Spanning is not really a good idea because if files are spanned across both drives and one drive fails, you lose the files.
I agree with ignatzatsonic - you need to free up space by uninstalling programs you don't need from C, cleaning out the clutter with Windows Disk Cleanup or CCleaner, and/or move (uninstall and reinstall) programs from C to D. You could also move your Documents folder to D as follows:
The
My Documents folder is part of the Windows 7 and Windows 8
Documents Library. A library combines multiple folders that contain similar types of files.
To move your documents to another drive, D drive in this example:
1. Create a new Documents folder on the D drive,
2. Right-click on the new folder and click Include in Library > Documents,
3. Click Start > Documents,
4. Double-click Documents to open and reveal its contents,
5. Drag and drop (or cut and paste) to move the files to the new folder,
6. Right-click in a blank area then click on Refresh, or press F5 to refresh the view,
7. Under Documents Library, click locations,
8. Right-click the new folder and click Set as default save location.
9. [Optional] Click the old Documents folder and click Remove.
Note Windows needs lots of free space to operate in. I like to keep at least 20Gb (30Gb is better) free on my boot drive.
