I have file server on Windows 2008 and I'm using Windows Server Backup - full server backup for it. When I look at used space on partitions I can see 426GB used space summary. At Windows Server Backup console there is information that:

space used for backup is: 328,11GB
space used for differences is: 208,22GB

I know that this backup don't include pagefile, but it is only 6GB. There are shadow copies turned on for one partition, but it is less than 64 shadow copies, so Windows Server Backup should back it up entirely.

Where is my 97,89GB of data in backup?

Thank you for your answer in advance.


The backed up data will be compressed. The difference is fairly large, but perfectly explicable if you have a large number of text files which have large compression ratios. The only time when this wouldn't necessarily be the case would be if you had file compression turned on on the server.

Also, 1GB of data in a single file will take up less disk space than 1GB of data split across 100 files. As the backup is effectively a single file there will also be some size savings there.

  • Thank's for answer. I can't find information about compression in windows server backup. Savings from single file vs. many file will not be as big as ~100GB IMHO. – met Apr 24 '12 at 13:05
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    could be, depends. if you have extra hardware/space available, try a restore from the backup you have and see what happens. – jhayes Apr 24 '12 at 13:12
  • Agreed with JHayes. You haven't done a responsible job of backing up your data if you're not periodically testing your restores. – mfinni Apr 24 '12 at 13:26
  • There is one thing against theory about compression. You can take this vhd file and run it in HyperV. It would work terrible if it is really compressed. I need to know why it is so big space gain with this backup. This backup is really important for me, as you can imagine ;) – met Apr 24 '12 at 13:29
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    VHDs will not "run terrible" if the data is compacted. As many others have mentioned in other ways- an untested backup is not a backup- it's a prayer. – Jim B Apr 24 '12 at 16:53

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