Windows 2008 full server backup smaller than data itself

backupwindows-server-2008

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.

Best Answer

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.