Backup too big

[GxG]

We have several Windows KVM machines installed on a Proxmox VE 1.3.
My question is related to their backup:
- a Vista machine has a 80GB allocated HDD; the used space in the operating system partion is around 22GB; the backup (snapshot, compressed) results around 10GB;
- a Windows 2003 server has a 100GB allocated HDD; the used space in the operating system partion is around 38GB; the backup (snapshot, compressed) results around 50GB.
Why the backup for Windows 2003 is so big? Is there any secret to make this backup smaller?

 

[dietmar]

Why the backup for Windows 2003 is so big? Is there any secret to make this backup smaller?

Defragment the disk and fill unused sectors with zero (but I do not know a tool which does that).

 

[GxG]

Thank you. I'll try!

 

[GxG]

Excelent advice!
After defragment disk and wipe unused space, the backup result is now only 13GB.

 

[dietmar]

What tool/tools did you use?

 

[GxG]

I defragmented the disk with the tool from Windows operating system (right click on partion in Windows Explorer, Properties, Tools tab, Defragment Now).
To wipe empty space I used Disk Redactor tool, from CEZEO.