在不使用Windows文件缓存的情况下复制文件

Question

有人知道将文件从路径A复制到路径B并抑制Windows文件系统缓存的方法吗？
典型用途是将大型文件从USB驱动器或服务器复制到本地计算机.如果文件非常大,Windows似乎会将所有内容都换掉,例如2GiB.首选C#中的示例,但我猜这将是某种Win32调用,如果可能的话.

Answer 1

在C#中,我发现这样的东西可以工作,可以将其更改为直接复制到目标文件:

    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

更重要的是,有FILE_FLAG_WRITE_THROUGH和FILE_FLAG_NO_BUFFERING.

MSDN上有一篇很好的文章:http://support.microsoft.com/kb/99794