Problems with backup of client / domain - mismatching file size

[udoersam]

Hi Support-Team,

I've got the problem with backing up one of my clients / backups. During the backup the sysem is working fine. Even with the GUI or the console backup system. The problem is that the size of the backup file couldn't be that the backup is creating.
Plesk is saying that the client is using 800 MB of disk space. The backup file is just 17 MB!
What is wrong?

Please help.

In that case the backup system is not useable for me!

Thanks.