The issue:
There is this little annoying file called hiberfil.sys that takes up 16GB (equate to my system memory) of my precious C:\ drive space that I cannot delete / rename. It would be wonderful if it can actually sleep/hibernate. But the problem is, I’m running Windows Server 2008 R2 with Hyper-V enabled which doesn’t support hibernate. So why should I pay 16GB of disk space for something that’s not even of use to me.
The journey:
I started off with hunting down the windows process with procmon (the new filemon) that’s locking the file and preventing me from deleting it. Boy, it did not end pretty. It BSoD’d on me. 
Lots of folks seem to suggest to run the following simple power configuration command line to disable hibernation and delete this little blood sucker. There is also a MSFT KB and FixIt for it http://support.microsoft.com/kb/920730
powercfg.exe –hibernate off
But the system seems to think that it’s already off, also it cannot be switched on. And rightly so!!!
Microsoft Windows [Version 6.1.7601]Copyright (c) 2009 Microsoft Corporation. All rights reserved.C:\Users\Administrator>powercfg -h offHibernation failed with the following error: The request is not supported.The following items are preventing hibernation on this system.An internal system component has disabled hibernation.
There also has been suggestions to boot into another OS and delete this file. But as soon as I boot up my server 08, the file just gets created again.
The solution:Thanks for http://forums.techarena.in/windows-server-help/1172294.htm
All it takes it to modify the registry key to 0 and a reboot to disable Hibernate…
[HKEY_LOCAL_MACHINE\SYSTEM\CurrentCongtrolSet\Control\Power\HibernateEnabled]
Posted by Ed Nicholas on October 13, 2012 at 5:42 am
Note that once you install the Hyper-V role, running “powercfg.exe -h off” will NOT disable hiberation. Instead, you will get an error “A internal system component has disabled hibernation”. This is because the Hyper-V role disables access to hiberation – you can’t turn it off or on using powercfg.exe. To work around this problem, remove the Hyper-V role using server manager. Then, “powercfg.exe -h off” WILL work. After that, you should be able to reinstall the Hyper-V role. I don’t know whether or not this is destructive to any virtual machines that you have configured.