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I've been testing out Windows Server Backup solution on a 2008r2 server. I've scheduled a daily backup covering everything on C:, bare metal and a couple of folders.

When I open the snap-in, it currently says that I have 10 copies, which are using 300 GB disk space. However, when I go to the volume where the backup is located, and check the file size of "WindowsImageBackup" folder, it's only 50gb, which is roughly 1 copy.

I can't figure out a rational explanation for this.

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You probably have a lot of small files. A file with only 3 bytes of data in it still takes up an entire allocation unit in the filesystem ... but not in the backup. – David Schwartz May 11 '14 at 10:44
There might be small files, but there are large binary blobs, which change during the 10 day priod. This should produce a large than 50gb on disk. At this point I am unsure of I actually have 10 days worth of backups or one. – TinyIO May 11 '14 at 10:50
The only 100% guaranteed way to tell what you have in a backup is to restore it. – David Schwartz May 11 '14 at 10:54
How would we know? I have a similar question for you. I have 8 750 GB disks, but when I look at them in disk manager, it only shows as a total of less than 4.5 TB. WHY?!?!? See the problem - there's no way to know because there isn't enough information here. – HopelessN00b May 12 '14 at 4:08
up vote 1 down vote accepted

The WindowsImageBackup folder contains metadata and the latest version of your backup as a VHD. The rest is in System Volume Information on that volume, as the changes are handled using VSS.

As others have said, don't worry about looking at the size on disk, run some test restores and satisfy yourself that the backups are restorable.

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Look like you are right. The "System Volume Information" uses roughly the amount I am missing. Thank you. A follow up question, if I limit the space available to shadow copies, would that limit the number of backup copies, as they use VSS? – TinyIO May 13 '14 at 14:38
Why would you do that? Just let Windows take care of the disk. when you set it up for backup windows will format and label the disk and remove any drive letters. – BlueCompute May 13 '14 at 15:55

I guess Windows uses some kind of compression / deduplication to store the data. Also, if you change a 50 GB file, that does NOT mean that Windows will backup the whole file again. It might just backup the changed blocks (but I'm not deep into Windows Backup)

Anyways, try to restore some sample files, and you will quickly see if you have a valid backup or not.

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Regrettably, Windows Server Backup does absolutely no compression or deduplication of the data backup. However, you're correct that multiple versions of backups only consume the amount of storage space necessary to capture the changed blocks in the data being protected, so in terms of storage space WSB is reasonably efficient. – Twisty Sep 23 '14 at 18:44

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