When you install Windows 2008 R2, Windows automatically creates a hibernation file. The hidden Hiberfil.sys system file is created in the root folder of the system drive. The Windows Kernel Power Manager reserves this file when you install Windows. The size of this file is equal to how much RAM was installed on the computer when Windows was originally installed. You can recover the wasted drive space by running this command in the Command Prompt:
powercfg.exe /hibernate off
You wouldn’t normally hibernate a server instance, so this isn’t something you would normally want to support. Removing the file will create additional free drive space on the system drive. You can read more on the subject from Microsoft.