Windows Small Business Server 2008 system disk space continuous reduction

I have installed Windows SBS 2008 standart to the server IBM Systex X server with 10GB RAM and two 600 GB SAS disk in Hardware RAID. Disk was split into 3 logical disks as following:
C:\ 60 GB - system - 40 GB used after instalation, 20 GB free
D:\ 240 GB - exchange & sql server databases
E:\ 300 GB - user data - shared folders

After 7 month of working system disk C: get just only 300 MB free space. To free space was done following:
- transfer WSUS files to disk D:
Result - I get 6 GB free space.

After 2 month again I get again around 300 MB free space on disk C:. To free space was done following:
- buy and install Paragon Disk Manager Server
- resize disk partition size to:
C: - 100 GB
D: - 200 GB
E: - 300 GB
Result - I get 40 GB free disk space on C;

After another 2 month again I get around 500 MB free space on disk C:. To free space was done following:
- transfer pagefile.sys to disk D:
- set shadow copy limit to 300 MB and then even compleatly switch it of
Result - I get 12,5 GB free space

I start daily monitor disk space on C: and After 2 week's I get 6,2 GB free space... 

Do any body know what need to do? or may be where to look to solve this problem?