Windows Server Backup has an option to switch from VSS Full to VSS Copy. VSS Copy is supposed to be used if you are using other backup programs that use VSS to backup the same files, such as a Cloud Backup program.  The option states the VSS Copy option means the archive attribute won't be changed on the files.

It is my understanding the archive attribute is used to determine if a file has been changed for incremental backups.

However, then if you enabled VSS Copy, wouldn't Windows Server Backup no longer be able to perform differential/incremental backups?  Or, if another backup program is setting the attribute (because it doesn't have a VSS Copy option), that also seems to me it would prevent Windows Server Backup from distinguishing the modified files.  (FYI in this instance I'm using CloudBerry with Windows Server Backup).  

Hi,

VSS Copy will keep the information on files whether they are changed or deleted. This could help in the following incremental backup.

For a third party backup application, if it is using VSS Full in backing up then yes it will afect following incremental backups as such information are cleared when the backup is finished. Detailed please see:

What is the difference between VSS Full Backup and VSS Copy Backup in Windows Server 2008?

http://blogs.technet.com/b/filecab/archive/2008/05/21/what-is-the-difference-between-vss-full-backup-and-vss-copy-backup-in-windows-server-2008.aspx