Copy a file without using the windows file cache

Question

Anybody know of a way to copy a file from path A to path B and suppressing the Windows file system cache?
Typical use is copying a large file from a USB drive, or server to your local machine. Windows seems to swap everything out if the file is really big, e.g. 2GiB. Prefer example in C#, but I'm guessing this would be a Win32 call of some sort if possible.

Answer 1

In C# I have found something like this to work, this can be changed to copy directly to destination file:

    public static byte[] ReadAllBytesUnbuffered(string filePath)
    {
        const FileOptions FileFlagNoBuffering = (FileOptions)0x20000000;
        var fileInfo = new FileInfo(filePath);
        long fileLength = fileInfo.Length;
        int bufferSize = (int)Math.Min(fileLength, int.MaxValue / 2);
        bufferSize += ((bufferSize + 1023) & ~1023) - bufferSize;
        using (var stream = new FileStream(filePath, FileMode.Open, FileAccess.Read, FileShare.None,
                                           bufferSize, FileFlagNoBuffering | FileOptions.SequentialScan))
        {
            long length = stream.Length;
            if (length > 0x7fffffffL)
            {
                throw new IOException("File too long over 2GB");
            }
            int offset = 0;
            int count = (int)length;
            var buffer = new byte[count];
            while (count > 0)
            {
                int bytesRead = stream.Read(buffer, offset, count);
                if (bytesRead == 0)
                {
                    throw new EndOfStreamException("Read beyond end of file EOF");
                }
                offset += bytesRead;
                count -= bytesRead;
            }
            return buffer;
        }
    }

Answer 2

Even more important, there are FILE_FLAG_WRITE_THROUGH and FILE_FLAG_NO_BUFFERING.

MSDN has a nice article on them both: http://support.microsoft.com/kb/99794

Answer 3

I am not sure if this helps, but take a look at Increased Performance Using FILE_FLAG_SEQUENTIAL_SCAN.

SUMMARY

There is a flag for CreateFile() called FILE_FLAG_SEQUENTIAL_SCAN which will direct the Cache Manager to access the file sequentially.

Anyone reading potentially large files with sequential access can specify this flag for increased performance. This flag is useful if you are reading files that are "mostly" sequential, but you occasionally skip over small ranges of bytes.