When performing backups and restores, the Backup Client will create temporary files. You will need to have as much free space as the largest file you need to back up. The cache file will be deleted automatically after the backup is done. If you do not have enough space on your primary drive, you can go setup an alternate location to store these files.
Here are the instructions:
Launch the backup client by double-clicking on the icon 
in the taskbar. (bottom right of the screen, beside the clock) Click on Options at the left menu and go to the Advanced Tab. Check the white box on “Specify Location for Temporary Files” and type in the desired path. The cache files will use this location for temporary storage.
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