Flush disk write cache

.NET FileStream.Flush() will NOT flush the Windows cache for that file content; Flush() only flushes the .NET internal file buffer. In .NET 4.0, Microsoft fixed the problem by adding an optional parameter to Flush() which if set true causes FlushFileSystemBuffers to be called. In .NET 3.5 and below your only choice is to call FlushFileBuffers via pinvoke. See MSDN'sFileStream.Flush community comment for how to do this.

You should not fix this at the time you close the file. Windows will cache, unless you open the file passing FILE_FLAG_WRITE_THROUGH to CreateFile().

You may also want to pass FILE_FLAG_NO_BUFFERING; this tells Windows not to keep a copy of the bytes in cache.

This is more efficient than FlushFileBuffers(), according to the CreateFile documentation on MSDN.

See also file buffering and file caching on MSDN.

You haven't specified the development environment, so:

.Net

IO streams have a .Flush method that does what you want.

Win32 API

There is the FlushFileBuffers call, which takes a file handle as argument.

EDIT (based on a comment from the OA): FlushFileBuffers does not need administrative privileges; it does only if the handle passed to it is the handle for a volume, not for a single file.