A memory dump during a crash of Windows 7 will fail if your system drive (%SystemRoot%) has less than 25GB of free space! Memory dumps help you diagnose crash issues and it is always recommended to allow enough free space on your system drive for debugging information to be logged and for better overall performance. You can set the dump file to be stored on a different local drive with ample storage space or disable this feature, but in cases where this is not possible and regardless of free space, you can force Windows 7 to create a dump file using the following new registry entry:
To start the registry editor, type regedit in the Start menu search text box and press enter.
DWORD (32-bit) Value name: AlwaysKeepMemoryDump
DWORD Value data: 1
A word of caution – incorrectly editing the registry may severely damage your system. The above modifications are intended for Windows advanced users who are familiar with the registry editor. Users are also reminded to back up the registry before making any critical changes.