsize=90%
   
3. If the command is successful, the message "Successfully added the shadow copy storage association" will be displayed.
   

Note: Existing shadow copy storage locations for each volume can be checked by executing the following CMD command: vssadmin list shadowstorage.

Alternatively, verify that the configured volume meets the minimum free space requirement for shadow copies (the volume must have a minimum free space of 300 MB to create a snapshot). Adjust the VSS storage size to "No limit" to ensure backups complete successfully.

To change the VSS storage size to "No Limit":

1. Right-click on the C:\ drive and choose "Properties."
2. On the Shadow Copies tab, click the "Settings" button.
3. Change the maximum size to "No Limit," then schedule the backup.