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

I do not understand this part:

Therefore, a copy backup cannot be used as a starting point for incremental/differential backups/restores.

Can somebody explain the real implication here? Will it simply use more data? Will it always do a full backup?

Thanks a lot, Carl

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My understanding is that full backup will mark the file as backed up, whereas copy backup will not. In order to create a differential or incremental backup, it is important to know what has already been backed up.

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I understand why vssCopy is used when other backup programs are used. But why "A copy backup cannot be used for incremental or differential backups or restores."? technet.microsoft.com/en-us/library/cc742130(WS.10).aspx – Malartre Apr 6 '11 at 13:40
    
I was just thinking that to do a differential or incremental backup, you would need to know what was already backed up. If you can't do that with copy backup, then it cannot be used as basis for those types of backup. – Nils Magne Lunde Apr 6 '11 at 14:02
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I see, but after testing it does seem to do incremental backup. The first backup is 600GB and the next one is 2GB. – Malartre Apr 6 '11 at 19:18

Actually, the answer is about Log files, that's what it really comes down to.

When you do a VSS Full Backup you do create a backup of all files, but after that the backup application has the potential to truncate logs on the file system.

In a VSS Copy Backup you persevere ALL application files including log files on the live system. Why is this important?

For incremental backups and differentials, if you constantly are writing over your File System logs certain VSS backups may not know where to pick off.

Source

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